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Spice question - small signal gain.

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alphacat

New Member
Hello.

I've drawn an CS amplifier as can be seen in the scheme.
I'm not sure what should I fill in these two fields in order to receive the small signal DC gain of this amplifier.
I'd love to receive help regarding that,

Thank you very much.

 

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millwood

Banned
the first box is the source of the dc "signal / disturbance". what it is depends on what you want to do. For example, this circuit is configured as a common source amplifier. so you want to know how a change in Vgs is going to produce a (bigger) change on the CCS. so the first box should be V1.

the 2nd box is essentially the output you desire from the circuit. it could be voltage on R1(V(r1)), or current on R1 (I(r1)).
 

alphacat

New Member
Hey,

I tried this out, and wrote:
V1 in the upper box.
R1(I(r1)) in the lower box (I also tried writing I(R1), and R1(I(R1))).

I received this error:
*Analysis directives:

.TF R1(I(r1)) V_V1
----$
ERROR -- Must be independent source (I or V)
.PROBE V(alias(*)) I(alias(*)) W(alias(*)) D(alias(*)) NOISE(alias(*))
.INC "..\SCHEMATIC1.net"

Do you have an idea what is the problem?

Thanks.
 

alphacat

New Member
Thank you very much :)
It worked out great.

I followed exactly what you have written there - calling the netlist 'Vout', placing a voltage prob on the netlist - otherwise it didnt work.

What would you write if you wanted the Output Variable to be the load (R1) current?

Here is what I wrote, and I received the same error message as before.
 

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