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FMCOMMS1- RF Bypass + J11/J13 behavior issues

Question asked by tescott on Jul 25, 2014
Latest reply on Aug 6, 2014 by tescott

We have the AD-FMCOMMS1-EBZ rev. C connected to a Zedboard.  We have modified all the jumpers to completely bypass the RF chain.  The problem I'm running into is that I'm seeing that the J11 and J13 inputs appear to be offset and attenuated in different ways where I'd expect them to be equivalent.  Can someone explain what is up?

 

Here's our hardware setup:

 

JP1/JP3 updated to connect J13 to VINA_P/VINA_N

JP2/JP7 updated to connect J11 to VINB_P/VINB_N

JP6/JP17 updated to connect AD9122-IOUT1P/IOUT1N to J7

JP4/JP5 updated to connect AD9122-IOUT2P/IOUT2N to J4

 

Driving a 1MHz output on J4 and connecting it to J11, I see the following plots.  The FFT is on the left.  The ADC plot is on the right.  J11 is channel "B" on the plot, displayed in yellow.

 

plot1_1MHzToJ11.png

 

Swapping the J4 output over to J13 from J11, I see the following plots.  J13 is channel "A" on the plot, displayed in green.

 

plot2_1MHzToJ13.png

 

I'd expect that they would be identical, but they are obviously not.  The peak-peak readings are different and they obviously have different offsets.  I read up on the Wiki page about I/Q correction and went into AD9643.c /ad9643_setup() and removed the "ADC_IQCOR_ENB" assuming that would change things.  I don't see any difference in behavior.

 

Am I missing something.  We simply want to use the A/D and D/A capabilities of this board.  What more should I be doing to achieve that?

 

Thanks,

--tim

 

Message was edited by: Tim Scott

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