Daewoo DUB-2850GB Service Manual page 54

CP-780 Service Manual
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.
FM AND AM DEMODULATION
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 output signal of the first demodulator can be used for further demodulation of multiplex
signals used in the BTSC, EIAJ and FM Radio standards.
FM IDENTIFICATION
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/AM DECODING
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.
FM PILOT CARRIER PRESENT DETECTOR
The TV Sound Processor provides FM A2 standard pilot carrier detection.
NICAM DEMODULATION
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.
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