CONFIDENTIAL
TW8836
FN8645 Rev 5.00 Page 18 of 153
November 3, 2016
Functional Description
Overview
Intersil’s TW8836 LCD video processor is a highly integrated TFT
panel controller. It integrates a high quality 2D comb
NTSC/PAL/SECAM video decoder, scalers and deinterlacer,
timing controller, flexible OSD (font based and SPI bitmap based
OSD engine) and a high performance MCU. This unique level of
mixed signal integration turns a TFT panel into a flexible display
system. TW8836 incorporates easy to operate features in a
single package for multipurpose in-car LCD display, portable DVD
and DVRs, media players and pico projectors. It contains all the
logic required to convert analog or digital video signals in various
formats to the signal formats that are necessary to drive various
kinds of TFT panels. It supports different panel resolutions
depending on the scaler and panel clock settings and has a
built-in TCON for direct connecting with low cost TCON-less panel.
The integrated analog front-end contains ADCs with clamping
circuits and Automatic Gain Control (AGC) circuits as well as
anti-aliasing filters to minimize the external component count.
The built-in video decoder employs proprietary 2D comb filter
Y/C separation technologies to produce exceptionally high
quality pictures.
The chip's internal logic synchronizes the panel frame rate to the
incoming input frame rate. A high quality image-scaling engine is
used to convert the different input resolution formats to the
output panel resolution. An internal deinterlacing engine also
allows interlaced video to be displayed.
In addition, TW8836 has an array of integrated value-added
features and input/output flexibility that makes it an extremely
versatile single chip solution. On-Screen Display (OSD) is supported
through an on-chip multiwindow OSD engine for maximum
flexibility. Integrated 12-bit ADCs for 4-wire resistive touch screen
control, single channel LVDS (Open LDI) input and output,
Short-to-Battery (STB)/Short-to-Ground (STG) detection function, as
well as an on-chip MCU are just a few of these features. The host
control interface supports a standard 2-wire serial bus.
Analog Front-End
The analog front-end converts analog video signals to the
required digital format. Each channel contains an automatic
clamping circuit, AGC circuit, antialiasing filter and high
performance ADCs to minimize the number of external
components needed. The clamping circuit restores the signal DC
level so it can be properly digitized. The analog inputs source
selections are software programmable. Different input sources
have different signal conditioning logic to properly convert the
signal into correct format for further processing.
Video Decoder
SYNC PROCESSOR
The decoder sync processor of the video input detects horizontal
synchronization and vertical synchronization signals in the
composite video or in the Y signal of an S-video input. The processor
contains a digital Phase Locked Loop (PLL) and decision logic to
achieve reliable sync detection in both stable signals as well as in
unstable signals, such as those from VCR fast forward or rewind.
HORIZONTAL SYNC PROCESSING
Horizontal synchronization processing contains a sync separator,
a Phase Locked Loop (PLL) and the related decision logic.
The horizontal PLL locks onto the extracted horizontal sync in all
conditions to provide a jitter free output image. From there, the
PLL also provides orthogonal sampling raster for the
downstream processor. It has a very wide lock-in range for
tracking any nonstandard video signal.
VERTICAL SYNC PROCESSING
The vertical sync separator detects the vertical synchronization
pattern in the input video signals. A detection window controls
the sync determination to provide a more reliable
synchronization and simulates the functionality of a PLL without
the complexity of a PLL. The field status is determined at the
vertical synchronization time based on the vertical and horizontal
sync relationship.
Color Decoding
Y/C SEPARATION
The color-decoding block contains the luma/chroma separation
engine for composite video signals and multistandard color
demodulation. For NTSC and PAL standard signals, the
luma/chroma separation can be done either by comb filter or
notch/bandpass filter combination. For SECAM standard signals,
only notch/bandpass filter is available. The default selection for
NTSC/PAL is comb filter. The characteristics of the bandpass
filter can be found in “
Filter Curves” on page 42.
In the case of comb filter, the decoder separates luma (Y) and
chroma (C) of a NTSC/PAL composite video signal using a
proprietary adaptive comb filter algorithm. It leads to good Y/C
separation with minimal cross luma and cross color at both
horizontal and vertical edges. Due to the nature of the line buffer
used in the comb filter, there is always a two line processing
delay in the output images regardless of what standard or filter
option is chosen.
COLOR DEMODULATION
The color demodulation for NTSC and PAL standards are done by
quadrature mixing of the chroma signal to the base band and
extracting the chroma components with the low-pass filter. The
low-pass filter characteristics can be selected for optimized
transient color performance. For the PAL system, the PAL ID or
the burst phase switching is identified to aid the PAL color
demodulation.
The SECAM color demodulation process consists of bell filtering,
FM demodulation and deemphasis filtering. The chroma carrier
frequency is identified in the process and used to control the
SECAM color demodulation.
The subcarrier signal used in the color demodulator is generated
by a direct digital synthesis PLL that locks onto the input
subcarrier reference (color burst). This arrangement allows any
substandard NTSC or PAL signal to be demodulated easily.