Cmos image sensor with global shutter, rolling shutter, and a variable conversion gain, having pixels employing several bcmd transistors coupled to a single photodiode and dual gate bcmd transistors for charge storage and sensing

Abstract

The invention describes a solid-state CMOS image sensor array and discloses image sensor array pixels with global and rolling shutter capabilities that utilize multiple BCMD transistors for a single photodiode, for charge storage and sensing. Thus, the valuable pixel area saved by employing the BCMD transistor for charge storage and sensing is used by placing several BCMD transistors coupled to one photodiode. This increases the Dynamic Range (DR) of the sensor, since the same photodiode can integrate charge for different integration times, both long and short. This allows sensing of two different image signals from a single pixel without saturation, a low level signal with long integration time followed by a high level signal with short integration time. The signal processing circuits located at the periphery of the array can then process these signals into a single Wide Dynamic Range (WDR) output. Further disclosed is an image sensor array with pixels that use BCMD transistors for charge storage and sensing having multiple concentric gates, which allows changing the conversion gain of the BCMD transistors by applying various biases to the gates. Variable conversion gain is a useful feature when building WDR sensors since low conversion gain and high well capacity allows detection of high level signals and the same structure can be used to detect, at the same time, low level signals with high conversion gain and thus low noise.