Display Driving Circuit Threshold Voltage Compensation

Solution Overview

Problem

Display apparatuses with current-driven light-emitting elements, such as organic electroluminescence (EL) elements, face issues with brightness variation due to changes in transistor threshold voltage over time, leading to inconsistent gradation levels in displayed images.

Innovation Solution

A display apparatus with a pixel driving circuit, precharge voltage source, voltage reader, and compensated gradation data signal generator that applies a precharge voltage, reads voltage differences at different times, and generates a compensated gradation data signal to maintain desired brightness levels despite threshold voltage variations in transistors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a current control thin film transistor is used to supply current to an organic EL element, then the brightness can be controlled by adjusting the voltage signal, but the threshold voltage of the transistor varies over time causing brightness variation

Engineering Contradiction:

Improvebrightness controlVSAvoidbrightness stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent applies a precharge voltage to the data line before writing the data voltage. This preliminary action initializes the voltage state of the data line and pixel circuit, creating a known starting condition that enables accurate measurement of threshold voltage variations through subsequent voltage readings during the transient response period.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent reads the voltage of the data line at multiple different timings during the transient response period and uses the voltage difference between these readings to calculate a compensation value. This feedback mechanism detects threshold voltage variations and generates corrective signals to compensate for brightness variations, resolving the reliability issue while maintaining ease of operation.

Inventive Principle:

Principle #23Feedback

2Adaptability or versatility

If voltage signals are applied to control the current in organic EL elements, then the gradation levels can be adjusted, but threshold voltage variations cause inconsistent gradation display

Engineering Contradiction:

Improvegradation controlVSAvoidgradation accuracy

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent implements a feedback loop that reads the data line voltage at multiple timings, calculates the voltage difference, and generates a compensation value based on this difference. This compensation value is added to the original data voltage to create a corrected voltage signal that maintains accurate gradation levels despite transistor threshold voltage variations.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the voltage parameter by applying a precharge voltage before the data voltage and by adjusting the data line voltage based on the measured transient response. This dynamic parameter adjustment ensures that the final voltage applied to the pixel circuit compensates for threshold voltage variations, maintaining precise gradation control.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If the threshold voltage of the transistor is allowed to vary naturally, then the device operation is simple, but the current supply to light-emitting elements becomes unstable

Engineering Contradiction:

Improvecircuit operationVSAvoidcurrent supply stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent applies a precharge voltage to the data line before writing the data voltage. This preliminary action initializes the voltage state of the data line and pixel circuit, creating a known starting condition that enables accurate measurement of threshold voltage variations through subsequent voltage readings during the transient response period.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent reads the voltage of the data line at multiple different timings during the transient response period and uses the voltage difference between these readings to calculate a compensation value. This feedback mechanism detects threshold voltage variations and generates corrective signals to compensate for brightness variations, resolving the reliability issue while maintaining ease of operation.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS7760168B2Display apparatus, display driving apparatus and method for driving same

Publication Date: 2010.07.20 SOLAS OLED LTD

AI summary

A light-emitting element capable of emitting light having a preferred gradation level depending on display data. During a precharge period, a data driver applies a precharge voltage to a capacitor via a data line. After the application of the precharge voltage, a voltage converter reads a first reference voltage Vref(t1) and a second reference voltage Vref(t2) to generate a compensation voltage based on a difference between the respective reference voltages. Based on the compensation voltage, a voltage calculator compensates an original gradation level voltage Vorg having a value in accordance with display data generated by a gradation level voltage generator. The voltage calculator generates a compensated gradation level voltage Vpix corresponding to a variation amount of an element characteristic for a transistor Tr13 for driving light emission to apply the compensated gradation level voltage Vpix to a data line Ld.