TDA9874APS/V2 データシートの表示（PDF） - Philips Electronics

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TDA9874APS/V2

Digital TB sound demodulator/processor

Philips Electronics 

Philips Semiconductors

Digital TV sound demodulator/decoder

Preliminary specification

TDA9874A

handbook, full pagewidth

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 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 I2C-bus; details are

given in Sections 10.3.2, 10.3.3 and 10.4.6.

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 10.3.5 and 10.3.6) or via Easy

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 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.

1999 Dec 03

9

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