Attenuated DAC Reference Circuit for Low-Noise Image Sensors
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Solution Overview
Problem
Conventional solid-state imaging devices face challenges in reducing random horizontal noise without increasing circuit area, which is essential for maintaining high signal-to-noise ratio as pixel size decreases with increasing resolution.
Innovation Solution
A voltage generation circuit with a control circuit, digital-to-analog conversion circuit, and an attenuator is used to reduce noise by attenuating the analog signal, allowing for accurate analog-to-digital conversion without significant circuit area expansion, utilizing either an active or passive type attenuator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resolution of solid-state imaging device is increased, then the imaging quality is improved, but the pixel size is reduced and signal component decreases, requiring noise reduction which increases circuit complexity
Solution Approach 1:
The voltage generation circuit is segmented into distinct functional blocks: control circuit (27b), digital-to-analog conversion circuit (27a), and attenuator (27d). This segmentation allows each block to be optimized independently for its specific function while contributing to overall noise reduction, resolving the contradiction between imaging quality and circuit complexity.
Solution Approach 2:
An attenuator is introduced as an intermediary component between the digital-to-analog conversion circuit and the imaging pixels. This attenuator reduces the amplitude of the reference signal, thereby reducing random horizontal noise generated in the voltage generation circuit without affecting the fundamental A/D conversion function, allowing noise reduction while maintaining circuit simplicity.
2Object-affected harmful factors
If noise reduction techniques are applied in voltage generation circuit, then random horizontal noise is reduced, but circuit area increases
Solution Approach 1:
The attenuator is designed as a simple, low-cost component that can be easily integrated into the voltage generation circuit. By using a straightforward attenuation approach rather than complex noise filtering circuits, the solution reduces random horizontal noise while minimizing the increase in circuit area, effectively treating noise reduction as an affordable add-on rather than a major structural change.
3Adaptability or versatility
If conventional voltage generation circuit with ladder resistors is used, then multi-level voltage reference signal is generated, but random horizontal noise occurs in the circuit
Solution Approach 1:
The attenuator serves as an intermediary that processes the reference signal after it is generated by the ladder resistor circuit. It reduces the signal amplitude and associated random horizontal noise without affecting the multi-level voltage reference functionality, allowing the circuit to maintain adaptability while reducing harmful noise effects.
Solution Approach 2:
The attenuator changes the amplitude parameter of the reference signal, reducing it to a level that minimizes random horizontal noise generation in subsequent circuit stages. This parameter adjustment allows the voltage generation circuit to maintain its multi-level reference capability while operating at lower noise levels.
Data Source
AI summary
A voltage generation circuit includes a control circuit which outputs a first digital signal, a DAC which outputs a first analog signal corresponding to the first digital signal, and an attenuator which is connected to an output terminal of the DAC and is configured to output a voltage signal obtained by attenuating the first analog signal input from the DAC.