Bitline settling improvement by using dummy pixels for clamp

Abstract

A photodiode is adapted to accumulate image charges in response to incident light. A transfer transistor is coupled between the photodiode and a floating diffusion to transfer the image charges accumulated in the photodiode to the floating diffusion. A reset transistor is coupled to supply a supply voltage to the floating diffusion. A source follower transistor is coupled to receive voltage of thefloating diffusion from a SF gate terminal and provide an amplified signal to a source follower source terminal. A row select transistor is coupled to receive the amplified signal from the SF sourceterminal and output the amplified signal to a bitline. A bitline enable transistor controlled by a bitline enable voltage is coupled to link between the bitline and a bitline source node. The bitlineis coupled to an idle voltage generator, a blacksun voltage generator, and a clamp voltage generator. These three voltage generators are each constructed out of a plurality of modified dummy pixels based on the dummy pixels in the dummy rows of an image sensor pixel array.

Description

technical field [0001] The present invention generally relates to complementary metal-oxide-semiconductor (CMOS) image sensors, and in particular, but not exclusively, to photodiode pixel cells and output lines (bit lines) of the photodiode pixel cells applied in image sensors An apparatus and method for an image sensor capable of rapidly stabilizing a bit line to reduce fixed pattern noise (FPN) and maintain stability of a power supply during readout of an image signal. Background technique [0002] Image sensors are ubiquitous. Image sensors are widely used in digital still cameras, cell phones, security cameras, as well as in medical, automotive and other applications. Many of these applications require the use of high dynamic range (HDR) image sensors. The human eye typically has a dynamic range of up to about 100 decibels (dB). For automotive applications, image sensors with more than 100dB of dynamic range are often required to handle different driving situations, s...

AI Technical Summary

Problems solved by technology

However, the performance under bright light conditions is still an issue, because the higher contrast of light intensity will cause a larger voltage drop on the bit line, which directly leads to a longer settling time

[0009] Also, as pixel sizes get smaller and the conversion gains utilized get higher, the FD capacitor can become too small such that the TX feedthrough can easily exceed the range of the analog-digital converter (ADC) input voltage

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