Final final 1kHz oscillator

Nov 08, 2024 Last reply: 1 year ago 58 Replies
B

It's got a nasty 163kHz generator embedded in it somewhere, and I've put in an RL filter to keep that under control.

The double Sallen and Keys network is a four pole Bessel filter which I'm using as a 250usec delay line - the output from the full wave rectifier has an appreciable 2kHz component, but the delayed contribution coming into the integrator through R9 roughly cancels the direct input through R20.

R10 in the integrator damps the amplitude feedback loop for a dead-beat response.

The harmonics in the 1kHz output are about 100dB below the fundamental. Not great, but respectable, and not worth trying to improve in a simulation.

The circuit still works with the worst case values for the 1% capacitors at C5 and C6.

Version 4 SHEET 1 3608 920 WIRE -832 -1952 -1136 -1952 WIRE 208 -1952 -768 -1952 WIRE 272 -1952 208 -1952 WIRE 416 -1952 352 -1952 WIRE 608 -1952 496 -1952 WIRE 800 -1952 608 -1952 WIRE 976 -1952 880 -1952 WIRE 2704 -1952 1056 -1952 WIRE -656 -1888 -912 -1888 WIRE -224 -1872 -336 -1872 WIRE -96 -1872 -160 -1872 WIRE 0 -1872 -96 -1872 WIRE -832 -1824 -1040 -1824 WIRE 208 -1824 208 -1952 WIRE 608 -1824 608 -1952 WIRE -912 -1792 -912 -1888 WIRE -912 -1776 -912 -1792 WIRE -832 -1776 -832 -1824 WIRE -832 -1776 -880 -1776 WIRE 2192 -1776 864 -1776 WIRE 2368 -1776 2272 -1776 WIRE 2432 -1776 2368 -1776 WIRE 2656 -1776 2512 -1776 WIRE -1040 -1760 -1040 -1824 WIRE -944 -1760 -1040 -1760 WIRE -832 -1744 -880 -1744 WIRE -704 -1744 -832 -1744 WIRE -592 -1744 -704 -1744 WIRE -368 -1744 -512 -1744 WIRE -336 -1744 -336 -1872 WIRE -336 -1744 -368 -1744 WIRE -240 -1744 -336 -1744 WIRE -96 -1744 -96 -1872 WIRE -96 -1744 -160 -1744 WIRE 208 -1696 208 -1760 WIRE 608 -1696 608 -1760 WIRE -656 -1680 -656 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-832 -656 -880 WIRE -656 -832 -912 -832 WIRE -544 -832 -656 -832 WIRE -288 -832 -288 -896 WIRE -288 -832 -544 -832 WIRE 432 -816 432 -912 WIRE 640 -816 432 -816 WIRE 864 -816 864 -912 WIRE 864 -816 704 -816 WIRE 64 -752 64 -768 WIRE 368 -752 368 -896 WIRE 368 -752 64 -752 WIRE 576 -752 576 -1168 WIRE 768 -752 768 -832 WIRE 768 -752 576 -752 WIRE 208 -688 208 -1152 WIRE 416 -688 208 -688 WIRE 576 -688 416 -688 WIRE 1312 -688 1312 -1280 WIRE 1312 -688 576 -688 WIRE 1984 -688 1984 -1296 WIRE 1984 -688 1312 -688 WIRE 2560 -688 2560 -1360 WIRE 2560 -688 1984 -688 FLAG 464 -1152 0 FLAG -80 -1024 0 FLAG -656 -1104 vcc FLAG -768 -992 0 FLAG 352 -1568 Vcc FLAG 416 -688 Vee FLAG -496 -1216 0 FLAG 0 -1872 Vout FLAG 2240 -960 0 FLAG 2496 -1248 vref-1.25 FLAG -976 -1408 Fet-gate FLAG 1296 -1648 filt1 FLAG 1968 -1664 filt2 FLAG 1504 -976 0 FLAG 1584 -1456 Vcc FLAG -544 -832 Vee FLAG 208 -1696 0 FLAG 608 -1696 0 SYMBOL Opamps\\LT1360 208 -1248 R0 SYMATTR InstName U1 SYMBOL res 48 -1344 R0 WINDOW 0 41 37 Left 2 WINDOW 3 36 71 Left 2 SYMATTR InstName R1 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res -96 -1152 R0 WINDOW 3 41 74 Left 2 WINDOW 0 43 31 Left 2 SYMATTR Value 4k02 SYMATTR InstName R2 SYMATTR SpiceLine tol=1 SYMBOL cap -208 -1136 R0 SYMATTR InstName C1 SYMATTR Value 3.3n SYMBOL schottky 352 -1264 R0 WINDOW 3 -99 -2 Left 2 SYMATTR Value BAS70L SYMATTR InstName D1 SYMBOL schottky 352 -1152 R0 WINDOW 3 -94 77 Left 2 SYMATTR Value BAS70L SYMATTR InstName D2 SYMBOL res 352 -1472 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1a SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 208 -1536 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 20k SYMATTR SpiceLine tol=1 SYMBOL res 480 -1408 R0 WINDOW 0 41 41 Left 2 WINDOW 3 47 81 Left 2 SYMATTR InstName R2a SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 576 -928 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2b SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 720 -928 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2c SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL cap 704 -832 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 220n SYMBOL cap 288 -1344 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 3.3p SYMBOL cap 192 -912 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 3.3p SYMBOL res 48 -864 R0 WINDOW 0 39 33 Left 2 WINDOW 3 40 74 Left 2 SYMATTR InstName R1b SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL OpAmps\\opamp2 -288 -1584 R0 WINDOW 3 11 165 Left 2 SYMATTR Value LME49710 SYMATTR InstName U3 SYMATTR SpiceModel LME49710 SYMBOL voltage -656 -1120 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL voltage -656 -976 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL cap -80 -1472 R0 SYMATTR InstName C5 SYMATTR Value 15nF SYMATTR SpiceLine V=63 Rser=0.04 Lser=12n SYMBOL res -128 -1360 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10.5k SYMATTR SpiceLine tol=1 SYMBOL cap -624 -1456 R0 SYMATTR InstName C6 SYMATTR Value 15nF SYMATTR SpiceLine V=63 Rser=0.04 Lser=12n SYMBOL res -480 -1280 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R5 SYMATTR Value 10.5k SYMATTR SpiceLine tol=1 SYMBOL njf -880 -1472 R0 SYMATTR InstName J1 SYMATTR Value MMBF4391 SYMBOL res -144 -1760 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 10.0k SYMATTR SpiceLine tol=1 SYMBOL res -496 -1760 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 4.87k SYMATTR SpiceLine tol=1 SYMBOL cap -160 -1888 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C7 SYMATTR Value 3.3p SYMBOL res -688 -1536 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R8 SYMATTR Value 220 SYMATTR SpiceLine tol=1 SYMBOL cap 2672 -1616 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C8 SYMATTR Value 6.8µ SYMBOL res 2416 -1760 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R10 SYMATTR Value 3.9k SYMBOL References\\LTC6655-1.25 2224 -1120 R0 SYMATTR InstName U4 SYMBOL Opamps\\LT1056A 2560 -1456 R0 SYMATTR InstName U5 SYMBOL cap 2480 -1120 R0 SYMATTR InstName C10 SYMATTR Value 1µF SYMBOL cap 2528 -1552 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C11 SYMATTR Value 3.3p SYMBOL diode -832 -1936 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL res -1152 -1568 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R11 SYMATTR Value 8.2k SYMATTR SpiceLine tol=0.1 SYMBOL Opamps\\OP27 576 -1264 R0 SYMATTR InstName U2 SYMBOL res 1296 -1520 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R12 SYMATTR Value 14k SYMBOL res 1136 -1232 R0 SYMATTR InstName R13 SYMATTR Value 62k SYMBOL cap 1232 -1168 R0 SYMATTR InstName C9 SYMATTR Value 2.2n SYMBOL cap 976 -1600 R0 SYMATTR InstName C12 SYMATTR Value 2.2n SYMBOL res 1136 -1312 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R14 SYMATTR Value 30k SYMBOL Opamps\\LT1013 1312 -1376 R0 SYMATTR InstName U6 SYMBOL res 880 -1280 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R15 SYMATTR Value 40.2k SYMBOL res 1968 -1536 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R16 SYMATTR Value 14k SYMBOL cap 1648 -1616 R0 SYMATTR InstName C13 SYMATTR Value 2.2n SYMBOL res 1808 -1328 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R17 SYMATTR Value 30k SYMBOL Opamps\\LT1013 1984 -1392 R0 WINDOW 3 -98 -2 Left 2 SYMATTR InstName U7 SYMBOL res 1488 -1296 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R18 SYMATTR Value 40.2k SYMBOL res 1808 -1184 R0 SYMATTR InstName R19 SYMATTR Value 62k SYMBOL cap 1904 -1120 R0 SYMATTR InstName C14 SYMATTR Value 2.2n SYMBOL FerriteBead 576 -1536 R0 SYMATTR InstName L1 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead 576 -720 R0 SYMATTR InstName L2 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap 752 -1408 R0 SYMATTR InstName C15 SYMATTR Value 100n SYMBOL cap 752 -896 R0 SYMATTR InstName C16 SYMATTR Value 100n SYMBOL res 2304 -1424 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 82k SYMBOL res 2288 -1792 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R20 SYMATTR Value 150k SYMBOL FerriteBead -288 -1648 R0 SYMATTR InstName L3 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead -288 -928 R0 SYMATTR InstName L4 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -448 -1600 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C17 SYMATTR Value 100n SYMBOL cap -448 -1168 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C18 SYMATTR Value 100n SYMBOL Opamps\\LT1013 -912 -1824 M0 SYMATTR InstName U8 SYMBOL res -1056 -1648 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R21 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL ind 256 -1936 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L5 SYMATTR Value 1m SYMATTR SpiceLine Ipk=40m Rser=40 Cpar=4.1p SYMBOL cap 192 -1824 R0 SYMATTR InstName C19 SYMATTR Value 1n SYMBOL ind 784 -1936 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L6 SYMATTR Value 1m SYMATTR SpiceLine Ipk=40m Rser=40 Cpar=4.1p SYMBOL cap 592 -1824 R0 SYMATTR InstName C20 SYMATTR Value 1n SYMBOL res 512 -1968 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R22 SYMATTR Value 1k SYMATTR SpiceLine tol=1 SYMBOL res 1072 -1968 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R23 SYMATTR Value 1k SYMATTR SpiceLine tol=1 TEXT -1176 -904 Left 2 !.MODEL BAS70L D \n+ IS = 3.22E-9 \n+ N = 1.018 \n+ BV = 77 \n+ IBV = 1.67E-7 \n+ RS = 20.89 \n+ CJO = 1.608E-12 \n+ VJ = 0.3891 \n+ M = 0.3683 \n+ FC = 0.5 \n+ EG = 0.69 \n+ XTI = 2 \n.ENDS TEXT -336 -528 Left 2 ;R2 a,b,c, Vishay Beschlag ACAS06S0830372P1AT precision 10k resistor array \n R1a, R1b Maxim MAX5492LB10000+T 10K resistive divider in a SOT-23-5 package TEXT -720 -464 Left 2 !.MODEL MMBF4391 NJF VTO=-4.6 BETA=0.02779 LAMBDA=0.00595 RD=1 RS=1 IS=1e-14 CGD=14p CGS=10.5p PB=1 B=1 KF=1e-18 AF=1 FC=0.5 mfg=Motorola TEXT -432 -408 Left 2 !.tran 0 10s 0 startup TEXT -720 -408 Left 2 !.lib LME49710.lib

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E

After fixing line wraps and the position of U1 I need LME49710.lib

I'll be back in a few days.

