The Flatness of Broadband IQ Demodulated Signals - RF Cafe Forums
Post subject: The flatness of broadband IQ demodulated
signals Posted: Tue Jul 29, 2008 7:52 am
Joined: Thu Sep 22, 2005 11:09 pm
I have a PCB board with poor gain flatness.
How to improve
the flatness of broadband IQ demodulated signals?
and no additional
group delay deteriorated.
change the coupled capacitance
between amplifiers? the bias inductor?
what about a High pass
filter added to the circuit?
what's the most effective way?
Post subject: Posted: Tue Jul 29, 2008 4:23 pm
Joined: Mon Jun 27, 2005 2:02 pm
is hard to give a simple answer out of the sleeve, you have to provide
some more information about your circuit:
1. Do you use
broadband amplifiers in your chain?
2. Are the amplifiers already
matched internally or do you use matching networks?
3. Do you
use fixed attenuators (pads)?
I also suggest to isolate
each gain stage and check its flatness separately, by this method
you might be able to find the problematic stage(s).
for flatness does not mean that you will have the best return loss,
have you designed your gain stages for optimal flatness or for optimal
Post subject: Posted:
Thu Jul 31, 2008 11:01 am
Joined: Thu Sep
22, 2005 11:09 pm
Thanks for your reply,the
amplifiers in my circuit are broadband.(SGA 6489,already matched
The circuit was designed by others,the transmission
line operating at L band is not 50 Ohm, but 80~95 Ohm.
situation, is it possible to improve the flatness?
Post subject: Posted: Thu Jul 31,
2008 4:36 pm
Joined: Mon Jun 27, 2005
So now you and I
know the problem.
The solution is not easy. I would make a new
You can try to match the line impedance to the amplifier's
impedance by using LC matching networks, but this again would require
layout change if you have a great number of gain blocks along the
Post subject: Posted: Sun
Aug 03, 2008 6:48 am
Joined: Thu Sep 22,
2005 11:09 pm
Thanks. I will have a try.