Daewoo DTX-21B4, Руководство по обслуживанию

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CP-520
V
Service Manual
44
decoding is done in the DEMDEC block of the Sound DSP. The DEMDEC processing will be
described in the next chapter.
The audio signals (AUD ADC IN) from the analogue crossbar pass the audio ADC and are fed
directly into the AUDIO part of the Sound DSP like the I2S signals, which is coming from I2S
processing hardware. After level adjust all signals from the DEMDEC and the I2S input are
available at the digital input crossbar. A special input is provided for the Noise/Silence Generator
needed for olby® Pro Logic® processing.
In standard TV applications the main channel signal(L,R) will be connected to the DAC2 for
reproduction at the speakers. With multichannel signals centre, surround or subwoofer channels
may be passed to the I2S outputs where external DACs may be applied. By this it is possible to
build Dolby Normal/Wide, Dolby Phantom Centre or Dolby 3 Stereo set-ups and also a VDS423
application.
5.4.3 Demodulator and decoder
INTRODUCTION
The TV sound processor provides an easy-to-use programming interface and built-in intelligence
for the demodulator and decoder part.
The sound demodulator is able to search for sound carriers and react to transmission mode
changes autonomously, without interaction of the micro controller software.
It is possible for a typical terrestrial TV application to setup the entire demodulator with
transmission of few control words.
The control interface still allows access to every detail, called demodulator expert mode, for
special applications such as satellite TV, more elaborated search algorithms etc.
The new TV Sound ProcessorDemodulator and
DecoderEasyProgramming(DDEP)interfaceprovides three possible approaches to setup the
demodulator and decoder parts:
n
Auto Standard Detection (ASD)
n
Static Standard Selection (SSS)
n
Demodulator and Decoder Expert Mode (DDXM)
MIXER
The digitized 2nd SIF input signal is fed to the mixers, which mix one or both input sound carriers
down to zero IF. The mixer frequency is derived by the standard setting (Easy Programming) or
in the Demodulator and Decoder Expert Mode (DDXM) by a 24-bit control word for each carrier.
For NICAM demodulation, a feedback signal is added to the control word of the second carrier
mixer to establish a carrier-frequency loop.
FMANDAMDEMODULATION
An FM or AM input signal is fed via a band-limiting filter to a one of two demodulators that can be
used for either FM or AM demodulation. Four filters with different bandwidth are available. The