Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

simulate differential pair with hspice

Not open for further replies.


Full Member level 4
Jun 30, 2012
Reaction score
Trophy points
Activity points
I read an article about parallel differential pair( shematic.PNG). This is desired output(output.PNG]).
I wanted to simulate this circuit with hspice but I didn't receive good result. this is my program in hspice:
.option post
M1a 1 v1 4 4 nch w=10u l=10u
M2a 1 v2 5 5 nch w=10u l=10u
M1b 3 v2 5 5 nch w=10u l=10u
M2b 3 v1 4 4 nch w=10u l=10u
M3a vdd vb 1 1 nch w=20u l=10u
M3b vdd vb 3 3 nch w=20u l=10u
M4 vdd vb 2 2 nch w=20u l=10u
M5a 2 v1 4 4 nch w=10u l=10u
M5b 2 v2 5 5 nch w=10u l=10u
M6a 4 6 vss vss nch w=10u l=10u
M6b 5 6 vss vss nch w=10u l=10u
R 6 0 1000meg
r1 v1 0 1000meg
r2 v2 0 1000meg
vdd vdd 0 dc 1.25
vss vss 0 dc -.75
vb vb 0 .2
.MODEL nch Nmos level=5
+ vt=.7 tox=292 frc=2.739e-2 dnb=2.423e16 ub=642.8
+ oxetch=-.98 xj=.29 latd=.34 ecv=4 vst=5.595e7
+ fsb=7.095e-5 scm=.4 fss=2.2e11 nwm=.93 phi=.61
+ tcv=1.45e-3 ptc=9e-5 bex=1.8
v1 v1 v2 SIN 0 10m 10kHZ
.TRAN 5US 200uS
.PRINT TRAN id(M1b) id(m1a)
circuit has some information: vdd=1.25, vss=-.75, bias current=1nA. and mos model is level 5 in 2um mosis process.
simulation in original article done with T-Spice.
which part of my program is incorect? I want to plot (idm vs vdm) and (gm vs vdm).

It's neither clear which circuit feature you want to implement with the parallel differential pairs nor what you are missing specifically in the results. Similar circuits known from literature are involving staggered offset voltages to implement arbitrary transfer functions.

The "desired output" curves seem to refer to a DC sweep. Why are you performing a transient analysis with sine source?
I want to calculate linearity of transconductor.I did dc sweep too but I don't get that result. also what should I do for plotting Gm vs Vdm?

gm is the differential dIout/dVin. Most SPICE variants have a differential operator available for plot post processing.
should I perform dc sweep for gm vs vdm too?

Not open for further replies.

Part and Inventory Search

Welcome to