Current Mirror Voltage Compensation for Uniform Pixel Brightness
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Solution Overview
Problem
Display devices face issues with maintaining uniform pixel brightness due to variations in transistor characteristics and external factors, leading to undesirable brightness and deteriorated image quality, especially when current or voltage differences occur in current mirror circuits.
Innovation Solution
A current supply circuit with a voltage compensation circuit between the drain terminals of transistors in a current mirror circuit, and switches that control current flow to disconnect or connect components based on time periods, ensuring uniform voltages and minimizing current differences, thereby maintaining consistent brightness across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a current mirror circuit is used to supply data current to pixels, then the brightness can be controlled according to image data, but the brightness varies due to transistor characteristic variations and voltage differences
Solution Approach 1:
The patent implements a feedback mechanism by measuring the actual voltage at the drain terminal of the first transistor and using this measured voltage to control the gate voltage of the second transistor. This closed-loop feedback ensures that the second transistor receives accurate voltage information, compensating for variations in transistor characteristics and maintaining uniform brightness across pixels even when transistor parameters vary.
Solution Approach 2:
The patent introduces an intermediary voltage signal that is derived from the drain terminal voltage of the first transistor and used to control the second transistor. This intermediary voltage acts as a mediator that transfers the actual operating condition information from the first transistor to the second transistor, ensuring they operate at matching voltages despite characteristic variations.
2Manufacturing precision
If additional components such as capacitors are added to reduce voltage changes in the driving transistor, then image quality can be improved, but voltage differences and current differences still occur due to external and internal causes
Solution Approach 1:
The patent uses feedback by continuously monitoring the drain terminal voltage of the first transistor and using this information to adjust the gate voltage of the second transistor. This feedback mechanism dynamically compensates for voltage differences caused by capacitor charging/discharging and other external/internal factors, maintaining voltage and current uniformity without requiring additional complex components.
Solution Approach 2:
The circuit uses its own internal voltage conditions (the drain terminal voltage of the first transistor) to automatically adjust and control the second transistor. This self-service approach allows the circuit to autonomously compensate for voltage differences and current mismatches without requiring external intervention or additional complex control mechanisms.
3Ease of operation
If the same data voltage is supplied from the data driving circuit to all pixels, then the data transmission is simplified, but the brightness varies due to transistor threshold voltage variations
Solution Approach 1:
The patent maintains simple data transmission by supplying the same data voltage to all pixels through the current mirror circuit, while simultaneously using feedback from the drain terminal voltage measurement to adjust the gate voltage of the second transistor. This feedback mechanism compensates for transistor threshold voltage variations, ensuring uniform brightness without complicating the data transmission process.
Solution Approach 2:
The patent changes the voltage parameter dynamically by adjusting the gate voltage of the second transistor based on the measured drain terminal voltage. This parameter change allows the circuit to adapt to transistor characteristic variations and maintain uniform brightness while keeping the data transmission simple and unchanged.
Data Source
AI summary
A current mirror circuit includes a first transistor configured to be supplied with a data current from a data driving circuit; a second transistor configured to drive a light emitting diode by mirroring the data current transferred to the first transistor; and a voltage compensation circuit disposed between one terminal of the first transistor and one terminal of the second transistor and configured to compensate for a difference between voltages of the one terminals of the first transistor and the second transistor.