CMOS image sensor with dual floating diffusions per pixel for flicker-free detection of light emitting diodes

Abstract

Apparatuses and methods for image sensors with pixels that reduce or eliminate flicker induced by high intensity illumination are disclosed. An example image sensor may include a photodiode, a transfer gate, an anti-blooming gate, and first and second source follower transistors. The photodiode may capture light and generate charge in response, and the photodiode may have a charge capacity. The transfer gate may selectively transfer charge to a first floating diffusion, and the anti-blooming gate may selectively transfer excess charge to a second floating diffusion when the generated charge is greater than the photodiode charge capacity. The first source-follower transistor may be directly coupled to the first floating diffusion by a gate, the first source-follower to selectively output a first signal to a first bitline in response to enablement of a first row selection transistor, and the second source-follower transistor may be capacitively-coupled to the second floating diffusion, the second source-follower to selectively output a second signal to a second bitline in response to enablement of a second row selection transistor.

Description

TECHNICAL FIELD[0001]This disclosure relates generally to image sensors, and in particular but not exclusively, relates to image sensors having pixels for detection of high intensity light sources without the inducement of flicker by the image sensor.BACKGROUND INFORMATION[0002]High-speed image sensors have been widely used in many applications in different fields including the automotive field, the machine vision field, and the field of professional video photography. Some applications in these fields require the detection and capture of LED lights, which has proven to be difficult. For example, automotive image sensors face the problem of LED flickering. Future automotive vehicle lights, traffic lights and signs will include LED that is pulsed at 90-300 Hz with high peak light intensity. This requires that the minimum exposure time be kept over 10 ms. A very high full well capacity or very low light intensity are thus needed to avoid pixels to get saturated and lose useful informa...

AI Technical Summary

Benefits of technology

The patent text describes a solution for image sensors to detect high intensity light sources without flickering. The technical effect of this invention is to enable the image sensor to capture LED lights without losing useful information due to saturation of pixels. The invention involves enhancing the full well capacity of the image sensor by using a lateral overflow integrating capacitor (LOFIC) or a non-linear sensor. The invention also involves using a pixel design that reduces flickering caused by high light intensity.

Problems solved by technology

Some applications in these fields require the detection and capture of LED lights, which has proven to be difficult.

For example, automotive image sensors face the problem of LED flickering.

However, the maximum full well capacity is thus limited by the floating drain capacitor rather than the photodiode full well capacity.

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