A Mulitiple-Exposure, Linear Response, Wide-Dynamic-Range CMOS Image Sensor Combining Electric-charge Voltage Conversions in Pixel Capacitor and Column Capacitor

Abstract

We discuss the operation methods for keeping a high S/N ratio at all switching points in multiple exposures and for shorting the total integration time of a wide dynamic range (DR) lateral overflow integration capacitor (LOFIC) CMOS image sensor that combines electric-charge voltage conversions in a pixel and a column capacitor. We have used these methods on a color LOFIC CMOS image sensor. This sensor had a pixel pitch of 5.6-um and the number of effective pixels was 800 (H) x 600 (V). It was made by using 0.18-um 2P3M CMOS technology. Fully linear responses were obtained, as well as a DR of 207 dB. Furthermore, the S/N ratio was 26-dB for the image of 18% gray card at all the switching points between the multiple exposures. The total exposure time was1/13-sec and was obtained by three photoelectric conversion operations at FD and LOFIC capacitors and one photoelectric conversion operation in the column capacitor.