2015-12-16 New 16-channel LED backlight controller from ams improves TV picture quality and saves power

ams introduced the AS3824, a 16-channel LED TV backlight controller which performs
local dimming of sections of a display screen to provide both improved picture quality
and valuable power savings of up to 20-30%.

The new backlight controller is intended for use in the latest 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 synchro-nized with an external
synchronization 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 reproduce faithfully even the blackest of 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 and daisy-chained to as many AS3824 devices as are needed in
the application.



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