Pixel AD Conversion With Stable Ramp Reference Supply
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Solution Overview
Problem
Current imaging devices face challenges in enhancing image quality, particularly in the AD conversion process, where the reference signal generation and voltage follower circuits play a crucial role in pixel signal processing.
Innovation Solution
The proposed imaging device incorporates a signal generation circuit that produces a ramp waveform and a voltage follower circuit with a specific amplifier configuration, including differential input and bias circuits, to generate and supply a stable reference signal to pixel circuits, enhancing image quality by improving dynamic range and frame rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional reference signal generation method is used, then the device complexity is reduced, but the image quality and dynamic range deteriorate
Solution Approach 1:
The reference signal generation function is segmented from the pixel circuit and implemented as a separate voltage follower circuit. This segmentation allows the reference signal to be generated with high precision using a dedicated circuit, improving image quality while managing device complexity through functional separation. The signal generation circuit creates a ramp waveform that is then processed by the voltage follower to provide a stable reference signal to multiple pixel circuits.
Solution Approach 2:
The voltage follower circuit acts as an intermediary between the signal generation circuit and the pixel circuits. It buffers and stabilizes the reference signal before distributing it to multiple pixels, ensuring consistent and accurate AD conversion across all pixel circuits. This intermediary component improves image quality by providing a stable reference voltage while isolating the signal generation circuit from load variations.
2Measurement precision
If the reference signal supply is not stabilized, then the device complexity is reduced, but the measurement precision deteriorates
Solution Approach 1:
The voltage follower circuit implements feedback control to stabilize the reference signal voltage. By continuously monitoring and adjusting the output voltage based on the input signal, the circuit maintains precise voltage levels despite variations in load or power supply. This feedback mechanism ensures high measurement precision in AD conversion while using a relatively simple circuit configuration.
Solution Approach 2:
The voltage follower circuit is self-regulating, automatically adjusting its output to match the input voltage level without requiring external control. This self-service capability stabilizes the reference signal inherently, improving AD conversion precision while avoiding the need for complex external control circuits.
3Productivity
If node voltage variations are not reduced, then the device complexity is reduced, but the dynamic range deteriorates
Solution Approach 1:
The voltage follower circuit maintains equipotential conditions by ensuring that the reference signal voltage remains stable and consistent across all pixel circuits. This equipotential approach reduces voltage variations that would otherwise limit the dynamic range, while the simple voltage follower structure avoids adding significant device complexity.
Data Source
AI summary
An imaging device of the present disclosure includes: a plurality of pixel circuits that each generates a pixel signal including a pixel voltage corresponding to an amount of received light, and performs AD conversion by comparing the pixel signal with a reference signal; and a reference signal generator including a signal generation circuit and a voltage follower circuit, the signal generation circuit that generates a voltage signal having a ramp waveform, and the voltage follower circuit that performs a voltage follower operation on the basis of the voltage signal to generate the reference signal, and supplies the reference signal to the plurality of pixel circuits.