Help on this question would be very gratefully received.

I have a netlist that if I run it in LTspice or SIMetrix, then to

about 4 significant figures, I get the same result:

`I(VXBIAS) = 259.5mA`

If I run the same netlist in ngspice release 25, I get:

`I(VXBIAS) = 266.5mA`

i.e. a 7mA dfference.

I have lightly edited the devices and their associated .model

statements to remove any unrecognised parameters and to ensure that

the models in the netlist are being used and that no external models

are being pulled in.

That way ngpsice, LTspice and SIMetrix should be using identical

models and paramater sets.

All simulations are being run at the same temperature.

In LTspice I have tried individually adjusting

GMIN: 1e-012 > 1e-011 Abstol: 1e-012 > 1e-011 Reltol: 0.001 > 0.01 Chgtol: 1e-014 > 1e-013 Trtol: 7 > 1 Voltol: 1e-006 > 1e-005 Sstol: 0.001 > 0.01 MinDeltaGmin > 0.0001 > 0.001

to see if I can change the value of I(VXBIAS) but have made no

significant difference (i.e. greater than about 1mA) to the result.

I have also tried running using different time steps and integration

methods and have run extended .tran sims with a

`V=15*(1-exp(-1*time/10u))`

ramped supply voltage B source in place of V1 to see if the initial

conditions could be the root cause of the steady state difference.

Again, all with no appreciable difference to the value of I(VXBIAS) in

any of the simulators.

#### So my question is:

Does anyone have any insight as to what ngspice might be doing - or

doing differently - that could account for the 7mA difference in the

values for I(VXBIAS)?

(Oh and I know the amplifier is not very good. It just happens to be

the circuit in which I spotted this value difference.)

:)

Andy.

signality.co.uk

Netlist follows:

