參數資料
型號: TDA9874APS
廠商: NXP SEMICONDUCTORS
元件分類: 接收器
英文描述: Digital TV sound demodulator/decoder
中文描述: AM/FM, AUDIO DEMODULATOR, PDIP42
封裝: 0.600 INCH, SHRINK, PLASTIC, MS-020, SOT-270-1, DIP-42
文件頁數: 9/68頁
文件大?。?/td> 231K
代理商: TDA9874APS
1999 Dec 03
9
Philips Semiconductors
Preliminary specification
Digital TV sound demodulator/decoder
TDA9874A
handbook, full pagewidth
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TDA9874AH
MHB586
SCK
WS
SDO
SDA
VDDA3
VSSA3
CRESET
SIF1
Vref1
SIF2
OUTL
OUTR
VDDA1
VSSA1
VSSD1
VDDD1
n.c.
TP2
TP1
SCL
O
P
V
E
E
M
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P
A
X
X
T
T
I
V
V
T
P
A
VSSD2
NICAM
Fig.3 Pin configuration (QFP44).
6
FUNCTIONAL DESCRIPTION
6.1
Description of the demodulator and decoder
section
6.1.1
SIF
INPUT
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
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 16.
The AGC can be controlled via the I
2
C-bus; details are
given in Sections 10.3.2, 10.3.3 and 10.4.6.
6.1.3
M
IXER
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
2
C-bus (see Sections 10.3.5 and 10.3.6) or via Easy
StandardProgramming(ESP,seeSection 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
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.
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