Matching Circuit Design

Hi,

I am designing matching circuits for a CMOS LNA. I measured the input
and output impedance by doing Spectre SP simulation. I measure the
real and imagine impedance by ZP. After that I designed "T match"
curcuits for both input and output. However I noticed that two
matching circuits affect each other, that means I can match input
impedance to 50 ohm with my matching circuit. Then I connect the
matching circuit at the output, the output impedance can be matched to
50 ohm, but the input impedance is changed, it is not 50 ohm anymore.

How can I design matching circuits to match both input and output to
50 ohm?

Thanks.


Regards,
Ocean

 

For LNA design, input and output matching networks do not correlate
that much because the signal level for LNA design is so low, called
'small signal'.
You first know what input signal level you are working with. Typically
it is below than -50 dBm.
If you must work with higher than -30 dBm, it is very hard to have both
matching networks matched to 50 ohm at the same time. The procedure
should be interative. In other words, once you match the input to 50
ohm, work on the output. Then, go back to input and see how much your
input matching is affected. However, remember that as long as you have
s11 and s22 below -10 dB, you are ok.