TD-dAJC: A 100 MS/s 2 pJ/Pixel Time-Domain Weight and Integrating-MAC-Based Direct Analog to MJPEG Compression for Video Sensor Nodes
Abstract
Always-on, high-quality video sensors are increasingly required in wearables, surveillance, and Internet-of-Things (IoT) devices, where stringent energy constraints make efficient in-sensor compression necessary. These systems must support high-definition (HD) and 4 K video, yet conventional digital video compression pipelines consume significant power because high-speed analog-to-digital converters (ADCs) must digitize every pixel, and digital signal processing incurs large switching and memory overhead. This makes compression a major energy bottleneck in edge cameras. This work enables analog-domain MJPEG compression using a time-domain processing technique that represents discrete cosine transform (DCT) and quantization coefficients as pulsewidth–encoded time weights and performs multiply–accumulate (MAC) and division operations through current integration. The architecture employs time weights generated by a 32-phase sub-sampling PLL-based pulse generator, enabling MAC computation directly on analog pixel values before digitization, reducing the ADC workload. Fabricated in 65-nm CMOS, the proposed time-domain direct-analog-to-MJPEG compression (TD-dAJC) circuit achieves 100 MS/s throughput, the fastest reported among MJPEG implementations, and supports real-time HD and 4 K compression. The architecture consumes ~2 pJ/pixel, achieving <inline-formula> <tex-math notation="LaTeX">$13\times $ </tex-math></inline-formula> lower energy than switched-capacitor (SC) analog compressors and <inline-formula> <tex-math notation="LaTeX">$25\times $ </tex-math></inline-formula> lower energy than digital MJPEG pipelines. Compared to state-of-the-art analog in-memory compute MJPEG engines, TD-dAJC achieves <inline-formula> <tex-math notation="LaTeX">$2.8\times $ </tex-math></inline-formula> better energy efficiency and <inline-formula> <tex-math notation="LaTeX">$25\times $ </tex-math></inline-formula> higher throughput.
