Sound Processing; Analogue Sound If - Input Section; Quadrature Mixers; Phase And Am Discrimination - Daewoo DDT-21H9ZDF(21") Service Manual

Service Manual CP-099/FS
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5-6 Sound processing (CP-099FS)

5-6-1 Analogue sound IF - input section

The input pins ANA_IN1+ and ANA_IN- offer the possibility to connect sound IF sources to the MSP 341xD. The
analogue-to-digital con version of the preselected sound IF signal is done by an A/D converter, whose output is used to
control an analogue automa tic gain circuit (AGC), providing an optimal level for a wide r ange of input levels.
5-6-2 Quadr ature Mixers
The digital input coming from the integrated A/D converter may contain audio information at a frequenc y range of
theoretically 0 to 9 MHz corresponding to the selected standards. By means of two programmable quadrature mixers,
two different audio sources ; for e xample, NICAM and FM-mono, may be shifted into baseband position.

5-6-3 Phase and AM discrimination

The filtered sound IF signals are demodulated by means of the phase and amplitude discr iminator block. On the output,
the phase and amplitude is a vailab le for further processing.
AM signals are derived from the amplitude information, whereas the phase information ser ves for FM and NICAM
demodulation.

5-6-4 NICAM decoder

In case of NICAM - mode, the phase samples are decoded according the DQPSK - coding scheme. The output of this
block contains the original NICAM bitstream.

5-6-5 DSP section

All audio baseband functions are performed by digital signal processing (DSP). The DSP section controls the source
and output selection, and the signals processing.

5-6-6 Sound Mode switching

In case of NICAM transmission, the controlling software reads the bit error rate and the operation mode from the
NICAM Decoder. When the set is in "Auto detection" mode ( default mode after ATSS ) the controlling software sets
automatically the sound mode ( NICAM mono, NICAM Dual 1 or NICAM Dual 2 ) depending on the transmitted
mode.
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