Scan Driving Circuit for OLED Using PMOS Bootstrap to Reduce Power
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Solution Overview
Problem
Conventional scan driving circuits for organic light emitting display devices suffer from high power consumption due to static current flow and deviations in output voltage levels, leading to inefficient operation and reduced discharge efficiency.
Innovation Solution
A scan driving circuit utilizing PMOS transistors and capacitors, driven by a 2-phase clock signal, which removes the static current flow path and switches the output voltage from a negative to a positive power supply using a bootstrap operation, thereby reducing power consumption and improving signal accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional master-slave flip-flop circuit is used in the scan driving circuit, then the circuit can sequentially shift the start pulse signal through multiple stages, but static current flows through the inverters causing increased power consumption
Solution Approach 1:
The patent extracts and removes the inverter component from the flip-flop circuit. By replacing the conventional master-slave flip-flop structure that uses inverters with a new circuit configuration using only PMOS transistors, the source of static current consumption is eliminated while retaining the signal shifting functionality across multiple stages
Solution Approach 2:
The patent changes the transistor type parameter from a mix of NMOS and PMOS (conventional flip-flop) to exclusively PMOS transistors. This parameter change in the circuit components eliminates the static current flow path that exists in conventional inverters, thereby reducing power consumption while maintaining the sequential signal shifting capability
2Productivity
If conventional flip-flop circuits are used with varying input voltage levels across stages, then the circuit can operate sequentially, but voltage level deviations occur causing erroneous operation
Solution Approach 1:
The patent changes the transistor characteristics parameter by using exclusively PMOS transistors with consistent threshold voltages across all stages. This uniformity in transistor parameters ensures that voltage levels remain stable and consistent throughout the sequential stages, preventing deviation and erroneous operation while maintaining sequential functionality
Solution Approach 2:
The patent applies the same PMOS-only circuit configuration uniformly across all stages of the scan driving circuit. This consistent local quality in terms of transistor type and circuit structure ensures that each stage operates with identical electrical characteristics, eliminating voltage level deviations that occur when different stages have varying input levels
3Productivity
If the output terminal is charged through the input transistor, then the output voltage can be updated, but the discharge efficiency deteriorates due to rapid reduction in discharge current
Solution Approach 1:
The patent changes the transistor type parameter from NMOS (conventional flip-flop) to PMOS throughout the circuit. This parameter change in transistor characteristics modifies the current flow behavior, enabling efficient charging through the input transistor while maintaining sustained discharge current flow, thereby improving discharge efficiency alongside output updating capability
Data Source
AI summary
Scan driving circuit having a number of stages coupled together in series and coupled with first and second lock signal input lines. Each of the stages receives a start signal or an output signal of a previous stage and includes a transfer unit, an inversion unit, and a buffer unit and produces the output signal. The output signal of each of the stages includes a low level signal, the low level signal of each stage is sequentially shifted by one half of the clock signal period with respect to the low level signal of a previous stage. The series of shifted low level signals form the scan signals output by the scan driving circuit for driving an organic light emitting display device.