Image Sensor Comparator Noise Cancellation With Adjustable Input Capacitance
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Solution Overview
Problem
The use of an ultra-low comparator in solid-state image capturing elements poses challenges in noise removal due to differing input capacities between pixel and D/A converter sides, preventing effective noise offsetting in the comparator's differential pair, which deteriorates image quality.
Innovation Solution
A solid-state image capturing element is designed with a noise-cancelling-signal generating circuit that generates and adjusts noise cancelling signals, a DA converter that converts currents to voltages, and a comparator with input capacity control, along with a gain controlling unit to manage the reference signal and input capacity, enabling precise noise cancellation and reduced conversion errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If an ultra-low comparator is employed to reduce power consumption, then power consumption is reduced, but input capacity becomes different between pixel side and D/A converter side, preventing effective noise offsetting
Solution Approach 1:
The patent applies dynamics by making the input capacity of the comparator adjustable rather than fixed. The gain controlling unit dynamically changes the input capacity based on the operating mode (pixel signal input or D/A converter output input) to ensure proper noise cancellation in both scenarios while maintaining ultra-low power consumption operation
Solution Approach 2:
The patent changes the input capacity parameter of the comparator according to different operating conditions. When pixel signals are input, one input capacity value is used, and when D/A converter outputs are input, a different input capacity value is used. This parameter adaptation resolves the contradiction between low power consumption and effective noise cancellation
2Device complexity
If both pixel signal and D/A converter output are input into the same side of differential pair, then device complexity is reduced, but noise offsetting capability is lost due to different input capacities
Solution Approach 1:
The patent maintains the simplified configuration of inputting both signals to the same side of the differential pair but introduces dynamic adjustment of the input capacity to compensate for the different impedance characteristics. This dynamic adjustment restores the noise offsetting capability without increasing structural complexity
Solution Approach 2:
By changing the input capacity parameter based on which signal is being processed, the patent enables the simplified single-sided differential pair configuration to achieve proper noise cancellation for both pixel signals and D/A converter outputs, resolving the contradiction between device simplicity and noise cancellation performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively cancels pixel-power-source noise, improves image quality, and reduces conversion errors even with ultra-low voltage comparators, while maintaining low power consumption.
Implementation Method 1
in a photodiode provided in a pixel, incident light from an object is photo-electrically converted
Data Source
AI summary
Solid-state image capturing elements are disclosed. In one example, a solid-state image capturing element includes a noise-cancelling-signal generating circuit connected to a pixel power source. It executes a gain change and a polarity inversion on a first noise cancelling signal to output a second noise cancelling signal. The element also includes a DA converter that outputs a reference signal and converts a current of the second noise cancelling signal into a voltage to superpose the converted voltage on the reference signal; a comparator that receives inputs of the reference signal and a pixel signal and outputs an inversion signal according to the pixel signal and a gain setting; a counter that converts an inversion timing of the comparator into a digital value; and a gain controlling unit that outputs, when changing a gradient of the reference signal and an input capacity to execute a gain control on the comparator.