TDA9874A Philips Semiconductors, TDA9874A Datasheet - Page 12

• Manufacturer Part Number: TDA9874A
• Description: Digital TV sound demodulator/decoder
• Manufacturer: Philips Semiconductors

Philips Semiconductors
6.2.4
A high-pass filter suppresses DC offsets from the FM
demodulator that may occur due to carrier frequency
offsets, and supplies the FM monitor function with DC
values, e.g. for the purpose of microprocessor controlled
carrier search or fine tuning functions.
An adaptive de-emphasis is available for
Wegener-Panda 1 encoded satellite programs.
The de-emphasis stage offers a choice of settings for the
supported TV standards.
The 2-channel decoder performs the dematrixing of
1
to L and R signals or of channel 1 and channel 2 to
L and R signals, as demanded by the different TV
standards or user preferences.
Automatic FM dematrixing is also supported.
Using the high deviation mode, only channel 1 (mono) can
be demodulated. The scaling is 6 dB compared to
2-channel decoding.
6.2.5
This function provides data words from the FM
demodulator outputs and FM and NICAM signals for
external use, such as carrier search or fine tuning.
The peak level of these signals can also be observed.
Source selection and data read-out are performed via the
I
6.2.6
The input channels are derived from the FM and NICAM
paths, while the output channels comprise I
audio DACs to the analog crossbar switch. It should be
noted that there is no connection from the external analog
audio inputs to the digital crossbar switch.
1999 Dec 03
2
2
C-bus.
(L + R), R to L and R signals of
Digital TV sound demodulator/decoder
FM (AM)
M
D
IGITAL CROSSBAR SWITCH
ONITOR
PATH
1
2
(L + R) and
2
S-bus and the
1
2
(L
R)
12
6.2.7
The digital audio output interface comprises an I
output port and a system clock output. The I
equipped with a level adjustment facility that can change
the signal level in a 15 dB range in 1 dB steps. Muting is
possible, too, and outputs can be disabled to improve EMC
performance.
The I
mono, stereo, channel swap, channel 1 or channel 2.
Automatic selection for TV applications is possible. In this
case the microcontroller program only has to provide a
user controlled sound A or sound B selection.
6.2.8
A level adjustment function is provided with control
positions of 0, 3, 6 and 9 dB in combination with the audio
DACs. The Automatic Volume Level (AVL) function
provides a constant output level of 20 dB (FS) for input
levels between 0 and 26 dB (FS). There are some fixed
decay time constants to choose from, i.e. 2, 4 or 8 s.
Automatic selection for TV applications is possible. In this
case the microcontroller program only has to provide a
user controlled sound A or sound B selection.
6.2.9
The level adjustment functions can provide signal gain at
multiple locations. Great care has to be taken when using
gain with large input signals, e.g., due to overmodulation,
in order not to exceed the maximum possible signal swing,
which would cause severe signal distortion. The nominal
signal level of the various signal sources to the digital
crossbar switch should be 15 dB below digital full-scale,
i.e., 15 dB (FS).
2
S-bus output matrix provides the functions for forced
D
S
G
TEREO CHANNEL TO THE ANALOG CROSSBAR PATH
IGITAL AUDIO OUTPUT
ENERAL
Preliminary specification
TDA9874A
2
S-bus port is
2
S-bus