Actual gain Vs. Bodeplot gain ?

[AAOAA]

Dear all,

I have the gain @100Khz in bode plot almost=0dB, while the actual
gain= 20 log(Vout/Vin)=20 log(3/0.005)= 55.56dB (from the transient vales)

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

Regards

 

[dick_freebird]

Begin with the validity of your AC analysis' operating
point solution, i.e. whether the amplifier is linear and
closed loop.

 

[crutschow]

I believe it's because your formula for generating the value of R3 only works in the transient mode.

 

[AAOAA]

Could you tell me please, what do you mean by this?

Begin with the validity of your AC analysis' operating
point solution, i.e. whether the amplifier is linear and
closed loop.

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"""I believe it's because your formula for generating the value of R3 only works in the transient mode"""

Here is R3 behaviour, I think its fine.

 

[keith1200rs]

You cannot expect a gain of 2000 at 100kHz from the LT1037.

Keith

 

[FvM]

Bad habbit of cross posting.

I believe it's because your formula for generating the value of R3 only works in the transient mode.

No, it does work (although you can't derive this from the transient waveforms).

The simulation however doesn't measure the OP "gain". It measures V(out) in dB which is OP gain multiply attenuation by the bridge modulation factor multiply V(in).

 

[AAOAA]

You cannot expect a gain of 2000 at 100kHz from the LT1037.

Keith

I didnt expect it 2000 at all, but my question was why the bode plot doesnt show the right gain (~0dB istead of 55dB)?

 

[keith1200rs]

I don't know why you think your gain is 55dB in the transient analysis. You are putting 1V peak in and getting around 1.4V peak out.

Keith

 

[AAOAA]

Begin with the validity of your AC analysis' operating
point solution, i.e. whether the amplifier is linear and
closed loop.

Could you please tell me what do you mean precisely by this?