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eHmm do you wire a two stage cap mult. different from a darlington cap-mult. ? (BTW should the darlington count as three? (emitter follower, common emitt er, common base.))
George H.
Phil,
Is that the best cap multiplier you use or do you have a super-duper version? ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
This one isn't actually that good, on reflection. When you load the emitter of the phase splitter, you get the same sort of swing at the collector that you would if you loaded that directly. So you'd want a follower on the emitter side as well.
You just put two normal cap multipliers in series. To get higher rejection, make sure you put all the base RCs in a single string, so that the second stage gets more filtering than the first. I often use four poles (two on each stage) plus an RC in the collector of the first stage to help knock down the capacitive blow-by.
You usually need a resistor to ground from the base of the second stage to keep it from saturating.
You can get over 140 dB rejection that way, though it'll need some shielding to keep it that high in real life. I have one in my new product, the QL-01 quantum limited photoreceiver, and the SMPS noise from the LM2594 two inches away from the photodiode isn't visible above the noise of the 10M feedback resistor even in a 100-Hz bandwidth, despite the fact that the bootstrap/TIA has very little in the way of supply rejection. Of course if the board isn't grounded to the case, it's another matter!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
My fave is the one I just told George about. I sometimes put a TLV431 on the last stage to make it regulate as well, but then you get most of the TLV431's noise, which is sometimes a problem. You can only put one pole's worth of rolloff on the 431 inside the loop.
My main tweak is hanging an RC in the collector of the first stage. You usually don't need all the headroom that the V_BE plus IR drop gives you, so it doesn't cost anything and it helps with the high frequency blow-by.
I like the 2SD2704K for things up to about 30 mA, but its beta starts tanking above there. It has very good BV_EBO, so that it doesn't die if you short the input.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On 07/22/2016 12:06 PM, Phil Hobbs wrote:
Here's a reasonably nice version of the two-stage cap multiplier that costs about 2V and knocks a 1-V sawtooth down to (numerically) zero. The frequency-domain sim predicts about 180 dB rejection at the 150 kHz switching frequency of my fave LM2594, and certainly the somewhat similar one in the QL-01 completely fixes the ripple problem.
(Also appended below for archival purposes.)
Cheers
Phil Hobbs
Version 4 SHEET 1 1352 680 WIRE 368 -224 -400 -224 WIRE 448 -224 432 -224 WIRE -400 -128 -400 -224 WIRE -400 -128 -592 -128 WIRE -320 -128 -400 -128 WIRE -272 -128 -320 -128 WIRE -128 -128 -192 -128 WIRE -80 -128 -128 -128 WIRE 208 -128 16 -128 WIRE 448 -128 448 -224 WIRE 448 -128 304 -128 WIRE 480 -128 448 -128 WIRE 592 -128 480 -128 WIRE 640 -128 592 -128 WIRE 704 -128 640 -128 WIRE -592 -112 -592 -128 WIRE -128 -112 -128 -128 WIRE -320 -80 -320 -128 WIRE 592 -48 592 -128 WIRE 704 -48 704 -128 WIRE 480 -32 480 -128 WIRE -128 -16 -128 -48 WIRE -592 0 -592 -32 WIRE 480 64 480 32 WIRE 592 64 592 32 WIRE 592 64 480 64 WIRE 704 64 704 32 WIRE 704 64 592 64 WIRE -320 80 -320 0 WIRE -288 80 -320 80 WIRE -176 80 -208 80 WIRE -32 80 -32 -64 WIRE -32 80 -176 80 WIRE 0 80 -32 80 WIRE 112 80 80 80 WIRE 144 80 112 80 WIRE 256 80 256 -64 WIRE 256 80 224 80 WIRE 368 80 256 80 WIRE 480 80 480 64 WIRE 368 96 368 80 WIRE -592 