P-Channel Drive Transistor Threshold Correction for Display Contrast
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Solution Overview
Problem
Existing display devices with current drive type electro-optical elements, such as organic EL display devices, face a reduction in contrast due to through currents flowing to light-emitting units during non-light emission periods, which is caused by the need for a threshold correction preparation period.
Innovation Solution
A display device configuration using a P-channel type drive transistor, a sampling transistor, a light emission control transistor, a storage capacitor, and an auxiliary capacitor, where a first voltage and a second voltage are applied to the source and gate electrodes of the drive transistor during threshold correction, with the difference between them being less than the threshold voltage, allowing the drive transistor to enter a non-conductive state and eliminating the need for a threshold correction preparation period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a threshold correction preparation period is provided to correct threshold voltage variations, then the reliability of the display device is improved, but through current flows to the light-emitting units during non-light emission periods causing contrast reduction
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage correction during the light emission period before the non-light emission period begins. The correction is completed in advance, eliminating the need for a separate preparation period that would cause unwanted through current and contrast reduction.
Solution Approach 2:
The patent maintains continuity of useful action by ensuring that the threshold correction process is integrated into the light emission period, so that the correction function continues to be performed without interrupting the normal operation or causing harmful through current during non-light emission periods.
2Reliability
If a threshold correction preparation period is provided, then threshold voltage correction is achieved, but light-emitting units emit light at constant brightness during non-light emission periods despite being non-light-emitting periods
Solution Approach 1:
The threshold correction is performed in advance during the light emission period, completing the correction action before the non-light emission period begins. This preliminary correction eliminates the need for ongoing correction during non-light emission periods that would cause unwanted light emission.
Solution Approach 2:
The patent implements periodic action by confining the threshold correction to specific periods (light emission periods) rather than continuously during all periods. This periodic correction approach ensures that correction is performed when light emission is expected, preventing unwanted light during non-light emission periods.
Data Source
AI summary
A display device includes a pixel array unit formed by disposing pixel circuits having a P-channel type drive transistor that drives a light-emitting unit, a sampling transistor that applies a signal voltage, a light emission control transistor that controls emission/non-emission of the light-emitting unit, a storage capacitor that is connected between a gate electrode and a source electrode of the drive transistor and an auxiliary capacitor that is connected to the source electrode, and a drive unit that, during threshold correction, respectively applies a first voltage and a second voltage to the source electrode of the drive transistor and the gate electrode thereof, the difference between the first voltage and the second voltage being less than a threshold voltage of the drive transistor, and subsequently performs driving that applies a standard voltage used in threshold correction to the gate electrode when the source electrode is in a floating state.