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MOSFET Gm vs Drain Current - Part 2

The LTSpice schematic is pasted below this monologue. The simulation shows a gain of over 130. The absolute value of the simulated circuit's imput impedance (@ 1kHz) is 2.18k.

Bench test at 1kHz contradicts as follows: Gain 45.8 at 5mV input. |Zin| = 18.4k

Not really surprising. It would be a bit of a problem to use a MOSFET as a linear amp just due to the input impedance at 20kHz. I certainly wouldn't recommend it.

Sorry for the long pasting. I wanted to include the device's model in the schematic rather than posting it separately and having to explain how to use it. Also, you are on your own with the line wraps.

Cheers, John S

Version 4 SHEET 1 1940 2448 WIRE 256 -160 128 -160 WIRE 320 -160 256 -160 WIRE 128 -128 128 -160 WIRE 320 -112 320 -160 WIRE 320 -16 320 -32 WIRE 128 0 128 -48 WIRE 128 0 -96 0 WIRE -96 32 -96 0 WIRE 128 48 128 0 WIRE 128 80 128 48 WIRE -528 160 -576 160 WIRE -448 160 -528 160 WIRE -320 160 -368 160 WIRE -272 160 -320 160 WIRE -96 160 -96 112 WIRE -96 160 -208 160 WIRE -16 160 -96 160 WIRE 80 160 -16 160 WIRE -576 192 -576 160 WIRE -96 208 -96 160 WIRE 128 208 128 176 WIRE -576 288 -576 272 WIRE -96 304 -96 288 FLAG 128 208 0 FLAG 320 -16 0 FLAG -96 304 0 FLAG -576 288 0 FLAG 128 48 d FLAG 256 -160 dd FLAG -320 160 in FLAG -16 160 g FLAG -528 160 source SYMBOL nmos 80 80 R0 SYMATTR InstName M1 SYMATTR Value FDB3632 SYMATTR Prefix X SYMBOL voltage 320 -128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res 112 -144 R0 SYMATTR InstName R1 SYMATTR Value 300 SYMBOL res -112 192 R0 SYMATTR InstName R2 SYMATTR Value 1meg SYMBOL res -112 16 R0 SYMATTR InstName R3 SYMATTR Value 740k SYMBOL voltage -576 176 R0 WINDOW 123 24 132 Left 0 WINDOW 39 24 160 Left 0 SYMATTR Value2 AC 1 SYMATTR InstName V2 SYMATTR Value SINE(0 .001 1000) SYMBOL cap -272 176 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName C1 SYMATTR Value 100µ SYMBOL res -464 176 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R4 SYMATTR Value 600 TEXT -296 -96 Left 0 !;op TEXT -360 -56 Left 0 !;dc v1 10.8 13.2 .001 TEXT -400 -16 Left 0 !.ac oct 10000 20 20000 TEXT -392 24 Left 0 !;tran 0 1 .1 1u TEXT 640 -144 Left 0 !.SUBCKT FDB3632 2 1 3\n*Spice model for FDB3632, FDP3632 & FDI3632\n*Nom Temp=25 deg C \n*May 2002\n \nCa 12 8 1.7e-9\nCb

