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Design >> Analog Design >> About the resistor to ground
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Message started by gaom9 on Apr 18^th, 2008, 7:50am

Title: About the resistor to ground
Post by gaom9 on Apr 18^th, 2008, 7:50am

Hi,
I want to know how to calculate the resistor to ground when calculate the POLE and ZERO.
I saw some examples about it, but in some node, I can not find the resistor to ground in small signal model.
And when calculate it, should we short the input and output to ground?

Is there any books about it, please?

Thank you.
Best regards!

Title: Re: About the resistor to ground
Post by Stefan on Apr 18^th, 2008, 9:10am

If anyone is able to understand this question, please let me know :)

Title: Re: About the resistor to ground
Post by gaom9 on Apr 18^th, 2008, 6:11pm

Let's wait for hero together.

;) :P

Best regards!

Title: Re: About the resistor to ground
Post by Stefan on Apr 19^th, 2008, 10:24am

Hi Gaom,

I meant that it's (at least for me) impossible to understand your question. If you want to get a good answer, please refine your question a little bit :)

Regards,

Stefan

Title: Re: About the resistor to ground
Post by gaom9 on Apr 19^th, 2008, 7:07pm

I am sorry, Stefan
My question is as shown below.

For example, when I calculate the POLE and ZERO of the common-gate amp as shown below. What is the resistor of note X to ground? in its small signal as shown below, Rs and 1/gm//1/gmb is in series, but both of them do not connect to ground, but in Razavi is book, the resistor of it to ground is RS//[1/(gm+gmb)], why? and also the question to note Y.
And should we short the output and input to ground when calculate?

common gate amp

small signal model

Thank you.
Best regards.

Title: Re: About the resistor to ground
Post by Geoffrey_Coram on Apr 25^th, 2008, 5:39am

Recall that any voltage source is an "ac ground" for small-signal analysis. Does this help?