Image Sensor ADC Comparator Layout for Low-Power Clean Conversion
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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 operations, particularly during inversion operations.
Innovation Solution
The proposed solution involves an imaging device with a comparator that includes a first capacitor for the pixel signal, a second capacitor for the reference signal, and transistors configured to reduce power consumption and minimize signal distortions during inversion operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional ADC comparators are used to perform analog-to-digital conversion, then the conversion function is achieved, but power consumption becomes excessively large
Solution Approach 1:
The comparator is divided into two operational modes: a first comparison mode for normal ADC conversion and a second comparison mode for calibration. This segmentation allows the system to optimize power consumption by selectively activating different operational modes, reducing the overall power consumption while maintaining conversion accuracy through periodic calibration operations.
Solution Approach 2:
The invention changes the operational parameters of the comparator by switching between different comparison modes. In the first mode, the comparator operates with standard sensitivity for accurate conversion. In the second mode, the comparator operates with enhanced sensitivity or different reference levels for calibration purposes. This parameter switching enables the system to achieve both low power consumption and high conversion accuracy.
2Productivity
If inversion operations are performed in the comparator, then the comparison function is completed, but undesirable artifacts and distortions are introduced in the output signals
Solution Approach 1:
The system performs calibration operations in advance (during the second comparison mode) to establish reference levels and compensate for potential artifacts before actual ADC conversion begins. This preliminary calibration ensures that when inversion operations are performed during normal conversion, any resulting artifacts are already accounted for and minimized, thereby maintaining signal quality while achieving fast comparison speeds.
3Measurement precision
If the comparator operates continuously for accurate conversion, then conversion precision is maintained, but power consumption increases
Solution Approach 1:
The comparator operates periodically by alternating between the first comparison mode (for accurate conversion) and the second comparison mode (for calibration). Instead of continuous operation, the system uses periodic calibration cycles to maintain precision. This periodic action reduces power consumption by keeping the comparator in a lower-power state between calibration events while still ensuring conversion precision when needed.
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 the formation of undesired artifacts in the comparator's signals during inversion operations, enhancing the performance of image sensors.
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
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.