Micro LED Sub-Pixel PWM Circuit for Accurate Brightness
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Solution Overview
Problem
Micro LEDs face challenges in accurately implementing desired brightness due to shifts in current center wavelength with pulse amplitude modulation, necessitating a more effective pixel driving method.
Innovation Solution
A sub-pixel design utilizing pulse width modulation (PWM) with specific transistor and capacitor configurations to control current flow and voltage levels for precise brightness control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If pulse amplitude modulation (PAM) is used to drive micro LEDs, then the response speed and brightness can be improved, but the brightness accuracy deteriorates due to current center wavelength shifts
Solution Approach 1:
The patent changes the driving parameter from current amplitude (PAM) to current pulse width (PWM). By controlling the duration of current flow rather than its amplitude, the system achieves both fast response and accurate brightness control without wavelength shifts affecting performance
Solution Approach 2:
The patent employs periodic current pulses with variable widths to control brightness. The light-emitting element receives periodic current signals where the pulse width varies according to the desired brightness level, enabling precise control while maintaining fast response characteristics
2Measurement precision
If PWM method is used to control brightness, then brightness accuracy is improved, but the circuit complexity increases due to additional transistors and capacitors
Solution Approach 1:
The patent designs transistors and capacitors to serve multiple functions. For example, the first transistor generates driving current while also acting as a switch, and capacitors store both initialization voltages and ramp signals. This multi-functionality reduces the need for separate dedicated components
Solution Approach 2:
The patent uses capacitors to pre-store initialization voltages and ramp signals before they are needed for driving the light-emitting element. This preliminary preparation of voltage signals simplifies the real-time control circuitry by eliminating the need for complex voltage generation circuits during the emission phase
Data Source
AI summary
A sub-pixel includes a light-emitting element configured to receive a driving current, and to emit light, a first transistor configured to generate the driving current, a second transistor configured to transmit the driving current to the light-emitting element in response to a signal from a first node, a third transistor configured to provide a first power voltage to the first node in response to a signal from a second node, a fourth transistor configured to provide a data voltage to the second node in response to a scan signal, and a first capacitor including a first electrode for receiving a ramp signal, and a second electrode connected to the second node.