Problem in Cadence Virtuoso AC analysis

My guess is that there's either something wrong with your models, or that the dimensions passed in are wrong. For example, your L is 20nm, but the W is 7 metres!

I did some adjustment (I don't have your models, so I made some up), and it's simulating OK for me:

 // Generated for: spectre
// Generated on: Mar 22 14:37:53 2013
// Design library name: Basic_Blocks
// Design cell name: DiffAmp_MOS
// Design view name: schematic
simulator lang=spectre
global 0 vdd!
parameters C=2p Ibias=1u Vac=0.1 VDD=0.4 VinNDC=0.2 VinPDC=0.2 Wnl=7 Wpl=7
 
// very simple models because I don't have your models...
inline subckt SubNMOS_noisy (d g s)
 parameters W=1 L=1
 SubNMOS_noisy (d g s 0) nch w=W*1u l=L*10
 model nch bsim4 type=n
ends SubNMOS_noisy

inline subckt SubPMOS_noisy (d g s)
 parameters W=1 L=1
 SubPMOS_noisy (d g s s) pch w=W*1u l=L*10
 model pch bsim4 type=p
ends SubPMOS_noisy

// Library name: Basic_Blocks
// Cell name: DiffAmp_MOS
// View name: schematic
I2 (net2 0) isource dc=Ibias type=dc
V2 (VinN 0) vsource dc=VinNDC type=dc
V3 (net012 0) vsource dc=VinPDC type=dc
V0 (vdd! 0) vsource dc=VDD type=dc
C0 (Vout 0) capacitor c=C
Vac (VinP net012) vsource dc=0 mag=Vac phase=0 type=sine sinedc=0 ampl=Vac \
        sinephase=0 freq=1K
I21 (net3 net3 vdd!) SubPMOS_noisy W=Wpl Temp=300 Gamma=1.2 Kox=12 L=2e-08 \
        Nit=1e+16 Tox_P=2.5e-09 Trap_depth=2e-09 attn=1.25e+10
I20 (Vout net3 vdd!) SubPMOS_noisy W=Wpl Temp=300 Gamma=1.2 Kox=12 L=2e-08 \
        Nit=1e+16 Tox_P=2.5e-09 Trap_depth=2e-09 attn=1.25e+10
I23 (Vout VinN net2) SubNMOS_noisy W=Wnl Temp=300 Gamma=1.2 Kox=12 L=2e-08 \
        Nit=1e+16 Tox_P=2.5e-09 Trap_depth=2e-09 attn=5e+09
I22 (net3 VinP net2) SubNMOS_noisy W=Wnl Temp=300 Gamma=1.2 Kox=12 L=2e-08 \
        Nit=1e+16 Tox_P=2.5e-09 Trap_depth=2e-09 attn=5e+09
simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 \
    tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 \
    digits=5 cols=80 pivrel=1e-3 sensfile="../psf/sens.output" \
    checklimitdest=psf
ac ac start=1 stop=1G dec=20 save=all annotate=status
modelParameter info what=models where=rawfile
element info what=inst where=rawfile
outputParameter info what=output where=rawfile
designParamVals info what=parameters where=rawfile
primitives info what=primitives where=rawfile
subckts info what=subckts  where=rawfile
saveOptions options save=allpub currents=all
//ahdl_include "~/Library_userDefined/Basic_Blocks/SubPMOS_noisy/veriloga/veriloga.va"
//ahdl_include "~/Library_userDefined/Basic_Blocks/SubNMOS_noisy/veriloga/veriloga.va"

(I fiddled with the lengths, because  I got very little gain with the values you'd entered, but my models are completely artificial).

Regards,

Andrew.

My guess is that there's either something wrong with your models, or that the dimensions passed in are wrong. For example, your L is 20nm, but the W is 7 metres!

I did some adjustment (I don't have your models, so I made some up), and it's simulating OK for me:

 // Generated for: spectre
// Generated on: Mar 22 14:37:53 2013
// Design library name: Basic_Blocks
// Design cell name: DiffAmp_MOS
// Design view name: schematic
simulator lang=spectre
global 0 vdd!
parameters C=2p Ibias=1u Vac=0.1 VDD=0.4 VinNDC=0.2 VinPDC=0.2 Wnl=7 Wpl=7
 
// very simple models because I don't have your models...
inline subckt SubNMOS_noisy (d g s)
 parameters W=1 L=1
 SubNMOS_noisy (d g s 0) nch w=W*1u l=L*10
 model nch bsim4 type=n
ends SubNMOS_noisy

inline subckt SubPMOS_noisy (d g s)
 parameters W=1 L=1
 SubPMOS_noisy (d g s s) pch w=W*1u l=L*10
 model pch bsim4 type=p
ends SubPMOS_noisy

// Library name: Basic_Blocks
// Cell name: DiffAmp_MOS
// View name: schematic
I2 (net2 0) isource dc=Ibias type=dc
V2 (VinN 0) vsource dc=VinNDC type=dc
V3 (net012 0) vsource dc=VinPDC type=dc
V0 (vdd! 0) vsource dc=VDD type=dc
C0 (Vout 0) capacitor c=C
Vac (VinP net012) vsource dc=0 mag=Vac phase=0 type=sine sinedc=0 ampl=Vac \
        sinephase=0 freq=1K
I21 (net3 net3 vdd!) SubPMOS_noisy W=Wpl Temp=300 Gamma=1.2 Kox=12 L=2e-08 \
        Nit=1e+16 Tox_P=2.5e-09 Trap_depth=2e-09 attn=1.25e+10
I20 (Vout net3 vdd!) SubPMOS_noisy W=Wpl Temp=300 Gamma=1.2 Kox=12 L=2e-08 \
        Nit=1e+16 Tox_P=2.5e-09 Trap_depth=2e-09 attn=1.25e+10
I23 (Vout VinN net2) SubNMOS_noisy W=Wnl Temp=300 Gamma=1.2 Kox=12 L=2e-08 \
        Nit=1e+16 Tox_P=2.5e-09 Trap_depth=2e-09 attn=5e+09
I22 (net3 VinP net2) SubNMOS_noisy W=Wnl Temp=300 Gamma=1.2 Kox=12 L=2e-08 \
        Nit=1e+16 Tox_P=2.5e-09 Trap_depth=2e-09 attn=5e+09
simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 \
    tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 \
    digits=5 cols=80 pivrel=1e-3 sensfile="../psf/sens.output" \
    checklimitdest=psf
ac ac start=1 stop=1G dec=20 save=all annotate=status
modelParameter info what=models where=rawfile
element info what=inst where=rawfile
outputParameter info what=output where=rawfile
designParamVals info what=parameters where=rawfile
primitives info what=primitives where=rawfile
subckts info what=subckts  where=rawfile
saveOptions options save=allpub currents=all
//ahdl_include "~/Library_userDefined/Basic_Blocks/SubPMOS_noisy/veriloga/veriloga.va"
//ahdl_include "~/Library_userDefined/Basic_Blocks/SubNMOS_noisy/veriloga/veriloga.va"

(I fiddled with the lengths, because  I got very little gain with the values you'd entered, but my models are completely artificial).

Regards,

Andrew.