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ngspice transfer function

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ced

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ngspice singular matrix

Hi,
I am a ngspice newbie and I'd like to get a frequential transfer function of a Wien filter
as an exercise .
I'd like to plot V(3)/ISRC versus frequency .

Here is the .sch file I simulate :

Tranfer 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 is the result I get :

ngspice 1 -> 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 has an idea about what's wrong in the scheme file ?
Thanks for your help,
ced
 

ced

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There was no dc path between node 1 and ground .
Adding a very large resistor between both nodes solved the problem
Good Bye,
Cédric
 

sudheerkm

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yes this how to cheat the dc bias problems for ac analys

you can do away with the resistor there it does not try to find bias point i suppose
 

s.jayaram88

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Alternatively to avoid this problem you can add high resistances to all the analog nodes in the netlist. This is a control option given in the .OPTIONS statement. For example if you would by default want a high resistance (say 1e12) on every node, use RSHUNT=1e12 within .OPTIONS
 

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