A variable topology partitioned pixel amplifier for low and high light level detection in a CMOS imager

In this work the concept of using a single partitioned pixel amplifier with variable topology for both low light level operation and Wide Dynamic Range (WDR) for CMOS imagers is presented. Low light level imaging is based on the Active Reset (AR) technique combined with the Active Column Sensor (ACS) readout technique for low noise operation. WDR for high light level detection is achieved by utilizing multiple resets via real-time feedback where each pixel in the field of view is independent and can automatically set an exposure time according to its illumination. Due to the commonalities in the low and high light level readout techniques, and the fact that they occur in staggered instances of time, we propose the use of a single column level partitioned pixel amplifier which can be configured in various modes of operation to satisfy the conditions for the suggested techniques. We also propose a Conditional Active Reset (CAR) scheme in which an AR is employed for every reset in the multiple-reset WDR algorithm, thereby reducing the overall noise involved in the technique. The advantages of the proposed column level partitioned pixel amplifier are simplicity in the analog readout path, reduced chip size and less power consumption. The Variable Topology Amplifier was designed and simulated in a mixed signal 0.18 um CMOS technology. Its design is discussed and simulation results are presented.