Analog PWM Pixel Circuit for Constant-Current iLED Brightness

The patent replaces complex variable current-control circuits with a simpler analog PWM circuit that uses a capacitor discharge mechanism controlled by a switch. Instead of continuously adjusting current through complex circuitry, the invention uses a timing-based approach where a capacitor is charged to a reference voltage and then discharged through an LED, with the discharge time controlled by a simple switch and resistor network. This substitution of mechanical/timing-based control for electronic current regulation reduces circuit complexity while maintaining brightness control capability.

The patent implements analog PWM control where a capacitor is periodically charged to a reference voltage and then discharged through the iLED for a duration proportional to the desired brightness. This periodic charge-discharge cycle creates a natural timing mechanism that operates at lower frequencies compared to digital PWM circuits. The discharge time constant, determined by the RC network, inherently controls the pulse width without requiring high-speed digital switching, thus reducing the operating frequency while maintaining effective brightness control.

The patent applies local quality by providing different reference voltages for different color iLEDs (red, green, blue) based on their specific efficiency characteristics. Each color LED has its own reference voltage level that optimizes its emission efficiency at the intended operating current density. The analog PWM circuit naturally adapts to each LED's requirements by comparing the capacitor discharge voltage against the appropriate reference voltage, eliminating the need for complex control logic while maintaining optimal efficiency for each color channel.