I am attempting to understand what the RX digital signal level over the data interface should be for a given RX input power level. According to the datasheet, a continuous wave input of -11.4 dBm corresponds to 0 dBFS at the ADC output, and a backoff of at least 2 dB is required. On my setup, if I input a CW tone at about -14 dBm, the digital signal level I see over the data interface is nowhere near full scale. During a call with ADI on Monday, I was told to check the RX interface gain setting and verify that it was set correctly. My setup defaults to 0 dB RX interface gain, and I also verified that I could change the value and see the appropriate (relative) change in digital signal level. I took the following measurements:
0 dB I/F gain = -33.3 dBFS digital signal level
6 dB I/F gain = -27.2 dBFS
12 dB I/F gain = -21.3 dBFS
So, I have some questions:
- What is the expected digital signal level as a function of RX input power and interface gain (assuming no RX attenuation)? While the datasheet mentioned the full scale input power, it was referring to the ADC output, and there are other steps between the ADC and the data interface. Is there any additional scaling there that would account for my measurements?
- My code changes the RX interface gain by calling adi_adrv9001_Rx_InterfaceGain_Set(), and eventually after a few times calling this function, an error code (-2) is returned. After that, any subsequent calls to adi_adrv9001_Rx_InterfaceGain_Set() or adi_adrv9001_Rx_InterfaceGain_Get() fail with the same code. What does this error code mean? Are there any known issues with these functions (I am using SDK v0.17.1)?
