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elementary transfer function with ngspice

Hi, I am a spice newbie and I'd like to plot the transfer function V/I (f) . Here is the scheme :

Transfer function : ISRC 1 0 AC 1 R1 1 2 1k C1 2 3 1u R2 3 0 1k C2 3 0 1u .AC DEC 10 1 10K .END

Here are the results I get :

ngspice 25 -> run Doing analysis at TEMP =3D 27.000000 and TNOM =3D 27.000000

Warning: Source isrc has no value, DC 0 assumed

Warning: singular matrix: check nodes 1 and 1

Note: starting dynamic Gmin stepping Trying gmin =3D 1.0000E-03 Note: One successful Gmin step Trying gmin =3D 1.0000E-04 Note: One successful Gmin step Trying gmin =3D 1.0000E-05 Note: One successful Gmin step Trying gmin =3D 1.0000E-06 Note: One successful Gmin step Trying gmin =3D 1.0000E-07 Note: One successful Gmin step Trying gmin =3D 1.0000E-08 Note: One successful Gmin step Trying gmin =3D 1.0000E-09 Note: One successful Gmin step Trying gmin =3D 1.0000E-10 Note: One successful Gmin step Trying gmin =3D 1.0000E-11 Note: One successful Gmin step Trying gmin =3D 1.0000E-12 Note: One successful Gmin step Trying gmin =3D 1.0000E-12 Note: One successful Gmin step Warning: singular matrix: check nodes 1 and 1

Warning: Dynamic Gmin stepping failed Note: starting source stepping Supplies reduced to 0.0000% Warning: singular matrix: check nodes 1 and 1

Trying gmin =3D 1.0000E-02 Note: One successful Gmin step Trying gmin =3D 1.0000E-03 Note: One successful Gmin step Trying gmin =3D 1.0000E-04 Note: One successful Gmin step Trying gmin =3D 1.0000E-05 Note: One successful Gmin step Trying gmin =3D 1.0000E-06 Note: One successful Gmin step Trying gmin =3D 1.0000E-07 Note: One successful Gmin step Trying gmin =3D 1.0000E-08 Note: One successful Gmin step Trying gmin =3D 1.0000E-09 Note: One successful Gmin step Trying gmin =3D 1.0000E-10 Note: One successful Gmin step Trying gmin =3D 1.0000E-11 Note: One successful Gmin step Trying gmin =3D 1.0000E-12 Note: One successful Gmin step Note: One successful source step Supplies reduced to 0.1000% Warning: singular matrix: check nodes 1 and 1

Supplies reduced to 0.0000% Warning: singular matrix: check nodes 1 and 1

Warning: source stepping failed

AC operating point failed -

Last Node Voltages

------------------

Node Last Voltage Previous Iter

---- ------------

-------------

1 0 0 2 0 0 3 0 0

doAnalyses: iteration limit reached

run simulation(s) aborted

Does someone sees what's wrong in the scheme file ?

Thanks very much,

C=E9dric

Reply to
cedric
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It doesn't like the fact that you've got a capacitor with no DC path to ground -- a current source doesn't count. Try adding a 10 meg resistor (or other ridiculously large value) from node 1 or 2 to ground, and see if it gets happier.

Alternate #1: take ISRC and R1 and turn them into their Thevenin equivalent; a voltage source provides a very positive path to ground, and the Thevenin equivalent source is easy to calculate when you've got a nice round number for the resistor value.

Alternate #2: just do it on paper -- this is sophomore signals and systems stuff; unless you're doing it as a warm up to something real or you're learning SPICE you shouldn't need to get close to a computer to do this.

--
www.wescottdesign.com
Reply to
Tim Wescott

.

in =3D

E-05

l

in =3D

E-11

l

s 1

in =3D

E-04

l

in =3D

E-10

l

s 1

s 1

=A0 Last Voltage =A0 =A0 =A0 =A0Previous Iter

=A0 ------------ -------------

=A0 =A0 =A0 =A0 =A0 =A0 =A0 0 0

=A0 =A0 =A0 =A0 =A0 =A0 =A0 0 0

=A0 =A0 =A0 =A0 =A0 =A0 =A0 0 0

Thanks very much,

the point was the missing DC path to ground of node 1 . Yes, as you guessed it, it was just a warm-up, before other doing something more difficult (for ngspice :-) ) . Bye cedric

Reply to
cedric

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