Philips Semiconductors
Preliminary specification
Digital Video Encoder (DENC2)
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/C
output. For transfer characteristics of the chrominance
interpolation filter see Figs 3 and 4.
The amplitude 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.
C
LOSED
C
APTION
E
NCODER
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
Ω.
It is also possible to encode Closed Caption Data for 50 Hz
field frequencies at 32 times horizontal line frequency.
Output Interface
In the output interface encoded Y and C signals are
converted from digital-to-analog in 10-bit resolution both Y
and C signals are combined to a 10-bit CVBS signal, also;
in front of the summation point, the luminance signal can
optionally be fed through a further filter stage, suppressing
components in the range of subcarrier frequency. Thus, a
type of Cross Colour reduction is provided, which is useful
in a standard TV set with CVBS input.
Slopes of synchronization pulses are not affected with any
Cross Colour reduction active.
Three different filter characteristics or bypass are
available, see Fig.5.
SAA7185
The CVBS output occurs with the same processing delay
as the Y and C outputs. Absolute amplitudes at the input
of the DAC for CVBS is reduced by
15
⁄
16
with respect to Y
and C DACs to make maximum use of conversion ranges.
Outputs of all DACs can be set together via software
control to minimum output voltage for either purpose.
Synchronization
The synchronization of the DENC2 is able to operate in
two modes; slave mode and master mode.
In the slave mode, the circuit accepts synchronization
pulses at the bidirectional RCV1 port. The timing and
trigger behaviour related to the video signal on VP (and
DP, if used) can be influenced by programming the polarity
and on-chip delay of RCV1. Active slope of RCV1 defines
the vertical phase and optionally the odd/even and colour
frame phase to be initialized, it can be also used to set the
horizontal phase.
If the horizontal phase is not be influenced by RCV1, a
horizontal pulse needs to be supplied at the RCV2 pin.
Timing and trigger behaviour can also be influenced for
RCV2.
If there are missing pulses at RCV1 and/or RCV2, the time
base of DENC2 runs free, thus an arbitrary number of
synchronization slopes may miss, but no additional pulses
(such with wrong phase) must occur.
If the vertical and horizontal phase is derived from RCV1,
RCV2 can be used for horizontal or composite blanking
input or output.
In the master mode, the time base of the circuit
continuously runs free. On the RCV1 port, the IC can
output:
•
A Vertical Sync signal (VS) with 3 or 2.5 lines duration,
or
•
An ODD/EVEN signal which is LOW in odd fields, or
•
A field sequence signal (FSEQ) which is HIGH in the first
of 4 respectively 8 fields.
On the RCV2 port, the IC can provide a horizontal pulse
with programmable start and stop phase; this pulse can be
inhibited in the vertical blanking period to build up e.g. a
composite blanking signal.
The phase of the pulses output on RCV1 or RCV2 are
referenced to the VP port, polarity of both signals is
selectable.
1996 Jul 08
8
PHILIPS [ NXP SEMICONDUCTORS ]
