Focal-Plane Spatially Oversampling CMOS Image Compression Sensor

Image compression algorithms employ computationally expensive spatial convolutional transforms. The CMOS image sensor performs spatially compressing image quantization on the focal plane yielding digital output at a rate proportional to the mere information rate of the video. A bank of column-parallel first-order incremental DeltaSigma-modulated analog-to-digital converters (ADCs) performs column-wise distributed focal-plane oversampling of up to eight adjacent pixels and concurrent weighted average quantization. Number of samples per pixel and switched-capacitor sampling sequence order set the amplitude and sign of the pixel coefficient, respectively. A simple digital delay and adder loop performs spatial accumulation over up to eight adjacent ADC outputs during readout. This amounts to computing a two-dimensional block matrix transform with up to 8times8-pixel programmable kernel in parallel for all columns. Noise shaping reduces power dissipation below that of a conventional digital imager while the need for a peripheral DSP is eliminated. A 128times128 active pixel array integrated with a bank of 128 DeltaSigma-modulated ADCs was fabricated in a 0.35-mum CMOS technology. The 3.1 mm times 1.9-mm prototype captures 8-bit digital video at 30 frames/s and yields 4 GMACS projected computational throughput when scaled to HDTV 1080i resolution in discrete cosine transform (DCT) compression