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B

John May posted it it a few weeks ago. Here's the text version I've been using.

  • LME49710
*****************************************************************************
  • (C) Copyright 2011 Texas Instruments Incorporated. All rights reserved.
***************************************************************************** ** This model is designed as an aid for customers of Texas Instruments. ** TI and its licensors and suppliers make no warranties, either expressed ** or implied, with respect to this model, including the warranties of ** merchantability or fitness for a particular purpose. The model is ** provided solely on an "as is" basis. The entire risk as to its quality ** and performance is with the customer. ***************************************************************************** * ** Released by: Analog eLab Design Center, Texas Instruments Inc.
  • Date: 2011-11-18
  • Model Type: ALL IN ONE
  • Simulator: PSPICE
  • Simulator Version: 16.2.0.p001
  • Datasheet: March 2007
  • EVM Order Number: N/A
  • EVM Users Guide: N/A
  • Model Version: 1.0
* ***************************************************************************** *
  • Updates:
*
  • Version 1.0 :
  • Release to Web
* *****************************************************************************
  • The LME49710 Macro Model represents the following parameters for
  • Vcc=+/-15V:
  • GBWP, input-referred voltage noise, the quiescent current,
  • output swing, input offset voltage, input bias current,
  • PSRR and CMRR, and the slew rate.
*
  • For any convergence problems, it is suggested to set the following simulation
  • options:
  • VNTOL: 10u
  • ABSTOL: 10n
  • ITL1: 1000
  • ITL2: 400
  • ITL4: 400
***************************************************************************** * ***************************************************************************** * *$ .SUBCKT LME49710 INP INN VCC VEE OUT *X_Ugnd VCC 0 VEE 0 GND_FLOAT 0 EPOLY2 PARAMS: COEFF1=0.5 COEFF2=0.5 Rgn1 0 GND_FLOAT 100MEG EVCVSgn1 GND_FLOAT 0 32 0 1 EVCVSgn2 33 0 VCC 0 1 EVCVSgn3 31 0 VEE 0 1 Cgn1 32 0 1 XRgn2 32 33 RNOISELESS PARAMS: ROHMS=1E6 XRgnd3 31 32 RNOISELESS PARAMS: ROHMS=1E6 X_U9 VCC VEE PD VIMON GND_FLOAT INP2 INN1 HPA_PD_I PARAMS: VTH=1.4
  • IMAX=4.8e-3 IMIN=3N IIBP=7n IIBN=7.1n

V_Vos INP2 INP_CMRR 33.2uVdc C_Cinp GND_FLOAT INP1 200f TC=0,0 C_Cinn GND_FLOAT INN1 200f TC=0,0 R_Rinp INP INP1 1 TC=0,0 R_Rinn INN INN1 1 TC=0,0 X_U12 INP1 INP2 VNSE X_UCN INP1 INN1 FEMT

X_Ug0 INP_CMRR INN3 GND_FLOAT AV1 VCCS_LIMIT PARAMS: GAIN=10e-6

  • IPOS=0.5 INEG=-0.5 X_Ug4 AV1 GND_FLOAT GND_FLOAT OVER_CLAMP VCCS_LIMIT PARAMS: GAIN=172.8u
  • IPOS=98u INEG=-98u X_U1 GND_FLOAT AV1 RNOISELESS PARAMS: R=1e6 X_U2 GND_FLOAT OVER_CLAMP RNOISELESS PARAMS: R=5.8e9

C_Ucl_Ccl2 GND_FLOAT Ucl_N01226 1p TC=0,0 C_Ucl_Ccl1 Ucl_N01131 GND_FLOAT 1p TC=0,0 V_Ucl_Vclp Ucl_N00774 GND_FLOAT 53Vdc V_Ucl_Vcln Ucl_N00760 GND_FLOAT -42Vdc X_Ucl_Ucl1 Ucl_N50037 Ucl_N01131 D_ideal X_Ucl_Ucl2 Ucl_N01226 Ucl_N50037 D_ideal E_Ucl_E1 Ucl_N01131 GND_FLOAT Ucl_N00774 VIMON 100 E_Ucl_E2 Ucl_N01226 GND_FLOAT Ucl_N00760 VIMON 100 R_Ucl_Rcl1 Ucl_N01131 N3310462 1 TC=0,0 R_Ucl_Rcl2 N3310462 Ucl_N01226 1 TC=0,0 R_Ucl_Rcl3 Ucl_N50037 CL_CLAMP 0.01 TC=0,0

E_E1 VCC_BUF GND_FLOAT VCC GND_FLOAT 1 E_E2 VEE_BUF GND_FLOAT VEE GND_FLOAT 1

C_Cc1 GND_FLOAT OVER_CLAMP 5p TC=0,0 C_Cc2 P0ZP1 GND_FLOAT 723.4e-18 TC=0,0 C_Cc3 CLAW_CLAMP GND_FLOAT 144.7f TC=0,0 C_Cc4 GND_FLOAT GND_FLOAT 4.11f TC=0,0

V_V1 VCC N3310020 1.89Vdc V_V4 N3310060 VEE 1.99Vdc X_Ud1 INP_CMRR N3310020 D_ideal X_Ud2 INN3 N3310020 D_ideal X_Ud3 N3310060 INP_CMRR D_ideal X_Ud4 N3310060 INN3 D_ideal

R_R2 GND_FLOAT N3309562 1G TC=0,0 R_R3 GND_FLOAT N3310462 1G TC=0,0 R_R4 VCC PD 1e-3 TC=0,0 G_G3 GND_FLOAT VSENSE OVER_CLAMP GND_FLOAT 1u G_G4 GND_FLOAT P0Z VSENSE GND_FLOAT 1u G_G5 GND_FLOAT P0ZP1 P0Z GND_FLOAT 1u G_G6 GND_FLOAT CLAW_CLAMP P0ZP1 GND_FLOAT 1m G_G7 GND_FLOAT CL_CLAMP CLAW_CLAMP GND_FLOAT 1m X_U3 VSENSE GND_FLOAT RNOISELESS PARAMS: R=1e6 X_U5 GND_FLOAT P0Z RNOISELESS PARAMS: R=1e6 X_U6 P0ZP1 GND_FLOAT RNOISELESS PARAMS: R=1e6 X_U7 CLAW_CLAMP GND_FLOAT RNOISELESS PARAMS: R=1e3 X_U8 CL_CLAMP GND_FLOAT RNOISELESS PARAMS: R=1e3

G_G1 GND_FLOAT N3309274 INP_CMRR GND_FLOAT 1u E_Ecmrr INN2 INN3 N3309274 GND_FLOAT 1 R_Rcmr N3309274 N33089240 1 TC=0,0 L_Lcmr N33089240 GND_FLOAT 560nH

G_G2 GND_FLOAT N3309420 VCC VEE 562.3n X_Upsrr N3309420 GND_FLOAT INN1 INN2 VCVS_LIMIT PARAMS: GAIN=-1

  • VPOS=20M VNEG=-20M R_Rpsr N3309420 N33093920 1 TC=0,0 L_Lpsr N33093920 GND_FLOAT 2uH

V_Uvcl_Vclo1 VCC_BUF Uvcl_N498931 3.95Vdc V_Uvcl_Vclo2 Uvcl_N50894 VEE_BUF 3.95Vdc X_Uvcl_Uvcl1 OVER_CLAMP Uvcl_N498931 D_ideal X_Uvcl_Uvcl2 Uvcl_N50894 OVER_CLAMP D_ideal

X_Uz_S1 N3309562 GND_FLOAT Uz_N45387 Uz_VZO_3 Zout_Uz_S1 X_Uz_S2 N3309562 GND_FLOAT Uz_N45507 Uz_VZO_3 Zout_Uz_S2 R_Uz_Ra Uz_N45387 Uz_VZO_4 10 TC=0,0 R_Uz_Rb Uz_N45507 Uz_VZO_4 10 TC=0,0 R_Uz_Rm Uz_VZO_3 Uz_VZO_4 10 TC=0,0 X_Uz_Uamp1 VCLP Uz_N36964 Uz_VZO_1 GND_FLOAT VCVS_LIMIT PARAMS:

  • GAIN=1e6 VPOS=6e4 VNEG=-6e4 X_Uz_Uamp2 GND_FLOAT Uz_N37614 Uz_VZO_3 GND_FLOAT VCVS_LIMIT PARAMS:
  • GAIN=1e6 VPOS=6e4 VNEG=-6e4 E_Uz_E1 Uz_VZO_2 GND_FLOAT Uz_VZO_1 Uz_VZO_4 -1 X_Uz_Rg1 GND_FLOAT Uz_N36964 RNOISELESS PARAMS: R=10e6 X_Uz_Rf1 Uz_N36964 Uz_VZO_1 RNOISELESS PARAMS: R=10e6 X_Uz_Rg2 Uz_VZO_2 Uz_N37614 RNOISELESS PARAMS: R=1e6 X_Uz_Rf2 Uz_N37614 Uz_VZO_3 RNOISELESS PARAMS: R=1e6 X_Uz_H1 Uz_VZO_4 OUT VIMON GND_FLOAT Zout_Uz_H1

