Full-Differential ADC Circuit for CMOS Image Sensor Resolution
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Solution Overview
Problem
Conventional CMOS image sensors with full-differential type AD converters require a gain block for signal amplification, which increases chip area and power consumption, and struggle with efficient conversion of video signals due to limitations in voltage range and resolution.
Innovation Solution
The proposed AD converter design includes weighted DAC circuits, a comparison circuit, and a control circuit to manage the connection between input nodes, allowing for full-differential signal generation without a gain block, and incorporates a reference and offset signal generating circuit to adjust voltage levels for improved resolution and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a gain block is used for signal amplification in conventional CMOS image sensors, then signal amplification is achieved, but chip area and power consumption increase
Solution Approach 1:
The patent extracts and eliminates the gain block from the conventional image sensor architecture. By using a full-differential ADC that directly processes differential signals from the pixel array, the gain block is removed entirely, reducing both chip area and power consumption while maintaining signal amplification functionality through the differential signaling approach
Solution Approach 2:
The full-differential ADC is designed to perform multiple functions: it directly converts differential analog signals to digital signals, inherently handles signal amplification through its differential architecture, and eliminates the need for separate gain blocks. This multi-functional design reduces overall device complexity and power consumption
2Measurement precision
If conventional full-differential ADC architecture is used, then signal conversion is achieved, but voltage range and resolution are limited
Solution Approach 1:
The patent implements dynamic voltage range adaptation by making the reference voltage adjustable. The ADC can adapt its voltage range to match different signal amplitudes from various video sources, thereby improving resolution for specific voltage ranges while maintaining versatility across different applications through configurable reference voltages
3Area of stationary object
If gain block is eliminated, then chip area and power consumption are reduced, but signal amplification capability must be maintained
Solution Approach 1:
The patent replaces the mechanical/amplifier-based gain block with an electronic full-differential ADC architecture. The signal amplification function is achieved through the differential signaling mechanism and reference voltage scaling rather than through traditional voltage amplification, eliminating the need for additional active components while maintaining amplification capability
Data Source
AI summary
An AD converter includes a first DAC circuit, a second DAC circuit, a comparison circuit, a control circuit, and a control switch. The comparison circuit is connected to a first output node of the first DAC circuit and a second output node of the second DAC circuit and compares an electric potential of the first output node with an electric potential of the second output node. The control circuit controls the first DAC circuit and the second DAC circuit in accordance with a result of the comparison acquired by the comparison circuit. The control switch controls turning on and off of connection between a first input node of the first DAC circuit and a second input node of the second DAC circuit.