112 -592 80 WIRE -320 112 -320 80 WIRE -176 112 -176 80 WIRE 112 112 112 80 WIRE 256 112 256 80 WIRE 112 192 112 176 WIRE 256 192 256 176 WIRE 368 192 368 176 WIRE -320 224 -320 176 WIRE -176 224 -176 176 FLAG -592 112 0 FLAG 256 192 0 FLAG -176 224 0 FLAG 480 80 0 FLAG 640 -128 out FLAG -128 -16 0 FLAG -320 224 0 FLAG 112 192 0 FLAG 368 192 0 SYMBOL voltage -592 -16 R0 WINDOW 123 -72 202 Left 2 WINDOW 39 0 0 Left 2 WINDOW 0 -76 104 Left 2 WINDOW 3 -209 170 Left 2 SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMATTR Value PULSE(12 13 100n 0.95u 5u 50n 6u) SYMBOL res -304 96 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R1 SYMATTR Value 499 SYMBOL res 128 96 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL npn 208 -64 R270 WINDOW 0 75 14 VRight 2 WINDOW 3 124 1 VRight 2 SYMATTR InstName Q1 SYMATTR Value 2SD2704K SYMBOL res 576 -64 R0 SYMATTR InstName R6 SYMATTR Value 500 SYMBOL current 704 -48 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName I1 SYMATTR Value 50m SYMBOL res -336 -96 R0 SYMATTR InstName R11 SYMATTR Value 499 SYMBOL res -16 96 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R12 SYMATTR Value 1k SYMBOL cap -336 112 R0 SYMATTR InstName C2 SYMATTR Value {Cf} SYMATTR SpiceLine Rser=10m SYMBOL cap -144 -112 R0 SYMATTR InstName C3 SYMATTR Value {Ccol} SYMATTR SpiceLine Rser=10m SYMBOL cap 96 112 R0 SYMATTR InstName C5 SYMATTR Value {Cf} SYMATTR SpiceLine Rser=10m SYMBOL cap 240 112 R0 SYMATTR InstName C6 SYMATTR Value {Cf} SYMATTR SpiceLine Rser=10m SYMBOL cap 464 -32 R0 SYMATTR InstName C7 SYMATTR Value {Cf} SYMATTR SpiceLine Rser=10m SYMBOL res 352 80 R0 SYMATTR InstName R4 SYMATTR Value 50k SYMBOL cap 432 -240 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 -26 -67 VTop 2 SYMATTR InstName C8 SYMATTR Value {Cstray} SYMBOL res -176 -144 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value {Rcol} SYMBOL voltage -592 -128 R0 WINDOW 123 -103 10 Left 2 WINDOW 39 0 0 Left 2 WINDOW 0 -90 56 Left 2 WINDOW 3 -207 -32 Left 2 SYMATTR Value2 AC 0 SYMATTR InstName V2 SYMATTR Value PULSE(0 -.50 100n 0.95u) SYMBOL cap -192 112 R0 SYMATTR InstName C1 SYMATTR Value {Cf} SYMATTR SpiceLine Rser=10m SYMBOL npn -80 -64 R270 WINDOW 0 75 14 VRight 2 WINDOW 3 124 1 VRight 2 SYMATTR InstName Q2 SYMATTR Value 2SD2704K TEXT 32 368 Left 2 !.tran 50u TEXT -168 440 Left 2 !.param Cf 1u\n;.step param Cf list 1u 10u 47u 100u TEXT 32 272 Left 2 ;.tran 50u\n.ac oct 100 1 1G\n.noise v(out) v1 dec
500 1 100meg TEXT 400 448 Left 2 !.param Cstray 1f\n;.step param Cstray list 0.01f 100f TEXT 416 384 Left 2 !.param Rcol 5\n;.step param Rcol list 1 5 TEXT 504 344 Left 2 !.step param Ccol list 1n 1u 100u TEXT -520 320 Left 2 !.options abstol=1e-13 reltol=1e-7 TEXT 824 -272 Left 2 !*\n* Superbeta low VCEsat device \n* 2SD2704K NPN model\n* Date: 2006/11/27\n.MODEL 2SD2704K NPN\n+ IS=250.00E-15\n+ BF=2.3219E3 VAF=100\n+ IKF=25.778E-3 ISE=270.34E-15\n+ NE=1.8069 BR=45.088\n+ VAR=100 IKR=9.4796\n+ ISC=411.09E-15 NC=2.0254\n+ NK=.54182 RE=.4\n+ RB=3.1823 RC=58.585E-3\n+ CJE=8.7706E-12 MJE=.66324\n+ CJC=15.709E-12 MJC=.53302\n+ TF=3.8352E-9 XTF=32.147\n+ VTF=472.13 ITF=85.294\n+ TR=7.0574E-9 XTB=1.5000\n.ENDS TEXT -720 -312 Left 2 ;Two sources summed \nto reduce transient in \naverage voltage TEXT -168 -400 Left 2 ;5-Pole, 2-Stage Capacitance Multiplier\n \nPhil Hobbs, \nElectroOptical Innovations LLC\nJuly 22, 2016 TEXT 624 -232 Left 2 ;Load TEXT 432 -352 Left 2 ;With a 1V p-p sawtooth at the input, \nthe output ripple cannot be resolved \nin LTspice. RECTANGLE Normal 800 128 528 -192 2-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
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