PWM Pixel Circuit With Constant Current Gate Stabilization

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Solution Overview

Problem

Display devices using pulse width modulation (PWM) for driving light-emitting elements, such as uLEDs or OLEDs, suffer from color shift phenomena due to variations in threshold voltages of CCG driving transistors, leading to distorted images.

Innovation Solution

A pixel design incorporating a PWM circuit and a CCG circuit with capacitors and transistors that stabilize the gate voltage of the CCG driving transistor, using capacitive coupling to maintain a constant gate voltage and compensate for threshold voltage deviations, thereby maintaining consistent emission current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If PAM method is used to drive light-emitting element, then gray level can be adjusted by current amplitude, but color shift phenomenon occurs due to wavelength change with driving current

Engineering Contradiction:

Improvegray level adjustmentVSAvoidcolor shift

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a CCG circuit as an intermediary between the PWM signal and the light-emitting element. This CCG circuit converts the PWM signal into a constant current that is independent of the light-emitting element's characteristics, thereby preventing color shift while maintaining gray level control capability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the direct PAM driving method with a PWM-based constant current generation system. Instead of directly controlling current amplitude (PAM), the system uses PWM signaling combined with a CCG circuit to generate stable constant current, substituting the direct mechanical control approach with a signal-processing-based approach

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Object-affected harmful factors

If CCG circuit is added to generate constant current, then color shift is prevented, but device complexity increases

Engineering Contradiction:

Improvecolor shift preventionVSAvoidcircuit complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent merges the CCG circuit functionality directly into the pixel structure, integrating the constant current generation capability with the existing PWM driving circuitry. This integration approach reduces overall system complexity compared to adding a separate CCG module

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The CCG circuit is designed to perform multiple functions: it generates constant current from PWM signals, compensates for threshold voltage variations in the CCG driving transistor, and interfaces with the light-emitting element. This multi-functionality reduces the need for additional separate circuits

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Manufacturing precision

If threshold voltage of CCG driving transistor varies, then manufacturing precision is affected, but image quality deteriorates due to emission current variation

Engineering Contradiction:

Improvetransistor threshold voltage consistencyVSAvoidimage quality

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent implements a feedback mechanism where the CCG circuit continuously adjusts the emission current based on the actual operating conditions. The circuit uses the PWM signal and internal capacitors to regulate the current through the CCG driving transistor, compensating for threshold voltage variations and maintaining consistent emission current

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the operating parameters of the CCG driving transistor by using capacitor coupling to stabilize the gate voltage. This parameter stabilization approach compensates for threshold voltage variations caused by manufacturing tolerances, ensuring consistent emission current across different pixels

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution ensures stable emission current levels, preventing color shifts and maintaining image quality by compensating for threshold voltage variations in the CCG driving transistors, thus enhancing the display device's performance.

Implementation Method 1

a second capacitor including a first electrode connected to the gate of the CCG driving transistor, and a second electrode which receives the PWM signal generated by the PWM circuit

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Data Source

PatentUS20260038427A1Pixel, display device including the same and electronic device including display device

Publication Date: 2026.02.05 SAMSUNG DISPLAY CO LTD

AI summary

A pixel of a display device includes a pulse width modulation (“PWM”) circuit configured to generate a PWM signal based on a PWM data voltage and a sweep voltage, a constant current generation (“CCG”) circuit configured to generate an emission current based on a CCG data voltage and the PWM signal, and a light-emitting element configured to emit light based on the emission current. The CCG circuit includes a CCG driving transistor configured to generate the emission current, a first capacitor including a first electrode which receives a first CCG power supply voltage having a relatively high power voltage level, and a second electrode connected to a gate of the CCG driving transistor, and a second capacitor including a first electrode connected to the gate of the CCG driving transistor, and a second electrode which receives the PWM signal generated by the PWM circuit.