X_Uthd N3309236 GND_FLOAT VCLP GND_FLOAT EPOLY1

*+PARAMS: COEFF1=0.0 COEFF2=0.0

X_U10 CL_CLAMP GND_FLOAT PD N3309236 GND_FLOAT VCC VEE HPA_PD_SGNL

  • PARAMS: GAIN=1 X_U11 VCC VEE VIMON GND_FLOAT Tran_Iout .ENDS LME49710
*$

.subckt Zout_Uz_S2 1 2 3 4 S_Uz_S2 3 4 1 2 _Uz_S2 RS_Uz_S2 1 2 1G .MODEL _Uz_S2 VSWITCH Roff=10e6 Ron=1.0 Voff=0.1V Von=-0.1V .ends Zout_Uz_S2

.subckt Zout_Uz_S1 1 2 3 4 S_Uz_S1 3 4 1 2 _Uz_S1 RS_Uz_S1 1 2 1G .MODEL _Uz_S1 VSWITCH Roff=10e6 Ron=1.0 Voff=-0.1V Von=0.1V .ends Zout_Uz_S1

*$ .subckt Zout_Uz_H1 1 2 3 4 H_Uz_H1 3 4 VH_Uz_H1 1e3 VH_Uz_H1 1 2 0V .ends Zout_Uz_H1 *$
  • .subckt D_ideal A C D1 A C DNOM .MODEL DNOM D (TT=10p CJO=1e-18 IS=1e-16 RS=1e-4)
*.MODEL DNOM D (TT=10p CJO=1e-18 IS=1e-16 RS=1e-4 N=1e-3) .ENDS D_ideal * *$ .SUBCKT VNSE 1 2 **************************
  • BEGIN SETUP OF NOISE GEN - NANOVOLT/RT-HZ
  • INPUT THREE VARIABLES
  • NLF - NV/RHZ AT (1/F) FREQ
  • FLW - FREQ FOR (1/F) VAL
  • NVR - NV/RHZ FLATBAND
**************************
  • START CALC VALS .PARAM NLF=6.4 .PARAM FLW=8.5 .PARAM NVR=2.5 .PARAM GLF={PWR(FLW,0.25)*NLF/1164} .PARAM RNV={1.184*PWR(NVR,2)} .MODEL DVN D KF={PWR(FLW,0.5)/1E11} IS=1.0E-16
  • END CALC VALS I1 0 7 10E-3 I2 0 8 10E-3 D1 7 0 DVN D2 8 0 DVN E1 3 6 7 8 {GLF} R1 3 0 1E9 R2 3 0 1E9 R3 3 6 1E9 E2 6 4 5 0 10 R4 5 0 {RNV} R5 5 0 {RNV} R6 3 4 1E9 R7 4 0 1E9 E3 1 2 3 4 1 C1 1 0 1E-15 C2 2 0 1E-15 C3 1 2 1E-15 .ENDS VNSE
*$

.SUBCKT FEMT 1 2

**************************
  • BEGIN SETUP OF NOISE GEN - FEMPTOAMPS/RT-HZ
  • INPUT THREE VARIABLES
  • NLFF - SET UP INSE 1/F
  • FLWF - FA/RHZ AT 1/F FREQ
  • NVRF - FA/RHZ FLATBAND
**************************
  • START CALC VALS .PARAM NLFF=3.1e3 .PARAM FLWF=7.5 .PARAM NVRF=1.6e3 .PARAM GLFF={PWR(FLWF,0.25)*NLFF/1164} .PARAM RNVF={1.184*PWR(NVRF,2)} .MODEL DVNF D KF={PWR(FLWF,0.5)/1E11} IS=1.0E-16
  • END CALC VALS I1 0 7 10E-3 I2 0 8 10E-3 D1 7 0 DVNF D2 8 0 DVNF E1 3 6 7 8 {GLFF} R1 3 0 1E9 R2 3 0 1E9 R3 3 6 1E9 E2 6 4 5 0 10 R4 5 0 {RNVF} R5 5 0 {RNVF} R6 3 4 1E9 R7 4 0 1E9 G1 1 2 3 4 1E-6 C1 1 0 1E-15 C2 2 0 1E-15 C3 1 2 1E-15 .ENDS FEMT
* *$ .SUBCKT Tran_Iout VCC VEE VIMON AGND X_Siq1 N1 GND_FLOAT VIMON N2 Amp_Dyn_Iout_Siq1 X_Siq2 N1 GND_FLOAT VIMON N3 Amp_Dyn_Iout_Siq2 C_Ciq1 N1 GND_FLOAT 10e-12 TC=0,0 R_Riq1 N1 VIMON 10 TC=0,0 R_Riq2 N2 GND_FLOAT 10e3 TC=0,0 R_Riq3 GND_FLOAT N3 10e3 TC=0,0 G_Gsourcing VCC GND_FLOAT N3 GND_FLOAT 0.001 G_Gsinking VEE GND_FLOAT N2 GND_FLOAT 0.001 .ENDS Tran_Iout *$ .subckt Amp_Dyn_Iout_Siq1 1 2 3 4 S_Siq1 3 4 1 2 _Siq1 RS_Siq1 1 2 1G .MODEL _Siq1 VSWITCH Roff=1e6 Ron=1.0 Voff=0.0V Von=-0.10V .ends Amp_Dyn_Iout_Siq1 *$

.subckt Amp_Dyn_Iout_Siq2 1 2 3 4 S_Siq2 3 4 1 2 _Siq2 RS_Siq2 1 2 1G .MODEL _Siq2 VSWITCH Roff=1e6 Ron=1.0 Voff=0.0V Von=0.10V .ends Amp_Dyn_Iout_Siq2

*$
  • .subckt VCCS_Limit VCP VCN IOUTP IOUTN PARAMS: Gain = 1.7e-3
  • Ipos = 0.100 Ineg = -0.165 G1 IOUTP IOUTN VALUE={LIMIT(Gain*V(VCP,VCN),Ipos,Ineg)} .ends VCCS_Limit
*$
  • .subckt VCVS_Limit VCP VCN VOUTP VOUTN PARAMS: Gain = -1
  • Vpos = 20m Vneg = -20m E1 VOUTP VOUTN VALUE={LIMIT(Gain*V(VCP,VCN),Vpos,Vneg)} .ends VCVS_Limit
*$
  • .SUBCKT HPA_PD_I VCC VEE PD Vimon AGND Ninp Ninn PARAMS: Vth = 1.4 Imax = 1e-3 Imin = 3n
  • IIBP= 0.55u IIBN= 0.56u
*GBIAS VCC VEE VALUE = {IF(V(PD) >= (V(VEE)+Vth),Imax,Imin)} GBIAS VCC VEE VALUE = {IF(V(PD) >= V(VCC),Imax,Imin)} Ebuf VDD 0 VCC 0 1 Ginp VDD Ninp VALUE = {IF(V(PD) >= V(VCC),IIBP,0)} Ginn VDD Ninn VALUE = {IF(V(PD) >= V(VCC),IIBN,0)} .ENDS *$ .SUBCKT HPA_PD_Sgnl CP CN DIS VP VN VCC VEE PARAMS: GAIN = 1 EVCVS VP VN VALUE = {IF(V(DIS,VEE) >= 1.4,V(CP,CN)*GAIN,0)} .ENDS HPA_PD_Sgnl *$ *$
  • .SUBCKT EPOLY2 1 2 3 4 7 8 PARAMS: Coeff1=0.5 Coeff2=0.5
*EINT 7 8 POLY(2) (1,2) (3,4) (0 Coeff1 Coeff2) EINT 7 8 POLY(2) (1,2) (3,4) (0 0.5 0.5) .ENDS EPOLY2 *$
  • .SUBCKT EPOLY1 1 2 3 4 PARAMS: Coeff1=0.0 Coeff2=0.0
*For distortion purpose EINT 3 4 POLY(1) (1,2) (0 1 8.5e-5 14.26e-4) *EINT 3 4 POLY(1) (1,2) (0 1 0 0) *EINT 3 4 1 2 1 .ENDS EPOLY1 *$
  • .subckt Rnoiseless a b PARAMS: R=1k ERES a 3 VALUE = { I(VSENSE) * R } Rdummy 30 3 1 VSENSE 30 b DC 0V .ends Rnoiseless
*$
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B

It looks as if the 163kHz might coming from the 1.25V precision reference. I'll have to dig into the data sheet to see if I can make sense of this.

It's being sold as a very quiet voltage source, and I had thought that I'd read up on what I needed to do to keep it quiet.

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B

It looks as if the 163kHz was coming from the LTC6655-1.25V precision reference.

Putting in 4.7uF at C10 - rather than the 1.0uF I started off with - seems to make the simulation run a lot faster - about 20 times faster - and cleaned out the visible hash coming from the voltage reference.

The data sheet says use something between 2.7uF and 100uF and recommends film parts - ESR less than 0.1R. They don't like ceramic parts.

Pulling out the LCR filter (L5,L6, C19, C20, R22 and R23) may have speeded up the simulation too.

The 2kHz and 3kHz harmonics aren't as good as they were - only about

65db below the fundamental - so Ill have to do some more digging.
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J

Because of common mode (non)linearity. In most op-amps (especially older designs) the distortion generated by the common mode signal is typically one to two orders of magnitude larger than the transfer distortion. If it is not clear from the data sheet, it is best to measure the CM performance or just assume that it's 40dB worse than the specified figure.

Note that it is seldom modeled in a (free) spice model.

This is a link to an extract discussing it's measurement.

formatting link

No idea. LTSpice is useless for handling large simulation data files so I don't bother trying to use it to check for that sort of thing.

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E

...

Thank you very much for that information.

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E

I changed C10 to 4.7uF and ran the simulation to 10 seconds. L5 etc are still present. FFT from 2s to 10s says 60dB down at 3kHz

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B

On 18/11/2024 2:58 pm, Edward Rawde wrote:

Here's another variation. This one take's John May's advice and spreads the phase shift oscillator over three op amps, all operating with the non-inverting input grounded.

U1 now has only one 3.3pF frequency compensation capacitor - the simulation started slowing down to picoseconds per second from time to time, and this made it happen less often. The two compensation capacitor scheme would probably be fine in real life.

The circuit takes a long time to settle down to stable operation - about

5 seconds,and that after I cut the integrating capacitor from 6.8uF to 680nF and put in D4 to minimise the initial overshoot on the FET gate drive - and the performance isn't wonderful. The second and third harmonics are about 75dB below the fundamental and 65dB down respectively. I'll play about a bit more but the main charm of the circuit is that it is easy to explain what each bit does.

