I am evaluating FMCOMMS4 through no-OS build. I am trying to transmit ramp digital data modulated on 2.4GHz carrier. FMCOMMS4 should run in FDD mode with both RX and TX enabled and with LVCMOS IO. I flash the fpga with the test build. I can measure at the first beginning the ramp digital data on the TX lines visible on some test points on FMCOMMS4. When I initialize FMCOMMS4 through SPI, the tx digital data lines got 500mv peak to peak random signal modulated on both high level and low level and no RF TX signal is present on the spectrum analyzer.
I tracked down the code to find what is causing this on the digital tx lines. I found out that whenever I enable the RX-synthesizer, the modulated signal appear and when disabling the rx synthesizer the signal get back normal.
I did another experiment, I swapped P0 and P1 data (basically RX and TX data) and did the test again. A peak at the spectrum analyzer showed at 2.4GHz. The RX digital lines show the ramp signal and the TX digital lines show high amplitude random signal. The signal that is present on TX digital line (TX_D5_P) is attached in the message.
I reperformed the first experiment but i injected a radio frequency signal, single tone, with a frequency 2.405. What i noticed is that no digital data appeared on RX digital lines and I got a 5MHz signal above the random signal i am getting on tx digital data lines. Any clue here to make this work?
Which FPGA platform are you using ? Is it a custom board.?
Can you try transmitting a BIST tone first.
FMCOMMS 4 board does not support CMOS mode. You have to configure the interface in LVDS mode to work with that board.
Please see below the list of carrier boards supported with this board:
This is so weird. I am already running wifi test scenario on FMCOMMS4 with KC705 carrier board in LVCMOS mode and it is running normally.
I did a digital loopback test and found that the data are not available at RX lines. After investigating more, it seems i swapped P0 and P1 ports as I am running LVCMOS FDD full port mode. When I swapped the ports, the spectrum analyzer showed correct waveform. Now I am driving the TX port from a HDL sine wave generator implemented on the FPGA. Some times the spectrum show a spectral line with correct offset and most of the times the spectral line disappear. Do you have any clue what might be causing this problem.
Refer to the below link: