Adaptive gain control using sample-and-hold circuit for analog cds

Abstract

An image processing circuit includes a first sample-and-hold circuit that samples a first data from a pixel, a second sample-and-hold circuit that samples a second data from the pixel, a voltage-to-current circuit that includes a resistor and a current source and receives the first and second data to output a difference data, an adaptive gain control determination circuit that determines whether a rate of change of a signal from the pixel exceeds a threshold based on an output of the second sample-and-hold circuit, and a current-mode ADC that converts the difference data from an analog form to a digital form.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This application relates generally to image sensor readout chains, which includes sample-and-hold circuits. More specifically, this application relates to an image sensor readout circuit that implements analog gain to improve noise performance and maintain dynamic range.[0003]2. Description of Related Art[0004]Image sensing devices typically consist of an image sensor, generally an array of pixel circuits, as well as signal processing circuitry and any associated control or timing circuitry. Within the image sensor itself, charge is collected in a photoelectric conversion device of the pixel circuit as a result of the impingement of light.[0005]One example of a pixel circuit is illustrated in FIG. 1. As shown in FIG. 1, a pixel circuit 100 includes a photoelectric conversion device 101 (for example, a photodiode), a floating diffusion FD, a transfer transistor 102, a reset transistor 103, an amplification transistor 104...

AI Technical Summary

Benefits of technology

The patent text is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. The text describes a method of disclosure that groups various features together in different embodiments to streamline the disclosure. The "technical effect" of the invention is that it allows the reader to quickly ascertain the nature of the disclosed invention without being limited to the specific features mentioned in the claims. Inventive subject matter lies in less than all features of a single disclosed embodiment, and the patent claims are incorporated into the Detailed Description with each claim standing on its own as a separately claimed subject matter.

Problems solved by technology

In many practical pixel readout circuits, there is a tradeoff between ADC noise floor and ADC maximum input level.

In summary, common attempts to improve noise performance may reduce the dynamic range of the image sensor.

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