STV82X7 datasheet(23/156 Pages) STMICROELECTRONICS

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STV82x7

Digital Demodulator

3.2

Demodulation

The demodulation system operates by default in Automatic mode. In this mode, the STV82x7 is able

to identify and demodulate any TV sound standard including NICAM and A2 systems (see

Table 4) without any external control via the I²C interface. It consists of the two demodulation

channels (Channel 1 = Mono Left and Channel 2 = Mono Right/Stereo) to simultaneously process

two sound carriers in order to handle all transmission modes (stereo and up to three mono

languages). 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 (see

Section 12.1). The programming is optimized for each standard to be identified and demodulated.

Each mono and stereo standard can be removed (or added) from the List of Standards to be

recognized by programming registers AUTOSTD_STANDARD_DETECT and

AUTOSTD_STEREO_DETECT, respectively. 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

must be reset by re-programming the MSBs of register AUTOSTD_CTRL while checking the

detected standard status by reading registers AUTOSTD_STATUS, NICAM_STAT and ZWT_STAT.

Moreover, the detection of Stereo mode during demodulation is also flagged in register

AUTOSTD_STATUS.

Important: L/L’ and D/K standards cannot be automatically processed because the same frequency

is used for the MONO carrier. An exclusive L/DK selection must programmed in register

AUTOSTD_CTRL. This may be externally controlled by detecting the RF modulation sign, which is

negative for all TV standards except L/L’.

To recover out-of standard FM deviations or the Sound Carrier Frequency Offset, additional I²C

controls are provided without interfering with the Automatic Standard Recognition System

(Autostandard).

DK-NICAM Overmodulation Recovery: Four different FM deviation ranges can be selected (via

maximum FM deviation is 500 kHz in DK Mono mode and 350 kHz in DK NICAM mode (limited by

overlapping FM and NICAM spectrum values). The demodulated signal peak level (proportional to

the FM deviation) is detected by the Peak Detector and written to registers PEAK_DET_L and

PEAK_DET_R. This value is used to implement Automatic Overmodulation Detection via an

external I²C control.

Important: Only the selection of the 50 kHz FM deviation standard is compatible with the other DK-

A2* standards (DK1, DK2 or DK3). These standards must be removed from the list of standards

(registers AUTOSTD_STANDARD_DETECT and AUTOSTD_STEREO_DETECT) when

programming larger FM deviations reserved only for DK-NICAM standards.

Table 4: Recognized Standards

System

Sound Type

Type

Name

Carrier 1

(MHz)

Carrier 2

(MHz)

FM Deviation

De-

emphasis

Roll

-off

(%)

Pilot

Frequency

(kHz)

Nom. Max. Over

B/G

FM Mono

5.5

FM/NICAM

5.5

5.850

J17

FM 2-Carrier

5.5

5.742

50 µs

54.6875

D/K

FM Mono

6.5

FM/NICAM

6.5

5.850

J17

D/K1

FM 2-Carrier

A2*

6.5

6.258

50 µs

54.6875

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