Specifications

- 78 -
- PAL/NTSC modulator: the sum of the signal generated by two AM
modulators.
- SECAM modulator: FM modulation of the Dr and Db signals synchronized
with the line frequency.
The chrominance signal obtained is added to the luminance (delayed in
SECAM). The composite video signal will be inverted or not, depending on the
system selected, to be transmitted to the RF modulator input.
g) Logotype generator
Based on the scanning of the data contained in an EPROM (at 20 MHz),
synchronized with the line and frame frequencies, it is also provided with
auxiliary signals indicating position and contents of the logo. The VTR signal
is also generated in this module.
h) Teletext and VPS generator
Based on the scanning of the data contained in an EPROM (at 5 MHz/VPS and
6.9375 MHz/teletext synchronized with the line frequency). This module is
responsible for the generation of the signals which control this board (frequency
switching, appearance of signals in the video signal, etc.).
i) L sound carrier generator
This module is divided into differentiated parts:
- Internal LF signal generator (Wien bridge oscillator), LF input stage
(pre-emphasis filters of 50 µs and 75 µs), and LF signal switching.
- Sound carrier generator and FM modulator synchronized with the line
frequency, programmable counter depending on the standard selected,
summator of the LF signal for the modulation of FM.
- AM modulator (Secam/L)
The circuit is responsible for the multiplexing of the signal in order to obtain
the correct signal at the output, depending on the standard selected.
j) R sound carrier generator (Zweiton)
This module is divided in three differentiated parts:
- Internal LF signal generator (Wien bridge oscillator), LF input stage
(pre-emphasis filter of 50 µs), and LF signal switching.
- Sound carrier 2 generator, FM modulator, summator of the LF signal for the
modulation of FM.
- Generator of the identification carrier and pilot frequencies (117 Hz and
234 Hz) identifying the stereo/dual mode, modulated in AM.
k) NICAM sound generator
This is composed of:
- The data of the coded LF signal are stored in an EPROM, which is sampled
at a frequency 8 times greater than the data transmission frequency
(5.824 MHz). The output signals are digitally filtered (at 40% cosine roll-off
in B/G and at 100% in I) and pass through a D/A converter. After being
filtered they will become the LF inputs of the modulators.
05/96 GV-698