Ramp Voltage Generation Circuit for High-Speed Imaging Readout
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Solution Overview
Problem
Existing imaging apparatuses face challenges in high-speed readout of high-quality image signals due to voltage fluctuations and variations among columns, leading to image degradation such as vertical lines and graininess, when A/D conversion gain is increased, and extended ramp signal duration hinders high-speed readout.
Innovation Solution
The imaging apparatus employs a ramp voltage generation circuit with two drive states, adjusting the voltage change amount per unit time and offset voltage to maintain accurate comparison between pixel signals and reference voltages, ensuring high-speed readout without compromising image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the A/D conversion gain is increased to improve signal quality, then the voltage variations among columns and voltage fluctuation of N-signals become greater than the ramp signal voltage range, causing A/D conversion to fail and image degradation such as vertical lines and graininess
Solution Approach 1:
The patent applies dynamics by making the ramp signal voltage range adjustable rather than fixed. The ramp signal generation circuit changes its voltage range according to the A/D conversion gain setting, allowing the system to adapt to different gain conditions. This dynamic adjustment ensures that the ramp signal voltage range always matches the actual voltage variations, preventing conversion failures and image degradation while maintaining high signal quality.
Solution Approach 2:
The patent changes the voltage range parameter of the ramp signal based on the A/D conversion gain. When conversion gain increases, the ramp signal voltage range is automatically adjusted to accommodate the increased voltage variations among columns and N-signal fluctuations. This parameter change ensures accurate comparison between the ramp signal and input signals, resolving the contradiction between signal quality and conversion reliability.
2Measurement precision
If the ramp signal voltage range is extended by increasing the time duration to maintain constant voltage change amount per unit time, then one horizontal period becomes longer, preventing high-speed readout
Solution Approach 1:
The patent changes two parameters simultaneously: the voltage range and the time duration of the ramp signal. When high conversion gain is selected, the system increases the voltage range while proportionally decreasing the time duration. This dual parameter adjustment maintains the voltage change amount per unit time constant, ensuring accurate comparisons are made within a shorter time window, thus achieving both precision and high-speed readout.
Solution Approach 2:
The patent preemptively adjusts the ramp signal characteristics before the A/D conversion process begins. By pre-setting the appropriate voltage range and time duration based on the conversion gain setting, the system prevents the contradiction from arising during operation. The ramp signal is configured in advance to match the expected signal conditions, ensuring both accuracy and speed without requiring real-time adjustments during conversion.
3Speed
If the ramp signal voltage range is reduced to enable high-speed readout, then the voltage variations among columns and voltage fluctuation of N-signals exceed the ramp signal voltage range, causing inappropriate comparison and A/D conversion failure
Solution Approach 1:
The patent makes the ramp signal voltage range dynamic and adaptive to the conversion gain setting. Rather than using a fixed reduced voltage range for high-speed operation, the system automatically adjusts the voltage range to match the actual signal conditions. This dynamic adaptation ensures that even when operating at high speeds with shorter time durations, the voltage range remains sufficient to accommodate column variations and N-signal fluctuations, maintaining comparison accuracy.
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 approach enables high-speed readout of high-quality image signals by maintaining accurate voltage comparisons and preventing image degradation, even when A/D conversion gain is changed, while allowing for efficient operation without extending the horizontal period.
Implementation Method 1
a pixel region in which pixel circuits configured to generate pixel signals by photoelectric conversion are arranged in a matrix
Data Source
AI summary
An imaging apparatus including a ramp voltage generation circuit having a first period for outputting an offset voltage that sets a reference voltage for the comparator circuit, and a second period for outputting a reference voltage having a slope-shaped voltage waveform that varies with time, wherein the generation circuit has a first drive state in which a voltage change amount per unit time of the reference voltage in the second period is a first voltage amount, and a second drive state in which the voltage change amount per unit time of the reference voltage in the second period is a second voltage amount that is less than the first voltage amount, and wherein the offset voltage in the second drive state is less than a value obtained by multiplying the offset voltage in the first drive state by a ratio of the second voltage amount to the first voltage amount.