I am testing a design with an AD7490 and I'm a bit unsure on how to determine the sampling rate. Given VDD of 5V, per the datasheet a 20 MHz SCLK should be equivalent to a 1MSPS sampling rate. Does that mean it's a 20:1 ratio for the sampling rate?
I'm seeing some artifacts in my sampled waveform that I'm unsure what the cause is. I am sampling the following 1 kHz sine wave on VIN8 (this is me probing directly on the ADC VIN8 pin):
After collecting the data with a SPI<->USB Master (Totalphase's Cheetah device) at an SCLK frequency of 16 MHz and importing to MATLAB, I plot this for 1021 samples:
The artifacts appear to have some periodicity to them, occurring every 25-30 samples on each wave. Also, trough to trough is about 500 samples, which gives a sampling rate of (500 samples/1 millisecond) = 500 kSPS, which is a 32:1 ratio with SCLK = 16 MHz.
I would appreciate any insight, thank you very much in advance!
Also here are a couple of screenshots of the SPI datastream:
Thanks for the response. We're using the ADR3425 for REFIN. Please see the attached image. Just a note about the schematic: the AAFx components are hierarchical blocks containing a programmable filter circuit.