STV82X8 datasheet(19/157 Pages) STMICROELECTRONICS

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STV82x8

Digital Demodulator

The Digital Demodulator (see Figure 10) consists of a channel demodulator and a stereo/SAP

decoder.

All channel parameters are programmed automatically by the built-in Automatic Standard

Recognition System (Autostandard) in order to find the STEREO or the SAP modes. Channel

parameters can also be programmed manually via the I²C interface for very specific standards not

included among the known standards.

3.1

Sound IF Signal

The Analog Sound Carrier IF is connected to the STV82x8 via the SIF pin. Before Analog-to-Digital

Conversion (ADC), an Automatic Gain Control (AGC) is performed to adjust the incoming IF signal

to the full scale of the ADC. A preliminary video rejection is recommended to optimize conversion

and demodulation performances. The AGC system provides a gain value allowing for a wide range

of SIF input levels.

The TQFP100 package provides a second SIF input.

3.2

Demodulation

The demodulation system operates by default in Automatic mode. In this mode, the STV82x8 is able

to identify and demodulate the BTSC TV sound standard including stereo and SAP modes

without any external control via the I²C interface.

The built-in Automatic Standard Recognition System (Autostandard) automatically programs

the appropriate bits in the I²C registers which are forced to Read-only mode for users.

STEREO and SAP modes can be removed (or added) from the List of modes to be recognized by

programming registers AUTOSTD_CTRL. The identified standard is displayed in register

AUTOSTD_STATUS and any change to standard is flagged to the host system via pin IRQ. This flag

Figure 10: Demodulator Block Diagram

Mixer

Channel

Filter

FIR1

Demodulator

AGC

Control

SIF

DCO1+

A/D

CARFQ1 (12-14h)

AGC

Amp

Stereo/SAP

Demodulator

(L+R)* or mono*

(L-R)dbx or SAPdbx

DSP Processing

Deemphasis,

DBX decoding

and dematrixing

AUTOSTD

DETECTION

DEMOD_STAT(0Dh)

STEREO_SAP_STATUS(4Ch)

FIR1C (15-1Ch)

ACOEFF1(1Dh)

BCOEFF1(1Eh)

SAP_CONF(47h)

*: Pre-emphasis signal

dbx: DBX -encoded signal

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