[time-nuts] low noise multiplication to 100 MHz
jimlux at earthlink.net
Thu Jan 21 19:43:04 UTC 2016
On 1/21/16 7:17 AM, Peter Reilley wrote:
> Have you considered synthesizers? I am using an Analog Devices AD9517
> to drive a A/D
> converter at 250 MHz. It has many clock outputs that are independently
> It is intended for low jitter applications.
So you run the PLL VCO at 1 GHz or something and program it to divide down?
I'm a bit leery of parts that talk about "low jitter" because they
typically integrate from 10kHz out to some MHz, and I'm concerned about
phase noise in the <10kHz offset range.
I guess that really depends on what the loop bandwidth is, the noise I'm
concerned about is probably inside the loop and will be driven by my
I'll take a look at the part.
> On 1/21/2016 9:43 AM, jimlux wrote:
>> 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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