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Re: [Help-gnucap] Bug? convergence problem?
From: |
gserdyuk |
Subject: |
Re: [Help-gnucap] Bug? convergence problem? |
Date: |
Fri, 11 Feb 2011 15:58:10 +0200 |
Hello Orestes,
likely that is relaxed convergence criterion. Opamp is very sensitive
to that stuff.
add
.options abstol=1.e-15
and it will fix this issue.
if you will make DC step finer - result will be the same (no peak).
regards
Gena
Thursday, February 10, 2011, 4:46:31 PM, you wrote:
OM> Hello,
OM> I'm facing a weird result when I simulate a simple inverter amplifier built
OM> around an operational amplifier. Basically I'm trying to obtain the input-
OM> output transfer characteristic (for educational purposes), but if the number
OM> of points in the DC command is low, I obtain an spurious peak at the output.
OM> The circuit is:
OM> -------
OM> .INCLUDE uA741.model
OM> Vcc 4 0 DC 15
OM> Vdd 0 5 DC 15
OM> vg 1 0 DC 2.5
OM> R1 1 2 2.2k
OM> R2 2 3 15k
OM> X1 0 2 4 5 3 uA741
OM> .PRINT DC v(3)
OM> .DC vg -5 5 0.5
OM> .END
OM> ---------
OM> If you simulate that you'll see an output peak of -17V for the Vg=2.5V
input.
**********>>>> NOTE: Using the "OP" command yelds the correct solution (or a
OM> more plausible one) of -14.613V ************
OM> I need some help to determine if this strange behaviour is originated by a
bug
OM> in gnucap, an expectable convergence issue, or a wrong macromodel adaption
OM> (see below)
OM> Can anyone help me? Thanks in advance.
OM> (((More info: The AO macromodel is the pspice one slightly modified to make
it
OM> work on gnucap. Here is the file:
OM>
*-------------------------------------------------------------------------------
OM> * Library of linear IC definitions
OM> * This is a reduced version of MicroSim's linear subcircuit library.
OM> * You are welcome to make as many copies of it as you find convenient.
OM> *
OM> * The parameters in the opamp library were derived from the data sheets for
OM> * each part. The macromodel used is similar to the one described in:
OM> *
OM> * Macromodeling of Integrated Circuit Operational Amplifiers
OM> * by Graeme Boyle, Barry Cohn, Donald Pederson, and James Solomon
OM> * IEEE Journal of SoliE-State Circuits, Vol. SC-9, no. 6, Dec. 1974
OM> *
OM> * Differences from the reference (above) occur in the output limiting stage
OM> * which was modified to reduce internally generated currents associated with
OM> * output voltage limiting, as well as short-circuit current limiting.
OM> *
OM> * The opamps are modelled at room temperature and do not track changes with
OM> * temperature. This library file contains models for nominal, not worst
case,
OM> * devices.
OM> *
OM> *$
OM>
*-----------------------------------------------------------------------------
OM> * connections: non-inverting input
OM> * | inverting input
OM> * | | positive power supply
OM> * | | | negative power supply
OM> * | | | | output
OM> * | | | | |
OM> .subckt uA741 1 2 3 4 5
OM> *
OM> c1 11 12 8.661E-12
OM> c2 6 7 30.00E-12
OM> dc 5 53 dx
OM> de 54 5 dx
OM> dlp 90 91 dx
OM> dln 92 90 dx
OM> dp 4 3 dx
OM> * POLY font rewritten to make it work under gnucap
OM> * egnd 99 0 poly(2) (3,0) (4,0) 0 .5 .5
OM> egnd1 99 98 3 0 .5
OM> egnd2 98 0 4 0 .5
OM> * POLY font rewritten to make it work under gnucap
OM> * fb 7 99 poly(5) vb vc ve vlp vln 0 10.61E6 -10E6 10E6 10E6 -10E6
OM> fb1 7 99 vb 10.61E6
OM> fb2 7 99 vc -10E6
OM> fb3 7 99 ve 10E6
OM> fb4 7 99 vlp 10E6
OM> fb5 7 99 vln -10E6
OM> ga 6 0 11 12 188.5E-6
OM> gcm 0 6 10 99 5.961E-9
OM> iee 10 4 dc 15.16E-6
OM> hlim 90 0 vlim 1K
OM> q1 11 2 13 qx
OM> q2 12 1 14 qx
OM> r2 6 9 100.0E3
OM> rc1 3 11 5.305E3
OM> rc2 3 12 5.305E3
OM> re1 13 10 1.836E3
OM> re2 14 10 1.836E3
OM> ree 10 99 13.19E6
OM> ro1 8 5 50
OM> ro2 7 99 100
OM> rp 3 4 18.16E3
OM> vb 9 0 dc 0
OM> vc 3 53 dc 1
OM> ve 54 4 dc 1
OM> vlim 7 8 dc 0
OM> vlp 91 0 dc 40
OM> vln 0 92 dc 40
OM> .model dx D(Is=800.0E-18 Rs=1)
OM> .model qx NPN(Is=800.0E-18 Bf=93.75)
OM> .ends
OM> _______________________________________________
OM> Help-gnucap mailing list
OM> address@hidden
OM> http://lists.gnu.org/mailman/listinfo/help-gnucap
--
Best regards,
Gserdyuk mailto:address@hidden