25th Feb 09
New interface technology to connect
timing controller IC with LCD driver IC
NEC Electronics has developed a technology named 'Advanced
PPmL', a new interface technology for connecting timing
controller ICs with LCD driver ICs. It uses clock-embedded
technology, which embeds a clock data recovery (CDR) circuit
in the interface in order to separate the video data from
the clock signal. The target application for this technology
is large screen LCD TV.
With the start of terrestrial digital television broadcasts,
the television market has been evolving recently toward
larger screens and higher video resolution. In particular,
LCD televisions require chips to drive the LCD as well as
a timing controller chip to send video data to multiple
driver chips without delay. With large-screen LCD televisions,
however, the wiring connecting the timing controller chip
with the driver chips grows quite long; this could push
the size of the boards to the limits of manufacturing capabilities,
which would make handling these connections via a conventional
bus interface
unfeasible. Conventionally, this was remedied by either
reducing the wiring distance by splitting up control using
multiple timing controller chips, or by reducing the frequency
by splitting the video into multiple regions, thereby reducing
the amount of data per bus. This method, however, increases
the number of components, which causes cost to increase.
NEC Electronics addressed this issue in April 2006 with
the release of PPmL, a point-to-point interface technology
that transmits display data between timing controller chips
and driver chips in a one-to-one relationship. PPmL makes
it possible to conduct high-speed transmission using a single
timing controller chip, regardless of wiring distance or
the number of driver chips. This technology also permits
system architecture with fewer components, helping to reduce
the cost of developing large-screen LCD televisions. The
new Advanced PPmL technology was developed to further reduce
development costs, as well as to satisfy market needs for
the development of large-screen televisions: improved design
aesthetic and faster LCD driving speeds in order to reduce
motion blur.
The key advantage of this new technology is the number of
wires reduced by half in comparison to NEC's own PPmL technology.
With conventional PPmL technology, the video data and clock
signal were transmitted in separate wires, but this new
technology uses single wire for the same task. The other
merits of this technology are, driver chips can be mounted
on thinner circuit boards, and making it easy to synchronize
the I/O timing of video data and clock signals.
The new technology was made possible through the use of
clock-embedded technology. Clock-embedded technology encodes
and decodes data to superimpose clock signal on data when
it is sent and received. It is widely used in such high-speed
digital communications as PCI Express and Ethernet. However,
LCD driver ICs are made with relatively slow transistors,
and this technology was not feasible until now because a
great deal of power was consumed during high-speed (Gigahertz-range)
communication, and the encoding/decoding logic circuit was
too complex. NEC Electronics solved these challenges by
developing a dedicated process for LCD driver ICs that enables
high-speed transistors to be manufactured at low cost, and
by developing a circuit with power consumption and scale
optimized for LCD driver ICs.
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