Image Sensor SAR ADC Circuit for Higher Bit Accuracy
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Solution Overview
Problem
Existing analog-to-digital converters (ADCs) in image sensors are large and consume high power, limiting their efficiency in converting analog voltage differences into digital signals effectively.
Innovation Solution
A semiconductor integrated circuit configuration using multiple capacitors and a comparator to perform successive approximation register (SAR) logic, optimizing the A-D conversion process by determining effective comparison stages to increase the number of bits in the output digital signal while reducing circuit area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ADC circuit configuration is used, then the ADC can convert analog voltage to digital signal, but the circuit area is large and power consumption is high
Solution Approach 1:
The ADC conversion process is divided into multiple comparison stages (first comparison stage, second comparison stage, third comparison stage) that sequentially determine different bit values. This segmentation allows the circuit to achieve high bit accuracy through time-multiplexed operations rather than requiring all comparison circuits to operate simultaneously, thereby reducing the overall circuit area.
Solution Approach 2:
The circuit uses dynamic switching of capacitor connections and voltage references across different comparison stages. The same physical capacitors and circuit elements are dynamically reconfigured for different comparison operations, allowing the ADC to achieve multiple bits of resolution without proportionally increasing the number of physical components, thus reducing circuit area while maintaining measurement precision.
2Measurement precision
If conventional ADC circuit configuration is used, then the ADC can convert analog voltage to digital signal, but the power consumption is high
Solution Approach 1:
The power consumption is reduced by segmenting the conversion process into sequential comparison stages that determine bit values one at a time. Instead of all comparison circuits operating simultaneously with high power draw, the circuit performs comparisons in sequence, allowing power-intensive operations to be distributed over time and reducing peak and average power consumption while still achieving high bit accuracy.
Solution Approach 2:
The circuit dynamically switches between different operating states and voltage levels during the conversion process. By using dynamic switching of capacitors and references, the circuit minimizes the time that high-voltage differential pairs are active, reducing dynamic power consumption while maintaining the ability to resolve multiple bit levels through the sequential comparison process.
3Measurement precision
If more comparison stages are added to increase bit accuracy, then the output digital signal has more bits, but the circuit complexity increases
Solution Approach 1:
The conversion process is segmented into distinct comparison stages, where each stage determines one bit of the output. This segmentation allows the circuit to achieve high bit accuracy through a structured sequence of simpler operations rather than requiring a single complex comparison circuit, thereby increasing measurement precision without proportionally increasing overall circuit complexity.
Solution Approach 2:
The same physical circuit elements (capacitors, switches, voltage references) are used across multiple comparison stages to determine different bit values. This multi-functionality allows the circuit to achieve high bit accuracy by reusing components in different configurations rather than requiring separate dedicated circuits for each bit, thus increasing measurement precision while controlling circuit complexity.
Data Source
AI summary
According to one embodiment, a semiconductor integrated circuit is configured to convert a difference between a first analog voltage and a second analog voltage into a digital signal. The semiconductor integrated circuit includes m (m is an integer greater than or equal to 2) first capacitors and second capacitors. Each of the m capacitors has a first electrode and a second electrode, and the first electrodes are connected to each other. Each of the m second capacitors has a third electrode and a fourth electrode, and the third electrodes are connected to each other. The semiconductor integrated circuits further includes: a comparator configured to compare a voltage of the first electrode and a voltage of the third electrode; and a logic circuit configured to generate the digital signal based on a comparison result of the comparator.