tda8374bh NXP Semiconductors, tda8374bh Datasheet - Page 16

• Manufacturer Part Number: tda8374bh
• Description: Tda837x Family I?c-bus Controlled Economy Pal/ntsc And Ntsc Tv-processors
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Colour decoder
Depending on the IC type the colour decoder can decode
NTSC signals (TDA8373 and TDA8377) or PAL/NTSC
signals (TDA8374 and TDA8375). The circuit contains an
alignment-free crystal oscillator, a killer circuit and two
colour difference demodulators. The 90 phase shift for the
reference signal is made internally.
The TDA8373 and TDA8377 contain an Automatic Colour
Limiting (ACL) circuit which prevents over saturation
occurring when signals with a high chroma-to-burst ratio
are received. This ACL function is also available in the
TDA8374 and TDA8375, however, it is only active during
the reception of NTSC signals.
The TDA8373 and TDA8377 have a switchable colour
difference matrix (via the I
reproduction can be adapted to the market requirements.
In the TDA8374 and TDA8375 the colour difference matrix
switches automatically between PAL and NTSC, however,
it is also possible to fix the matrix in the PAL standard.
The TDA8374 and TDA8375 can operate in conjunction
with the SECAM decoder TDA8395 so that an automatic
multistandard decoder can be realized. The subcarrier
reference output for the SECAM decoder can also be used
as a reference signal for a comb filter. Consequently, the
reference signal is continuously available when PAL or
NTSC signals are detected and only present during the
vertical retrace period when a SECAM signal is detected.
Which standard the TDA8374 and TDA8375 can decode
depends on the external crystals. The crystal to be
connected to pin 34 must have a frequency of 3.5 MHz
(NTSC-M, PAL-M or PAL-N). Pin 35 can handle crystals
with a frequency of 4.4 and 3.5 MHz. Because the crystal
frequency is used to tune the line oscillator, the value of
the crystal frequency must be communicated to the IC via
the I
‘3-norma’ mode for South America. In that event one
crystal must be connected to pin 35 and the other two to
pin 34. Switching between the 2 latter crystals must be
performed externally. Consequently, the search loop of the
decoder must be controlled by the microcontroller.
To prevent calibration problems of the horizontal oscillator
the external switching between the two crystals should be
performed when the oscillator is forced to pin 35.
1997 Jul 01
I
and NTSC TV-processors
2
2
C-bus controlled economy PAL/NTSC
C-bus. It is also possible to use the IC in the so called
2
C-bus) so that the colour
16
For a reliable calibration of the horizontal oscillator it is
very important that the crystal indication bits (XA and XB)
are not corrupted. For this reason the crystal bits can be
read in the output bytes so that the software can check the
I
RGB output circuit and black current stabilization
The colour difference signals are matrixed with the
luminance signal to obtain the RGB signals. Linear
amplifiers have been chosen for the RGB inputs so that the
circuit is suited for signals that are input from the SCART
connector. The insertion blanking can be switched on or off
using the IE1 bit. To ascertain whether the insertion pin
has a (continuous) HIGH level or not can be read via the
IN1 bit. The contrast and brightness control operate on
internal and external signals.
The output signal has an amplitude of approximately 2 V
(black-to-white) at nominal input signals and nominal
settings of the controls. To increase the flexibility of the IC
it is possible to add OSD and/or teletext signals directly at
the RGB outputs. This insertion mode is controlled via the
insertion input. The action to switch the RGB outputs to
black has some delay which must be compensated for
externally.
The black current stabilization is realized by using a
feedback from the video output amplifiers to the RGB
control circuit. The black current of the 3 guns of the
picture tube is internally measured and stabilized.
The black level control is active during 4 lines at the end of
the vertical blanking. The vertical blanking is adapted to
the incoming CVBS signal (50 or 60 Hz). When the flyback
time of the vertical output stage is longer than the 60 Hz
blanking time, or when additional lines need to be blanked
(e.g. for close captioning lines) the blanking can be
increased to the same value as that of the 50 Hz blanking.
This can be set using the LBM bit. The leakage current is
measured during the first line and, during the following
3 lines, the 3 guns are adjusted to the required level.
The maximum acceptable leakage current is 100 A.
The nominal value of the black current is 10 A. The ratio
of the currents for the various guns automatically tracks
with the white point adjustment so that the background
colour is the same as the adjusted white point.
2
C-bus transmission.
TDA837x family
Preliminary specification