Circuit Descriptions, Abbreviation List, and IC Data Sheets
9.
ratio belonging to the display and does not show black
bars. This is done by the control software. Auto Format
is controlled via main software by reading out the black
bar information from the FBX.
•
Field Rate Upconversion.
In order to remove large area
flicker from the TV screen, the field-rate of the video is
doubled by the Feature Box. A 50/60 Hz video input is
converted to 100/120 Hz. The line frequency (16 kHz) is
also doubled (32 kHz). When the video input contains fields
A, B etc..., the conversion provides an AABB sequence
scanning on the display. The actual up-conversion is done
in the first Field Memory (FM1) by reading it twice at double
speed, while writing once.
•
Input Phase.
The horizontal phase of the input video
acquisition can be shifted to allow compensation for
processing delay of other components in front of the
Feature Box.
•
Miscellaneous Features.
To be sure that On Screen
Display (OSD) is always readable, even when no video
signal is received, the feature box can be switched to
stable OSD mode. Free running but stable horizontal and
vertical deflection drive signals will be generated, so that
OSD information and PIP can be displayed jitter free, and
thus clearly readable on the screen. Specially for tuning
purposes and smooth channel switching a stable OSD
mode is implemented that uses the horizontal time base
correction combined with a slow PLL, and a small vertical
catch window. This mode enables undisturbed reading of
OSD while the set is tuning.
9.5
Columbus
9.5.1
Introduction
The Columbus is a combination of:
•
A
2D/3D Comb filter
for both PAL and NTSC, and
•
A
spatial/temporal noise reduction system
for both
colour and luminance signals.
The Columbus 3D Comb filter uses digitalized CVBS, U, and V
(or C) signals and can be used with or without an external 16
Mbit SDRAM. Without external 16Mbit SDRAM, 3D comb
filtering and temporal noise reduction are not possible.
The noise reduction part of the Columbus is controlled by the
FBX software using the SNERT interface (the “Limeric” noise
reduction in the PICNIC is “off” in case of a Columbus
application). The 2D/3D Comb filter part is controlled by the
Main software using the I2C bus.
9.5.2
2D/3D Comb Filter
Introduction
The “3D Comb filter Columbus” is a combined 2D/3D Comb
filter function that is part of the Columbus chip (item 7752). It is
a comb filter for both PAL and NTSC.
The 3D Comb filter is used to separate chroma and luminance
components out of a CVBS signal. It is of no use when the
CVBS signal is a SECAM signal (SECAM signals cannot be
combed) The Columbus chip can be used with or without 16
Mbit external SDRAM (item 7753). When an external SDRAM
is connected to the IC, the Comb filter function can work in
combined 2D/3D processing (depending on the detected pixel
based motion). When no external SDRAM is connected, only
2D Comb filtering is possible.
The Columbus can comb the following standard signals:
•
PAL B, PAL G, PAL H, PAL I, PAL D, PAL K: Colour
standard PAL, Colour carrier at 4.43 MHz, field frequency:
50 Hz
•
PAL M: Colour standard PAL, Colour carrier at 3.58 MHz,
field frequency: 60 Hz
•
PAL N: Colour standard PAL, Colour carrier at 3.58 MHz,
field frequency: 50 Hz
•
NTSC M: Colour standard NTSC, Colour carrier at 3.58
MHz, field frequency: 60 Hz
For NTSC signals, the PAL delay line must always be
bypassed.
The following signals CANNOT be combed:
•
Double Window signals or Multi PIP. For these signals,
only one part or even no part of the signal is in relation with
the burst. The part that is not in relation with the burst can
become very blurred when combed by the Columbus
Comb filter. Such a signal must be bypassed. Notch mode
is not even an option since e.g. in double window, one part
can be a PAL signal while the other part is NTSC or
SECAM.
•
In cases where a SECAM signal is presented to the
Columbus Comb filter; both the luminance and UV path
must be bypassed. The PAL delay line inside the
Columbus cannot be used for SECAM signals so it must
also be bypassed. The luminance path must have
luminance at its input instead of CVBS. A chroma delay line
outside Columbus must be used for SECAM signals.
Reason for this: the Columbus PAL delay line halves the
output of the chroma signals in case of SECAM.
•
Y/C, YPbPr, and RGB signals do not have to be combed.
So both the luminance and UV path must be bypassed.
The PAL delay line will also be bypassed.
•
In cases where the Columbus Comb filter does not receive
a CVBS signal with burst at the right place according to the
standard (this includes black and white signals without
burst), phase correction results become unpredictable and
the Comb filter must be set in bypass (= luminance path
bypassed, UV path bypassed, PAL delay line bypassed)
•
VCR signals cannot be combed and must be processed in
notch mode, or bypassed.
Columbus Modes
The several modes of the Columbus 3D Comb filter are:
•
Bypass mode.
•
Band-Pass-Notch mode.
•
2D Comb filter modes.
–
Simple median.
–
Median.
•
Field Comb filter mode.
•
Frame Comb filter mode.
Bypass Mode
The 3D Comb filter can be set in bypass mode. In this mode,
the CVBS, U and V signals are just bypassed to the output.
Band-Pass-Notch Mode
This is a mode where no Comb filtering is applied. A “Band
Pass Filter” is used to filter the chroma information out of the
CVBS signal. A “Notch Filter” is used to subtract the sub carrier
out of the CVBS in order to make a luminance signal without
chroma sub carrier.
In terms of cross colour and cross luminance, this mode has
the worst performance of all. It is only used on these signals
where no comb filtering can be applied (non-standard signals
and most VCR signals for example).
2D Comb filter modes
A Comb filter does an action on a current pixel and a delayed
pixel. When the delayed pixel is a line-delayed pixel, we talk
about a “Spatial or 2D Comb Filter” (for NTSC the delay must
be 1 line, for PAL it must be 2 lines).
Spatial or 2D Comb filters show problems on vertical colour
transients and on single coloured lines. For these situations,
extra hardware is added in the Columbus chip to avoid these
kinds of problems. However even with these extra measures,
there are still situations where the 2D Comb filter does not
perform optimally (diagonal resolution and single lines with
equal luminance content). In order to restrict the working area
http://jdwxzlw.5d6d.com/?fromuser=森林
家电维修资料网
免费下载各种维修资料
