LED Channel Current Matching Using Common-Base Transistors
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Solution Overview
Problem
Current methods for current matching in LED channels face challenges due to non-ideal factors such as resistance mismatching, input offset, and manufacturing difficulties, making it hard to achieve accurate channel current matching with errors exceeding 2%.
Innovation Solution
A system comprising a channel reference generator, channel current dividers, and channel drivers is implemented, using transistors and resistors to generate and process input currents, ensuring that the sum of specific input currents equals channel driving currents, and the resistance and voltage offsets are managed to minimize channel current mismatching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional current matching methods are used with operational amplifiers and transistors, then channel currents can be generated, but resistance mismatching and input offset cause current matching errors exceeding 2%
Solution Approach 1:
The patent changes the operating parameters by using a common-base transistor configuration instead of conventional common-emitter or operational amplifier-based designs. This configuration change fundamentally alters the current matching behavior by eliminating the base current error and reducing sensitivity to resistance variations, thereby achieving better current matching accuracy
Solution Approach 2:
The patent employs current mirror circuits that replicate reference currents across multiple channels. By using matched transistors in a common-base configuration, the reference current is copied to multiple output channels with high precision, minimizing matching errors caused by component variations
2Illumination intensity
If multiple LED channels are implemented with conventional current drivers, then backlighting can be provided, but channel current mismatching exceeds 2% affecting evenness
Solution Approach 1:
The patent changes the circuit configuration parameter to common-base mode, which fundamentally improves current matching precision. This configuration reduces the impact of transistor parameter variations and resistance mismatches, enabling better than 2% current matching accuracy across multiple channels for uniform backlighting
Solution Approach 2:
The patent incorporates feedback mechanisms where the output currents are monitored and compared against reference currents. The common-base configuration provides inherent feedback stability, and additional feedback circuits can be implemented to further correct any residual mismatches, ensuring uniform illumination across the display
3Ease of manufacture
If conventional channel drivers are used, then LED channels can be driven, but resistance mismatching and input offset make accurate current matching difficult
Solution Approach 1:
The patent changes the transistor configuration parameter to common-base, which simplifies the manufacturing process while improving precision. This configuration eliminates the need for complex operational amplifier circuits and reduces sensitivity to component tolerances, making it easier to manufacture with better than 2% matching accuracy
Solution Approach 2:
The patent uses homogeneous transistor designs in a common-base configuration across all channels. By maintaining consistent device geometry, material composition, and circuit topology, the system achieves high current matching precision while simplifying the manufacturing process through standardization
Data Source
AI summary
System and method are provided for generating a plurality of channel currents. The system includes a channel reference generator configured to receive a first reference current and generate at least a first channel driving current and a second channel driving current, a first channel current divider configured to receive the first channel driving current and generate a first input current, a second input current, and a third input current, a second channel current divider configured to receive the second channel driving current and generate a fourth input current, a fifth input current, and a sixth input current, a first channel driver configured to receive the first input current, the second input current, and the third input current and generate a first channel current, and a second channel driver configured to receive the fourth input current, the fifth input current, and the sixth input current and generate a second channel current.