OLED Drive Device Overdrive PWM Pulse Width Control
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Solution Overview
Problem
OLEDs experience significant delays in starting light emission during overdrive under PWM control due to large parasitic capacitance, which is exacerbated by varying brightness, making it difficult to synchronize with high-speed camera shutter release in machine vision applications.
Innovation Solution
An OLED driving device with a controller that sets a PWM signal with an initial pulse width larger than subsequent pulses to ensure timely light emission, reducing the delay in starting light emission and synchronizing with camera shutter release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If PWM control is applied to execute overdrive to OLED, then brighter light emission is achieved, but significant delay occurs in the start of light emission due to large parasitic capacitance
Solution Approach 1:
The controller applies a preliminary overdrive current to the OLED before the actual light emission is needed. This preliminary action charges the parasitic capacitance in advance, so that when the light emission is required, the OLED can start emitting light immediately without significant delay. The overdrive current is applied during a predetermined period before the expected light emission timing.
Solution Approach 2:
The controller dynamically adjusts the PWM signal characteristics based on the brightness level. When high brightness is required, the controller modifies the PWM duty cycle and timing to account for the increased current needed to charge the parasitic capacitance faster. This dynamic adjustment ensures that the delay is minimized across different brightness levels.
2Use of energy by moving object
If brightness of OLED is reduced, then energy consumption decreases, but delay in start of light emission becomes significantly longer
Solution Approach 1:
The controller changes the parameters of the PWM signal based on the required brightness level. For lower brightness levels, the controller adjusts the duty cycle and pulse width to optimize the charging time of the parasitic capacitance. This parameter adjustment ensures that even at lower brightness levels, the delay remains minimized while still achieving the desired energy efficiency.
Solution Approach 2:
The controller applies a preliminary overdrive current to the OLED before the actual light emission is needed. This preliminary action charges the parasitic capacitance in advance, so that when the light emission is required, the OLED can start emitting light immediately without significant delay. The overdrive current is applied during a predetermined period before the expected light emission timing.
3Productivity
If high speed inspection is performed with many targets, then productivity increases, but synchronization between OLED light emission and camera shutter release becomes difficult due to delay
Solution Approach 1:
The controller applies a preliminary overdrive current to the OLED before the actual light emission is needed. This preliminary action charges the parasitic capacitance in advance, so that when the light emission is required, the OLED can start emitting light immediately without significant delay. The overdrive current is applied during a predetermined period before the expected light emission timing.
Solution Approach 2:
The controller uses feedback from the inspection system to adjust the timing and characteristics of the overdrive signal. By monitoring the inspection cycle and camera shutter timing, the controller optimizes the overdrive application timing to ensure precise synchronization between light emission and camera exposure, maintaining reliability at high inspection speeds.
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 effectively reduces the delay in OLED light emission and maintains synchronization with camera shutter release across varying brightness levels, eliminating the need to adjust camera shutter speed based on OLED brightness.
Implementation Method 1
For the purpose of causing the OLED to execute light emitting (an emission of light), the OLED needs a voltage exceeding a threshold which allows the OLED to execute the light emitting
Implementation Method 2
The OLED emits light on a plane basis, and thus has a relatively large parasitic capacitance. It takes a longer time to charge the load as the parasitic capacitance is larger
Data Source
AI summary
An OLED driving device includes an overdrive controller (ODC) which executes an overdrive of applying to an OLED an electric current larger than a rated electric current for the OLED for a predetermined period (period for the overdrive) to cause the OLED to emit brighter light for the predetermined period than at the rated electric current for the OLED for light emitting. The controller (ODC) executes a PWM control to the electric current flowing to the OLED for the predetermined period, and sets a PWM signal in the predetermined period so that at least one pulse of a pulse before the OLED starts the light emitting and a pulse at a just time when the OLED starts the light emitting has a width larger than a width of a pulse after the OLED starts the light emitting.