Hej Magnus Magnus Danielson wrote: > Hej Bruce, > > >> Hej Magnus >> >> Thats true, but I had the more general case in mind wherein which one >> adds coarse fixed delay increments as required and merely uses the >> variable gain mixer to make a fine adjustment to the phase. >> > > How do you intend that to work? Slightly introduce the signal with a > different but nearby phase? > > Simple, use a splitter (0 degree, 90 degree, 180 degree as appropriate) to separate the signal into 2 parts one for the LO, one for the DUT. Add some fixed delay to the LO branch then use a 90 degree splitter, attenuate the 90 degree output and add it (a hybrid combiner/splitter) to the 0 degree output, thus phase shifting the final output by a small adjustable amount. >> No real need for sine and cosine weighting for small phase adjustments >> as the effect on the amplitude will be small and phase noise measurement >> systems are usually relatively insensitive to AM. >> > > Certainly, but various delay-adjustments will provide different output > levels, which can be handled in a sub-sequent scaling or by weighing the > signal of different levels. > Probably a simple calibration will suffice when using a saturated mixer used as a phase detector. > To achieve an arbitrary (0-360 degree) phase-shift with such a system > may be a viable question. Running a set of cables and a programable > multiplexer of some sort would be possible. > > Well, that was not what was asked for originally, and also not apparent > from your original comment. Surely you can achieve better performance > than this quad-phase circuit provides, but since it was not described > what type of circuit you intended it never became clear what you meant. > > The original question infact was for a system where you do not use fixed > delays such as cables. > I reinterpreted it to mean that some fixed delays would be OK as long as they don't have to be accurate to within better than a few nanosec. In most cases ( eg when measuring isolation amplifier phase noise at 10MHz ) such lumped delays probably wont be necessary as the amplifier delay will be relatively small. > Cheers, > Magnus > > Bruce
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