Organic EL Driver Circuit With Selective High-Voltage Transistors
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Solution Overview
Problem
The existing organic EL drive circuits for active matrix type organic EL display panels face challenges in reducing circuit size and minimizing luminance variation due to the need for high-voltage resistant elements in D/A converter circuits, which increases circuit area and degrades current conversion precision.
Innovation Solution
The organic EL drive circuit employs a D/A converter circuit with a current mirror configuration, utilizing transistors with lower proof voltages on the input and output sides, and a low-proof voltage reset switch, reducing the number of high-voltage transistors and improving element matching precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-voltage resistant elements are used in D/A converter circuits, then the circuit can operate at high power source voltages (10V to 20V), but the circuit area increases and element matching precision deteriorates
Solution Approach 1:
The patent applies different voltage resistance characteristics to different parts of the circuit. Specifically, the reset switch (third transistor) is designed with low voltage resistance, while only critical elements like the current mirror circuit transistors maintain high voltage resistance. This localized approach reduces overall circuit area while preserving necessary voltage handling capabilities in key functional blocks.
2Strength
If high-voltage resistant elements are used in D/A converter circuits, then the circuit can operate at high power source voltages (10V to 20V), but element matching precision and current conversion accuracy deteriorate
Solution Approach 1:
The patent selectively applies high voltage resistance only where absolutely necessary for circuit operation (e.g., current mirror circuit transistors that must handle power source voltage), while using low voltage resistance elements elsewhere (e.g., reset switch). This reduces oxide film thickness variation across the circuit, thereby improving element matching precision and current conversion accuracy.
3Reliability
If the number of high-voltage resistant elements is increased, then the circuit can handle high power source voltages more reliably, but the IC area increases
Solution Approach 1:
The patent extracts the high voltage resistance requirement from the entire circuit and concentrates it only in the essential elements that must handle power source voltage (current mirror circuit transistors). Non-essential elements like the reset switch use low voltage resistance, reducing the total number of high-voltage resistant elements and thereby reducing IC area while maintaining voltage handling reliability.
4Area of stationary object
If D/A converter circuits are provided externally to reduce panel size, then the panel area decreases, but the drive circuit requires high-voltage resistant elements that increase overall system complexity
Solution Approach 1:
The patent reduces drive circuit complexity by applying high voltage resistance only to essential elements (current mirror transistors) while using low voltage resistance for others (reset switch). This selective approach simplifies the overall drive circuit design and reduces the number of high-voltage resistant elements that would otherwise be required in an external D/A converter configuration.
Data Source
AI summary
To provide an organic EL drive circuit including D/A converter circuits capable of reducing the number of elements, which are proof against relatively high voltage, restricting an increase of circuit size and restricting variation of luminance of a display screen and an organic EL display device using the organic EL drive circuit.An organic EL drive circuit for generating, in response to a predetermined current inputted to an input terminal of a D/A converter circuit constructed with a current mirror circuit, drive currents to be outputted to terminal pins of the organic EL display panel or a current, on which the drive currents are generated, by converting digital display data into analog signal by the D/A converter circuit, comprises a first transistor provided between an input side transistor of the current mirror circuit and the input terminal, a second transistor provided between an output side transistor of the current mirror circuit and an output terminal and a third transistor provided between the output terminal and a power source line, wherein proof voltages of the input side transistor, the output side transistor and the third transistor are lower than proof voltage of the first and second transistors.