tda9874h NXP Semiconductors, tda9874h Datasheet - Page 11

• Manufacturer Part Number: tda9874h
• Description: Digital Tv Sound Demodulator/decoder
• Manufacturer: NXP Semiconductors

Philips Semiconductors
6.2
6.2.1
All input channels to the digital crossbar switch are
equipped with a level adjust facility to change the signal
level in a range of 15 dB. Adjusting the signal level is
intended to compensate for the different modulation
parameters of the various TV standards. It is
recommended to scale all input channels to be 15 dB
below full-scale ( 15 dB full-scale) under nominal
conditions. This will create sufficient headroom to cope
with overmodulation and avoids changes of the volume
impression when switching from FM to NICAM or vice
versa.
6.2.2
The NICAM path has a switchable J17 de-emphasis.
6.2.3
If NICAM is received, the auto-mute is enabled and the
signal quality becomes poor, the digital crossbar switches
automatically to FM, channel 1 or the analog mono input,
as selected by bit AMSEL. This automatic switching
depends on the NICAM bit error rate. The auto-mute
function can be disabled via the I
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
1
to L and R signals, as demanded by the different
TV standards or user preferences.
2000 Jun 26
2
2
(L + R) and R to L and R signals, of
(L
Digital TV sound demodulator/decoder
R) to L and R signals or of channel 1 and channel 2
Description of the DSP
L
NICAM
NICAM
FM (AM)
EVEL SCALING
PATH
AUTO
PATH
-
MUTE
2
C-bus.
1
2
(L + R) and
11
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. Source
selection and data read out are performed via the I
6.2.6
Input channels come from the FM and NICAM paths, while
output channels comprise I
analog crossbar switch. Note that there is no connection
from the external analog audio inputs to the digital
crossbar switch.
6.2.7
The digital audio output interface comprises an I
port and a system clock output. The I
with a level adjust 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.
6.2.8
A level adjust function is provided with control positions
0 dB, +3 dB, +6 dB and +9 dB in combination with the
audio DACs.
6.2.9
The level adjust 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
( 15 dB full-scale).
2
S-bus output matrix provides the functions of forced
FM
D
D
C
G
IGITAL CROSSBAR SWITCH
IGITAL AUDIO OUTPUT
HANNEL TO THE ANALOG CROSSBAR PATH
ENERAL
MONITOR
2
S and the audio DACs to the
Product specification
2
S port is equipped
TDA9874H
2
S output
2
C-bus.