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-1760 -1408 Fet-gate FLAG 1296 -1648 filt1 FLAG 1968 -1664 filt2 FLAG 1504 -976 0 FLAG 1584 -1456 Vcc FLAG -1328 -832 Vee FLAG -288 -1456 0 FLAG -1104 -1440 0 FLAG -688 -1472 0 SYMBOL Opamps\\LT1360 208 -1248 R0 SYMATTR InstName U1 SYMBOL res 48 -1344 R0 WINDOW 0 41 37 Left 2 WINDOW 3 36 71 Left 2 SYMATTR InstName R1 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res -64 -1152 R0 WINDOW 3 41 74 Left 2 WINDOW 0 43 31 Left 2 SYMATTR Value 4k02 SYMATTR InstName R2 SYMATTR SpiceLine tol=1 SYMBOL cap -160 -1136 R0 SYMATTR InstName C1 SYMATTR Value 3.3n SYMBOL schottky 352 -1264 R0 WINDOW 3 -99 -2 Left 2 SYMATTR Value BAS70L SYMATTR InstName D1 SYMBOL schottky 352 -848 R0 WINDOW 3 -99 -6 Left 2 SYMATTR Value BAS70L SYMATTR InstName D2 SYMBOL res 352 -1472 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1a SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 208 -1728 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 20k SYMATTR SpiceLine tol=1 SYMBOL res 480 -1408 R0 WINDOW 0 41 41 Left 2 WINDOW 3 47 81 Left 2 SYMATTR InstName R2a SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 576 -928 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2b SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 720 -928 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2c SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL cap 704 -832 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 220n SYMBOL cap 192 -1008 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 3.3p SYMBOL res 48 -864 R0 WINDOW 0 39 33 Left 2 WINDOW 3 40 74 Left 2 SYMATTR InstName R1b SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL OpAmps\\opamp2 -176 -1584 R0 WINDOW 3 13 108 Left 2 SYMATTR Value LME49710 SYMATTR InstName U3 SYMATTR SpiceModel LME49710 SYMBOL voltage -1376 -1120 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL voltage -1376 -976 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL cap -528 -1664 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 15n SYMATTR SpiceLine V=63 Rser=0.04 Lser=12n SYMBOL res -448 -1520 R270 WINDOW 0 27 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName R4 SYMATTR Value 10.7k SYMATTR SpiceLine tol=1 SYMBOL cap -64 -1792 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C6 SYMATTR Value 15n SYMATTR SpiceLine V=63 Rser=0.04 Lser=12n SYMBOL res -848 -1536 R270 WINDOW 0 34 53 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName R5 SYMATTR Value 10.7k SYMATTR SpiceLine tol=1 SYMBOL njf -1664 -1472 R0 SYMATTR InstName J1 SYMATTR Value MMBF4391 SYMBOL res -1248 -1312 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 4.99k SYMATTR SpiceLine tol=1 SYMBOL res -1424 -1536 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R8 SYMATTR Value 180 SYMATTR SpiceLine tol=1 SYMBOL cap 2784 -1664 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C8 SYMATTR Value 680n SYMBOL res 2528 -1760 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R10 SYMATTR Value 3.9k SYMBOL References\\LTC6655-1.25 2336 -1120 R0 SYMATTR InstName U4 SYMBOL Opamps\\LT1056A 2672 -1456 R0 SYMATTR InstName U5 SYMBOL cap 2576 -1120 R0 SYMATTR InstName C10 SYMATTR Value 4.7µF SYMBOL cap 2592 -1552 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C11 SYMATTR Value 3.3p SYMBOL diode -1616 -1936 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL res -1936 -1568 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R11 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL Opamps\\OP27 576 -1264 R0 SYMATTR InstName U2 SYMBOL res 1296 -1520 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R12 SYMATTR Value 14k SYMBOL res 1136 -1232 R0 SYMATTR InstName R13 SYMATTR Value 62k SYMBOL cap 1232 -1168 R0 SYMATTR InstName C9 SYMATTR Value 2.2n SYMBOL cap 976 -1600 R0 SYMATTR InstName C12 SYMATTR Value 2.2n SYMBOL res 1136 -1312 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R14 SYMATTR Value 30k SYMBOL Opamps\\LT1013 1312 -1376 R0 SYMATTR InstName U6 SYMBOL res 880 -1280 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R15 SYMATTR Value 40.2k SYMBOL res 1968 -1536 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R16 SYMATTR Value 14k SYMBOL cap 1648 -1616 R0 SYMATTR InstName C13 SYMATTR Value 2.2n SYMBOL res 1808 -1328 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R17 SYMATTR Value 30k SYMBOL Opamps\\LT1013 1984 -1392 R0 WINDOW 3 -98 -2 Left 2 SYMATTR InstName U7 SYMBOL res 1488 -1296 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R18 SYMATTR Value 40.2k SYMBOL res 1808 -1184 R0 SYMATTR InstName R19 SYMATTR Value 62k SYMBOL cap 1904 -1120 R0 SYMATTR InstName C14 SYMATTR Value 2.2n SYMBOL FerriteBead 576 -1536 R0 SYMATTR InstName L1 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead 576 -720 R0 SYMATTR InstName L2 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap 752 -1408 R0 SYMATTR InstName C15 SYMATTR Value 100n SYMBOL cap 752 -896 R0 SYMATTR InstName C16 SYMATTR Value 100n SYMBOL res 2416 -1424 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 82k SYMBOL res 2400 -1792 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R20 SYMATTR Value 162k SYMBOL FerriteBead -176 -928 R0 SYMATTR InstName L4 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -336 -1888 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C17 SYMATTR Value 100n SYMBOL cap -336 -1168 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C18 SYMATTR Value 100n SYMBOL Opamps\\LT1013 -1696 -1792 M0 SYMATTR InstName U8 SYMBOL res -1840 -1648 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R21 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL cap 2048 -1184 R0 SYMATTR InstName C21 SYMATTR Value 100n SYMBOL FerriteBead 2064 -1408 R0 SYMATTR InstName L7 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL OpAmps\\opamp2 -1040 -1568 R0 WINDOW 3 12 120 Left 2 SYMATTR Value LME49710 SYMATTR InstName U9 SYMATTR SpiceModel LME49710 SYMBOL FerriteBead -1040 -2000 R0 SYMATTR InstName L5 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -1232 -1888 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C19 SYMATTR Value 100n SYMBOL cap -1184 -1152 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C20 SYMATTR Value 100n SYMBOL FerriteBead -1040 -912 R0 SYMATTR InstName L6 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL res -912 -1728 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R22 SYMATTR Value 4.87k SYMATTR SpiceLine tol=1 SYMBOL FerriteBead -320 -2000 R0 SYMATTR InstName L8 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -912 -1600 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C22 SYMATTR Value 10p SYMBOL OpAmps\\opamp2 -640 -1600 R0 WINDOW 3 13 108 Left 2 SYMATTR Value LME49710 SYMATTR InstName U10 SYMATTR SpiceModel LME49710 SYMBOL cap -736 -1872 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C7 SYMATTR Value 100n SYMBOL FerriteBead -656 -2016 R0 SYMATTR InstName L3 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead -640 -896 R0 SYMATTR InstName L9 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -864 -1152 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C23 SYMATTR Value 100n SYMBOL diode 2704 -1632 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D4 SYMATTR Value 1N4148 SYMBOL res -1072 -1728 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 56 SYMATTR SpiceLine tol=1 TEXT -1960 -904 Left 2 !.MODEL BAS70L D \n+ IS = 3.22E-9 \n+ N = 1.018 \n+ BV = 77 \n+ IBV = 1.67E-7 \n+ RS = 20.89 \n+ CJO = 1.608E-12 \n+ VJ = 0.3891 \n+ M = 0.3683 \n+ FC = 0.5 \n+ EG = 0.69 \n+ XTI = 2 \n.ENDS TEXT -336 -528 Left 2 ;R2 a,b,c, Vishay Beschlag ACAS06S0830372P1AT precision 10k resistor array \n R1a, R1b Maxim MAX5492LB10000+T 10K resistive divider in a SOT-23-5 package TEXT -720 -464 Left 2 !.MODEL MMBF4391 NJF VTO=-4.6 BETA=0.02779 LAMBDA=0.00595 RD=1 RS=1 IS=1e-14 CGD=14p CGS=10.5p PB=1 B=1 KF=1e-18 AF=1 FC=0.5 mfg=Motorola TEXT -432 -408 Left 2 !.tran 0 10s 0 startup TEXT -720 -408 Left 2 !.lib LME49710.lib

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On 18/11/2024 2:58 pm, Edward Rawde wrote:

I've taken John May seriously, and reworked my phase shift oscillator to use three op amps, all with their non-inverting inputs tied to ground.

The results aren't all that impressive, the lower harmonics are about

65dB below the fundamental. Start-up is slow - it takes about five seconds of simulation before the circuit settles down into steady state operation, and that after I dropped the integrating capacitor from 6.8uF to 680nF. The nice thing about the circuit is that I can explain what each bit is doing. I can see a few tweaks that might be worth trying.

