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how to simulate the stability of the TOM-THOMAS biquad ?

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viyag

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thomas biquad hi pass filter

i am designing an activeRC filter , and
how to simulate the stability of the TOM-THOMAS biquad ?
or it is stabled if the opamps in it have enough phase margin.

thanks very much.
 

Yes, the filter circuit will be always stable if the used opamps do not exhibit to much phase deviations. As a rule of thumb the GBW of the opamps should be at least 20 times higher than the pole frequency.
 

So does that mean in active RC filter design, one does not check the loop gain stability? Only need to check opamp's stablility?

If one does want to run the RC filter's loop stability, how to do it? I found that the classical way of breaking loop is not working because the R of RC filter's input may not be large, hence the analysis is not correct.

But I am not sure though... can you give me some suggestions?

thx
 

You can use "cmdmprobe" for your closed-loop stability simulation, you can find it in Cadence "basic" Library.
Where there is a loop , there is stability issue. So, principlely you should check every loop in your design. In fact , stability will not a big issue in Active-RC filter design.
 

My company does not use Cadence and only support hspice.

In active low pass filter, vin to vout is low pass but if I break the loop at the input of opamp and check the loop stability, I get a high pass filter response.

Is the stablity check you run have the same response?
 

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