The common-mode voltage on each output leg varies when VOP changes. In the application when DC-coupling interface is necessary, the Vcm needs to be fixed to match external devices in general. The following two options are available for a consistent common mode voltage:
- Backwards compatibility mode
- In backwards compatibility mode, the common mode voltage is fixed as in Gen 1 and Gen 2 and the VOP feature is unavailable in this mode.
- DC coupling mode
- The RF-DAC DC coupling mode fixes the common-mode voltage while it enables the VOP feature. In this mode, the VOP range is reduced.
See the Zynq UltraScale+ RFSoC Data Sheet: DC and AC Switching Characteristics (DS926) for information on VOP range while in DC coupling mode.