TDA9874AHB View Datasheet(PDF) - NXP Semiconductors.
Part Name
Description
MFG CO.
'TDA9874AHB' PDF : 69 Pages View PDF
Philips Semiconductors
Digital TV sound demodulator/decoder
handbook, full pagewidth
Product specification
TDA9874A
OUTL 1
OUTR 2
VDDA1 3
VSSA1 4
VSSD1 5
VDDD1 6
VSSD2 7
n.c. 8
TP2 9
NICAM 10
TP1 11
TDA9874AH
33 SCK
32 WS
31 SDO
30 SDA
29 SCL
28 VDDA3
27 VSSA3
26 CRESET
25 SIF1
24 Vref1
23 SIF2
MHB586
Fig.3 Pin configuration (QFP44).
6 FUNCTIONAL DESCRIPTION
6.1 Description of the demodulator and decoder
section
6.1.1 SIF INPUTS
Two inputs are provided, pin SIF1 and pin 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 AGC
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 14).
The AGC can be controlled via the I2C-bus; details are
given in Sections 7.3.2, 7.3.3 and 7.4.6.
6.1.3 MIXER
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
I2C-bus (see Sections 7.3.5 and 7.3.6) or via Easy
Standard Programming (ESP, see Section 7.3.23). 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 FM AND AM DEMODULATION
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.
2000 Aug 04
9
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