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WIRE 416 -688 208 -688 WIRE 576 -688 416 -688 WIRE 1312 -688 1312 -1280 WIRE 1312 -688 576 -688 WIRE 1984 -688 1984 -1296 WIRE 1984 -688 1312 -688 WIRE 2672 -688 2672 -1360 WIRE 2672 -688 1984 -688 FLAG 464 -1152 0 FLAG -48 -1024 0 FLAG -1552 -992 0 FLAG 336 -2064 Vcc FLAG 416 -688 Vee FLAG -544 -1152 0 FLAG 32 -1520 Vout FLAG 2352 -960 0 FLAG 2544 -1152 vref-1.25 FLAG -1760 -1408 Fet-gate FLAG 1296 -1648 filt1 FLAG 1968 -1664 filt2 FLAG 1504 -976 0 FLAG 1584 -1456 Vcc FLAG -1328 -832 Vee FLAG -288 -1456 0 FLAG 2592 -1344 0 SYMBOL Opamps\\LT1360 208 -1248 R0 SYMATTR InstName U1 SYMBOL res 48 -1344 R0 WINDOW 0 41 37 Left 2 WINDOW 3 36 71 Left 2 SYMATTR InstName R1 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res -64 -1152 R0 WINDOW 3 41 74 Left 2 WINDOW 0 43 31 Left 2 SYMATTR Value 4k02 SYMATTR InstName R2 SYMATTR SpiceLine tol=1 SYMBOL cap -160 -1136 R0 SYMATTR InstName C1 SYMATTR Value 3.3n SYMBOL schottky 384 -1264 R180 WINDOW 3 24 0 Left 2 WINDOW 0 24 64 Left 2 SYMATTR Value BAS70L SYMATTR InstName D1 SYMBOL schottky 384 -832 R180 WINDOW 3 24 0 Left 2 WINDOW 0 24 64 Left 2 SYMATTR Value BAS70L SYMATTR InstName D2 SYMBOL res 352 -1472 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1a SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 208 -1728 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 20k SYMATTR SpiceLine tol=1 SYMBOL res 480 -1408 R0 WINDOW 0 41 41 Left 2 WINDOW 3 47 81 Left 2 SYMATTR InstName R2a SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 576 -928 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2b SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 720 -928 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2c SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL cap 704 -832 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 220n SYMBOL cap 192 -1008 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 3.3p SYMBOL res 48 -864 R0 WINDOW 0 39 33 Left 2 WINDOW 3 40 74 Left 2 SYMATTR InstName R1b SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL OpAmps\\opamp2 -176 -1584 R0 WINDOW 3 13 108 Left 2 SYMATTR Value LME49710 SYMATTR InstName U3 SYMATTR SpiceModel LME49710 SYMBOL voltage -1376 -1120 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL voltage -1376 -976 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL cap -528 -1664 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 15n SYMATTR SpiceLine V=63 Rser=0.04 Lser=12n SYMBOL res -448 -1520 R270 WINDOW 0 27 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName R4 SYMATTR Value 10.7k SYMATTR SpiceLine tol=1 SYMBOL cap -64 -1792 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C6 SYMATTR Value 15n SYMATTR SpiceLine V=63 Rser=0.04 Lser=12n SYMBOL res -848 -1536 R270 WINDOW 0 34 53 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName R5 SYMATTR Value 10.7k SYMATTR SpiceLine tol=1 SYMBOL njf -1664 -1472 R0 SYMATTR InstName J1 SYMATTR Value MMBF4391 SYMBOL res -1248 -1312 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 4.99k SYMATTR SpiceLine tol=1 SYMBOL res -1424 -1536 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R8 SYMATTR Value 180 SYMATTR SpiceLine tol=1 SYMBOL cap 2784 -1664 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C8 SYMATTR Value 680n SYMBOL res 2528 -1760 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R10 SYMATTR Value 3.9k SYMBOL References\\LTC6655-1.25 2336 -1120 R0 SYMATTR InstName U4 SYMBOL Opamps\\LT1056A 2672 -1456 R0 SYMATTR InstName U5 SYMBOL cap 2592 -1120 R0 SYMATTR InstName C10 SYMATTR Value 4.7µF SYMBOL cap 2592 -1552 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C11 SYMATTR Value 3.3p SYMBOL res -1840 -1392 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R11 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL Opamps\\OP27 576 -1264 R0 SYMATTR InstName U2 SYMBOL res 1296 -1520 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R12 SYMATTR Value 14k SYMBOL res 1136 -1232 R0 SYMATTR InstName R13 SYMATTR Value 62k SYMBOL cap 1232 -1168 R0 SYMATTR InstName C9 SYMATTR Value 2.2n SYMBOL cap 976 -1600 R0 SYMATTR InstName C12 SYMATTR Value 2.2n SYMBOL res 1136 -1312 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R14 SYMATTR Value 30k SYMBOL Opamps\\LT1013 1312 -1376 R0 SYMATTR InstName U6 SYMBOL res 880 -1280 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R15 SYMATTR Value 40.2k SYMBOL res 1968 -1536 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R16 SYMATTR Value 14k SYMBOL cap 1648 -1616 R0 SYMATTR InstName C13 SYMATTR Value 2.2n SYMBOL res 1808 -1328 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R17 SYMATTR Value 30k SYMBOL Opamps\\LT1013 1984 -1392 R0 WINDOW 3 -98 -2 Left 2 SYMATTR InstName U7 SYMBOL res 1488 -1296 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R18 SYMATTR Value 40.2k SYMBOL res 1808 -1184 R0 SYMATTR InstName R19 SYMATTR Value 62k SYMBOL cap 1904 -1120 R0 SYMATTR InstName C14 SYMATTR Value 2.2n SYMBOL FerriteBead 576 -1536 R0 SYMATTR InstName L1 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead 576 -720 R0 SYMATTR InstName L2 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap 752 -1408 R0 SYMATTR InstName C15 SYMATTR Value 100n SYMBOL cap 752 -896 R0 SYMATTR InstName C16 SYMATTR Value 100n SYMBOL res 2416 -1424 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 82k SYMBOL res 2400 -1792 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R20 SYMATTR Value 162k SYMBOL FerriteBead -176 -928 R0 SYMATTR InstName L4 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -336 -1888 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C17 SYMATTR Value 100n SYMBOL cap -336 -1168 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C18 SYMATTR Value 100n SYMBOL Opamps\\LT1013 -1696 -1792 M0 SYMATTR InstName U8 SYMBOL res -1840 -1648 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R21 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL cap 2048 -1184 R0 SYMATTR InstName C21 SYMATTR Value 100n SYMBOL FerriteBead 2064 -1408 R0 SYMATTR InstName L7 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL OpAmps\\opamp2 -1040 -1568 R0 WINDOW 3 12 120 Left 2 SYMATTR Value LME49710 SYMATTR InstName U9 SYMATTR SpiceModel LME49710 SYMBOL FerriteBead -1040 -2000 R0 SYMATTR InstName L5 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -1232 -1888 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C19 SYMATTR Value 100n SYMBOL cap -1184 -1152 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C20 SYMATTR Value 100n SYMBOL FerriteBead -1040 -912 R0 SYMATTR InstName L6 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL res -912 -1728 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R22 SYMATTR Value 4.87k SYMATTR SpiceLine tol=1 SYMBOL FerriteBead -320 -2000 R0 SYMATTR InstName L8 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -912 -1600 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C22 SYMATTR Value 10p SYMBOL OpAmps\\opamp2 -640 -1600 R0 WINDOW 3 13 108 Left 2 SYMATTR Value LME49710 SYMATTR InstName U10 SYMATTR SpiceModel LME49710 SYMBOL cap -736 -1872 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C7 SYMATTR Value 100n SYMBOL FerriteBead -656 -2016 R0 SYMATTR InstName L3 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead -640 -896 R0 SYMATTR InstName L9 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -864 -1152 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C23 SYMATTR Value 100n SYMBOL npn -1888 -1152 R0 SYMATTR InstName Q1 SYMATTR Value BC547B SYMBOL npn -1984 -1152 M0 SYMATTR InstName Q2 SYMATTR Value BC547B SYMBOL res -1840 -1024 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R23 SYMATTR Value 1.2k SYMATTR SpiceLine tol=0.1 SYMBOL res -2064 -1024 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R24 SYMATTR Value 1.2k SYMATTR SpiceLine tol=0.1 SYMBOL res -2064 -1392 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R25 SYMATTR Value 6.8k SYMATTR SpiceLine tol=0.1 SYMBOL res 2512 -1344 R0 WINDOW 0 41 41 Left 2 WINDOW 3 47 81 Left 2 SYMATTR InstName R26 SYMATTR Value 100k SYMATTR SpiceLine tol=0.1 SYMBOL res -1072 -1728 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 82 TEXT -1712 -776 Left 2 !.MODEL BAS70L D \n+ IS = 3.22E-9 \n+ N = 1.018 \n+ BV = 77 \n+ IBV = 1.67E-7 \n+ RS = 20.89 \n+ CJO = 1.608E-12 \n+ VJ = 0.3891 \n+ M = 0.3683 \n+ FC = 0.5 \n+ EG = 0.69 \n+ XTI = 2 \n.ENDS TEXT -336 -528 Left 2 ;R2 a,b,c, Vishay Beschlag ACAS06S0830372P1AT precision 10k resistor array \n R1a, R1b Maxim MAX5492LB10000+T 10K resistive divider in a SOT-23-5 package TEXT -720 -464 Left 2 !.MODEL MMBF4391 NJF VTO=-4.6 BETA=0.02779 LAMBDA=0.00595 RD=1 RS=1 IS=1e-14 CGD=14p CGS=10.5p PB=1 B=1 KF=1e-18 AF=1 FC=0.5 mfg=Motorola TEXT -432 -408 Left 2 !.tran 0 10s 0 startup TEXT -720 -408 Left 2 !.lib LME49710.lib

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"Bill Sloman" snipped-for-privacy@ieee.org wrote in message news:vhibce$1t7v2$ snipped-for-privacy@dont-email.me...

The simulation died after 3 seconds, as if insufficient gain to sustain oscillation.

You seem to have a lot of components. Are you sure you really need all those ferrites?

Here's my really definitely final final offering.

A comfortable 90dB down at 2kHz and > 100 dB elsewhere. Also looks clean either side of 1kHz. Whether or not this has anything to do with reality I do not know. The diode stabilizer string will be temperature dependent, requiring readjustment of R4 and a total of three adjustments are needed. Only three op amps (two packages) are needed.

