Daewoo DTL-2950K, Руководство по обслуживанию

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CP-650 Service Manual
DTV R&D Europe 47
output signal of the first demodulator can be used for further demodulation of multiplex signals
used in the BTSC, EIAJ and FM Radio standards.
FMIDENTIFICATION
The identification of the FM sound mode is performed by AM synchronous demodulation of the
pilot signal and narrow-band detection of the identification frequencies. The result is available via
the control bus interface. A selection can be made for three different modes that represent
different trade-offs between speed and reliability of identification. The mode is set by DDEP (for
FM two-carrier standards) or via expert mode. DDEP also performs automatic FM de-matrix
control in dependence on the identification.
FM/AMDECODING
A high-pass filter suppresses DC offsets from the FM/AM demodulators due to carrier frequency
offsets and supplies the monitor/peak function with DC values and an un-filtered signal, e.g. for
the purpose of carrier detection.
The audio bandwidth is approx. 15 kHz.
The de-emphasis function offers fixed settings for the supported standards (50s, 60s, 75s and
J17).
A matrix performs the de-matrixing of the A2 stereo, dual and mono signals to obtain the left (L)
and right (R) or language A and B signals.
FMPILOTCARRIERPRESENTDETECTOR
The TV Sound Processor provides FM A2 standard pilot carrier detection.
NICAMDEMODULATION
The NICAM signal is transmitted via DQPSK modulation at a bit rate of 728kBit/s. The NICAM
demodulator performs DQPSK demodulation and feeds the resulting bit stream and clock signal
to the NICAM decoder.
A timing loop controls the sample rate conversion circuitry to lock the sampling rate to the symbol
timing of the NICAM data.
NICAM DECODER
The NICAM decoder performs all decoding functions in accordance with theEBU NICAM 728
specification. After locking to the frame alignment word, the data is de scrambled by applying the
defined pseudo-random binary sequence; the NICAM decoder will then synchronize to the
periodic frame flag bitC0.
The status of the NICAM decoder can be read out from the NICAM status register by the user
(see the control-bus register description). The OSB bit indicates that the decoder has locked to
the NICAM data. The VDSP bit indicates that the decoder has locked to the NICAM data and that
the data is valid sound data. The C4 bit indicates that the sound conveyed by the FM mono
channel is identical to the sound conveyed by the NICAM channel. The error byte contains the