About PZ simulation in cadence

[rficdesigner]

Hello,

I would like to ask about PZ analysis.

After running PZ simulation, the output we have is a list of Poles.

How can we find out the Pole of a specific node in the schematic?

And which node in the schematic is the dominant poles of the circuit?

Do you have any idea, pls share

Thanks you.

 

[dedalus]

Hi, rficdesigner.

After running PZ simulation, the output we have is a list of Poles.

Some poles can be canceled by zeros. You should use both list of poles and list of zeros to define which poles have influence on frequency response.

How can we find out the Pole of a specific node in the schematic?

And which node in the schematic is the dominant poles of the circuit?

You can estimate values of the poles using next expressions (order of the poles corresponds to order of the nodes from left-to-right):

f1 = 1/[2*pi*(C1+C3+(1-A1)*CdsM0+CgsM0)*(R2||R5/(1-A))]
f2 = 1/[2*pi*(CdsM0+CgsM1+(1-A2)CdsM1)*(R1||roM0)]
f3 = 1/[2*pi*(CdsM1+CgsM2+(1-A3)CdsM2)*(R0||roM1)]
f4 = 1/[2*pi*CdsM1*(R0||roM1||R5)]

A1 - gain of the first stage; A2 - gain of the second stage; A3 - gain of the third stage; A = A1*A2*A3.

 

[rficdesigner]

Thanks dedalus,

Without any manual calculations, can we guess the dominant pole of the circuit from the PZ simulation results?

 

[dedalus]

Hi.

And which node in the schematic is the dominant poles of the circuit?

Node is not a pole. In some particular cases we can say that node introduces a pole, but in general this is not true. We use the concept of association of poles with nodes only for intuitive analysis. Please refer to Razavis' "Desing of Analog CMOS Integrated Circuits", section 6.1.2. for detailed explanation.

Without any manual calculations, can we guess the dominant pole of the circuit from the PZ simulation results?

As far as I understand you want to determine which node "introduces" dominant pole. As I said before there is no correspondence between poles and nodes in general, so PZ analysis cannot provide such information. You can get only numerical value of the dominant pole (if it exists).