A trivial question on the Razavi's Book "RFMicroelectro

[hjzs18]

razavi rfmicroele

Hi, all
I am just reading Razavi's book "RF Microelectronics", and i am confused by the formula (2.90) of computing the R_out. Could anyone here give me a clue or a detailed explaination on how to get the formula????


TIA

 

[safwatonline]

interestingly, i tried to calculate it few days ago but i didnt get the same formula.

Added after 23 seconds:

i was going to ask here but i got lazy

 

[hjzs18]

Re: A trivial question on the Razavi's Book "RFMicroele

can guys there help me see this?

 

[tyassin]

Re: A trivial question on the Razavi's Book "RFMicroele

Hi

I have tried as well, but can not get the same answer from the book.

But if you use his expression for Rs you can simplify it.

regards

 

[teteamigo]

Re: A trivial question on the Razavi's Book "RFMicroele

The expression in Razavi book is correct.

Your problem is related with a simplification/assumption that Rin=Rs

by this way gm2*Rs=1/(1+gm1*RD)

 

[tyassin]

Re: A trivial question on the Razavi's Book "RFMicroele

Hi teteamigo

Yes you are correct I get the same result now.

 

[hjzs18]

HI teteamigo & Tyassin
I still dont get it. Can you show me your derivation here, or the specific approach you use to compute the output resistance?

Thanks

 

[teteamigo]

Re: A trivial question on the Razavi's Book "RFMicroele

The expression in Razavi book is correct.

Your problem is related with a simplification/assumption that Rin=Rs

by this way gm2*Rs=1/(1+gm1*RD)

First get the relationship between vin and vout, then applies matching for power condition Rin=Rs.

 

[tyassin]

Re: A trivial question on the Razavi's Book "RFMicroele

Hi

The output resistance can be written as:

Then you can identify the matching relationship with R2 and Rin (gm2*Rs).

If you insert this then it simplyfies to the formula in the book.

Regards