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received ad9361 BB signal polarity change

Question asked by zorrozhang on Jun 18, 2016
Latest reply on Jun 27, 2016 by larsc


I am using two sets of ZC706+AD-FMCOMMS3 for transceiver design, one transmitter and one receiver, and output from AD-FMCOMMS3 transmitter is connected to receiver AD-FMCOMMS3 with a 300MHz low pass filter.


the configurations are:

LO freq = 160Mhz,

Sampling freq = 4.9152Mhz,

Baseband bandwidth = 100KHz

RX manual gain = 14 db.


when using the examples from IIO to transmit a sine wave, the receiver side ADC can see the correct waveform (with Logic Analyzer to probe FPGA), so it looks single tone is OK. but if transmitter sends my own baseband signal, a burst of TX data about 20ms duration for every 2s, the receiver ADC shows unstable waveform-- it looks it drifts with time from the correct waveform to inverted one. pls see the following pics:


the top one is TX simulation result, the center pic is correct RX ADC  , and below one is with inverted polarity. to remove any clock issue, both TX RX AD-FMCOMMS3 side share the same 40MHz clock from a signal gen.


could you please help about this?


thanks in advance