Version 4 SHEET 1 2196 932 WIRE -64 -672 -96 -672 WIRE 48 -672 0 -672 WIRE -96 -576 -96 -672 WIRE -64 -576 -96 -576 WIRE 48 -576 48 -672 WIRE 48 -576 16 -576 WIRE 128 -528 112 -528 WIRE 208 -528 192 -528 WIRE 288 -528 272 -528 WIRE 368 -528 352 -528 WIRE 448 -528 432 -528 WIRE 528 -528 512 -528 WIRE 640 -528 592 -528 WIRE 640 -512 640 -528 WIRE -32 -464 -32 -480 WIRE 48 -448 48 -576 WIRE 48 -448 0 -448 WIRE -96 -432 -96 -576 WIRE -64 -432 -96 -432 WIRE 112 -416 112 -528 WIRE 112 -416 0 -416 WIRE 160 -416 112 -416 WIRE 208 -416 160 -416 WIRE 336 -416 288 -416 WIRE 400 -416 336 -416 WIRE 512 -416 400 -416 WIRE 624 -416 512 -416 WIRE -96 -384 -96 -432 WIRE -32 -384 -32 -400 WIRE 48 -368 48 -448 WIRE 336 -368 336 -416 WIRE 160 -352 160 -416 WIRE 400 -352 400 -416 WIRE 512 -288 512 -416 WIRE 624 -288 624 -416 WIRE -96 -272 -96 -304 WIRE -96 -272 -192 -272 WIRE -96 -240 -96 -272 WIRE 48 -240 48 -288 WIRE 160 -240 160 -288 WIRE 336 -240 336 -288 WIRE 400 -240 400 -288 WIRE -192 -176 -192 -272 WIRE -224 -128 -256 -128 WIRE -96 -128 -96 -160 WIRE -96 -128 -128 -128 WIRE -80 -128 -96 -128 WIRE 16 -128 -80 -128 WIRE 176 -128 96 -128 WIRE 288 -128 176 -128 WIRE 512 -128 512 -224 WIRE 512 -128 368 -128 WIRE -256 -48 -256 -128 WIRE -208 -48 -256 -48 WIRE -80 -48 -80 -128 WIRE -80 -48 -128 -48 WIRE 176 -16 176 -128 WIRE 176 -16 64 -16 WIRE 240 -16 176 -16 WIRE 368 -16 320 -16 WIRE 512 -16 512 -128 WIRE 512 -16 448 -16 WIRE -256 0 -256 -48 WIRE 144 48 144 32 WIRE 64 96 64 -16 WIRE 112 96 64 96 WIRE 512 96 512 -16 WIRE 512 96 272 96 WIRE -32 128 -96 128 WIRE 112 128 -32 128 WIRE 624 144 624 -224 WIRE 656 144 624 144 WIRE 752 144 720 144 WIRE -320 160 -400 160 WIRE -256 160 -320 160 WIRE -32 160 -32 128 WIRE 112 160 64 160 WIRE 624 160 624 144 WIRE 624 160 272 160 WIRE 752 176 752 144 WIRE -400 208 -400 160 WIRE -256 224 -256 160 WIRE 144 224 144 208 WIRE -32 256 -32 224 WIRE 64 272 64 160 WIRE 160 272 64 272 WIRE 288 272 160 272 WIRE 400 272 352 272 WIRE 512 272 512 96 WIRE 512 272 480 272 WIRE 64 288 64 272 WIRE 160 288 160 272 WIRE 752 288 752 256 WIRE 880 288 752 288 WIRE 928 288 880 288 WIRE 928 320 928 288 WIRE -96 336 -96 128 WIRE -400 384 -400 288 WIRE -400 384 -480 384 WIRE 64 384 64 368 WIRE 160 384 160 352 WIRE 160 384 64 384 WIRE -480 400 -480 384 WIRE -400 400 -400 384 WIRE -256 400 -256 288 WIRE -256 400 -400 400 WIRE 64 416 64 384 WIRE 208 432 128 432 WIRE 320 432 288 432 WIRE 432 432 384 432 WIRE 928 432 928 400 WIRE 512 448 512 272 WIRE 624 448 624 160 WIRE -400 480 -400 400 WIRE -256 496 -256 400 WIRE 288 544 288 528 WIRE 432 560 432 432 WIRE 432 560 320 560 WIRE 624 560 624 512 WIRE 624 560 432 560 WIRE -96 576 -96 416 WIRE -48 576 -96 576 WIRE 0 576 -48 576 WIRE 128 576 128 432 WIRE 128 576 80 576 WIRE 192 576 128 576 WIRE 256 576 192 576 WIRE 432 592 320 592 WIRE 512 592 512 512 WIRE 512 592 432 592 WIRE 624 592 624 560 WIRE 704 592 624 592 WIRE -96 624 -96 576 WIRE -48 624 -48 576 WIRE 288 624 288 608 WIRE 512 624 512 592 WIRE 704 624 704 592 WIRE 432 640 432 592 WIRE 624 640 624 592 WIRE -400 656 -400 560 WIRE -320 656 -400 656 WIRE -256 656 -256 560 WIRE -256 656 -320 656 WIRE -96 736 -96 688 WIRE -48 736 -48 688 WIRE -48 736 -96 736 WIRE 432 736 432 704 WIRE 512 736 512 704 WIRE 512 736 432 736 WIRE 624 736 624 704 WIRE 624 736 512 736 WIRE 704 736 704 704 WIRE 704 736 624 736 WIRE -96 768 -96 736 WIRE 432 768 432 736 FLAG -480 400 0 FLAG 288 528 V+ FLAG 144 224 V- FLAG -320 160 V+ FLAG -320 656 V- FLAG 880 288 output FLAG 144 32 V+ FLAG 288 624 V- FLAG 432 768 0 FLAG -32 256 0 FLAG -32 -480 V+ FLAG -32 -384 V- FLAG -256 0 0 FLAG 400 -240 0 FLAG 160 -240 0 FLAG 64 416 0 FLAG 336 -240 0 FLAG -96 768 0 FLAG 192 576 dc-trim FLAG 640 -512 0 FLAG 48 -240 0 FLAG 928 432 0 SYMBOL voltage -400 192 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 12 7 Left 2 WINDOW 3 15 104 Left 2 SYMATTR SpiceLine Rser=0.01 SYMATTR InstName V1 SYMATTR Value 6 SYMBOL res 496 256 R90 WINDOW 0 1 52 VBottom 2 WINDOW 3 33 45 VTop 2 SYMATTR InstName R11 SYMATTR Value 10.5k SYMBOL cap 352 256 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 35 30 VTop 2 SYMATTR InstName C8 SYMATTR Value 15n SYMATTR SpiceLine V=16 Irms=271m Rser=0.594318 Lser=0 mfg="KEMET" pn="C0603C153K4RAC" type="X7R" SYMBOL res 112 -144 R90 WINDOW 0 -1 46 VBottom 2 WINDOW 3 35 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 6.34k SYMBOL res 384 -144 R90 WINDOW 0 -4 61 VBottom 2 WINDOW 3 39 55 VTop 2 SYMATTR InstName R8 SYMATTR Value 13k SYMBOL njf -128 -176 R90 WINDOW 0 -37 23 VRight 2 WINDOW 3 -9 -3 VRight 2 SYMATTR InstName J1 SYMATTR Value J113 SYMBOL voltage -400 464 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 10 0 Left 2 WINDOW 3 15 104 Left 2 SYMATTR SpiceLine Rser=0.01 SYMATTR InstName V2 SYMATTR Value 6 SYMBOL res 48 272 R0 WINDOW 3 36 65 Left 2 SYMATTR Value 10.5k SYMATTR InstName R10 SYMBOL schottky 496 -288 R0 WINDOW 3 -17 -26 VRight 2 SYMATTR Value BAS40HY SYMATTR InstName D1 SYMATTR Description Diode SYMATTR Type diode SYMBOL res -112 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 82 SYMBOL OpAmps\\LT1994 176 128 R0 WINDOW 3 10 -65 Left 2 WINDOW 0 11 -95 Left 2 SYMATTR InstName U1 SYMBOL schottky 528 448 M0 WINDOW 3 52 -26 VRight 2 WINDOW 0 -18 3 Left 2 SYMATTR Value BAS40HY SYMATTR InstName D3 SYMATTR Description Diode SYMATTR Type diode SYMBOL schottky 640 448 M0 WINDOW 3 49 -26 VRight 2 WINDOW 0 -21 4 Left 2 SYMATTR Value BAS40HY SYMATTR InstName D4 SYMATTR Description Diode SYMATTR Type diode SYMBOL res 528 608 M0 WINDOW 3 25 87 Left 2 SYMATTR Value 220k SYMATTR InstName R16 SYMBOL res 720 608 M0 WINDOW 3 27 87 Left 2 SYMATTR Value 220k SYMATTR InstName R17 SYMBOL res -112 -256 R0 WINDOW 0 38 42 Left 2 WINDOW 3 36 66 Left 2 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL res 320 -384 R0 WINDOW 0 -50 69 Left 2 WINDOW 3 -54 98 Left 2 SYMATTR InstName R13 SYMATTR Value 220k SYMBOL res 464 -32 R90 WINDOW 0 -1 60 VBottom 2 WINDOW 3 32 57 VTop 2 SYMATTR InstName R9 SYMATTR Value 600k SYMBOL res -80 -288 R180 WINDOW 0 40 70 Left 2 WINDOW 3 45 42 Left 2 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL res -80 432 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R5 SYMATTR Value 33k SYMBOL res 192 416 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R15 SYMATTR Value 220 SYMBOL res -16 560 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R14 SYMATTR Value 10k SYMBOL cap 176 352 R180 WINDOW 0 -37 41 Left 2 WINDOW 3 -50 13 Left 2 SYMATTR InstName C7 SYMATTR Value 15n SYMATTR SpiceLine V=16 Irms=271m Rser=0.594318 Lser=0 mfg="KEMET" pn="C0603C153K4RAC" type="X7R" SYMBOL cap 720 128 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C13 SYMATTR Value 100000n SYMATTR SpiceLine V=6.3 Irms=0 Rser=0.002 Lser=0 mfg="TDK" pn="C575OX5ROJI07M" type="X5R" SYMBOL res 736 160 R0 SYMATTR InstName R18 SYMATTR Value 600 SYMBOL res 192 -400 R270 WINDOW 0 35 55 VTop 2 WINDOW 3 -6 55 VBottom 2 SYMATTR InstName R12 SYMATTR Value 220k SYMBOL cap 176 -352 M0 WINDOW 0 -22 9 Left 2 WINDOW 3 -75 48 Left 2 SYMATTR InstName C6 SYMATTR Value 10000n SYMATTR SpiceLine V=6.3 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60J106ME15" type="X5R" SYMBOL cap 416 -352 M0 WINDOW 0 -32 51 Left 2 WINDOW 3 -72 7 Left 2 SYMATTR InstName C10 SYMATTR Value 10000n SYMATTR SpiceLine V=6.3 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60J106ME15" type="X5R" SYMBOL cap 384 448 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName C9 SYMATTR Value 10000n SYMATTR SpiceLine V=6.3 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60J106ME15" type="X5R" SYMBOL cap 416 640 R0 WINDOW 0 -37 6 Left 2 WINDOW 3 -77 53 Left 2 SYMATTR InstName C11 SYMATTR Value 10000n SYMATTR SpiceLine V=6.3 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60J106ME15" type="X5R" SYMBOL cap 608 640 R0 WINDOW 0 -33 9 Left 2 WINDOW 3 -72 51 Left 2 SYMATTR InstName C12 SYMATTR Value 10000n SYMATTR SpiceLine V=6.3 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60J106ME15" type="X5R" SYMBOL cap -272 224 R0 WINDOW 0 -22 9 Left 2 WINDOW 3 -79 48 Left 2 SYMATTR InstName C1 SYMATTR Value 10000n SYMATTR SpiceLine V=6.3 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60J106ME15" type="X5R" SYMBOL cap -272 496 R0 WINDOW 0 -22 9 Left 2 WINDOW 3 -75 50 Left 2 SYMATTR InstName C2 SYMATTR Value 10000n SYMATTR SpiceLine V=6.3 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60J106ME15" type="X5R" SYMBOL cap -16 224 R180 WINDOW 0 23 78 Left 2 WINDOW 3 -74 78 Left 2 SYMATTR InstName C4 SYMATTR Value 10000n SYMATTR SpiceLine V=6.3 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60J106ME15" type="X5R" SYMBOL diode -80 688 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D5 SYMATTR Value 1N4148 SYMBOL cap -64 688 M180 WINDOW 0 24 56 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C5 SYMATTR Value 1000n SYMATTR SpiceLine V=6.3 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM032R60J105ME05" type="X5R" SYMBOL OpAmps\\LT1678 -32 -432 M0 WINDOW 0 -56 49 Left 2 WINDOW 3 -47 89 Left 2 SYMATTR InstName U2A SYMBOL diode 192 -544 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D6 SYMATTR Value 1N4148 SYMBOL diode 272 -544 R90 WINDOW 0 58 31 VBottom 2 WINDOW 3 -28 34 VTop 2 SYMATTR InstName D7 SYMATTR Value 1N4148 SYMBOL diode 352 -544 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D8 SYMATTR Value 1N4148 SYMBOL diode 432 -544 R90 WINDOW 0 58 27 VBottom 2 WINDOW 3 -27 31 VTop 2 SYMATTR InstName D9 SYMATTR Value 1N4148 SYMBOL diode 512 -544 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D10 SYMATTR Value 1N4148 SYMBOL schottky 608 -288 R0 WINDOW 3 -16 -25 VRight 2 SYMATTR Value BAS40HY SYMATTR InstName D2 SYMATTR Description Diode SYMATTR Type diode SYMBOL res -80 -560 R270 WINDOW 0 33 55 VTop 2 WINDOW 3 -3 55 VBottom 2 SYMATTR InstName R4 SYMATTR Value 3.3k SYMBOL res 32 -384 R0 SYMATTR InstName R6 SYMATTR Value 10k SYMBOL diode 592 -544 R90 WINDOW 0 59 29 VBottom 2 WINDOW 3 -25 30 VTop 2 SYMATTR InstName D11 SYMATTR Value 1N4148 SYMBOL res 912 304 R0 SYMATTR InstName R19 SYMATTR Value 600 SYMBOL OpAmps\\LT1678 288 576 M0 WINDOW 0 23 -47 Left 2 WINDOW 3 19 37 Left 2 SYMATTR InstName U2B SYMBOL cap 0 -688 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 47p SYMBOL res 336 -32 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R20 SYMATTR Value 470k TEXT -496 696 Left 2 !.tran 0 350s 50s startup TEXT 72 -664 Left 2 ;R4 18k ten turn. TEXT 72 -640 Left 2 ;Adjust for correct gate voltage, TEXT 72 -616 Left 2 ;minimum distortion and good TEXT 72 -592 Left 2 ;settling time at power on. TEXT -328 40 Left 2 ;R3 150 ohm ten turn. TEXT -328 72 Left 2 ;Adjust for minimum distortion. TEXT 296 48 Left 2 ;R9 1Meg ten turn. TEXT 952 272 Left 2 ;1kHz, > 90dB harmonic purity TEXT 744 504 Left 2 ;Copyright Edward Rawde, Nov 2024. TEXT 744 536 Left 2 ;rawde dot edward at the popular email TEXT 744 472 Left 2 ;Not for commercial use. TEXT -448 -640 Left 2 ;1kHz sinewave oscillator, TEXT -448 -616 Left 2 ;> 90dB harmonic purity. TEXT 744 568 Left 2 ;service everyone uses for some reason.

