Polyphase DPD on AI Engine

Automatic Digital Pre-distortion Design Generation for AI Engine (XAPP1391)

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When the sample rate exceeds 983.04 MSPS, a polyphase DPD can be constructed with the monophase design as building blocks. More specifically, Figure 2 can be rewritten into the following format where P is the number of phases.

Figure 1. DPD GMP Model for Polyphase Architecture

The following figure visualizes the equation by coloring possible LUT locations of the phases differently. For the case of P = 3, there are nine possible combinations of three data phases and three magnitude phases, so at least nine AI Engines are required for each phase of output. There are three output phases, and a total of 9 × 3 = 27 AI Engines are required. Because each AI Engine processes 16 LUTs, the tri-phase DPD can support at least 16 × 9 = 144 LUTs. The following figure shows one possible implementation on AI Engine. The floorplan looks like three monophase DPDs stacked on top of each other with slightly different routing for data and magnitude.

Figure 2. Diagram of Polyphase DPD (P = 3)
Figure 3. Diagram of Tri-phase DPD

For the polyphase DPD, in the LUT configuration file, two more columns are added in each line to specify the phase of data and magnitude. As an example, the following figure shows a case of quad-phase DPD where (a) is the configuration file, (b) is the LUT configuration plotted by MATLAB, and (c) is the AI Engine compilation result using the code automatically generated by MATLAB.

Figure 4. Diagram of Quad-phase DPD