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Measurements >> RF Measurements >> How to feed 4 RF signals with phase relationship for mixer ?
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Message started by Tiger on Oct 12^th, 2009, 12:15am

Title: How to feed 4 RF signals with phase relationship for mixer ?
Post by Tiger on Oct 12^th, 2009, 12:15am

hi, all
I have met a problem when measuring a ssb-mixer:
I have to feed four signals(9GHz) with phase relationship (LOinIP,LOinIN,LOinQP, LOinQN ) for mixer(IC), and to ensure the relationship of the signals does not change when arriving at the pads of IC (the IC`s pads are connected by bondwires to PCB`s pads, and then to the SMA connectors through microstrip).
By using 90 & 180 degree Hybrids, we can generate the 4 signals from one signal source. Then, we use cables of good phase stability to transmit the four signals to the PCB`s SMA connectors.
However, we find the phase relationship of the hybrids`output are sensitive to their loads; by this I mean, if the load is exact 50om, the phase is 90 or 180 degree, while if the load is not 50om, the phase is not 90 or 180 degree either..Here comes my problem: from the SMA connector to the IC, the impedance is not exact 50 om, so the relationship of signals arriving at the IC`s pads is not what I want either..
I`d like to know your suggestions, and how you feed 4 RF signals with phase relationship to your IC.
Many thanks!

Title: Re: How to feed 4 RF signals with phase relationship for mixer ?
Post by Tiger on Oct 13^th, 2009, 1:49am

truely hope someone can help me
thanks!

Title: Re: How to feed 4 RF signals with phase relationship for mixer ?
Post by RFICDUDE on Oct 13^th, 2009, 11:38am

Well, the not so helpful answer is that we design the phase splitter on chip using frequency dividers and symmetrical layout techniques.

On a board or hybrid I would imagine that you may need a way to tweak the phase and amplitude balance of the LO signal right at the inputs of the IC. If you do not need wideband (relative to the LO frequency) operation then you could get away with tweaking a little attenuation and capacitance for phase right at the inputs, but I suspect you need something more versatile than that for your application.

Title: Re: How to feed 4 RF signals with phase relationship for mixer ?
Post by Tiger on Oct 13^th, 2009, 6:48pm

Many thanks, RFICDUDE

Title: Re: How to feed 4 RF signals with phase relationship for mixer ?
Post by pancho_hideboo on Nov 2^nd, 2009, 10:59pm

Tiger wrote on Oct 12^th, 2009, 12:15am:

However, we find the phase relationship of the hybrids`output are sensitive to their loads;
by this I mean, if the load is exact 50om, the phase is 90 or 180 degree, while if the load is not 50om, the phase is not 90 or 180 degree either..
Here comes my problem: from the SMA connector to the IC, the impedance is not exact 50 om,
so the relationship of signals arriving at the IC`s pads is not what I want either..

Try to insert attenuators(e.g. 3dB) between Hybrid's output and DUT's input.