參數(shù)資料
型號: STV8237
廠商: 意法半導(dǎo)體
英文描述: Digital Audio Decoder/Processor for A2 and NICAM Television/Video Recorders
中文描述: 數(shù)字音頻解碼器/處理器為A2和麗音電視/錄像機(jī)
文件頁數(shù): 21/149頁
文件大小: 2775K
代理商: STV8237
21/149
STV82x7
Digital Demodulator
3
Digital Demodulator
The Digital Demodulator (see
Figure 10
) is composed of two channels. The first channel
demodulates an FM or an AM signal. The second channel demodulates FM 2-carrier or NICAM
signals (stereo demodulation).
All channel parameters are programmed automatically by the
built-in Automatic Standard
Recognition System
(Autostandard) in order to find the correct sound standard. Channels 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 STV82x7 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 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 the transmitted
audio signal. A preset I2C parameter is provided to define the gain of the AGC used in Manual mode
(Registers
AGC_CTRL
and
AGC_GAIN
).
Note:
For optimum AM demodulation performance, it is recommended to use the MONO Input.
Figure 10: Demodulator Block Diagram
Mixer
Mixer
DCO2 +
Channel
Filter
FIR1
Channel
Filter
FIR2
AM
Demodulator
FM
Demodulator
FM
Demodulator
DQPSK
Demodulator
AUTOSTD
AGC
Control
SIF
NICAM
Decoder
DCO1+
Zweiton
Decoder
A/D
NICAM L
NICAM R
AM/FM Mono
(To Sound Preprocessing)
AM
FML
FM Stereo
AUTOSTD_CTRL (8Ah)
AUTOSTD_STANDARD_DETECT (8Bh)
AUTOSTD_STEREO_DETECT (8Ch)
AUTOSTD_STATUS (8Eh)
DEMOD_STAT(0Dh)
ZWT_STAT (42h)
NICAM_STAT(3Fh)
CAROFFSET1 (22h)
CAROFFSET2 (3Ah)
Channel 1 = Mono Left
Channel 2 = Stereo/Mono Right
AGC_CTRL (0Eh)
AGC_GAIN (0Fh)
(To Sound Preprocessing)
(To Sound Preprocessing)
AGC
Amp
AUTOSTD_TIMERS (8Dh)
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