A CMOS area image sensor with pixel-level A/D conversion

Charge-coupled devices (CCD) are at present the most widely used technology for implementing area image sensors. However, they suffer from low yields, consume too much power, and are plagued with SNR limitations due to the shifting and detection of analog charge packets, and the fact that data is communicated off chip in analog form. This paper describes an area image sensor that can potentially circumvent the limitations of CCDs and their alternatives. It uses a standard CMOS process and can therefore be manufactured with high yield. Digital circuitry for control and signal processing can be integrated with the sensor. Moreover, CMOS technology advances such as scaling and extra layers of metal can be used to improve pixel density and sensor performance. The analog image data is immediately converted to digital at each pixel using a one-bit sigma-delta modulator. The use of sigma-delta modulation allows the data-conversion circuitry to be simple and insensitive to process variations. A global shutter provides variable light input attenuation to achieve wide dynamic range. Data is communicated off chip in a digital form, eliminating the SNR degradation of analog data communication. To demonstrate the viability of the approach, an area image sensor chip is fabricated in a 1.2 /spl mu/m CMOS technology. The device consists of an array of 64x64 pixel blocks, a clock driver, a 6:64 row address decoder, 64 latched sense amplifiers, and 16 4:1 column multiplexers. The chip also contains data compression circuitry.>