The ADRV902x (9026, 2029, and 9022) User Guide shows how one must couple the transmit signal back to an observation receiver, in order to have an effective LO leakage calibration. This coupling must take place external to the ADRV9026 IC.
The Evaluation Board (EVB) from ADI for this part, has the Tx1 output being converted from single-ended to differential through a balun. Then the signal is connected to an SMA connector. In order to run a successful LO leakage calibration on the EVB, the user must connect the Tx1 output SMA, to a splitter or coupler, and send one output of that splitter back to an SMA connector as Tx feedback for an observation receiver. That Tx feedback signal gets converted from single-ended to differential on the EVB, and then the differential signal connects to the differential input pins of the observation receiver on the ADRV9026.
In a call today with ADI, we were advised that the Tx1 output must be converted from differential to single-ended, and then back from single-ended to differential before input to the observation receiver, in order for the LO leakage calibration to be successful.
My question is, why is the conversion from SE to DIFF and back again necessary? Why can't we take the differential Tx output, and use a differential coupler to couple the differential signal directly back into to the observation receiver? (assuming the levels are correct).
We'd really appreciate a quick reply on this, since it has a major effect on out PCB layout and design.
Thanks and Kind Regards,
Aaron Netsell
