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AD9680 PN Sequence Issues

Category: Hardware
Product Number: AD9680


I have the AD9680 setup in the following configuration: 

I am able to run and successfully verify all the ADC Test Patterns, except the PN23 and PN9 test modes from the ADC. I am even noticing correct JESD Interface PN23 and PN9 sequences at my ILA in the FPGA, but for some reason I am not seeing the expected sequences for the ADC PN test modes. I think I am not understanding something correctly...

Here is a snapshot of the ILA, where I am only looking at Converter 0 (m0) samples:

I triggered on 0x125B in the above image for PN9, but then I don't see the next value of 0x3C9A anywhere close. is the PN sequence being copied and sent out on each Lane and sample like below:

Or Should I expect it to be sequential like this:

Or something else? I am confused though, because I am able to trigger on other sequence values, but they don't look close to one another... 


  • So, im noticing that once I put the ADC in 14-bit mode, which is the pure resolution of the ADC, I get the right sequences in bits 15:2, as noted in the datasheet. But with my configuration shown above its actually 16-bits since the DDCs output 16-bits. In this case, does the PN sequences change? Should I be using a 16-bit output for the PN9 and 23 sequences? Which also changes how many times to shift the PN9? 

  • I figured it out. While using the DDCs, the output is 16bits and the PN sequences use a 16bit output. I was having issues figuring out why the PN23 sequence still wasnt looking right...but it was because I was triggering on one of the first words in the sequence, but since we only see 16-bits of the 24-bit sequence, that 16-bit word I was triggering on actually shows up multiple times and was in a random part of the sequence, not the start like I expected. 

    Once I triggered on 2 back to back 16-bit words that I expected, the rest of the sequence looked right.