SAA7120 Просмотр технического описания (PDF) - Philips Electronics
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SAA7120 Datasheet PDF : 32 Pages
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Philips Semiconductors
Digital Video Encoder (ConDENC)
Preliminary specification
SAA7120; SAA7121
handbook, h2alfpage
Gv
(dB)
0
−2
MBE735
(1)
(2)
−4
−6
0
0.4
0.8
1.2 f (MHz) 1.6
(1) SCBW = 1.
(2) SCBW = 0.
Fig.6 Chrominance transfer characteristic 2.
In order to enable easy analog post-filtering, luminance is
interpolated from 13.5 MHz data rate to 27 MHz data rate,
providing luminance in 10-bit resolution. This filter is also
used to define smoothed transients for synchronization
pulses and blanking period. For transfer characteristic of
the luminance interpolation filter see Figs 3 and 4.
Chrominance is modified in gain (programmable
separately for U and V), standard dependent burst is
inserted, before baseband colour signals are interpolated
from 6.75 MHz data rate to 27 MHz data rate. One of the
interpolation stages can be bypassed, thus providing a
higher colour bandwidth, which can be made use of for
Y and C output. For transfer characteristics of the
chrominance interpolation filter see Figs 5 and 6.
The amplitude, beginning and ending of inserted burst is
programmable in a certain range, suitable for standard
signals and for special effects. Behind the succeeding
quadrature modulator, colour in 10-bit resolution is
provided on subcarrier.
The numeric ratio between Y and C outputs is in
accordance with set standards.
signal TTXRQ a single teletext bit has to be provided after
a programmable delay at input pin.
Phase variant interpolation is achieved on this bitstream in
the internal teletext encoder, providing sufficient small
phase jitter on the output text lines.
TTXRQ provides a fully programmable request signal to
the teletext source, indicating the insertion period of
bitstream at lines selectable independently for both fields.
The internal insertion window for text is set to 360
(PAL-WST), 296 (NTSC-WST) or 288 (NABTS) teletext
bits including clock run-in bits. For protocol and timing
see Fig.7.
CLOSED CAPTION ENCODER
Using this circuit, data in accordance with the specification
of closed caption or extended data service, delivered by
the control interface, can be encoded (Line 21).
Two dedicated pairs of bytes (two bytes per field), each
pair preceded by run-in clocks and framing code, are
possible.
The actual line number where data is to be encoded in, can
be modified in a certain range.
Data clock frequency is in accordance with definition for
NTSC-M standard 32 times horizontal line frequency.
Data LOW at the output of the DACs corresponds to 0 IRE,
data HIGH at the output of the DACs corresponds to
approximately 50 IRE.
It is also possible to encode Closed Caption Data for 50 Hz
field frequencies at 32 times horizontal line frequency.
ANTI-TAPING (SAA7120 ONLY)
For more information contact your nearest Philips
Semiconductors sales office.
Data manager
In the data manager, real time arbitration on the data
stream to be encoded is performed.
A pre-defined colour look-up table located in this block can
be read out in a pre-defined sequence (8 steps per active
video line), achieving a colour bar test pattern generator
without the need for an external data source. The colour
bar function is under software control only.
TELETEXT INSERTION AND ENCODING
Pin TTX receives a WST- or NABTS-Teletext bitstream
sampled at the LLC clock. At each rising edge of output
Output interface/DACs
In the output interface encoded Y and C signals are
converted from digital to analog in 10-bit resolution.
1997 Jan 06
8
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