[time-nuts] ADCs for phase noise measurement
dan at irtelemetrics.com
Mon Jun 13 11:02:42 EDT 2016
The 2378-20 is a pretty nice ADC. I expect the 2368-24 to be good also.
It should be easy to see at least -130dBfs noise floor with an FFT. Keep
in mind supply rail noise, and REF voltage noise etc. That's a lot of
resolution and bandwidth in one unit!
The DC890B board appears to run an FTDI FT245BM. I wouldn't expect that
to be able to transfer data at the full rate from the ADC to the PC. So
you'll be limited to the buffer size on board (memory or FPGA buffer)
for snapshots of data. That may not matter for what you'd be doing...
On 6/12/2016 12:00 PM, time-nuts-request at febo.com wrote:
>> Alternatively, I would suggest using one of the modern sigma-delta
>> >or SAR ADCs, which can deliver increadibly high ENOB and SNR at
>> >astonishing sampling rates. Good candidates might be:
>> >AD7982, 18bit 1Msps
>> >AD7984, 18bit 1.33Msps
>> >LTC2378-20, 20bit 1Msps
>> >LTC2368-24, 24bit 1Msps
>> >Eval boards for these are available (between 100 and 200€) and interface
>> >with SPI. You can either use an USB SPI dongle (between 5 and 50€) or
>> >use a small uC board to interface with the PC. Saving the samples in
>> >a wav file and using one of the many FFT tools shouldn't be a problem.
> Good call on the LTC2368-24. The eval board for it has considerably
> better support (like p-scope) than do the Analog Devices eval boards.
> I think this might work for me. What are the tradeoffs between SAR
> and sigma-delta ADC? Can you point me to a few of the "many" FFT
> tools? Maybe I don't have to buy spectrum analyzer software.
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