Quadrature mixing from 2xLO PLL?
 

Hi group,
An associate is proposing a mixer design that I'm having a hard time
understanding. I did some Google searching and haven't found an answer, so
perhaps some kind sould can help.

The basic porposal is to generate a clock at twice the LO frequency, divide
it by two and use some sort of differential mixer circuit. This is for
wideband (broadcast) FM reception. He says that the key is the use of
differential circuits within the mixer. Of course, this is intended to be
used with quadrature demodulation.

Sitting down and thinking about it, I could see how it would work if one
were to take the rising edges of the 2X LO clock for one phase and the
falling edges for the 90d phase, but it seems like doing it that would way
would likely result in the I+Q not being perfectly orthagonal due to things
like different delays in rising vs falling edge logic, imperfect duty
cycle, etc. And even then it wouldn't need to be differential.

Well, if anyone has a suggestion for a mixer architecture that does what he
says (ie uses 2x LO clock and requries differential circuitry) then I'd
appreciate the help.
Regards,
Matt