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Below are all of the forum threads, including all
the responses to the original posts.
Post subject: rat-race coupler / 180 degree phase shifter
Posted: Wed Sep 07, 2005 7:45 am
I need to take a single
ended signal at 8GHz and convert it to a balanced signal. i.e. two outputs
are 180 degrees out of phase. This is in order to drive a PLL differentially.
I've simulated a microstrip rat-race coupler in order to achieve
this. It seems to work ok.
Another option is to use a microstrip
wilkinson power divider, then after the divider, have a meandering line
on one leg which basically delays the signal to give the 180 degree
phase shift necessary.
Any opinions on which is better? From
my sims, the isolation with the wilkinson power divider is good, whereas
the S11 is about -9dB - only ok. With the rat-race coupler, the isolation
is poor, but the S11 is pretty good.
Post subject: Posted: Wed
Sep 07, 2005 7:48 am
I guess the real question is - how important
is isolation between the two lines? They're carrying the same signal,
180 degrees out of phase....
Posted: Wed Sep 07, 2005 12:01 pm
I would say use the rat-race.
No, actually use the Wilkinson.
Post subject: Wilkinson vs. rat-race for differential
conversionPosted: Wed Sep 07, 2005 12:34 pm
If I "read between the
lines" accurately, the single-ended signal is coming from a VCO.
The important factor here is going to be minimizing the effects
of the following circuitry on the VCO (noise, detuning, pulling, etc).
So either a very uniform S11 over the band of interest, or a very low
S11, would be important.
If the S11 is very low, it can't vary
very much and stay very low. That would tend to point to the rat-race
coupler - IF the input impedance of the driven stage is constant. But,
again, "reading between the lines", the driven stage might be a divider.
Depending on its input structure, "digital" circuits (like dividers)
don't always present a constant S11 themselves... which would tip the
stage toward the Wilkinson. Enough? good question.
So the "devil
is in the details" - as always.
Post subject: reg: coupler 180 degPosted: Thu Sep 08,
2005 5:43 pm
Joined: Wed Jul 06, 2005 5:54
familiar with genesys then this tool provides a synthesis option for
180 coupler. mebbe u can optimise to get the required S11 and then mebbe
introduce non-ideality into the circuit.
all the best