* Amplifier sanity check VXBIAS V1_1 Q4_2 0v .SAVE I(VXBIAS) V2 V2_1 0 SIN(0 000m 1k) AC 1 0 ; yes it is supposed to be zero amplitude! V1 V1_1 0 15 R9 R7_2 R9_2 22k R8 0 R8_2 470 R7 R7_1 R7_2 1 R6 R7_2 R6_2 1 R4 C1_2 R4_2 27k R3 0 C1_2 100k R2 R2_1 R9_2 1k R13 R8_2 D2_C 1m R12 R1_2 R4_2 27k R11 V1_1 R1_2 330 R10 0 VOUT 8 R1 R1_1 R1_2 15k Q4 Q4_2 Q2_3 R6_2 BD139x Q3 0 R8_2 R7_1 BD140x Q2 Q2_3 R1_1 V1_1 Q2N3906 Q1 R1_1 C1_2 R9_2 BC109Cx D2 D2_A D2_C D1N4148 D1 Q2_3 D2_A D1N4148 C6 0 R4_2 470u C5 0 R2_1 330u C4 0 V1_1 2200u C3 R7_2 VOUT 2200U C2 0 R1_2 220u C1 V2_1 C1_2 10u .save V(VOUT) ************************************** * by MODPEX * *Copyright(c) Symmetry Design Systems* * All Rights Reserved * * UNPUBLISHED LICENSED SOFTWARE * * Contains Proprietary Information * * Which is The Property of * * SYMMETRY OR ITS LICENSORS * *Commercial Use or Resale Restricted * * by Symmetry License Agreement * ************************************** * on Aug 7, 01 * : SPICE2 .MODEL Q2N3906 pnp +IS=7.75521e-12 BF=194.093 NF=1.35509 VAF=156.436 +IKF=0.0660057 ISE=1.88546e-12 NE=1.81673 BR=3.41317 +NR=1.5 VAR=5.86061 IKR=1.70599 ISC=7.64281e-10 +NC=1.92376 RB=6.48961 IRB=0.1 RBM=0.1 +RE=0.0001 RC=2.45044 XTB=0.1 XTI=1 +EG=1.05 CJE=6.11928e-12 VJE=0.4 MJE=0.248812 +TF=5.21843e-10 XTF=0.932702 VTF=9.1046 ITF=0.0106472 +CJC=6.85007e-12 VJC=0.4 MJC=0.279018 XCJC=0.9 +FC=0.478887 CJS=0 VJS=0.75 MJS=0.5 +TR=4.30605e-07 PTF=0 KF=0 AF=1 *.model D1n4148 D(IS=1.6f RS=1.0 IKF=22m CJO=3p M=0.3 VJ=0.75 ISR=2.6n BV=70 TT=20n) .model D1n4148 D(IS=1.6f RS=1.0 IKF=22m CJO=3p M=0.3 VJ=0.75 BV=70 TT=20n) *.model BC109Cx NPN(Is=7.049f Xti=3 Eg=1.11 Vaf=28.14 Bf=677 Ise=7.049f Ne=1.38 *+ Ikf=96.23 Nk=.5 Xtb=1.5 Br=2.209 Isc=250.3p Nc=2.002 Ikr=10.73 *+ Rc=1.433 Cjc=5.38p Mjc=.329 Vjc=.6218 Fc=.5 Cje=11.5p Mje=.2717 *+ Vje=.5 Tr=10n Tf=437.8p Itf=3.097 Xtf=12.85 Vtf=10) * PHILIPS pid=bc108c case=TO18 * 91-08-02 dsq .model BC109Cx NPN(Is=7.049f Xti=3 Eg=1.11 Vaf=28.14 Bf=677 Ise=7.049f Ne=1.38 + Ikf=96.23 Xtb=1.5 Br=2.209 Isc=250.3p Nc=2.002 Ikr=10.73 + Rc=1.433 Cjc=5.38p Mjc=.329 Vjc=.6218 Fc=.5 Cje=11.5p Mje=.2717 + Vje=.5 Tr=10n Tf=437.8p Itf=3.097 Xtf=12.85 Vtf=10) * PHILIPS pid=bc108c case=TO18 * 91-08-02 dsq ************************************** * Model Generated by MODPEX * *Copyright(c) Symmetry Design Systems* * All Rights Reserved * * UNPUBLISHED LICENSED SOFTWARE * * Contains Proprietary Information * * Which is The Property of * * SYMMETRY OR ITS LICENSORS * * Modeling services provided by * * Interface Technologies www.i-t.com * ************************************** .MODEL bd140x pnp +IS=1e-09 BF=650.842 NF=0.85 VAF=10 +IKF=0.0950125 ISE=1e-08 NE=1.54571 BR=56.177 +NR=1.5 VAR=2.11267 IKR=0.950125 ISC=1e-08 +NC=3.58527 RB=41.7566 IRB=0.1 RBM=0.108893 +RE=0.000347052 RC=1.32566 XTB=19.5239 XTI=1 +EG=1.05 CJE=1e-11 VJE=0.75 MJE=0.33 +TF=1e-09 XTF=1 VTF=10 ITF=0.01 +CJC=1e-11 VJC=0.75 MJC=0.33 XCJC=0.9 +FC=0.5 CJS=0 VJS=0.75 MJS=0.5 +TR=1e-07 PTF=0 KF=0 AF=1 * Model generated on Feb 14, 2004 * Model format: SPICE3 ************************************** * Model Generated by MODPEX * *Copyright(c) Symmetry Design Systems* * All Rights Reserved * * UNPUBLISHED LICENSED SOFTWARE * * Contains Proprietary Information * * Which is The Property of * * SYMMETRY OR ITS LICENSORS * * Modeling services provided by * * Interface Technologies www.i-t.com * ************************************** .MODEL bd139x npn +IS=1e-09 BF=222.664 NF=0.85 VAF=36.4079 +IKF=0.166126 ISE=5.03418e-09 NE=1.45313 BR=1.35467 +NR=1.33751 VAR=142.931 IKR=1.66126 ISC=5.02557e-09 +NC=3.10227 RB=26.9143 IRB=0.1 RBM=0.1 +RE=0.000472454 RC=1.04109 XTB=0.727762 XTI=1.04311 +EG=1.05 CJE=1e-11 VJE=0.75 MJE=0.33 +TF=1e-09 XTF=1 VTF=10 ITF=0.01 +CJC=1e-11 VJC=0.75 MJC=0.33 XCJC=0.9 +FC=0.5 CJS=0 VJS=0.75 MJS=0.5 +TR=1e-07 PTF=0 KF=0 AF=1 * Model generated on Feb 14, 2004 * Model format: SPICE3 .tran 20u 2m ; for ngspice *.tran 0 2m 0 20u ; for LTspice and SIMetrix .END