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