Two-step Single Slope ADC를 사용한 고속 CMOS 이미지 센서

In this paper, a high speed CMOS Image Sensor(CIS) based on a two-step single slope ADC is described. Although the conventional CIS based on a single slope ADC(SS-ADC) has a good performance, the frame rate is not enough for video application because of slow conversion time. Therefore, a two-step single-slope ADC faster than SS-ADC is used to obtain high speed operation. Further, we discuss a high gain OTA to reduce the chip area and power dissipation. The proposed CIS has been fabricated with 0.13um CMOS process. The chip includes 320×240 pixels whose pitch is 2.25um and whose structure is 4TR Active Pixel Sensor. The measured conversion time of two-step SS-ADC is 10us, which is ten times faster than the conventional SS-ADC. The measured frame rate is 390 frame/s.