Design of a Multi-mode Block Adaptive Quantizer for High-Resolution Synthetic Aperture Radar Imaging

An advanced synthetic aperture radar imaging system needs a multi-mode block adaptive quantizer (BAQ) for high-resolution image requirements. However, the Lloyd-Max quantizer inside the BAQ consists of non-uniform thresholds for comparison. Consequently, the arithmetic complexity grows exponentially if the BAQ output word-length becomes larger. In this work, a multi-mode BAQ is designed to support real-time compression for high sampling-frequency radar signals. Various output word-lengths are provided so that different compression ratios can be set depending on the applications. To solve the problem of exponential growth in complexity due to the large BAQ output word-lengths, we propose two strategies, input scaling and hybrid comparators. Significant saving in complexity is attained. From the synthesis result in 40 nm CMOS technology, the proposed design supports 14-bit ADC at 800-MHz sample frequency with output word-lengths of 2, 3, 4, 6, 8 bits. Its gate count is 45.6 K and power consumption is only 11.8 mW at 0.9 V.