[time-nuts] low noise multiplication to 100 MHz
jimlux at earthlink.net
Thu Jan 21 09:43:01 EST 2016
My tiny 100 MHz low noise OCXOs are unexpectedly delayed at the mfr, and
I'm looking at alternative schemes.
One is to get 10 or 20 MHz OCXOs (typically in stock) and multiply them
up. I've got the Wenzel ap notes on 2diode and using HCMOS (and I've
used the packaged Wenzel multipliers), and I think I have some spare
board real estate on another board.
The 2diode multiplier describes using 1n5711 or 1n914, but I was
wondering if anyone has run this sort of multiplier up to 100 MHz?
What sort of symmetry does the resulting waveform have (yeah, it's
basically a filtered sinewave, because you're picking a harmonic, but
I've been surprised before)?
I'm driving an FPGA and a couple of ADCs. The ADCs have differential
input that is 10kohms with 9pF in parallel offset from ground in the
usual way (we're using a transformer and appropriate bias resistors).
Not a 50 ohm load, in any case. And it wants a clock that is high for
about 47.5% to 52.5% in one mode and much wider (30%-70% in another).. I
need to check.
The FPGA is less critical noise-wise, and has a AD8138 buffer in any
case, which can fix a variety of evils.
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