Actual gain Vs. Bode plot gain?

Alshatri

Joined May 14, 2013
4
Dear all,

I have the gain @100Khz in bode plot almost=1dB, while the actual gain= 20 log(Vout/Vin)=20 log(3/0.005)= 55.56dB (from the transient values)

Could someone please explain why I have this weird bode plot gain reading?

Regards

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ronv

Joined Nov 12, 2008
3,770
I think it is because the bode plot is expecting an input of 1 volt so the scale is wrong. I didn't draw it up and try it but I think that's it.

Alshatri

Joined May 14, 2013
4
I think it is because the bode plot is expecting an input of 1 volt so the scale is wrong. I didn't draw it up and try it but I think that's it.
Could you tell me please what is the 1V that are you talking about?

WBahn

Joined Mar 31, 2012
26,076
I think the problem might be related to having a resistor whose value is dependent on the signal. I think the AC analysis linearizes things and so I don't know how it would deal with a voltage-dependent resistance.

LvW

Joined Jun 13, 2013
1,078
Alshatri, when you like to see the gain (Vout/Vin) you must display the ratio Vout/Vin.
However, your Bode plot shows only Vout.
Only in case your AC input is 1Volt it is sufficient to display Vout (because it is identical to the gain).
Remark: I cannot see which resistor value is "dependent on the signal".

EDIT: Sorry, a sharper look on the drawing has revealed that R3 depends on the input.

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