15 14 2.5e-9\nCin 6 8 6.0e-9\n \nDbody 7 5 DbodyMOD\nDbreak 5 11 DbreakMOD\nDplcap 10 5 DplcapMOD\n \nEbreak 11 7 17 18 102.5\nEds 14 8 5 8 1\nEgs 13 8 6 8 1\nEsg 6 10 6 8 1\nEvthres 6 21 19 8 1\nEvtemp 20 6 18 22 1\n \nIt 8 17 1\n \nLgate 1 9 5.61e-9\nLdrain 2 5 1.0e-9\nLsource 3 7 2.7e-9\n \nRLgate 1 9 56.1\nRLdrain 2 5 10\nRLsource 3 7 27\n \nMmed 16 6 8 8 MmedMOD\nMstro 16 6 8 8 MstroMOD \nMweak 16 21 8 8 MweakMOD \n \nRbreak 17 18 RbreakMOD 1\nRdrain 50 16 RdrainMOD 3.8e-3\nRgate 9 20 1.1\nRSLC1 5 51 RSLCMOD 1.0e-6\nRSLC2 5 50 1.0e3\nRsource 8 7 RsourceMOD 2.5e-3\nRvthres 22 8 RvthresMOD 1\nRvtemp 18 19 RvtempMOD 1\nS1a 6 12 13 8 S1AMOD\nS1b 13 12 13 8 S1BMOD\nS2a 6 15 14 13 S2AMOD\nS2b 13 15 14 13 S2BMOD\n \nVbat 22 19 DC 1\n \nESLC 51 50 VALUE={(V(5,51)/ABS(V(5,51)))*(PWR(V(5,51)/(1e-6*350),3))}\n \n.MODEL DbodyMOD D (IS=5.9E-11 N=1.07 RS=2.3e-3 TRS1=3.0e-3 TRS2=1.0e-6\n+ CJO=4e-9 M=0.58 TT=4.8e-8 XTI=4.2)\n.MODEL DbreakMOD D (RS=0.17 TRS1=3.0e-3 TRS2=-8.9e-6)\n.MODEL DplcapMOD D (CJO=15e-10 IS=1.0e-30 N=10 M=0.6)\n \n.MODEL MstroMOD NMOS (VTO=4.1 KP=200 IS=1e-30 N=10 TOX=1 L=1u W=1u)\n.MODEL MmedMOD NMOS (VTO=3.4 KP=10.0 IS=1e-30 N=10 TOX=1 L=1u W=1u RG=1.1)\n.MODEL MweakMOD NMOS (VTO=2.75 KP=0.05 IS=1e-30 N=10 TOX=1 L=1u W=1u RG=1.1e+1 RS=0.1) \n \n.MODEL RbreakMOD RES (TC1=1.0e-3 TC2=-1.7e-6)\n.MODEL RdrainMOD RES (TC1=8.5e-3 TC2=2.8e-5)\n.MODEL RSLCMOD RES (TC1=2.0e-3 TC2=2.0e-6)\n.MODEL RsourceMOD RES (TC1=4e-3 TC2=1e-6)\n.MODEL RvthresMOD RES (TC1=-4.0e-3 TC2=-1.8e-5)\n.MODEL RvtempMOD RES (TC1=-4.4e-3 TC2=2.2e-6)\n \n.MODEL S1AMOD VSWITCH (RON=1e-5 ROFF=0.1 VON=-4 VOFF=-2)\n.MODEL S1BMOD VSWITCH (RON=1e-5 ROFF=0.1 VON=-2 VOFF=-4)\n.MODEL S2AMOD VSWITCH (RON=1e-5 ROFF=0.1 VON=-0.8 VOFF=0.4)\n.MODEL S2BMOD VSWITCH (RON=1e-5 ROFF=0.1 VON=0.4 VOFF=-0.8)\n \n.ENDS\n \n\n.SUBCKT FDB3632_THERMAL TH TL\n*Thermal Model Subcircuit\n*May 2002\n \nCTHERM1 TH 6 7.5e-3\nCTHERM2 6 5 8.0e-3\nCTHERM3 5 4 9.0e-3\nCTHERM4 4 3 2.4e-2\nCTHERM5 3 2 3.4e-2\nCTHERM6 2 TL 6.5e-2\n \nRTHERM1 TH 6 3.1e-4\nRTHERM2 6 5 2.5e-3\nRTHERM3 5 4 2.2e-2\nRTHERM4 4 3 8.1e-2\nRTHERM5 3 2 1.35e-1\nRTHERM6 2 TL 1.5e-1\n \n.ends
Reply to
John S
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"John S" schrieb im Newsbeitrag news:j2pfb6$oap$ snipped-for-privacy@dont-email.me...

Hello John,

I guess there is no specification for gain for this power mosfets. The SPICE-model maybe made for on/off switching behavior.

I have attached your schematic to make it easier for others to run the simulation. It's really hard to unwrap the text to get a working schematic.

Best regards, Helmut

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Reply to
Helmut Sennewald

^^^^^^^^^^^ an audio amp

Sorry.

John S

Reply to
John S

On 8/20/2011 6:17 PM, John S wrote:

Well, that didn't seem to work well. I'll try it a different way. The LTSpice schematic follows but won't work without the subcircuit which follows that. Once you have the schematic loaded, cut & paste the subcircuit into a spice directive window and you should be ready to go. I hope.

John S

Version 4 SHEET 1 1940 2448 WIRE 256 -160 128 -160 WIRE 320 -160 256 -160 WIRE 128 -128 128 -160 WIRE 320 -112 320 -160 WIRE 320 -16 320 -32 WIRE 128 0 128 -48 WIRE 128 0 -96 0 WIRE -96 32 -96 0 WIRE 128 48 128 0 WIRE 128 80 128 48 WIRE -528 160 -576 160 WIRE -448 160 -528 160 WIRE -320 160 -368 160 WIRE -272 160 -320 160 WIRE -96 160 -96 112 WIRE -96 160 -208 160 WIRE -16 160 -96 160 WIRE 80 160 -16 160 WIRE -576 192 -576 160 WIRE -96 208 -96 160 WIRE 128 208 128 176 WIRE -576 288 -576 272 WIRE -96 304 -96 288 FLAG 128 208 0 FLAG 320 -16 0 FLAG -96 304 0 FLAG -576 288 0 FLAG 128 48 d FLAG 256 -160 dd FLAG -320 160 in FLAG -16 160 g FLAG -528 160 source SYMBOL nmos 80 80 R0 SYMATTR InstName M1 SYMATTR Value FDB3632 SYMATTR Prefix X SYMBOL voltage 320 -128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res 112 -144 R0 SYMATTR InstName R1 SYMATTR Value 300 SYMBOL res -112 192 R0 SYMATTR InstName R2 SYMATTR Value 1meg SYMBOL res -112 16 R0 SYMATTR InstName R3 SYMATTR Value 740k SYMBOL voltage -576 176 R0 WINDOW 123 24 132 Left 0 WINDOW 39 24 160 Left 0 SYMATTR Value2 AC 1 SYMATTR InstName V2 SYMATTR Value SINE(0 .001 1000) SYMBOL cap -272 176 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName C1 SYMATTR Value 100µ SYMBOL res -464 176 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R4 SYMATTR Value 600 TEXT -296 -96 Left 0 !;op TEXT -360 -56 Left 0 !;dc v1 10.8 13.2 .001 TEXT -400 -16 Left 0 !.ac oct 10000 20 20000 TEXT -392 24 Left 0 !;tran 0 1 .1 1u

