PSRR Compensation Circuitry for Image Sensor Noise Cancellation
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Solution Overview
Problem
Conventional image sensors face limitations in compensating for low Power Supply Rejection Ratio (PSRR) in Active Pixel Sensor (APS) arrays, especially when pixel sizes reach the sub-micrometer range, leading to degraded image quality due to insufficient noise suppression.
Innovation Solution
The implementation of a PSRR compensation circuitry that performs amplitude and phase corrections by introducing amplified power supply noise into the ramp signals on a correction path, matching the phase delay of power supply noise on the pixel path, thereby enhancing the PSRR compensation range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size is reduced to sub-micrometer range to increase resolution, then the image sensor can capture finer details, but the PSRR is degraded leading to increased power supply noise in analog signals
Solution Approach 1:
The patent captures power supply noise present in the analog signal path and deliberately introduces it into the ramp signal through an amplifier. By doing so, the harmful noise is transformed into a useful compensation mechanism where the noise in the ramp signal cancels out the noise in the analog signal during comparison, thereby converting the harmful power supply noise into a beneficial correction tool
Solution Approach 2:
The patent introduces an amplifier as an intermediary component that captures power supply noise from the power supply path and injects it into the ramp signal path. This amplifier acts as a mediator that transfers the noise characteristic from one path to another, enabling the noise cancellation mechanism between the analog signal path and ramp signal path
2Object-affected harmful factors
If conventional PSRR compensation is used in the read-out circuit, then compensation is achieved for PSRR of approximately 12 dB, but compensation fails when PSRR drops below 8 dB as occurs with sub-micrometer pixels
Solution Approach 1:
The patent introduces a new dimension to PSRR compensation by adding an amplifier stage that provides gain control. This dimensional addition allows the compensation mechanism to handle larger noise amplitudes that occur with sub-micrometer pixels, extending the compensation capability from PSRR of 12 dB down to PSRR below 8 dB by amplifying the noise injection signal proportionally
3Object-affected harmful factors
If the read-out circuit attempts to compensate for severely degraded PSRR without additional circuitry, then device complexity is minimized, but the compensation capability is insufficient for sub-micrometer pixels
Solution Approach 1:
The patent merges the PSRR compensation function with the existing ramp signal generation path by injecting the amplified power supply noise directly into the ramp signal. This integration allows the compensation mechanism to be implemented within the existing read-out circuit architecture without requiring completely separate compensation circuits, thereby limiting the increase in device complexity
Data Source
AI summary
A method for compensating a Power Supply Rejection Ratio (PSRR) in an image sensor, the method includes receiving, by processing circuitry, at least one analog signal from an active pixels sensor (APS) array, the at least one analog signal including power supply noise, combining, by the processing circuitry, amplified power supply noise with at least one ramp signal to obtain combined power supply noise, and compensating, by the processing circuitry, the PSRR of the APS array by cancelling the power supply noise of the at least one analog signal using the combined power supply noise.