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Unwanted signal is driving at the input of DAC

Question asked by s.kannan on Apr 5, 2018
Latest reply on Apr 6, 2018 by Vinod

We are using AD9364 in our custom board. Our AD9364 is interfaced with Microsemi FPGA and we are using No-OS driver for configuring AD9364. When we run just ad9361_init() only, we are seeing a tone exactly at LO frequency in the Tx path and when we try to change the LO frequency, the tone is also changing correspondingly. Then we tried bist_tone, feeding some waveform from FPGA and feeding only zeros from FPGA to ad9364 but, still we are seeing the tone at LO only. We thought it was LO leakage but when we power down the Tx DAC using 0x056 register, we don't see any tone at LO on Tx port. So we assume some signal is driving at the input of DAC.

When we do the bist loopback of digital Tx-> digital Rx, we are seeing exactly the data we are feeding in. Since we are seeing this properly, why is the modulation is not happening properly?