Column Amplifier Comparator Reset Without Input Capacitance
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Solution Overview
Problem
Conventional column amplifier circuits in image sensors face challenges with input capacitance, which increases area occupation and reduces gain due to parasitic capacitance, leading to worse input referred noise and reduced efficiency in analog to digital conversion.
Innovation Solution
The implementation of a column amplifier circuit that eliminates the need for input capacitance by using an auto-zero switch to reset the comparator, allowing the column amplifier to be reset without an input capacitor, thereby reducing parasitic capacitance effects and improving gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an input capacitor is used in the column amplifier circuit, then the comparator can be reset, but the input capacitance increases area occupation and reduces gain due to parasitic capacitance
Solution Approach 1:
The patent extracts and removes the input capacitor from the conventional column amplifier circuit. By eliminating this component, the design achieves comparator reset capability through alternative means (using the pixel's inherent capacitance and a feedback capacitor), thereby reducing area occupation while maintaining the essential reset function.
Solution Approach 2:
The patent applies local quality by utilizing the pixel's inherent capacitance at the specific location where charge is generated, rather than adding a general-purpose input capacitor. This localized use of existing capacitance properties eliminates the need for additional capacitor components while maintaining circuit functionality.
2Reliability
If an input capacitor is used in the column amplifier circuit, then the comparator can be reset, but parasitic capacitance reduces gain and worsens input referred noise
Solution Approach 1:
By removing the input capacitor, the patent eliminates the source of parasitic capacitance that degrades gain and increases input referred noise. The alternative reset mechanism using pixel capacitance and feedback capacitor introduces minimal parasitic effects, preserving signal integrity and noise performance.
3Reliability
If an input capacitor is used in the column amplifier circuit, then the comparator can be reset, but the efficiency of analog to digital conversion is reduced
Solution Approach 1:
The removal of the input capacitor eliminates the bottleneck it creates in the analog to digital conversion process. By using the pixel's inherent capacitance instead, the circuit achieves faster charging and resetting, thereby improving conversion efficiency and overall productivity of the image sensor.
Data Source
AI summary
A column amplifier with a comparator for use in an image sensor includes an amplifier coupled to receive an input signal representative of an image charge from a pixel cell of the image sensor. An amplifier auto-zero switch is coupled between an input of the amplifier and an output of the amplifier. A feedback capacitor coupled to an input of the amplifier. An amplifier output switch coupled between the output of the amplifier and the feedback capacitor. A comparator includes a first input coupled the amplifier output switch. A comparator auto-zero switch is coupled between the first input of the comparator and an output of the comparator.