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Simulators >> Circuit Simulators >> the differential amp CM sweep
https://designers-guide.org/forum/YaBB.pl?num=1260433102

Message started by ericX on Dec 10^th, 2009, 12:18am

Title: the differential amp CM sweep
Post by ericX on Dec 10^th, 2009, 12:18am

Hi,I'm new here.
I simulate the differential amp, when I connect the substrate of the M1 and M2 to the source terminal,there comes a strange current at the tail current source M3 when the input is 0,and until reaching the saturation region is the sum of the two mosfet equal to the tail current.But if I connect the substrate to the ground, everything turns normal.I don't know why, so I come here asking for help.Thank you! The *.sp file is as follow:

.lib 'cmos90.sp' tt
*the lib is the 90nm cmos lib from UCB
m1 out1 in pp pp nmos l=1u w=2u
m2 out2 in pp pp nmos l=1u w=2u
m3 pp bb gnd gnd nmos l=1u w=4u

rd1 dd out1 10k
rd2 dd out2 10k

vdd dd gnd dc 3
vbb bb gnd dc 0.6
vin in gnd

.op
.dc vin 0 3 10m
.print lx4(m1) lx4(m3) par("lx4(m1)+lx4(m2)")
.end

Title: Re: the differential amp CM sweep
Post by Mayank on Dec 10^th, 2009, 12:22am

Hi,
Prefix a line .connect gnd 0 to your spice netlist...I think that should solve the problem....There's no node 0 in your ckt....

--mayank.

Title: Re: the differential amp CM sweep
Post by ericX on Dec 10^th, 2009, 12:34am

It doesn't work...I don't think it is the ground that causes the problem...