Micro-LED PWM Driving Circuit for Low-Grayscale Uniformity
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Solution Overview
Problem
Traditional Micro-LED display technologies face issues with display uniformity at low grayscales due to long rising edge times during transitions from dark to bright states and mottling, which are not adequately addressed by existing Pulse Width Modulation (PWM) and Pulse Amplitude Modulation (PAM) hybrid driving circuits.
Innovation Solution
A display device with an optimized pulse width modulation module incorporating a comparator and a duty cycle control module, which significantly shortens the rising edge time from dark to bright states and adjusts the light-emitting duty cycle to improve display uniformity, particularly at low grayscales.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional PWM driving circuits are used to control light emission time for low grayscales, then grayscale switching is achieved, but the rising edge time from dark to bright state is relatively long, reducing actual light emission time
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor during the data writing phase before the light emission phase begins. The capacitor is charged to a voltage level corresponding to the desired grayscale value, so when the light emission phase starts, the comparator can immediately compare this pre-charged voltage with the ramp signal and generate the PWM output without delay. This eliminates the rising edge delay and maximizes actual light emission time.
2Manufacturing precision
If traditional PHM driving circuits are used, then high grayscales use PAM and low grayscales use PWM, but mottling still occurs in displayed images at low grayscales, affecting display uniformity
Solution Approach 1:
The patent applies feedback by using a comparator to continuously compare the capacitor voltage (representing the desired grayscale level) with a ramp signal during the light emission phase. This comparison provides real-time feedback control that precisely determines when to switch the light emission state, ensuring accurate grayscale rendering without mottling artifacts. The feedback mechanism compensates for variations and maintains display uniformity at low grayscales.
3Ease of operation
If the rising edge time varies at different grayscales in traditional PHM circuits, then grayscale transitions are achieved, but display uniformity is affected, especially at low grayscales
Solution Approach 1:
The patent applies parameter changes by using a ramp signal with a fixed, known slope for comparison against the capacitor voltage. This standardized ramp signal ensures that the time required to traverse any voltage range (and thus any grayscale transition) is consistent and predictable across all grayscale levels. The capacitor voltage is linearly related to the stored charge, and the ramp signal provides a linear time reference, creating uniform transition characteristics across the entire grayscale range.
Data Source
AI summary
The present disclosure provides a display device and a driving method thereof. The pixel driving circuit of the display device panel comprises a pulse amplitude modulation driving module and a pulse width modulation driving module. The pulse width modulation driving module includes a comparator, a plurality of transistors, and a capacitor. The comparator is configured to compare the voltage of the ramp signal and the voltage of the data signal and control the conduction state of the light-emitting device of the display panel. The driving method includes comparing a voltage of a ramp signal and a voltage of a data signal in a light-emitting phase to control a light emission time of a light-emitting device. The present disclosure can improve the low grayscale display effect and improve the display uniformity.