elementary transfer function with ngspice

C

cedric

Guest
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 = 27.000000 and TNOM = 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 = 1.0000E-03 Note: One successful Gmin step
Trying gmin = 1.0000E-04 Note: One successful Gmin step
Trying gmin = 1.0000E-05 Note: One successful Gmin step
Trying gmin = 1.0000E-06 Note: One successful Gmin step
Trying gmin = 1.0000E-07 Note: One successful Gmin step
Trying gmin = 1.0000E-08 Note: One successful Gmin step
Trying gmin = 1.0000E-09 Note: One successful Gmin step
Trying gmin = 1.0000E-10 Note: One successful Gmin step
Trying gmin = 1.0000E-11 Note: One successful Gmin step
Trying gmin = 1.0000E-12 Note: One successful Gmin step
Trying gmin = 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 = 1.0000E-02 Note: One successful Gmin step
Trying gmin = 1.0000E-03 Note: One successful Gmin step
Trying gmin = 1.0000E-04 Note: One successful Gmin step
Trying gmin = 1.0000E-05 Note: One successful Gmin step
Trying gmin = 1.0000E-06 Note: One successful Gmin step
Trying gmin = 1.0000E-07 Note: One successful Gmin step
Trying gmin = 1.0000E-08 Note: One successful Gmin step
Trying gmin = 1.0000E-09 Note: One successful Gmin step
Trying gmin = 1.0000E-10 Note: One successful Gmin step
Trying gmin = 1.0000E-11 Note: One successful Gmin step
Trying gmin = 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,

Cédric
 
On Sun, 23 Aug 2009 12:16:44 -0700, cedric wrote:

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 = 27.000000 and TNOM = 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 = 1.0000E-03 Note: One successful Gmin step Trying gmin =
1.0000E-04 Note: One successful Gmin step Trying gmin = 1.0000E-05
Note: One successful Gmin step Trying gmin = 1.0000E-06 Note: One
successful Gmin step Trying gmin = 1.0000E-07 Note: One successful
Gmin step Trying gmin = 1.0000E-08 Note: One successful Gmin step
Trying gmin = 1.0000E-09 Note: One successful Gmin step Trying gmin =
1.0000E-10 Note: One successful Gmin step Trying gmin = 1.0000E-11
Note: One successful Gmin step Trying gmin = 1.0000E-12 Note: One
successful Gmin step Trying gmin = 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 = 1.0000E-02 Note: One successful Gmin step Trying gmin =
1.0000E-03 Note: One successful Gmin step Trying gmin = 1.0000E-04
Note: One successful Gmin step Trying gmin = 1.0000E-05 Note: One
successful Gmin step Trying gmin = 1.0000E-06 Note: One successful
Gmin step Trying gmin = 1.0000E-07 Note: One successful Gmin step
Trying gmin = 1.0000E-08 Note: One successful Gmin step Trying gmin =
1.0000E-09 Note: One successful Gmin step Trying gmin = 1.0000E-10
Note: One successful Gmin step Trying gmin = 1.0000E-11 Note: One
successful Gmin step Trying gmin = 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,

CĂŠdric
Click to expand...
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
 
On 24 aoűt, 18:13, Tim Wescott <t...@seemywebsite.com> wrote:
On Sun, 23 Aug 2009 12:16:44 -0700, cedric wrote:
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 = 27.000000 and TNOM = 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 =   1.0000E-03 Note: One successful Gmin step Trying gmin > >  1.0000E-04 Note: One successful Gmin step Trying gmin =   1.0000E-05
Note: One successful Gmin step Trying gmin =   1.0000E-06 Note: One
successful Gmin step Trying gmin =   1.0000E-07 Note: One successful
Gmin step Trying gmin =   1.0000E-08 Note: One successful Gmin step
Trying gmin =   1.0000E-09 Note: One successful Gmin step Trying gmin > >  1.0000E-10 Note: One successful Gmin step Trying gmin =   1.0000E-11
Note: One successful Gmin step Trying gmin =   1.0000E-12 Note: One
successful Gmin step Trying gmin =   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 =   1.0000E-02 Note: One successful Gmin step Trying gmin > >  1.0000E-03 Note: One successful Gmin step Trying gmin =   1.0000E-04
Note: One successful Gmin step Trying gmin =   1.0000E-05 Note: One
successful Gmin step Trying gmin =   1.0000E-06 Note: One successful
Gmin step Trying gmin =   1.0000E-07 Note: One successful Gmin step
Trying gmin =   1.0000E-08 Note: One successful Gmin step Trying gmin > >  1.0000E-09 Note: One successful Gmin step Trying gmin =   1.0000E-10
Note: One successful Gmin step Trying gmin =   1.0000E-11 Note: One
successful Gmin step Trying gmin =   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,

 Cédric

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
Click to expand...
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
 
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