LED Driving Device PWM Compensation for Forward Voltage Delay
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Solution Overview
Problem
Existing LED display devices face challenges in accurately controlling the ON period of PWM signals to match gray scale values, leading to inefficiencies in light emission, as the actual brightness of LEDs does not reach the intended level due to the delay in reaching the forward voltage.
Innovation Solution
An LED driving device comprising a driving current source, a sample and hold circuit, and a PWM compensating circuit that measures the time for an LED's voltage to reach the forward voltage and adjusts the PWM signal accordingly, ensuring accurate brightness control and compensation without requiring a separate sequence, and continuously updating the forward voltage to account for panel characteristic changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If driving current is supplied during the ON period of PWM signal, then LED brightness control is simplified, but actual brightness does not reach the gray scale value due to forward voltage delay
Solution Approach 1:
The patent applies preliminary action by measuring the forward voltage reaching time of the LED before the PWM signal is applied. This measurement is stored and used to pre-calculate the compensated PWM ON period, ensuring that the LED receives current for the exact duration needed to achieve the desired gray scale brightness, thereby eliminating the brightness shortfall caused by forward voltage delay.
Solution Approach 2:
The patent implements feedback by continuously measuring the forward voltage reaching time of LEDs and using this information to adjust and compensate the PWM signal parameters. The measured forward voltage time serves as feedback that enables dynamic adjustment of the PWM ON period, ensuring accurate brightness control that adapts to individual LED characteristics and maintains precision across different gray scale values.
2Measurement precision
If forward voltage reaching time is measured for each LED, then brightness accuracy is improved, but measurement complexity and time increase
Solution Approach 1:
The patent applies self-service by using the LED's own forward voltage reaching time characteristic as the measurement target. Instead of requiring complex external test equipment or sequences, the system measures the time it takes for each LED to reach its forward voltage naturally during normal operation. This self-service approach simplifies the measurement system while maintaining high accuracy for brightness compensation.
3Measurement precision
If PWM ON period is extended to compensate for forward voltage delay, then brightness accuracy is improved, but energy consumption increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the PWM signal parameters based on the measured forward voltage reaching time. Instead of using a fixed or overly conservative ON period that would waste energy, the system calculates the precise compensated ON period needed for each LED to reach the target gray scale brightness. This parameter optimization ensures that energy is consumed only for the minimum necessary duration to achieve accurate brightness control.
Data Source
AI summary
The present disclosure relates to an LED driving technique. The present disclosure provides a technique of measuring a time for reaching a forward voltage of a currently driven LED by comparing a forward voltage sensed in a previous scan line and an LED voltage sensed in a current scan line and for compensating for an ON period of a PWM (pulse width modulation) signal by the measured time for reaching the forward voltage.