tda9874h NXP Semiconductors, tda9874h Datasheet - Page 9

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

Philips Semiconductors
6
6.1
6.1.1
Two input pins are provided. SIF1 e.g. for terrestrial TV
and SIF2 e.g. for a satellite tuner. As no specific filters are
integrated, both inputs have the same specification giving
flexibility in application. The selected signal is passed
through an AGC and then digitized by an 8-bit ADC
running at 24.576 MHz.
6.1.2
The gain of the AGC amplifier is controlled from the ADC
output by means of a digital control loop employing
hysteresis. The AGC has a fast attack behaviour to
prevent ADC overloads, and a slow decay behaviour to
prevent AGC oscillations. For AM demodulation the AGC
must be switched off. When switched off, the control loop
is reset and fixed gain settings can be chosen
(see Table 11).
The AGC can be controlled via the I
found in Sections 7.3.1, 7.3.2 and 7.4.6.
6.1.3
The digitized input signal is passed on to the mixers, which
mix one or both input sound carriers down to zero IF.
A 24-bit control word for each carrier sets the required
frequency. Access to the mixer control word registers is via
the I
receiving NICAM programs, a feedback signal is added to
the control word of the second carrier mixer to establish a
carrier-frequency loop.
6.1.4
An FM or AM input signal is passed through a
band-limiting filter onto a demodulator that can be used for
either FM or AM demodulation. Apart from the standard
(fixed) de-emphasis characteristic, an adaptive
de-emphasis is available for Wegener-Panda 1 encoded
satellite programs.
6.1.5
A 2-carrier stereo decoder recovers the left and right
signal channels from the demodulated sound carriers.
Both the European and Korean stereo systems are
supported.
2000 Jun 26
Digital TV sound demodulator/decoder
FUNCTIONAL DESCRIPTION
2
C-bus (see Sections 7.3.4 and 7.3.5). When
Description of the demodulator and decoder
section
SIF
AGC
M
FM
FM
IXER
AND
DECODING
INPUTS
AM
DEMODULATION
2
C-bus. Details can be
9
6.1.6
The identification of the FM sound mode is performed by
AM synchronous demodulation of the pilot and
narrow-band detection of the identification frequencies.
The result is available via the I
A selection can be made via the I
and M standards, and for three different time constants
that represent different trade-offs between speed and
reliability of identification.
6.1.7
The NICAM signal is transmitted in a DQPSK code at a bit
rate of 728 kbits/s. The NICAM demodulator performs
DQPSK demodulation and passes the resulting bitstream
and clock signal to the NICAM decoder and, for evaluation
purposes, to pins.
A timing loop controls the frequency of the crystal oscillator
to lock the sampling instants to the symbol timing of the
NICAM data. The polarity of the control signal is selectable
to support applications, in which external circuitry is used
to boost the tuning voltage of the oscillator.
6.1.8
The device performs all decoding functions in accordance
with the “EBU NICAM 728 specification” . After locking to
the frame alignment word, the data are de-scrambled by
application of the defined pseudo-random binary
sequence, and the device synchronizes to the periodic
frame flag bit C0.
The status of the NICAM decoder can be read out from the
NICAM Status Register by the user (see Section 7.4.2).
Bit OSB indicates that the decoder has locked to the
NICAM data. Bit VDSP indicates that the decoder has
locked to the NICAM data and that the data is valid sound
data. Bit C4 indicates that the sound conveyed by the
FM mono channel is identical to the sound conveyed by
the NICAM channel. The error byte contains the number of
sound sample errors, resulting from parity checking, that
occurred in the past 128 ms period. The Bit Error Rate
(BER) can be calculated using the following equation:
BER
=
bit errors
---------------------- -
total bits
FM
NICAM
NICAM
IDENTIFICATION
DEMODULATION
DECODING
error byte 1.74 10
2
C-bus interface.
2
C-bus for B/G, D/K
Product specification
TDA9874H
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