Positive-Feedback Comparator for Stable Imaging AD Conversion
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Solution Overview
Problem
Conventional comparators in imaging devices are prone to malfunctions due to variations in element characteristics, leading to errors in analog-to-digital conversion.
Innovation Solution
A comparator with a differential unit, an amplifier unit including a load element, and a positive feedback circuit that enhances signal change rates, connected to a counter circuit for digital data output based on the comparison period, is employed to stabilize signal levels and reduce conversion errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional comparator is used for AD conversion, then the device structure is simple, but malfunctions occur due to variation of element characteristics leading to AD conversion errors
Solution Approach 1:
The patent introduces a positive feedback circuit that feeds back a portion of the output signal to the input, creating a regenerative effect that accelerates the transition of the output signal when it inverts. This feedback mechanism ensures rapid and decisive switching behavior, preventing malfunctions due to element characteristic variations while maintaining a relatively simple overall structure.
Solution Approach 2:
The patent makes the comparator's response dynamic by using the positive feedback to automatically adjust the transition rate. When the output signal inverts, the feedback dynamically increases the gain temporarily, causing a rapid transition. This dynamic behavior compensates for element variations without requiring complex static design adjustments.
2Adaptability or versatility
If element characteristics are varied, then manufacturing flexibility is improved, but comparator malfunction and AD conversion errors increase
Solution Approach 1:
The positive feedback circuit compensates for element characteristic variations by providing a regenerative effect that ensures the output signal transitions decisively. The feedback mechanism automatically adjusts to variations in element parameters, maintaining reliable operation across different manufacturing tolerances without requiring precise element matching.
3Measurement precision
If a positive feedback circuit is added to increase transition rate, then AD conversion accuracy is improved, but device complexity increases
Solution Approach 1:
The patent implements a positive feedback circuit that is integrated into the existing comparator structure. The feedback path uses available circuit elements to create a regenerative effect that accelerates the output transition without requiring completely separate additional components, thus improving measurement precision while limiting the increase in overall device complexity.
Solution Approach 2:
The positive feedback circuit is merged with the existing comparator architecture, sharing common elements such as the output node and input nodes. This integration approach allows the transition rate enhancement function to be added while minimizing the increase in total circuit complexity by reusing existing structural elements.
Data Source
AI summary
A disclosed comparator includes a comparison circuit including a differential unit that compares an input signal with a reference signal and changes a level of a signal output to a first node in accordance with a result of comparison and an amplifier unit that includes a load element and outputs a signal in accordance with a potential of the first node to a second node, and a positive feedback circuit that is connected to the second node and a third node and changes a level of a signal at the third node at a rate higher than a change rate of a level of a signal at the second node in accordance with a change in a level of a signal at the second node.