High-Frequency Pulse Width Modulation (PWM): what it is, how it works and what it does

Definition and Operating Principle

Pulse Width Modulation (PWM) is the standard method used in OLED displays to regulate brightness. Unlike LCD screens, which adjust backlight voltage, OLED panels emit light individually per subpixel. To reduce brightness, the panel rapidly turns pixels on and off, creating an optical illusion of lower intensity.

The frequency of this modulation, measured in Hertz (Hz), determines the speed at which pixels switch on and off. A low frequency (e.g., 240 Hz or 480 Hz) can result in perceptible flicker for some users, potentially causing eye strain. High-frequency PWM, such as 1440 Hz, significantly increases the speed of these cycles, reducing flicker amplitude and bringing the visual experience closer to continuous light.

Architecture and Technical Context

This technology is often integrated into next-generation panels, such as LTPO OLED. The combination of LTPO (Low Temperature Polycrystalline Oxide) and high-frequency PWM allows for optimizing both energy consumption and visual quality. LTPO dynamically adjusts the image refresh rate, while high-frequency PWM manages brightness more smoothly.

In technical specifications, the mention of "1440Hz PWM" indicates that the brightness modulation cycle occurs 1440 times per second. This specification is independent of the image refresh rate (which can be 60 Hz, 120 Hz, etc.), although both often coexist in high-end devices.

Applications and Scope

• High-End Mobile Devices: Common in premium smartphones aiming to minimize visual fatigue during prolonged use.
• HDR Compatibility: Frequently associated with high dynamic range standards, such as HDR Vivid, to maintain color fidelity and brightness in high-contrast scenes.
• Color Reproduction: In panels supporting 1B colors (1 billion colors), high-frequency PWM helps maintain color consistency when varying brightness.

Limitations and Interpretation

Although 1440 Hz PWM is superior to standard frequencies, it does not completely eliminate flicker, as the nature of pulse modulation remains present. However, human perception is much less sensitive to frequencies above 1000 Hz.

When interpreting the presence of this specification in a product, it should be understood as a visual comfort and screen quality feature, not as an improvement in motion fluidity (which depends on the refresh rate). It should not be confused with the screen's refresh rate, but rather is a brightness control parameter.

Note: The perceived effectiveness of high-frequency PWM may vary depending on the individual user's sensitivity to flicker.