In the TX time slot, some RX channels can be reused as TX observation channels for PA linearization. The observation channel, in general, requires a wider bandwidth than the RX channel; this results in different decimation factors and data rates between the RX and Obs configurations.
When enabling the TDD RX/Obs sharing mode in the IP configuration, there
are two AXI4-Stream interfaces available for each
RF-ADC channel. Note they are not active at the
same time. The decimation factor, output data rate, and FIFO configurations for each
AXI4-Stream are preserved independently, and can
be switched dynamically using PL inputs (tdd_obs). Note
that the RX and Obs configurations share other function blocks in RF-ADC, such as the complex mixer/NCO, DSA, etc. For
example, choose the same real/complex mode and the same NCO frequencies for both RX and
Obs channels. The DSA value can vary when RF-ADC
switches from one mode to another. You should set your desired DSA value each time
through real time ports or RFdc API.
For RX/Obs shared channels, when DSA values are different for RX mode and Obs mode, user should set desired DSA value for each mode before or after switching from one mode to another, the real time DSA ports enable fast DSA values updating.
Two PL clocks (AXIS_aclk, AXIS_obs_aclk) are available for different data rates.
The following diagram illustrates the TDD RX/Obs sharing mode.
