Image Sensor Read-Out Circuit With Matched Reference Noise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Image sensors face challenges in reducing noise, particularly due to power supply noise, which affects the quality of the signals generated by pixel arrays in CMOS image sensors.
Innovation Solution
A read-out circuit is introduced that includes a ramp signal generator, a bias voltage generator, and conversion circuits to adjust noise components, ensuring that the magnitude of noise in the reference voltage matches the noise in the analog signals from pixels, thereby canceling out noise components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If power supply voltage is used directly for generating reference voltage, then device complexity is reduced, but noise in the reference voltage increases due to power supply noise components
Solution Approach 1:
A bias voltage generator is introduced as an intermediary component between the power supply voltage and the reference voltage generation. This bias voltage generator processes the power supply voltage to create a bias voltage with controlled noise characteristics, which then serves as an input to the reference voltage generator. This intermediary structure allows noise management without directly exposing the reference voltage to raw power supply noise.
Solution Approach 2:
The patent adjusts the noise characteristics of the bias voltage by modifying its AC component parameters. Specifically, the bias voltage generator is configured to set the AC component level such that when combined with the ramp signal, the resulting reference voltage noise matches the analog signal noise level. This parameter adjustment transforms the noise profile from harmful to beneficial.
2Device complexity
If noise components are not matched between reference voltage and analog signal, then read-out circuit operation is simplified, but noise cancellation effectiveness deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the noise characteristics of the analog signal are used to determine the appropriate AC component level for the bias voltage. By monitoring or estimating the analog signal noise level and adjusting the bias voltage accordingly, the system achieves adaptive noise matching. This feedback loop ensures that the reference voltage noise consistently matches the analog signal noise despite variations in operating conditions.
Data Source
AI summary
A read-out circuit of an image sensor includes a ramp signal generator, a bias voltage generator and a conversion circuit. The ramp signal generates a ramp signal that linearly varies at a constant slope. The bias voltage generator generates a bias voltage based on a power supply voltage having a first noise component. The conversion circuit generates a reference voltage based on the bias voltage and the ramp signal, and performs an analog-to-digital conversion on an analog signal from a pixel to generate a digital signal corresponding to the analog signal. The analog signal has second noise component. The bias voltage generator adjusts an alternating current component included in the bias voltage such that a magnitude of a third noise component added to the reference voltage is substantially the same as a magnitude of the second noise component.