Coarsely Quantized Digital Correlators for Passive Millimeter Wave Imagers: A Hardware Perspective

Passive imaging using Interferometric Aperture Synthesis requires intensive signal processing to form an image, with correlation as its core operation and the most compute intensive part. Correlators for power and space optimized applications, quite often, are designed with only a few levels of quantization e.g. 2-level, 3-level or 4-level. This article presents correlators with three different quantization schemes having same number of channels and sampling frequency. All three correlators are implemented for the same device to highlight the difference in hardware utilization, making it a reference for any relevant work. The 64-channel correlators are implemented for 2-level, 3-level and 4-level quantized input data. It requires to calculate 2016 real time correlations whereas the integration stage is capable of accumulating the correlation results for approximately 85 seconds with 800 MHz sampling frequency. The de-multiplexed architecture enables a collective throughput of 800M Correlations/second while running each parallel datapath at a clock frequency of 200 MHz. The design is implemented in Xilinx Vivado for Kintex family device whereas the design verification is accomplished by comparing register-transfer-level simulation results with ideal MATLAB results. The comparison made on the basis of device utilization shows that no big difference exists between 2-level, 3-level and 4-level correlators from hardware perspective.