Hi all,

I am not very familiar with impedance matching. I have a circuit with its input impedance that is a low pass equivalent to 1k // 2pF. It is connected to a 50 ohm source via a 50 ohm tline. I would like to match the 1k // 2pF input to 50 ohm so that the source always sees a 50 ohm load. The problem is I need the match to work from 1 GHz to 2 GHz. Any idea? Please assist.

thanks and regards,
chase

From Bode-Fano criteria for Parallel RC load matched with reactive networks,
the best reflection coefficient averaged over 1GHz ~ 2GHz is like following.

    Averaged_Gamma >= exp{-1/(2*BW*R*C)}, Here BW=2GHz-1GHz=1GHz, R=1kOhm, C=2pF.

Then Averaged_Gamma_dB >= -2.17dB
dB(S(5,5)) can almost achieve this theoretical limit.

chase.ng wrote on May 10^th, 2008, 7:36pm:

It depends on your applications.
If you have importance in reflection, this return loss is too large.
But if you have importance in transmitted power, this return loss could be acceptable.

chase.ng wrote on May 10^th, 2008, 7:36pm:

This also depends on your applications.

If you invoke hybrid matching of resistive and reactive, you can achieve better S11.

What application do you intend to design ?
What signal scheme do you apply ?
Is there frequency channel control signal. e.g. for PLL ?
Is there any possibility to change matching networks using such control signal ?

Varactor, Pin-diode, etc...