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Design >> RF Design >> voltage gain and S21 relationship
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Message started by cybq on Jun 15^th, 2006, 5:01am

Title: voltage gain and S21 relationship
Post by cybq on Jun 15^th, 2006, 5:01am

Hi all,
How to caculate the volatge gain of a two port network, knowing S21, S11, S22?

I made a simple passive network in ADS and run the S paraamters and transient simualtion,
and found S21 is less more than the voltage gain caculated using transient voltage when
S11/S22 are not matched.

What is those relationship between them? Any answer are welcome.

cybq

Title: Re: voltage gain and S21 relationship
Post by milkdragon on Jun 15^th, 2006, 9:39am

Voltage gain (let's call it Vg) = 20log(Vout/Vin) dB

Power Gain (S21,let's call it Pg) = 10log(Pout/Pin) = 10log[(Vout^2/Rout)/(Vin^2/Rin)]=10log[{(Vout/Vin)^2} * (Rin/Rout)]=20log(Vout/Vin)+10log(Rin/Rout) dB

So you will see that if the input and output impedance are the same, Pg is essentially equal to Vg.

However, if Rin <> Rout, you will see the difference between voltage gain and power gain

Title: Re: voltage gain and S21 relationship
Post by cheelee on Jun 15^th, 2006, 6:39pm

Have a look at this paper:

George D. Vendelin, Jose Carlos Pedro and Pedro Miguel Cabral, "Amplifier and Transistor Gain Revisited", Microwave Journal, Apr 2005

It has the equations relating 2-port S-parameters to voltage, current and power gain. Hope it helps.

Title: Re: voltage gain and S21 relationship
Post by cybq on Jun 15^th, 2006, 9:13pm

Thanks cheelee.

I want to say that S parameter is defined with voltage, for example, S21=b2/a1|a2=0, instead of power gain.

I'll search the paper you recommended.

cybq