Single-Input Comparator Quantizer for Compact Low-Voltage Image Sensors
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Solution Overview
Problem
Conventional digital image sensors have large footprints and performance degradation at lower supply voltages, making them unsuitable for integration into smaller devices.
Innovation Solution
A digital image sensor using a single-input comparator with a charge storage device and a ramp generator, which reduces the overall footprint and improves performance at lower voltages by employing a smaller comparator and voltage protection circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional comparator is used in the digital image sensor, then the sensor can perform analog-to-digital conversion, but the footprint of the sensor becomes large
Solution Approach 1:
The patent extracts only the essential comparison function needed for quantization, removing unnecessary circuitry from conventional comparators. The single-input comparator design takes out only the critical elements required for comparing the pixel signal against the ramp voltage, eliminating redundant components that contribute to large footprint while preserving the core ADC functionality.
Solution Approach 2:
The patent uses a simplified model of comparator operation that copies only the essential behavior needed for quantization. Instead of implementing a full conventional comparator with all its supporting circuits, the design creates a functional equivalent that replicates the necessary comparison operation with minimal components, achieving the same ADC capability in a compact form.
2Reliability
If conventional image sensor designs are used, then the sensor can operate at standard supply voltages, but performance degrades at lower supply voltages
Solution Approach 1:
The patent changes the operational parameters of the comparator to optimize performance at lower supply voltages. The single-input comparator is designed with modified biasing and operating conditions that allow it to function reliably at reduced voltage levels, unlike conventional comparators that require standard supply voltages for proper operation. This parameter optimization enables low-voltage operation while maintaining quantization accuracy.
3Measurement precision
If conventional comparators are used, then the sensor can achieve adequate conversion accuracy, but power consumption increases
Solution Approach 1:
The patent extracts only the essential comparison function needed for quantization, removing unnecessary circuitry from conventional comparators. The single-input comparator design takes out only the critical elements required for comparing the pixel signal against the ramp voltage, eliminating redundant components that contribute to large footprint while preserving the core ADC functionality.
Solution Approach 2:
The patent uses a simplified model of comparator operation that copies only the essential behavior needed for quantization. Instead of implementing a full conventional comparator with all its supporting circuits, the design creates a functional equivalent that replicates the necessary comparison operation with minimal components, achieving the same ADC capability in a compact form.
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
The solution enables the integration of digital image sensors into smaller devices while maintaining performance, with reduced power consumption and increased gain due to the single-input comparator's efficient current usage and voltage protection mechanisms.
Implementation Method 1
Each pixel cell may include a photodiode to sense light by converting photons into electric charge (e.g., electrons or holes)
Data Source
AI summary
One example described herein includes the digital image sensor having a pixel cell with a photodiode and a quantizer circuit coupled to the pixel cell. The quantizer circuit includes a charge storage device that generates a voltage based on electric charge from the photodiode. The quantizer circuit also includes a single-input comparator that can switch from a first output state to a second output state in response to a ramp signal provided by a ramp generator. The quantizer circuit further includes a memory switch that can cause a counter value from a digital counter to be stored in a digital memory in response to the single-input comparator switching from the first output state to the second output state. The counter value can serve as a digital pixel value associated with the pixel cell.