PWM Pixel Circuit for Fast Falling Edge and Low Grayscale Control
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Solution Overview
Problem
Conventional pixel circuits driven in pulse width modulation methods suffer from long falling times, making it difficult to display low grayscale ranges and causing color shifts due to wavelength shifts in light emitting elements, and voltage drops occur when switching high power voltages due to large turn-on resistances.
Innovation Solution
The pixel circuit includes a light emitting element, first and second switching elements, a driving element, and capacitors, where the current is quickly controlled through a pulse width modulation method, eliminating the need to switch high power voltages and preventing voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a conventional pixel circuit is driven in a pulse width modulation method, then the light emission duration can be controlled, but the falling time is relatively long causing difficulty in displaying low grayscale ranges and color shifts
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks including a light emitting element, first switching element, second switching element, third switching element, driving element, first capacitor, and second capacitor. Each component has a specific function in controlling the current waveform, with the second switching element specifically designed to quickly control the current of the light emitting element during the falling edge, thereby reducing the falling time and improving grayscale display precision.
2Power
If a switch is used for each pixel row to switch the high power voltage, then the voltage can be controlled, but a voltage drop occurs due to large turn-on resistance
Solution Approach 1:
Instead of switching the high power voltage for the entire pixel row, the invention applies partial switching action only where necessary. The second switching element is strategically placed to control only the current path of the light emitting element, avoiding the need to switch high power voltage across the entire row, thereby eliminating voltage drops while still achieving precise power control.
Solution Approach 2:
The invention introduces intermediate voltage levels and current control mechanisms. Rather than directly switching high power voltage, the circuit uses intermediate capacitors and switching elements to control the current flow to the light emitting element, thereby avoiding direct high power voltage switching and the associated voltage drops.
Data Source
AI summary
A pixel circuit includes a light emitting element, a first switching element including a control electrode connected to a second node, a first electrode connected to a third node and a second electrode connected to the light emitting element, a second switching element including a control electrode connected to a first node, a first electrode receiving a power and a second electrode connected to the second node, a third switching element including a control electrode receiving the gate signal, a first electrode receiving the data voltage and a second electrode connected to the first node, a driving element including a control electrode receiving a reference voltage, a first electrode receiving the power and a second electrode connected to the third node, a first capacitor receiving the ramp signal and connected to the first node and a second capacitor receiving the emission signal and connected to the second node.