CMOS imager with current-mode sub-band image coding at the focal plane

• Published in: Analog integrated circuits and signal processing 2015-10, Vol.85 (1), p.91-106
• Main Authors: Cardoso, Bruno Bastos, de Oliveira, Fernanda Duarte Vilela Reis, Gomes, José Gabriel Rodriguez Carneiro, de Faria Lopes, Tiago Monnerat
• Format: Article
• Language: English
• Subjects: Circuits and Systems; Electrical Engineering; Engineering; Signal,Image and Speech Processing
• ISSN: 0925-1030; 1573-1979
• DOI: 10.1007/s10470-015-0584-1

A great advantage of the CMOS image sensors, as compared to CCDs, that were conventional up to the middle 90’s, is that data processing circuitry can be implemented in the same chip where photo-sensitive elements are fabricated. Complete imaging systems can thus be integrated into a single chip. A large number of recent articles have explored this feature. This paper presents a detailed explanation of the design of a chip that performs image compression at the focal plane by means of an algorithm based on wavelet transform, namely the embedded zero-tree wavelet algorithm. The imager performs current-mode five-level Haar wavelet decomposition on a 32 × 32 image, and, from numerical simulations, decoded image peak signal-to-noise ratio around 20 dB is expected for compression ratio around 4:1. Electrical simulations comparing image quality and bit rate for different images are presented, as well as experimental measurements regarding the imager modulation transfer function.