Imaging Device Readout Circuit Gain Switching Timing
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Solution Overview
Problem
Imaging devices that switch the gain of the amplifier circuit for each pixel based on incident light amount face errors in signal readout, leading to inadequate correction of luminance level differences near gain switching boundaries, resulting in deteriorated image quality.
Innovation Solution
An imaging device with a readout circuit unit that includes an amplifier circuit, a sample-and-hold circuit, and a gain switching circuit, where the control unit manages overlapping reset and connection periods for the amplifier circuit and sample-and-hold circuit, ensuring the timing of switch transitions minimizes signal errors and maintains high readout speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a sample-and-hold circuit is applied to increase readout speed, then readout speed is improved, but signal error occurs when reading pixel reset level
Solution Approach 1:
The amplifier circuit is reset in advance during the first period before the sample-and-hold circuit connects during the second period. This preliminary reset action ensures that when the pixel reset level signal is read out, the amplifier circuit is already in a stable state, preventing signal errors while maintaining high readout speed through the overlapping period design.
2Adaptability or versatility
If gain switching is performed to achieve wide dynamic range, then dynamic range is improved, but luminance level difference occurs near boundary
Solution Approach 1:
The amplifier circuit is reset in advance during the first period before signal readout. This preliminary reset ensures that when signals near the gain switching boundary are read out, the amplifier circuit has already stabilized, enabling accurate correction of luminance level differences and preventing image quality deterioration.
3Device complexity
If reset period and connection period are performed sequentially, then circuit operation is simple, but readout speed decreases
Solution Approach 1:
The reset period (first period) and connection period (second period) are merged to overlap in time. The amplifier circuit is reset during the first period while the pixel exposes, and the sample-and-hold circuit connects during the second period with overlap. This merging of periods enables parallel operation, increasing readout speed without significantly increasing control circuit complexity.
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
The solution enables high-quality image acquisition without reducing readout speed by effectively correcting luminance level differences near gain switching boundaries, thereby improving image quality and maintaining high readout speed.
Implementation Method 1
a pixel (12) including a photoelectric converter (PD) and outputting a pixel signal based on an amount of charge generated by the photoelectric converter
Data Source
AI summary
The imaging device includes a pixel including a photoelectric converter, an output line, a readout circuit unit connected to the output line, and a control unit. The readout circuit unit includes an amplifier circuit, a first switch for resetting the amplifier circuit, a sample-and-hold circuit, a second switch provided between the amplifier circuit and the sample-and-hold circuit, and a gain switching circuit. The control unit performs a first period of resetting the amplifier circuit by first switch, and a second period of connecting the amplifier circuit and the sample-and-hold circuit by the second switch. The first and second periods at least partially overlap with each other, and a timing at which the second switch transitions from an on state to an off state in the second period is later than a timing at which the first switch transitions from an on state to an off state in the first period.