TDA9874A Philips Semiconductors, TDA9874A Datasheet - Page 9

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

Philips Semiconductors
6
6.1
6.1.1
Two input pins are provided, SIF1 and SIF2. For higher
SIF signal levels the SIF input can be attenuated with an
internal switchable 10 dB resistor divider. As no specific
filters are integrated, both inputs have the same
specification giving flexibility in application. The selected
signal is passed through an AGC circuit and then digitized
by an 8-bit ADC operating 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 16.
1999 Dec 03
handbook, full pagewidth
Digital TV sound demodulator/decoder
FUNCTIONAL DESCRIPTION
Description of the demodulator and decoder
section
SIF
AGC
INPUT
V DDD1
V DDA1
V SSA1
V SSD1
V SSD2
NICAM
OUTR
OUTL
TP2
TP1
n.c.
10
11
1
2
3
4
5
6
7
8
9
Fig.3 Pin configuration (QFP44).
TDA9874AH
9
The AGC can be controlled via the I
given in Sections 10.3.2, 10.3.3 and 10.4.6.
6.1.3
The digitized input signal is fed 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
Standard Programming (ESP, see Section 10.3.23). When
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 fed through a switchable
band-limiting filter into 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.
2
C-bus (see Sections 10.3.5 and 10.3.6) or via Easy
M
FM
IXER
AND
AM
MHB586
DEMODULATION
33
32
31
28
30
29
27
26
25
24
23
SCK
WS
SDO
SDA
SCL
V DDA3
V SSA3
CRESET
SIF1
V ref1
SIF2
Preliminary specification
2
C-bus; details are
TDA9874A