some questions about gmin

[ColsonZhang]

Environment (OS, Python version, PySpice version, simulator)

OS-WIN10 Python-3.6.3 PySpice-1.4.3 simulator-ngspice

Expected Behaviour

I am trying to build a common simulator for the CMOS amp. When I adjust the offset of the V, I hope I can get the different curve. However, sometimes the code does work normally. I am guessing that the reason maybe the gain of the amp is too big that the ngspice cannot calculate the number normally?

Actual Behaviour

NgSpiceCommandError: Command 'run' failed and the details are here: 2020-08-21 16:02:33,261 - PySpice.Spice.NgSpice.Shared.NgSpiceShared - Shared.ERROR - Note: Starting true gmin stepping 2020-08-21 16:02:33,276 - PySpice.Spice.NgSpice.Shared.NgSpiceShared - Shared.ERROR - Trying gmin = 1.0000E-03 Warning: Further gmin increment ...... 2020-08-21 16:02:33,531 - PySpice.Spice.NgSpice.Shared.NgSpiceShared - Shared.ERROR - Trying gmin = 1.0000E-12 Note: One successful gmin step 2020-08-21 16:02:33,538 - PySpice.Spice.NgSpice.Shared.NgSpiceShared - Shared.ERROR - Note: Dynamic gmin stepping completed

The code

analysis = simulator.transient(step_time=u_ms(step_time), end_time=u_ms(end_time)) The simulator's netlist is below.

The netlist

.title AMP Simulation .include D:\Project_2020\Python\libraries\cmos\180nm_cmos.mod Vpower vdd 0 5V M1 OUTPUT INPUT_N s12 0 CMOSN_180nm l=1um w=148um M2 d2 INPUT_P s12 0 CMOSN_180nm l=1um w=148um M3 d2 d2 vdd vdd CMOSP_180nm l=1um w=16um M4 OUTPUT d2 vdd vdd CMOSP_180nm l=1um w=16um M5 s12 g5 0 0 CMOSN_180nm l=1um w=8um C1 OUTPUT 0 5pF Iref vdd g5 200uA M6 g5 g5 0 0 CMOSN_180nm l=1um w=8um Vincom INPUT_COM 0 1.8V Vinp INPUT_P INPUT_COM DC 0V AC 1V SIN(0V 0.0001V 1kHz 0s 0Hz) Vinn INPUT_COM INPUT_N DC 0V AC 1V SIN(0V 0.0001V 1kHz 0s 0Hz) .options TEMP = 25C .options TNOM = 25C .ic .end

the cmos bsim mode 180nm_cmos.mod

• DATE: Oct 17/01
• LOT: T18H WAF: 7006
• Temperature_parameters=Default

*http://bwrcs.eecs.berkeley.edu/Classes/icdesign/ee241_s02/Assignments/t18h_lo_epi-params-mod.txt

.MODEL CMOSN_180nm NMOS LEVEL = 49
+VERSION = 3.1 TNOM = 27 TOX = 4.2E-9 +hdif = 0.25e-6 acm = 3 +XJ = 1E-7 NCH = 2.3549E17 VTH0 = 0.3710619 +K1 = 0.5940793 K2 = 2.070131E-3 K3 = 1E-3 +K3B = 2.7158495 W0 = 1E-7 NLX = 2.005089E-7 +DVT0W = 0 DVT1W = 0 DVT2W = 0 +DVT0 = 1.4615376 DVT1 = 0.3798134 DVT2 = 0.0692378 +U0 = 293.522312 UA = -6.73646E-10 UB = 1.164182E-18 +UC = -2.84532E-11 VSAT = 9.286324E4 A0 = 1.7591856 +AGS = 0.3162202 B0 = -5.950938E-8 B1 = -1E-7 +KETA = 0.0111532 A1 = 3.896574E-4 A2 = 1 +RDSW = 139.0465393 PRWG = 0.5 PRWB = -0.2 +WR = 1 WINT = 0 LINT = 9.265899E-9 +XL = -2E-8 XW = -1E-8 DWG = -1.343579E-9 +DWB = -1.391607E-8 VOFF = -0.0765575 NFACTOR = 2.4791597 +CIT = 0 CDSC = 2.4E-4 CDSCD = 0 +CDSCB = 0 ETA0 = 0 ETAB = -0.0608407 +DSUB = 1 PCLM = 0.8853499 PDIBLC1 = 0.116863 +PDIBLC2 = 0.01 PDIBLCB = -0.0475298 DROUT = 0.5922434 +PSCBE1 = 8E10 PSCBE2 = 5.248199E-10 PVAG = 0.089248 +DELTA = 0.01 RSH = 6.8 MOBMOD = 1 +PRT = 0 UTE = -1.5 KT1 = -0.11 +KT1L = 0 KT2 = 0.022 UA1 = 4.31E-9 +UB1 = -7.61E-18 UC1 = -5.6E-11 AT = 3.3E4 +WL = 0 WLN = 1 WW = 0 +WWN = 1 WWL = 0 LL = 0 +LLN = 1 LW = 0 LWN = 1 +LWL = 0 CAPMOD = 2 XPART = 0.5 +CGDO = 7.75E-10 CGSO = 7.75E-10 CGBO = 1E-12 +CJ = 9.955315E-4 PB = 0.7345743 MJ = 0.3629904 +CJSW = 2.586055E-10 PBSW = 0.6451808 MJSW = 0.1296914 +CJSWG = 3.3E-10 PBSWG = 0.6451808 MJSWG = 0.1296914 +CF = 0 PVTH0 = 1.33957E-3 PRDSW = -5 +PK2 = -1.7189E-4 WKETA = 0.010864 LKETA = -0.0102793 +PU0 = 37.4749547 PUA = 1.762367E-10 PUB = 9.411793E-25 +PVSAT = 2E3 PETA0 = -1E-4 PKETA = -1.356792E-3