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B

The circuit starts off by reducing gain. I think I can do something about that.

But I know what they all do.

No, but they are cheap, and op amps injecting hash into the power rails are never a good idea. Power supply rejection drops with frequency, and U1 in particular pulls spikes of current from the power rails twice per cycle.

I'll take a look at it.

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B

Simulate for 350 seconds? Don't collect data for the first 50 seconds?

I've no idea why you are using the LT1994. The circuit doesn't have a common mode problem, so why are you using an op amp designed to deal with one?

This is sci.electronics.design not sci.electronics.incremental-development.

And the six diode "stabiliser string" is nuts. If you need a 3.6V reference voltage there are lots of ways to do it with more precision and better temperature stability.

__ Bill Sloman, Sydney

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E

Simulate for 100 seconds will be enough but will still need a few hours. It takes at least 20 seconds to fully stabilize.

In that case please show a circuit with better performance. It may be that some of the circuits JM posted can do better but if so then why are you using a circuit with so many components? My circuit has far fewer components than yours.

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J

Thats a pretty unusual circuit. Was the original intent to create a balanced output?

If you're trying to measure harmonics at a low level with ltspice you need to set it up correctly. You need to turn off the raw file compression (plotwinsize=0 option) and make sure the data is not stored as single precision (the default) by setting option numdgt > 6. Your also need to set the maximum timestep to something in the region of 1/1000 (or 1/2000) of the fundamental period. If there's convergence issues you might try setting vntol=1e-12 and reltol=1e-6, and possibly setting itl2-4 to about 1000.

I tried your circuit with the dc servo removed (it was just complicating things) and changed the fet control a little. The fet your using isn't a great choice - look for something with a large pinchoff voltage and a large idss, and jig things so that it operates with vgs close to zero and with very little voltage swing across it. As it was you were operating it pretty much at pinchoff.

You dont need to run your sims for long as some others have said. A few cycles is all you need. See if the attached runs for you. When doing the fft use a blackman-harris window, H2,H3 should be about

-120,-150dBc. You should test the LT1944 in isolation as it may not model distortion at all (most LT spice models are works of fiction).

There is an option in ltspice to stop it turning U's into mu.

Version 4 SHEET 1 2196 932 WIRE -96 -672 -192 -672 WIRE 32 -672 -32 -672 WIRE 224 -672 112 -672 WIRE 512 -672 304 -672 WIRE 512 -640 512 -672 WIRE -192 -624 -192 -672 WIRE -192 -576 -192 -624 WIRE -96 -576 -192 -576 WIRE 32 -576 32 -672 WIRE 32 -576 -16 -576 WIRE -64 -464 -64 -480 WIRE 32 -448 32 -576 WIRE 32 -448 -32 -448 WIRE 112 -448 112 -672 WIRE 112 -448 32 -448 WIRE 224 -448 112 -448 WIRE 384 -448 304 -448 WIRE 512 -448 448 -448 WIRE -192 -432 -192 -576 WIRE -192 -432 -288 -432 WIRE -96 -432 -192 -432 WIRE 32 -416 -32 -416 WIRE -288 -384 -288 -432 WIRE -64 -384 -64 -400 WIRE 32 -384 32 -416 WIRE -288 -272 -288 -304 WIRE -192 -272 -288 -272 WIRE -192 -240 -192 -272 WIRE 256 -192 64 -192 WIRE 512 -192 512 -448 WIRE 512 -192 336 -192 WIRE -288 -176 -288 -272 WIRE -320 -128 -352 -128 WIRE -192 -128 -192 -160 WIRE -192 -128 -224 -128 WIRE -144 -128 -192 -128 WIRE -96 -128 -144 -128 WIRE 64 -128 64 -192 WIRE 64 -128 -16 -128 WIRE -560 -80 -560 -128 WIRE -352 -48 -352 -128 WIRE -304 -48 -352 -48 WIRE -144 -48 -144 -128 WIRE -144 -48 -224 -48 WIRE 688 -32 688 -144 WIRE 720 -32 688 -32 WIRE 144 -16 144 -32 WIRE -352 0 -352 -48 WIRE 720 0 720 -32 WIRE 64 32 64 -128 WIRE 112 32 64 32 WIRE 352 32 272 32 WIRE 512 32 512 -192 WIRE 512 32 352 32 WIRE 112 64 -32 64 WIRE -560 96 -560 0 WIRE -560 96 -640 96 WIRE -32 96 -32 64 WIRE 112 96 64 96 WIRE 336 96 272 96 WIRE -640 112 -640 96 WIRE 720 112 720 80 WIRE 848 112 720 112 WIRE 896 112 848 112 WIRE 896 144 896 112 WIRE 144 160 144 144 WIRE -560 192 -560 96 WIRE 896 256 896 224 WIRE 64 272 64 96 WIRE 192 272 64 272 WIRE 256 272 192 272 WIRE 288 272 256 272 WIRE 400 272 352 272 WIRE 512 272 512 32 WIRE 512 272 480 272 WIRE 64 336 64 272 WIRE 192 336 192 272 WIRE -560 368 -560 272 WIRE 64 432 64 416 WIRE 192 432 192 400 WIRE 192 432 64 432 WIRE 64 464 64 432 FLAG -640 112 0 FLAG 144 160 V- FLAG -560 -128 V+ FLAG -560 368 V- FLAG 848 112 output FLAG 144 -32 V+ FLAG -64 -480 V+ FLAG -64 -384 V- FLAG -352 0 0 FLAG 64 464 0 FLAG 896 256 0 FLAG 32 -384 0 FLAG 512 -560 0 FLAG 352 32 vop FLAG 336 96 von FLAG -192 -624 vg FLAG 256 272 vx FLAG -32 160 0 SYMBOL voltage -560 -96 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 12 7 Left 2 WINDOW 3 15 104 Left 2 SYMATTR InstName V1 SYMATTR Value 6 SYMBOL res 496 256 R90 WINDOW 0 1 52 VBottom 2 WINDOW 3 33 45 VTop 2 SYMATTR InstName R11 SYMATTR Value 10.5k SYMBOL cap 352 256 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 35 30 VTop 2 SYMATTR InstName C8 SYMATTR Value 15n SYMATTR SpiceLine V=16 Irms=271m Rser=0.594318 Lser=0 mfg="KEMET" pn="C0603C153K4RAC" type="X7R" SYMBOL res 0 -144 R90 WINDOW 0 -1 46 VBottom 2 WINDOW 3 35 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 6470 SYMBOL res 352 -208 R90 WINDOW 0 -4 61 VBottom 2 WINDOW 3 39 55 VTop 2 SYMATTR InstName R8 SYMATTR Value 13k SYMBOL njf -224 -176 R90 WINDOW 0 -37 23 VRight 2 WINDOW 3 -9 -3 VRight 2 SYMATTR InstName J1 SYMATTR Value J113 SYMBOL voltage -560 176 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 10 0 Left 2 WINDOW 3 15 104 Left 2 SYMATTR InstName V2 SYMATTR Value 6 SYMBOL res 48 320 R0 WINDOW 3 36 65 Left 2 SYMATTR Value 10.5k SYMATTR InstName R10 SYMBOL schottky 448 -464 R90 WINDOW 3 32 32 VTop 2 WINDOW 0 0 32 VBottom 2 SYMATTR Value BAS40HY SYMATTR InstName D1 SYMATTR Description Diode SYMATTR Type diode SYMBOL res -208 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 50 SYMBOL OpAmps\\LT1994 176 64 R0 WINDOW 3 10 -65 Left 2 WINDOW 0 11 -95 Left 2 SYMATTR InstName U1 SYMBOL res -208 -256 R0 WINDOW 0 38 42 Left 2 WINDOW 3 36 66 Left 2 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL res -304 -288 M180 WINDOW 0 40 70 Left 2 WINDOW 3 45 42 Left 2 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL cap 208 400 R180 WINDOW 0 -37 41 Left 2 WINDOW 3 -50 13 Left 2 SYMATTR InstName C7 SYMATTR Value 15n SYMATTR SpiceLine V=16 Irms=271m Rser=0.594318 Lser=0 mfg="KEMET" pn="C0603C153K4RAC" type="X7R" SYMBOL res 704 -16 R0 SYMATTR InstName R18 SYMATTR Value 600 SYMBOL OpAmps\\LT1678 -64 -432 M0 WINDOW 0 -56 49 Left 2 WINDOW 3 -47 89 Left 2 SYMATTR InstName U2A SYMBOL res -112 -560 R270 WINDOW 0 33 55 VTop 2 WINDOW 3 -3 55 VBottom 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL res 320 -464 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 10k SYMBOL res 880 128 R0 SYMATTR InstName R19 SYMATTR Value 600 SYMBOL cap -32 -688 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 100u SYMBOL res 320 -688 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 10K SYMBOL voltage 512 -656 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value -0.2 SYMBOL cap -48 96 R0 SYMATTR InstName C1 SYMATTR Value 1u TEXT -800 -536 Left 2 !.tran 0 2 0 1u uic TEXT -448 56 Left 2 ;R3 150 ohm ten turn. TEXT -456 88 Left 2 ;Adjust for minimum distortion. TEXT 288 -40 Left 2 ;R9 1Meg ten turn. TEXT 920 96 Left 2 ;1kHz, > 90dB harmonic purity TEXT 712 328 Left 2 ;Copyright Edward Rawde, Nov 2024. TEXT 712 360 Left 2 ;rawde dot edward at the popular email TEXT 712 296 Left 2 ;Not for commercial use. TEXT 712 392 Left 2 ;service everyone uses for some reason. TEXT -800 -600 Left 2 !.options plotwinsize=0 numdgt=7 method=trap TEXT -800 -568 Left 2 !.ic v(vg)=-0.8 v(vx)=0.5

