The Design Of Differential Active Pixel Image Senor

Conventional image sensor occurs performance degradation and inactivation working under low power supply. Much attention has been focused on image sensor with low power supply and power consumption since the growth in the market of portable electronic devices. CMOS image sensor, instead of CCD image sensor, has become the main solution of image sensor system for its low power supply and power consumption.Pixel array and readout circuitr are the most important constituents of a CMOS image sensor. In this paper, they are designed to meet the demand of a 1024*768, 70frame/s, 8bit image sensor which are consist of pixel, multiplexer, S/H circuit, A/D converter.In this paper, the ability of pixel working under low power supply, resisting noise and its stability are considered. Both redundancy and differential signal are used at the same time, of which, the redundancy is able to reduce the failure probolity of pixel and the differential signal is able to resist the noise in power supply and environment. In the layout design, the differential signal passage is placed symmetrically to resist common mode noise and the earth connection is placed appropriately to avoid litch-up. The differential active pixel proposed in this paper works more stably and accurately in harsh environment, its minimum power supply is 1.75V, power consumption is 7.48μW/Pixel and its DR is 71.9dB.During the design of readout circuit, the possibily of CDS using ADC is analysed and the performance index of ADC is affirmed. After that, a 0.54M sample/s 9bit pipeline ADC is designed, the DNL and INL of which is 0.48LSB and 0.92LSB respectively. The whole readout circuit is designed by using differential circuit to avoid noise influence. The self-correction function is also integrated in readout circuit by adding judgment circuit to direct the following signal processing. The proposed readout circuit is able to drive a 1024*768 differential active pixel array at a speed of 70frame/s to implement a 8bit image sensor with self-correction function.