Ultra-High Compression of Twiddle Factor ROMs in Multi-Core DSP for FMCW Radars

The increasing density of Multiple-Input Multiple-Output (MIMO) arrays in imaging radars for the automotive industry demands highly parallel systems with low-footprint accelerators, which would enable the concurrent processing of a high number of virtual channels with a low-latency, and without a high area overhead. In this paper, we design, implement, and test multiple handcrafted compression schemes for Twiddle Factor (TF) Read-Only Memories (ROM), aiming to reduce the footprint of a variable-length and dual-radix Fast Fourier Transform (FFT) accelerator in a Multi-core Digital Signal Processor (DSP) for Frequency Modulated Continuous Wave (FMCW) radars. The compression schemes proposed in this paper involve double delta encoding, Radix-specific address optimizations per port, symmetry inclusion, and exploitation of the bit resolution changes within the radar processing chain. All schemes are verified in an FPGA in terms of logic utilization and quantization using a 77-GHz radar, and implemented in a RISCV-based Processing Element (PE) of a Multi-core DSP with an Adaptive Body Bias (ABB) approach in 22FDX technology for assessing area, leakage, and relative latency savings when compared with a dual-ROM equivalent in the state-of-the-art.