STV82X6 STMICROELECTRONICS [STMicroelectronics], STV82X6 Datasheet - Page 10

• Manufacturer Part Number: STV82X6
• Description: Multistandard TV Audio Processor and Digital Sound Demodulator
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Demodulator Block
2
Note:
2.1
2.1.1
2.1.2
10/95
SIF
Demodulator Block
Zweiton is the Dual (Two Tone) FM stereo or A2 system.
Digital Demodulator
Sound IF Signal
The Analog Sound Carrier IF is connected to STV82x6 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 wide range of SIF input levels and is
activated for all standards, except L/L’. In this particular case, the sound carrier is AM-modulated
and an automatic level adjustment would only damage transmitted audio signal. A preset I²C
parameter is required to define the gain of the AGC used in Manual mode (Registers
AGCS).
Demodulation
The demodulation system operates by default in Automatic mode. In this mode, the STV82x6 is able
to identify and demodulate any TV sound standard including NICAM and A2 systems (see
Table
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 (AUTOSTD) automatically
programs the appropriate bits in the I²C registers which are forced to Read-only mode for users
(see
demodulated.
AGC
Amp
Section
2) without any external control via the I²C interface. It consists of the two demodulation
AGCC(0Eh)
AGCS(0Fh)
Control
AGC
9.1). The programming is optimized for each standard to be identified and
A/D
CAROFFSET2(3Ah)
AUTO_STAT(54h)
AUTO_SCKM(51h)
AUTO_SCKST(52h)
AUTO_CTRL(50h)
CAROFFSET1(22h)
Figure 6: Demodulator Block Diagram
DCO2 +
DCO1+
Mixer
Mixer
Channel 1 = Mono Left
AUTOSTD
Channel 2 = Stereo/Mono Right
Channel
Channel
Filter
FIR1
Filter
FIR2
DEMOD_STAT(0Dh)
ZWT_STAT(41h)
NICAM_STAT(3Fh)
Demodulator
Demodulator
Demodulator
Demodulator
DQPSK
AM
FM
FM
AM
FML
Decoder
NICAM
Decoder
Zweiton
(To Sound Preprocessing)
(To Sound Preprocessing)
(To Sound Preprocessing)
AM/FM Mono
NICAML
NICAMR
FM Stereo
AGCC
STV82x6
and