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ngspice transfer function

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ced

New Member
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
 

MikeMl

Well-Known Member
Most Helpful Member
I know nothing about NGSpice (No Good Spice?).

Driving the Wien Bridge network with a current source is a problem. The input should be from a voltage source. Look at the two frequency sweeps in the attachment. The second is the correct behavior.

Get the free LTSpice.
 

Attachments

ced

New Member
Hi,
ngspice is a linux spice simulator, it was a bad joke :) !
Actually it works fine as long as their is a dc path between any node and ground.
I've added a large resistor between node 1 and ground, and it works fine .
I'll try soon LTspice
Thanks and bye,
Cédric
 

Roff

Well-Known Member
Hi,
ngspice is a linux spice simulator, it was a bad joke :) !
Actually it works fine as long as their is a dc path between any node and ground.
I've added a large resistor between node 1 and ground, and it works fine .
I'll try soon LTspice
Thanks and bye,
Cédric
I think that Mike was implying that the Vout/Iin transfer function is almost trivial, because the values of R3 and C3 (in his schematic) are irrelevant. If you don't believe me, try changing R3 and C3.:eek:
 
Last edited:

ced

New Member
I think that Mike was implying that the Vout/Iin transfer function is almost trivial, because the values of R3 and C3 (in his schematic) are irrelevant. If you don't believe me, try changing R3 and C3.:eek:
I agree that the Vout/Iin transfer function is trivial .
I am spice beginner, so to gain confidence, I'd like to see well-known results, before
trying to simulate circuits that I don't precisely know .
I thought it would an easy way to get the impedance versus frequency of a network
plotting the voltage between the nodes of the network versus frequency with a 1A AC
input current .

Does that seem right to you ?
 

Roff

Well-Known Member
Vout/Iin is definitely a good way to plot impedance. With 1 Amp in, the result is in Ohms, which is of course what you were implying. It's not a great way to plot Vout/Vin, which is what you need for a Wien network. You can do it with current stimulus, but you have to do some math in the plot (Vout/Vin) to get useful information.
 
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