Does the AD9371 auxADC have an internal reference? The users guide or datasheet makes no mention I could find of needing an external reference, and the users guide shows a plot (figure 108) of ADC codes vs input voltage.
However, in the API comments, there is the following:
* \brief Sets up the auxiliary ADC
* This function configures the AuxADC with the requested decimation. The AuxADC clock is set as close
* as possible to 40MHz. The AuxADC conversion time = (1/40Mhz) * decimation, where the decimation ranges
* from 256 AuxADC clock cycles to 32768 AuxADc clock cycles.
* Note: The AuxADC is intended for relative measurements. Two back to back measurements can allow a delta
* measurement with 12bit resolution. If absolute measurements are required, an accurate
* reference should be first measured on AuxADC0 input and used to calibrate the offset/gain error of the AuxADC.
* The reference would need to be measured before each measurement to account for measurement variations caused
* by the transmitter/receiver transients as other circuits in the device are being powered up/down.
Is this correct? We would need to use channel 0 for a reference, and make a measurement there before taking any other measurement to get an absolute voltage?