**********************************************

.SUBCKT FDB3632 2 1 3

*Spice model for FDB3632, FDP3632 & FDI3632 *Nom Temp=25 deg C *May 2002

Ca 12 8 1.7e-9 Cb 15 14 2.5e-9 Cin 6 8 6.0e-9

Dbody 7 5 DbodyMOD Dbreak 5 11 DbreakMOD Dplcap 10 5 DplcapMOD

Ebreak 11 7 17 18 102.5 Eds 14 8 5 8 1 Egs 13 8 6 8 1 Esg 6 10 6 8 1 Evthres 6 21 19 8 1 Evtemp 20 6 18 22 1

It 8 17 1

Lgate 1 9 5.61e-9 Ldrain 2 5 1.0e-9 Lsource 3 7 2.7e-9

RLgate 1 9 56.1 RLdrain 2 5 10 RLsource 3 7 27

Mmed 16 6 8 8 MmedMOD Mstro 16 6 8 8 MstroMOD Mweak 16 21 8 8 MweakMOD

Rbreak 17 18 RbreakMOD 1 Rdrain 50 16 RdrainMOD 3.8e-3 Rgate 9 20 1.1 RSLC1 5 51 RSLCMOD 1.0e-6 RSLC2 5 50 1.0e3 Rsource 8 7 RsourceMOD 2.5e-3 Rvthres 22 8 RvthresMOD 1 Rvtemp 18 19 RvtempMOD 1 S1a 6 12 13 8 S1AMOD S1b 13 12 13 8 S1BMOD S2a 6 15 14 13 S2AMOD S2b 13 15 14 13 S2BMOD

Vbat 22 19 DC 1

ESLC 51 50 VALUE={(V(5,51)/ABS(V(5,51)))*(PWR(V(5,51)/(1e-6*350),3))}

.MODEL DbodyMOD D (IS=5.9E-11 N=1.07 RS=2.3e-3 TRS1=3.0e-3 TRS2=1.0e-6

  • CJO=4e-9 M=0.58 TT=4.8e-8 XTI=4.2) .MODEL DbreakMOD D (RS=0.17 TRS1=3.0e-3 TRS2=-8.9e-6) .MODEL DplcapMOD D (CJO=15e-10 IS=1.0e-30 N=10 M=0.6)

.MODEL MstroMOD NMOS (VTO=4.1 KP=200 IS=1e-30 N=10 TOX=1 L=1u W=1u) .MODEL MmedMOD NMOS (VTO=3.4 KP=10.0 IS=1e-30 N=10 TOX=1 L=1u W=1u RG=1.1) .MODEL MweakMOD NMOS (VTO=2.75 KP=0.05 IS=1e-30 N=10 TOX=1 L=1u W=1u RG=1.1e+1 RS=0.1)

.MODEL RbreakMOD RES (TC1=1.0e-3 TC2=-1.7e-6) .MODEL RdrainMOD RES (TC1=8.5e-3 TC2=2.8e-5) .MODEL RSLCMOD RES (TC1=2.0e-3 TC2=2.0e-6) .MODEL RsourceMOD RES (TC1=4e-3 TC2=1e-6) .MODEL RvthresMOD RES (TC1=-4.0e-3 TC2=-1.8e-5) .MODEL RvtempMOD RES (TC1=-4.4e-3 TC2=2.2e-6)

.MODEL S1AMOD VSWITCH (RON=1e-5 ROFF=0.1 VON=-4 VOFF=-2) .MODEL S1BMOD VSWITCH (RON=1e-5 ROFF=0.1 VON=-2 VOFF=-4) .MODEL S2AMOD VSWITCH (RON=1e-5 ROFF=0.1 VON=-0.8 VOFF=0.4) .MODEL S2BMOD VSWITCH (RON=1e-5 ROFF=0.1 VON=0.4 VOFF=-0.8)

.ENDS

.SUBCKT FDB3632_THERMAL TH TL

*Thermal Model Subcircuit *May 2002

CTHERM1 TH 6 7.5e-3 CTHERM2 6 5 8.0e-3 CTHERM3 5 4 9.0e-3 CTHERM4 4 3 2.4e-2 CTHERM5 3 2 3.4e-2 CTHERM6 2 TL 6.5e-2

RTHERM1 TH 6 3.1e-4 RTHERM2 6 5 2.5e-3 RTHERM3 5 4 2.2e-2 RTHERM4 4 3 8.1e-2 RTHERM5 3 2 1.35e-1 RTHERM6 2 TL 1.5e-1

.ends

Reply to
John S

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