Zero-Transition Serial Encoding for Image Sensors

Off-chip serial buses are the most common interfaces between sensors and processing elements in embedded systems. Due to their length, these connections dissipate a large amount of energy, contributing significantly to the total consumption of the system. The error-tolerant feature of many sensor applications can be leveraged to reduce this energy contribution by means of an approximate serial data encoding. In this paper, we propose one such encoding called Serial T0, particularly, effective for image sensors data. By exploiting the correlation among pixels colors, Serial T0 significantly reduces the energy dissipation on a serial connection, with minimal impact on image quality, and extremely low codec overheads. Moreover, it allows runtime quality reconfiguration, and can be integrated with standard serial protocols (SPI, I2C, CSI-2, and so on) without requiring modifications to legacy peripherals. We show that Serial T0 is superior to both accurate and approximate state-of-the-art encodings, not only in terms of pure energy saving, but also when combined with realistic error tolerant applications (OCR and face recognition). In the best case, the energy on the bus can be reduced of more than 75% with less than 4% maximum error on the decoded data.