.MODEL CMOSP_180nm PMOS (LEVEL = 49 hdif = 0.25e-6 acm = 3 +VERSION = 3.1 TNOM = 27 TOX = 4.2E-9 +XJ = 1E-7 NCH = 4.1589E17 VTH0 = -0.4220357 +K1 = 0.5813738 K2 = 0.0303955 K3 = 0 +K3B = 11.3426872 W0 = 1E-6 NLX = 9.876034E-8 +DVT0W = 0 DVT1W = 0 DVT2W = 0 +DVT0 = 0.5131166 DVT1 = 0.2665264 DVT2 = 0.1 +U0 = 120.5316596 UA = 1.645481E-9 UB = 1E-21 +UC = -1E-10 VSAT = 2E5 A0 = 1.671928 +AGS = 0.3934127 B0 = 1.830733E-6 B1 = 4.739218E-6 +KETA = 0.0202801 A1 = 0.1976849 A2 = 0.5787213 +RDSW = 265.2609374 PRWG = 0.5 PRWB = -0.2145086 +WR = 1 WINT = 0 LINT = 2.176517E-8 +XL = -2E-8 XW = -1E-8 DWG = -4.223522E-8 +DWB = 7.670464E-9 VOFF = -0.096172 NFACTOR = 2 +CIT = 0 CDSC = 2.4E-4 CDSCD = 0 +CDSCB = 0 ETA0 = 0.023671 ETAB = -0.3005133 +DSUB = 1.2320494 PCLM = 2.2844319 PDIBLC1 = 4.836921E-3 +PDIBLC2 = 0.0442167 PDIBLCB = -1E-3 DROUT = 9.991187E-4 +PSCBE1 = 1.732893E9 PSCBE2 = 5E-10 PVAG = 14.9616148 +DELTA = 0.01 RSH = 7.6 MOBMOD = 1 +PRT = 0 UTE = -1.5 KT1 = -0.11 +KT1L = 0 KT2 = 0.022 UA1 = 4.31E-9 +UB1 = -7.61E-18 UC1 = -5.6E-11 AT = 3.3E4 +WL = 0 WLN = 1 WW = 0 +WWN = 1 WWL = 0 LL = 0 +LLN = 1 LW = 0 LWN = 1 +LWL = 0 CAPMOD = 2 XPART = 0.5 +CGDO = 6.6E-10 CGSO = 6.6E-10 CGBO = 1E-12 +CJ = 1.183858E-3 PB = 0.8534482 MJ = 0.4124158 +CJSW = 2.066263E-10 PBSW = 0.6189346 MJSW = 0.2893774 +CJSWG = 4.22E-10 PBSWG = 0.6189346 MJSWG = 0.2893774 +CF = 0 PVTH0 = 2.308546E-3 PRDSW = 13.6874174 +PK2 = 2.657069E-3 WKETA = 2.467864E-3 LKETA = -2.56649E-3 +PU0 = -1.846164 PUA = -8.06063E-11 PUB = 1E-21 +PVSAT = -50 PETA0 = 1E-4 PKETA = 2.794471E-3 )

[ColsonZhang]

I suppose that when the gain is too big, the simulation would not work well.

[ColsonZhang]

Temporarily I add a resistor at the ouput node, and then the circuit's simulation has less troubles