ADC I/Q imbalance

SrG on Jun 23, 2020

We work with the EVB using the no os software.

We have a problem: it seems that some times after configuration everything is OK, but many times ADC I/Q mismatch is very poor: we transmit CW at 800k from the center and we observe very nice sine waves for I and Q - but they are not equal in power. In fact, they are very different - one is 8-10 db higher than the other.
Any idea what might cause this?

Thank you,

Sorin

srimoyi

on Jun 23, 2020 1:21 PM
You can plot the received IQ data in FFT and then check the image power to know about the imbalance between I and Q. Refer to datasheet for the dBc levels
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SrG on Jun 23, 2020 1:33 PM in reply to srimoyi

Blue is I. Red is Q.

Q power is 14 db higher than I power !!!
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srimoyi

on Jun 24, 2020 8:07 AM in reply to SrG
Are you seeing this behaviour randomly or at regular intervals? Is the QEC tracking ON? Can you try by disabling it? Are you using AGC or MGC? What is the tone frequency offset from LO that you are injecting at RX?
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cpeters on Sep 28, 2020 9:01 PM in reply to SrG

FYI, we saw this very same issue and determined it was caused by not having our RX port terminated into a 50 ohm load during calibration.
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