Photo-detection Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
Conventional photo-detection apparatus, such as X-ray monitoring systems, suffer from low signal-to-noise ratios in their photoelectric readout circuits, which can be exacerbated by the introduction of additional transistors intended to enhance signal quality, leading to reduced reliability.
Innovation Solution
A photo-detection pixel circuit with a reset sub-circuit, photoelectric-conversion sub-circuit, driving sub-circuit, compensation sub-circuit, integration sub-circuit, and output-control sub-circuit, controlled by specific control signals to generate a current signal independent of the threshold voltage of the driving transistor, utilizing a photodiode and pixel capacitor to convert optical signals into electrical signals with improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional transistors are introduced to enhance signal-to-noise ratio, then signal quality is improved, but manufacturing reliability deteriorates due to increased transistor variations
Solution Approach 1:
The patent extracts and eliminates the driving transistor from the signal path that determines the output current. By using a current mirror configuration where the output current is copied from a reference branch rather than directly controlled by the driving transistor, the harmful influence of transistor threshold voltage variations is removed from the measurement signal.
Solution Approach 2:
The patent introduces a current mirror as an intermediary mechanism between the photoelectric conversion stage and the output stage. The current mirror transfers the signal current while isolating it from direct control by the driving transistor, thereby mediating the signal transmission to avoid degradation from transistor variations.
2Device complexity
If conventional photoelectric readout circuit is used, then device complexity is low, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent merges the photoelectric conversion function with the current mirroring function in a unified pixel circuit structure. The photodiode, storage capacitor, and current mirror transistors are integrated into a single pixel unit, allowing simultaneous signal conversion and noise reduction without requiring separate complex stages.
Solution Approach 2:
The driving transistor serves multiple functions: it controls the reset operation, enables the compensation phase, and drives the output stage. This multi-functional design reduces the total number of transistors needed while maintaining the improved signal-to-noise ratio through the current mirror architecture.
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 enhances signal accuracy and reduces noise in the output of photo-detection circuits, making them more reliable and independent of threshold voltage variations, thereby improving the overall performance of photo-detection systems.
Implementation Method 1
a photoelectric-conversion sub-circuit coupled to the first node and configured to convert an optical signal to a first voltage at the first node
Data Source
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Figure 5~6
AI summary
A pixel circuit of a photo detector panel. The pixel circuit includes a reset sub-circuit (300) for resetting voltages at a first node (A) and a second node (B), a photoelectric-conversion sub-circuit (100) coupled to the first node (A) and configured to convert an optical signal to a first voltage (V A) at the first node (A), a compensation sub-circuit (200) coupled between the first node (A) and the second node (B) and configured to store the first voltage (V A) and determine a second voltage (V B1) at the second node (B). The pixel circuit further includes an integration sub-circuit (500) coupled to the first node (A) and to determine a third voltage (V B2) at the second node (B) to be applied to a gate of a driving transistor (DTFT) to generate a current (I ds) flowing from an input port provided with a bias voltage (V Bias) to an output port (Output). The current (I ds) is substantially independent from a threshold voltage (V th) of the driving transistor (DTFT) and the bias voltage (V Bias).