Image Sensor ADC Comparator Using Inverted Reference Signal
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Solution Overview
Problem
Conventional analog-to-digital converters (ADCs) in image sensors face high power consumption and introduce undesirable distortions due to comparator artifacts, particularly during inversion operations.
Innovation Solution
The proposed solution involves a comparator configuration with specific capacitor and transistor arrangements that reduce power consumption and artifacts, including a first capacitor for the pixel signal, a second capacitor for the reference signal, and transistors with controlled gate voltages to manage the comparison process efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional ADC with comparator is used for pixel signal conversion, then AD conversion function is achieved, but power consumption becomes large
Solution Approach 1:
The patent extracts the inversion operation from the critical comparison path by performing it on the reference signal before comparison rather than on the pixel signal during comparison. This separation allows the comparator to operate without inversion artifacts while still achieving the desired signal transformation, thus reducing power consumption without sacrificing signal accuracy.
Solution Approach 2:
The patent introduces an intermediary reference signal that undergoes inversion before being compared with the pixel signal. This intermediary approach allows the inversion operation to be decoupled from the direct pixel signal path, eliminating the generation of inversion artifacts in the comparator output while maintaining the necessary signal transformation for accurate conversion.
2Ease of operation
If inversion operation is performed in comparator, then signal transformation is achieved, but artifacts are generated in comparator signals
Solution Approach 1:
The inversion operation is extracted from the comparator's direct signal path and applied only to the reference signal input. This ensures that the pixel signal passes through the comparator without inversion, eliminating the generation of inversion artifacts while still achieving the necessary signal transformation through the inverted reference signal comparison.
Solution Approach 2:
Instead of inverting the pixel signal path which causes artifacts, the patent inverts the reference signal path. This reverse approach achieves the same functional transformation effect but avoids the harmful artifacts because the inversion occurs in a non-critical path that does not directly affect the pixel signal integrity.
3Productivity
If comparator operates continuously, then AD conversion is performed, but power consumption increases
Solution Approach 1:
The patent implements periodic reset operations for the capacitors in the comparator circuit, allowing the comparator to operate in a controlled cyclic manner rather than continuously. The reset phase prepares the capacitors for the next comparison cycle, enabling efficient batch processing of pixel signals while reducing overall power consumption by keeping the comparator in a low-power state between active comparison periods.
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 reduces power consumption and minimizes distortion in the comparator signals, enhancing the performance of image sensors by optimizing the ADC's power usage and signal accuracy.
Implementation Method 1
a first capacitor configured to receive the pixel signal
Implementation Method 2
a second capacitor configured to receive a reference signal
Implementation Method 3
a third capacitor coupled between a gate of the second transistor and a first line supplied with a first voltage
Implementation Method 4
a first transistor having a gate coupled to the node, a second transistor coupled to the first transistor
Data Source
AI summary
Provided is an image sensor including: a pixel section configured to include a plurality of pixels arranged therein; and an AD conversion unit configured to perform analog-to-digital (AD) conversion on a pixel signal on the basis of a result of comparison between a first voltage of a signal, which is obtained by adding, via capacitances, the pixel signal of the pixel and a reference signal that linearly changes in a direction opposite to the pixel signal, with a second voltage serving as a reference.