Pixel Signal Summing in Solid-State Imagers
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Solution Overview
Problem
Conventional solid-state imaging devices experience a decrease in sensitivity when mixing pixel signals, particularly in moving-picture mode, due to the averaging of signals which results in lower output signal values and reduced light amount, leading to decreased sensitivity.
Innovation Solution
The implementation of a solid-state imaging device with a series connection of accumulation circuits and switch circuits, allowing for the summation of electric charges from photoelectric conversion elements, which enhances sensitivity by summing voltages and utilizing high input impedance circuits to prevent voltage loss, enabling effective pixel summing in both row and column directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If signals of multiple pixels are mixed by connecting accumulation circuits in parallel, then the number of effective photoelectric conversion elements increases for moving picture capture, but the output signal value decreases because only the average value is obtained instead of the sum
Solution Approach 1:
The patent applies dynamics by making the connection configuration of accumulation circuits changeable between parallel and series based on the operating mode. A control circuit dynamically switches the connection state of switch circuits to connect accumulation circuits in parallel during still picture capture and in series during moving picture capture, allowing the system to adapt its signal processing characteristics to different operational requirements.
2Speed
If the accumulation time period is shortened for high-speed signal mixing in moving picture mode, then the frame rate increases, but the light amount decreases and sensitivity is reduced
Solution Approach 1:
The patent changes the electrical connection parameter of accumulation circuits from parallel to series configuration during moving picture mode. This parameter change transforms the output characteristic from average value to summed value, compensating for the reduced light amount caused by shorter accumulation time and maintaining sensitivity despite high-speed signal mixing.
3Reliability
If accumulation circuits are connected in series to sum signals, then the output signal value increases, but the circuit complexity increases
Solution Approach 1:
The patent uses dynamically controllable switch circuits to change the connection configuration of accumulation circuits between parallel and series based on operating mode. This dynamic approach allows the circuit to achieve series connection for signal summation only when needed for moving picture mode, rather than maintaining a permanently complex series configuration, thereby reducing overall device complexity.
Solution Approach 2:
The switch circuits serve multiple functions: they act as connection elements for both parallel and series configurations, and also function as control elements that respond to mode signals. This multi-functionality reduces the need for separate dedicated components for each configuration, simplifying the overall circuit design while enabling both still picture and moving picture modes.
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 increases output signal values, maintains sensitivity even with shorter accumulating times, and allows for excellent color reproduction and image compression, resulting in higher picture quality.
Implementation Method 1
a photoelectric conversion element; a plurality of accumulation circuits, each of which individually accumulates electric charges corresponding to a signal outputted from the photoelectric conversion element
Data Source
AI summary
A solid-state imaging device is provided in which sensitivity is prevented from lowering even when signals of pixels are mixed. The solid-state imaging device includes a plurality of pixel units each of which has a photoelectric conversion element, and is capable of summing signals corresponding to respective outputs of the photoelectric conversion elements of the pixel units. The device includes: a plurality of capacitors, each of which individually accumulates electric charges corresponding to a signal outputted from the associated photoelectric conversion element; and a plurality of MOS transistors which are alternately connected with the associated capacitor. By disconnecting the MOS transistor, the electric charges of the signal outputted from each of the photoelectric conversion elements are accumulated in each associated capacitor, and by conducting the MOS transistors to sum the signals of the pixel units, the capacitors are connected in series.