16-channel LED backlight controller applies local dimming

December 17, 2015 // By Graham Prophet
ams presents its LED controller as a means of improving TV picture quality and saving power: the AS3824 controller enables independent, flexible PWM control of each of 16 LED channels for local dimming and true reproduction of the darkest shades of black.

Sensor and analogue IC maker ams (Unterpremstaetten, Graz, Austria) cites improved picture quality and valuable power savings of up to 20-30%: its backlight controller is intended for use in high-definition (HD) and ultra high-definition (UHD, or ‘4K’) televisions, as well as high dynamic range (HDR) monitors and displays.

The AS3824 includes a fully flexible 12-bit PWM generator for each of its 16 channels, to enable sections of a display screen to be dimmed independently. Each PWM generator may be synchronised with an external signal.

The 16-channel independent dimming capability means that the backlight intensity of each section can be precisely controlled to match the picture content of each successive frame on display. When a section of the frame needs to be dark, the LEDs illuminating just that section may be dimmed independently of the rest, enabling a TV to better reproduce blacks, and enhancing the perceived picture quality. By contrast, conventional global backlight controllers cannot prevent some light from leaking into sections of the display screen that should be black, thus reproducing black as grey.

The local dimming enabled by the AS3824 also provides for additional system power savings compared to global backlight controllers.

The AS3824 backlight controller features a precise internal 10-bit DAC, which provides accurate (±0.5%) global control of the current through external MOSFETs or bipolar transistors. It supports all LED backlight topologies, with no limit on the current through or voltage across the LEDs.

The device also includes a supplementary 8-bit current-control DAC for each of the 16 channels, which can be used to boost or lower the current locally through the LEDs in certain frames, thereby increasing dynamic contrast ratios. This enables the AS3824 to support HDR monitors and HDR TVs.

The AS3824 is backed by a comprehensive set of protection functions, including thermal shutdown when the temperature exceeds 140°C, and open and short LED detection. The device may be pro-grammed via a serial peripheral interface