A high speed asynchronous multi input pipeline for compaction and transfer of parallel SIMD data

Image sensors with programmable, highly parallel signal processing, so called Vision-Systems-on-Chip, perform computationally intensive tasks directly on the sensor itself. Therefore it is possible to limit the amount of output data to relevant image features only. Reading out such features presents a major challenge, since the position and number of features often is not known. Conventional synchronous buses as well as special event-based readout paths are unsuitable for such a system, since both continuous data, e.g. complete images, and sparse data, like feature coordinates, have to be transfered. A readout path based on an asynchronous pipeline is presented, which supports both readout modes with high speed. Furthermore, a method is introduced that, by serialization, allows for arbitrary data word widths without storing any control information within the data stream. The developed circuit components were measured on a proof-of-concept test chip in a 180 nm CMOS technology and were compared with implementations of asynchronous pipelines found in literature. In addition, the use of the pipeline in a Vision-System-on-Chip, which is still in production, is demonstrated.