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B

But you don't seem to be able to tell us what they do.

I think I've found my conceptual problem with my circuit. Tweaking the gain around the three-amplifier ring tweaks both amplitude and frequency

- with more gain a lower frequency signal can still propagate around the ring.

I've got to find a mechanism that will separate amplitude from frequency. My copy of Williams and Taylor on electronic filter design may get perused again. __ Bill Sloman, Sydney

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J

To quote Jim Williams, "always invert."

Just the ESD diodes are a distortion hazard. I've seen people bootstrap the power supplies to improve CMRR.

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P

“Except when you can’t.”

Pease has an article somewhere about how to measure CMR and PSR correctly—as he says, most of the obvious methods actually measure open-loop gain.

Cheers

Phil Hobbs

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J

I just had a look at the LT1994 datasheet - it looks like you need 20 swg to connect up the inputs (40ish uA bias) so the feedback impedances need to be reduced by a factor or 50 or 100 to eliminate that huge offset (say 320,500n and 960,480). That will result in a large increase in the fet drop and the distortion products.

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E

"JM" snipped-for-privacy@gmail.com wrote in message news: snipped-for-privacy@4ax.com...

..

Actually it was so that the diodes feeding the level control circuit made equal contribution. Also I wanted to reduce component count if possible so I went looking for differential output op amps and found the LT1994. I wasn't very happy with the +/- 6V rail limitation but decided I could live with it.

Thank you very much for this information. I learn something new about LTSpice every day.

I chose the J113 to be sure of sufficient gate control range since the output of the driving op amp isn't going to go below 6V in an LT1994 circuit.

That makes sense. If it's a continuous repeating signal then why would you need more than a few cycles as long as you wait for the circuit to settle?

It runs fine and has the best performance I've seen so far in a simulation.

This is certainly a big concern. I likely won't get to build this circuit in reality but it wouldn't be a surprise to me if a real circuit has very different behaviour, particularly from a distortion point of view.

Where is it?

Thank you very much for your contribution, it is much appreciated.

My goal was to find out whether a very low distortion sinewave oscillator could be made without using lamps, thermistors or opto devices.

Based on the circuit you posted and in an attempt to get rid of the LT1994 I used the two op amp oscillator from one of your previous posts and came up with the following circuit. It works but shows an issue at 2kHz not even 80dB down. What's causing that harmonic?

You may want to shorten the simulation time and put initial conditions in.

Version 4 SHEET 1 2196 932 WIRE 352 -592 256 -592 WIRE 480 -592 416 -592 WIRE 784 -592 672 -592 WIRE 1072 -592 864 -592 WIRE 1072 -560 1072 -592 WIRE 256 -544 256 -592 WIRE 256 -496 256 -544 WIRE 352 -496 256 -496 WIRE 480 -496 480 -592 WIRE 480 -496 432 -496 WIRE 1072 -464 1072 -480 WIRE -192 -432 -192 -480 WIRE 384 -384 384 -400 WIRE 480 -368 480 -496 WIRE 480 -368 416 -368 WIRE 672 -368 672 -592 WIRE 672 -368 480 -368 WIRE 784 -368 672 -368 WIRE 944 -368 864 -368 WIRE 1168 -368 1008 -368 WIRE 256 -352 256 -496 WIRE 352 -352 256 -352 WIRE 480 -336 416 -336 WIRE 256 -304 256 -352 WIRE 384 -304 384 -320 WIRE 480 -304 480 -336 WIRE -192 -256 -192 -352 WIRE -192 -256 -272 -256 WIRE -272 -240 -272 -256 WIRE 448 -192 368 -192 WIRE 560 -192 512 -192 WIRE 960 -192 880 -192 WIRE 1072 -192 1024 -192 WIRE 256 -176 256 -224 WIRE 256 -176 160 -176 WIRE -192 -160 -192 -256 WIRE 160 -112 160 -176 WIRE 368 -96 368 -192 WIRE 432 -96 368 -96 WIRE 560 -96 560 -192 WIRE 560 -96 512 -96 WIRE 880 -96 880 -192 WIRE 944 -96 880 -96 WIRE 1072 -96 1072 -192 WIRE 1072 -96 1024 -96 WIRE 256 -32 256 -176 WIRE 448 0 448 -16 WIRE -192 16 -192 -80 WIRE 160 16 160 -32 WIRE 160 16 112 16 WIRE 192 16 160 16 WIRE 320 16 288 16 WIRE 368 16 368 -96 WIRE 368 16 320 16 WIRE 416 16 368 16 WIRE 960 16 960 0 WIRE 560 32 560 -96 WIRE 560 32 480 32 WIRE 624 32 560 32 WIRE 672 32 624 32 WIRE 752 32 736 32 WIRE 880 32 880 -96 WIRE 880 32 832 32 WIRE 928 32 880 32 WIRE 416 48 368 48 WIRE 1072 48 1072 -96 WIRE 1072 48 992 48 WIRE 1168 48 1168 -368 WIRE 1168 48 1072 48 WIRE 928 64 880 64 WIRE 448 80 448 64 WIRE 112 96 112 16 WIRE 192 96 112 96 WIRE 320 96 320 16 WIRE 320 96 272 96 WIRE 960 96 960 80 WIRE 368 112 368 48 WIRE 880 112 880 64 WIRE 112 192 112 96 WIRE 640 192 112 192 WIRE 1168 192 1168 48 WIRE 1168 192 720 192 FLAG -272 -240 0 FLAG -192 -480 V+ FLAG -192 16 V- FLAG 384 -400 V+ FLAG 384 -304 V- FLAG 480 -304 0 FLAG 1072 -464 0 FLAG 256 -544 vg FLAG 880 112 0 FLAG 368 112 0 FLAG 624 32 vout2 FLAG 448 -16 V+ FLAG 448 80 V- FLAG 960 0 V+ FLAG 960 96 V- SYMBOL voltage -192 -448 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 12 7 Left 2 WINDOW 3 15 104 Left 2 SYMATTR InstName V1 SYMATTR Value 6 SYMBOL njf 192 -32 M90 WINDOW 0 -37 23 VRight 2 WINDOW 3 -9 -3 VRight 2 SYMATTR InstName J1 SYMATTR Value J113 SYMBOL voltage -192 -176 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 10 0 Left 2 WINDOW 3 15 104 Left 2 SYMATTR InstName V2 SYMATTR Value 6 SYMBOL schottky 1008 -384 R90 WINDOW 3 32 32 VTop 2 WINDOW 0 0 32 VBottom 2 SYMATTR Value BAS40HY SYMATTR InstName D1 SYMATTR Description Diode SYMATTR Type diode SYMBOL res 176 80 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 50 SYMBOL res 176 -128 M0 WINDOW 0 38 42 Left 2 WINDOW 3 36 66 Left 2 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL res 272 -208 R180 WINDOW 0 40 70 Left 2 WINDOW 3 45 42 Left 2 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL OpAmps\\LT1678 384 -352 M0 WINDOW 0 -56 49 Left 2 WINDOW 3 -47 89 Left 2 SYMATTR InstName U2A SYMBOL res 336 -480 R270 WINDOW 0 33 55 VTop 2 WINDOW 3 -3 55 VBottom 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL res 880 -384 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 10k SYMBOL cap 416 -608 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 100µ SYMBOL res 880 -608 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 10K SYMBOL voltage 1072 -576 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value -0.2 SYMBOL res 1040 -112 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 16K SYMBOL res 848 16 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R12 SYMATTR Value 8K SYMBOL cap 1024 -208 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 10n SYMBOL cap 736 16 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 20n SYMBOL res 528 -112 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R13 SYMATTR Value 10.02K SYMBOL cap 512 -208 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 10p SYMBOL res 736 176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R14 SYMATTR Value 9870 SYMBOL OpAmps\\LT1679 448 32 R0 SYMATTR InstName U1 SYMBOL OpAmps\\LT1679 960 48 R0 SYMATTR InstName U4 TEXT -496 136 Left 2 !.tran 0 200 0 1u uic TEXT -496 88 Left 2 !.options plotwinsize=0 numdgt=7 method=trap TEXT -248 -584 Left 2 ;1kHz sinewave oscillator. 20 Nov 2024.

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