Photodiode Readout Circuit Isolates Leak Current
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Solution Overview
Problem
Existing imaging devices using photodiodes face challenges in accurately detecting light due to leak current, which complicates setting the magnitude of leak current from the photodiode to match that of the leak current cancellation diode, leading to inaccurate imaging signals.
Innovation Solution
The imaging device employs transistors to control electrical connections between photodiode electrodes and wiring lines, allowing for the disconnection of leak current paths and accurate voltage reading at the photodiode electrodes, enabling precise detection of light received by the photodiode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a leak current cancellation diode is used to replenish electric charge lost due to leak current, then the electric charge loss is compensated, but the imaging signal accuracy deteriorates because it is difficult to set the leak current magnitudes equal
Solution Approach 1:
The patent extracts the harmful leak current path from the system by turning off the first transistor during the read period, isolating the photodiode's second electrode from the first electrode and preventing leak current flow, while still allowing voltage reading through the second transistor
Solution Approach 2:
The patent dynamically controls the switching state of transistors based on operational phase: during light exposure, the first transistor is on to allow charge accumulation; during read period, the first transistor is turned off to block leak current while the second transistor remains on for voltage reading
2Ease of operation
If the first transistor is kept on to maintain electrical connection for voltage reading, then voltage can be continuously read, but leak current flows and reduces electric charge
Solution Approach 1:
The patent segments the transistor control functions by using two separate transistors: the first transistor controls the charge accumulation path and is turned off during read period to block leak current, while the second transistor controls the voltage reading path and remains on to enable continuous voltage measurement without affecting charge
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 configuration allows for accurate detection of light received by the photodiode, minimizing the impact of leak current and improving the accuracy of imaging signals, even when used in applications like biological information measurement.
Implementation Method 1
electric charge according to the amount of received light is excited
Data Source
AI summary
An imaging device includes a photodiode having a first electrode and a second electrode, a first transistor that controls electrical connection between the first electrode and a first wiring line through which first voltage is supplied, and a second transistor that controls electrical connection between the first electrode and a second wiring line through which second voltage different from the first voltage is supplied, and voltage at the second electrode is read with the first transistor and the second transistor turned off.