Pixel Circuit Threshold Voltage Compensation via Feedback
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Solution Overview
Problem
CMOS image sensors experience non-uniform output currents during photoelectric conversion due to differences in source follower transistors' threshold voltages, leading to display distortion.
Innovation Solution
A pixel circuit comprising a resetting sub-circuit, charging sub-circuit, compensating sub-circuit, and reading sub-circuit, which includes specific transistors and capacitors to control node potentials and output signals, compensating for source follower transistors to make output current independent of their threshold voltages, and sharing driving and scanning signals for high-resolution display and environmental image monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If source follower transistors are used in the pixel circuit for photoelectric conversion, then the circuit can be simplified and manufacturing is easier, but the output current becomes non-uniform due to threshold voltage differences causing display distortion
Solution Approach 1:
The patent introduces a feedback mechanism where the output current of the source follower transistor is fed back through a feedback transistor to adjust the gate voltage of the source follower. This feedback loop compensates for threshold voltage variations, ensuring uniform output current across different pixels while maintaining the simplicity of using source follower transistors in the circuit.
Solution Approach 2:
The patent changes the operating parameters of the source follower transistor by dynamically adjusting its gate voltage through the feedback mechanism. By varying the gate voltage parameter in response to threshold voltage differences, the circuit maintains consistent output current characteristics across different transistors with different threshold voltages.
2Manufacturing precision
If multiple transistors and capacitors are added to compensate for threshold voltage differences, then output current uniformity is improved, but the device complexity increases
Solution Approach 1:
The patent designs the feedback transistor to serve multiple functions: it acts as a switching element, a current mirror, and a feedback mechanism simultaneously. This multi-functionality reduces the need for separate dedicated components for each function, thereby compensating for threshold voltage differences without proportionally increasing the overall device complexity.
Solution Approach 2:
The patent merges the compensation function with the existing transistor structure by integrating the feedback mechanism into the pixel circuit's natural signal path. The feedback transistor is combined with the source follower and other circuit elements to form a unified structure that performs both signal processing and threshold voltage compensation, reducing the need for separate compensation circuits.
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 ensures output current independence from source follower transistor threshold voltages, maintaining signal accuracy and enabling high-resolution displays and environmental image monitoring capabilities.
Implementation Method 1
The charging sub-circuit may be connected to a second electrode of a photosensitive device having a first electrode connected to the ground, wherein the photosensitive device comprises a photodiode
Data Source
AI summary
Embodiments of the present disclosure provide a pixel circuit, a driving method thereof and a display apparatus. The pixel circuit comprises a resetting sub-circuit configured to control potentials of the first node, the second node and the third node according to inputting signals of the first signal terminal and the second signal terminal; a charging sub-circuit configured to control a potential of the second node according to an inputting signal of the second signal terminal; a compensating sub-circuit configured to control the potentials of the first node and the third node according to an inputting signal of the third signal terminal and the potential of the second node; a reading sub-circuit is configured to control outputting signals of the first terminal of the light emitting device and the reading terminal according to the inputting signal of the fourth signal terminal.