TDA9874AHB View Datasheet(PDF) - NXP Semiconductors.
Part Name
Description
MFG CO.
'TDA9874AHB' PDF : 69 Pages View PDF
Philips Semiconductors
Digital TV sound demodulator/decoder
Product specification
TDA9874A
6.2.4 FM (AM) PATH
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
1⁄2(L + R), R to L and R signals of 1⁄2(L + R) and 1⁄2(L − R)
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 MONITOR
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
I2C-bus.
6.2.6 DIGITAL CROSSBAR SWITCH
The input channels are derived from the FM and NICAM
paths, while the output channels comprise I2S-bus and the
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.
6.2.7 DIGITAL AUDIO OUTPUT
The digital audio output interface comprises an I2S-bus
output port and a system clock output. The I2S-bus port is
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 I2S-bus output matrix provides the functions for forced
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 STEREO CHANNEL TO THE ANALOG CROSSBAR PATH
A level adjustment function is provided with control
positions of 0 dB, +3 dB, +6 dB and +9 dB in combination
with the audio DACs. The Automatic Volume Level (AVL)
function provides a constant output level of
−20 dB (full-scale) for input levels between
0 dB (full-scale) and −26 dB (full-scale). There are some
fixed decay time constants to choose from, i.e.
2, 4 or 8 seconds.
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 GENERAL
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
(−15 dB full-scale).
2000 Aug 04
12
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