Pixel Circuit Threshold Voltage Drift Compensation
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Solution Overview
Problem
Existing CMOS camera detection circuits face issues due to the drift of the threshold voltage of the driving transistor, leading to a difference between the output current and the current generated by illumination, resulting in image distortion.
Innovation Solution
A pixel circuit comprising a photodiode, a driving circuit, an initialization circuit, a transmission circuit, a voltage write-in circuit, and a compensation circuit, where the compensation circuit performs threshold voltage compensation on the driving circuit, ensuring that the output current is not affected by the threshold voltage drift, by writing data voltage into the driving circuit based on illumination intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a driving transistor is used in the pixel circuit, then the circuit can function as a source electrode follower to amplify the signal, but the threshold voltage of the driving transistor drifts over time and due to manufacturing variations, causing distortion in the output signal
Solution Approach 1:
The patent applies preliminary action by storing the threshold voltage value of the driving transistor in a storage circuit before it affects the output signal. The compensation circuit reads the threshold voltage from the storage circuit and uses it to pre-compensate the gate voltage of the driving transistor, thereby eliminating the distortion caused by threshold voltage drift before it impacts the signal amplification process
Solution Approach 2:
The patent implements feedback by using the stored threshold voltage information to adjust the driving transistor's operation. The compensation circuit continuously references the threshold voltage from the storage circuit and dynamically adjusts the gate voltage to compensate for drift, creating a closed-loop system that maintains signal accuracy despite transistor parameter variations
2Device complexity
If the threshold voltage of the driving transistor is not compensated, then the circuit structure remains simple, but the output current differs from the actual illumination-generated current, causing image distortion
Solution Approach 1:
The patent applies segmentation by dividing the pixel circuit into distinct functional modules: a driving circuit for signal amplification, a storage circuit for threshold voltage storage, and a compensation circuit for signal correction. This modular approach allows the compensation function to be added without completely redesigning the entire circuit, maintaining relative simplicity while improving output accuracy
Solution Approach 2:
The patent introduces an intermediary storage circuit that holds the threshold voltage information. This storage circuit acts as a mediator between the driving transistor and the output signal, allowing the threshold voltage to be read and used for compensation without directly affecting the signal path, thus improving accuracy while maintaining circuit simplicity
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 effectively compensates for the threshold voltage drift, ensuring accurate signal data by making the output current independent of the driving transistor's threshold voltage, thereby preventing image distortion.
Implementation Method 1
When incident light illuminates on a PN junction of the photodiode PD, light quantum excitation generates electron-hole pairs on the PN junction
Data Source
AI summary
A pixel circuit, a semiconductor camera detection circuit and a display device. The pixel circuit includes: a photodiode, a driving circuit, an initialization circuit, a transmission circuit, a voltage write-in circuit (2 and a compensation circuit. One end of the photodiode is electrically connected to a grounding end, and another end is electrically connected to the transmission circuit; the initialization circuit is configured to pull a voltage of a first node to an initialization voltage under control of the initialization signal end; the transmission circuit is configured to pull down the voltage of the first node from the initialization voltage to a data voltage under control of the first scanning signal end; the voltage write-in circuit is configured to write the data voltage into the driving circuit and output a grounding voltage to the compensation circuit; the compensation circuit is configured to perform threshold voltage compensation on the driving circuit.