Comments on: Dual Gate MOSFET Investigations - Gain and AGC http://www.nt7s.com/blog/2008/07/dual-gate-mosfet-investigations-gain-and-agc/ Emanations from Amateur Radio Station NT7S Thu, 02 Feb 2012 14:01:01 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Volker Kible http://www.nt7s.com/blog/2008/07/dual-gate-mosfet-investigations-gain-and-agc/comment-page-1/#comment-616 Volker Kible Mon, 31 Oct 2011 16:14:16 +0000 http://www.nt7s.com/blog/?p=19#comment-616 Hello Jason, I'm trying to reproduce your measuerements with LTSpice, but it doesn't really work, my amplifier doesn't amplify. Maybe there's something wrong with the model i'm using, or my circuit is not correct. I hope you have some experience with Spice and can help me. I'm new to Spice... Thanx & Regards! Volker This is the model i'm using (i changed the original model of NXP [http://www.nxp.com/models/spicespar/fet/BF998.html] a bit to get it running in LTSpice IV, maybe i destroyed it): * BF998 SPICE MODEL OCTOBER 1993 PHILIPS SEMICONDUCTORS * ENVELOPE SOT143 (R) * 1.: SOURCE; 2.: DRAIN; 3.: GATE 2; 4.: GATE 1; .SUBCKT BF998 1 2 3 4 L10 1 10 0.12N L20 2 20 0.12N L30 3 30 0.12N L40 4 40 0.12N L11 10 11 1.20N L21 20 21 1.20N L31 30 31 1.20N L41 40 41 1.20N C13 10 30 0.085P C14 10 40 0.085P C23 20 30 0.085P C24 20 40 0.005P D11 42 11 ZENER D12 42 41 ZENER D21 32 11 ZENER D22 32 31 ZENER RS 10 12 100 MOS1 61 41 11 12 GATE1 MOS2 21 31 61 12 GATE2 .MODEL ZENER D(BV=10 CJO=1.2E-12 RS=10) .MODEL GATE1 + NMOS(W=1.1E-6 L=1150E-6 LEVEL=3 UO=600 VTO=-0.250 NFS=300E9 TOX=42E-9 + NSUB=3E15 VMAX=140E3 RS=2.0 RD=2.0 XJ=200E-9 THETA=0.11 + ETA=0.06 KAPPA=2 LD=0.1E-6 + CGSO=0.3E-9 CGDO=0.3E-9 CBD=0.5E-12 CBS=0.5E-12) .MODEL GATE2 + NMOS(W=2.0E-6 L=1150E-6 LEVEL=3 UO=600 VTO=-0.250 NFS=300E9 TOX=42E-9 + NSUB=3E15 VMAX=100E3 RS=2.0 RD=2.0 XJ=200E-9 THETA=0.11 + ETA=0.06 KAPPA=2 LD=0.1E-6 + CGSO=0.3E-9 CGDO=0.3E-9 CBD=0.5E-12 CBS=0.5E-12) .ENDS BF998 Hello Jason,

I'm trying to reproduce your measuerements with LTSpice, but it doesn't really work, my amplifier doesn't amplify. Maybe there's something wrong with the model i'm using, or my circuit is not correct. I hope you have some experience with Spice and can help me. I'm new to Spice...

Thanx & Regards!
Volker

This is the model i'm using (i changed the original model of NXP [http://www.nxp.com/models/spicespar/fet/BF998.html] a bit to get it running in LTSpice IV, maybe i destroyed it):
* BF998 SPICE MODEL OCTOBER 1993 PHILIPS SEMICONDUCTORS
* ENVELOPE SOT143 (R)
* 1.: SOURCE; 2.: DRAIN; 3.: GATE 2; 4.: GATE 1;
.SUBCKT BF998 1 2 3 4
L10 1 10 0.12N
L20 2 20 0.12N
L30 3 30 0.12N
L40 4 40 0.12N
L11 10 11 1.20N
L21 20 21 1.20N
L31 30 31 1.20N
L41 40 41 1.20N
C13 10 30 0.085P
C14 10 40 0.085P
C23 20 30 0.085P
C24 20 40 0.005P
D11 42 11 ZENER
D12 42 41 ZENER
D21 32 11 ZENER
D22 32 31 ZENER
RS 10 12 100
MOS1 61 41 11 12 GATE1
MOS2 21 31 61 12 GATE2

.MODEL ZENER D(BV=10 CJO=1.2E-12 RS=10)

.MODEL GATE1
+ NMOS(W=1.1E-6 L=1150E-6 LEVEL=3 UO=600 VTO=-0.250 NFS=300E9 TOX=42E-9
+ NSUB=3E15 VMAX=140E3 RS=2.0 RD=2.0 XJ=200E-9 THETA=0.11
+ ETA=0.06 KAPPA=2 LD=0.1E-6
+ CGSO=0.3E-9 CGDO=0.3E-9 CBD=0.5E-12 CBS=0.5E-12)

.MODEL GATE2
+ NMOS(W=2.0E-6 L=1150E-6 LEVEL=3 UO=600 VTO=-0.250 NFS=300E9 TOX=42E-9
+ NSUB=3E15 VMAX=100E3 RS=2.0 RD=2.0 XJ=200E-9 THETA=0.11
+ ETA=0.06 KAPPA=2 LD=0.1E-6
+ CGSO=0.3E-9 CGDO=0.3E-9 CBD=0.5E-12 CBS=0.5E-12)

.ENDS BF998

]]> By: NT7S http://www.nt7s.com/blog/2008/07/dual-gate-mosfet-investigations-gain-and-agc/comment-page-1/#comment-27 NT7S Wed, 19 Nov 2008 11:09:30 +0000 http://www.nt7s.com/blog/?p=19#comment-27 Hello Kari, I did not make the variable drain current measurements that you have described, but that would make for a great follow up experiment. The intriguing thing about dual-gate MOSFETs is the different ways that you can bias them. If you get around to that experiment before I do, please let me know what you find. 73, Jason NT7S Hello Kari,

I did not make the variable drain current measurements that you have described, but that would make for a great follow up experiment. The intriguing thing about dual-gate MOSFETs is the different ways that you can bias them. If you get around to that experiment before I do, please let me know what you find.

73,
Jason NT7S

]]> By: kba http://www.nt7s.com/blog/2008/07/dual-gate-mosfet-investigations-gain-and-agc/comment-page-1/#comment-26 kba Wed, 19 Nov 2008 09:09:33 +0000 http://www.nt7s.com/blog/?p=19#comment-26 Hello OM Just read the AGC characteristics with great interest... One thing I became curious was the very odd AGC/gain constant which varies so much as the gain decreases... Did you happen to measure the fet Id current / gain dependency ? I have IF amplifier under construction and have plan to base the signal strength indication to fet Id current value which I believe is more linear in relation to gain reduction. This takes some time to verify as measurement waits the whole IF strip & AGC to be finished... br Kari B Oh6io Hello OM

Just read the AGC characteristics with great interest...
One thing I became curious was the very odd AGC/gain constant
which varies so much as the gain decreases...
Did you happen to measure the fet Id current / gain dependency ? I have IF amplifier under construction and have plan to base the signal strength indication to fet Id current value which I believe is more linear in relation to gain reduction.
This takes some time to verify as measurement waits the whole
IF strip & AGC to be finished...

br Kari B
Oh6io

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