Selecting input impedance point.

Hello all,

I'm at the learning stage of amplifier design.I have selected the Transistor device and able to draw gain and noise circles in simulation software.
But I dont know how to select the input impedance point of the transistor.Can anybody help me how to select input impedance point for the transistor based on gain and noise circles.

regards,
johnson.

Hi

Your noise circles are drawn in the gamma_s plane and your gain could also be in gamma_s, depending on what sort of gain you are specifying.

So you chose a reflection coefficient(gamma_s) that gives you a desired noise figure or desired gain. You will properly see that the two are a compromise.
If you do not like using reflection coefficient you can just calculate to have a resistance and reactance.

Regards

hi tyassin,

Thanks for your reply.
Actually i'm trying to repeat the design(amplifier tutorial) given in below link in ansoft designer.
http://www.zen118213.zen.co.uk/RFMic...p_tutorial.pdf

As per page no:9 in above mention tutorial i've repeated in ansoft designer, available gain (Source) -12.5 dB and noise circle-2dB.From these how to select input impedance point of the device. Attached here is the screen shot of smith tool with above mention circles.

Hi

I just noticed that your Gain_max and Noise_min is not located in the same spots as in the tutorial?

I can see that the data in the tutorial is generated from a S-parameter file, are you using the same?

Regards

yes i'm using s parameter file for simulation (t414358a.s2p)
if that is not the correct file kindly send me the specific file.

Hi

It looks like the right file, but your noise circles do not like they are in the correct place.

thanks for your reply.
any amplifier tutorial in Ansoft designer?

Hi

Yes I think so. If you search her on this site, I believe that you can find it.

Regards