Buffer Circuit Switching for Imaging Device Power Reduction
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Solution Overview
Problem
Imaging devices with column-parallel analog-to-digital converters face challenges in suppressing power consumption and image quality deterioration due to through-currents in comparator and buffer circuits, particularly during signal inversion operations.
Innovation Solution
Incorporating a switch in the buffer circuit to control its connection state between power source nodes, ensuring it is non-conductive during comparator comparison operations, thereby preventing through-currents and maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a buffer circuit is used in the post-stage of the comparator, then signal buffering is improved, but power consumption increases due to through-current flowing in the buffer circuit during comparator operations
Solution Approach 1:
The switch is controlled to be in the non-conductive state before the comparator performs comparison operations, preventing through-current from flowing in the buffer circuit during the comparison period. This preliminary action eliminates the power consumption issue before it occurs.
Solution Approach 2:
The switch dynamically changes its conduction state based on the comparator's operation phase. During comparison operations, the switch is non-conductive to prevent through-current; during other phases, it can be conductive to allow normal buffer circuit operation. This dynamic control resolves the contradiction between maintaining buffering functionality and reducing power consumption.
2Productivity
If a buffer circuit operates during comparator comparison, then signal transmission is maintained, but image quality deteriorates due to current fluctuation and noise from through-current
Solution Approach 1:
The switch is set to non-conductive state in advance before the comparator performs comparison operations, preventing through-current from flowing in the buffer circuit during the comparison period. This preliminary action eliminates the power consumption issue before it occurs.
Solution Approach 2:
The switch dynamically changes its conduction state based on the comparator's operation phase. During comparison operations, the switch is non-conductive to prevent through-current; during other phases, it can be conductive to allow normal buffer circuit operation. This dynamic control resolves the contradiction between maintaining buffering functionality and reducing power consumption.
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 effectively reduces power consumption and minimizes image quality degradation by preventing through-currents between power source and ground nodes during AD conversion operations.
Implementation Method 1
a switch provided at least one of a part between the buffer circuit and a first node supplied with a first power source voltage and a part between the buffer circuit and a second node supplied with a second power source voltage
Implementation Method 2
a pixel that outputs a signal based on charges generated by photoelectric conversion
Data Source
AI summary
An imaging device includes a pixel that outputs a signal based on charges generated by photoelectric conversion, a comparator that compares a pixel signal output from the pixel with a reference signal and outputs a signal in accordance with a comparison result, a buffer circuit that buffers a signal output from the comparator, a switch provided at least one of a part between the buffer circuit and a first node supplied with a first power source voltage and a part between the buffer circuit and a second node supplied with a second power source voltage, and a control circuit that controls the switch to a non-conductive state in a period in which the comparator performs a comparison operation to compare the pixel signal with the reference signal.