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negative DB gain --- in the stb virtuoso simulation

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zizbear

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Hello,

I did a stb simulation for a differential current input amplifier in a normal feedback setting.

I put the vsource in one of the input node of this amplifier, then run the stb simulation to check the openloop gain and phase for the stablity, but I get a negative loop gain( about -50dB in DC, then increse to 0dB with frequency increase) in one of the input. While do the same simulation for another input , get the normal possitive DB gain ( about 50dB).

but the difference for these two input loop gain should only have the 180 deg phase differense, right? why their gain have the + - difference? It tells that one of the loop is not amplifier signal but attenuate it, why this is happen?

Thank you very much !!
 

zizbear said:
Hello,

I did a stb simulation for a differential current input amplifier in a normal feedback setting.

I put the vsource in one of the input node of this amplifier, then run the stb simulation to check the openloop gain and phase for the stablity, but I get a negative loop gain( about -50dB in DC, then increse to 0dB with frequency increase) in one of the input. While do the same simulation for another input , get the normal possitive DB gain ( about 50dB).

but the difference for these two input loop gain should only have the 180 deg phase differense, right? why their gain have the + - difference? It tells that one of the loop is not amplifier signal but attenuate it, why this is happen?

Thank you very much !!
Click to expand...

Your bias maybe not right。
 

Hi, Thank you very much for your reply!

but could you say it a bit more? Do you mean it is not working in the right operation point?

I use it as a gain boost loop. so the out come function seems right, but the stb simulation for these inside two loops, I just don't understand it... it still could be wrong?

Thank you!!
 

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