Panasonic EURO 4 Chassis, Техническое руководство

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3DQDVRQLF
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When Wagner stereo, which is a 2 carrier system, is
transmitted
an identification signal is also
transmitted along with the second sound carrier.
This identification signal which is a 54.7KHz
amplitude
modulated pilot signal carrier is
suppressed so that only the modulated
characteristic frequencies are made available for
further processing.
Operating mode Characteristic Frequency
Mono un-modulated
Stereo 117.5Hz
Dual Tone 274.1Hz
These characteristic frequencies are fed to the
signal identification circuit, here the type of signal
transmission
is identified, with the following
switching being made available :
1. F.M. - Stereo transmission
2. Dual tone transmission (where available)
3. F.M. - Mono
This identification signal is also used to inform the
microprocessor
IC1101 as to which of the above
three modes is being transmitted, this information
being fed via I
2
C bus 1. The microprocessor IC1101
then uses this information to trigger the required
switching and OSD display for user information.
When NICAM / FM or Wagner stereo I.F. sound
signals are input to the MSP
IC2101 , the signals are
firstly fed via an analogue AGC circuit. This AGC
circuit is used to provide an optimum signal level for
a wide range of input levels. This AGC circuit can
also be set to a fixed input range. To provide the
optimum level the input range of the A/D converter
should be completely covered by the sound source.
From the output of the AGC circuit the SIF signal is
then fed to an A/D converter, here the signal is
converted to digital. From the output of the A/D
converter the signal processing splits into two paths.
1. SIF channel 1
SIF channel 1 is used to process NICAM or FM2
this being sound carrier 2 of the FM stereo
system.
2. SIF channel 2
SIF channel 2 is used to process FM mono or
FM1 again this being sound carrier 1 of the FM
stereo system.
20.2.2.Clock Generator
To aid processing an external crystal is connected to
pins 51, 52 of the MSP3410
IC2101 this provides the
required audio clock frequency for audio processing.
For Nicam / F.M. Mono processing the MSP3410
IC2101 requires a clock frequency of 18.432MHz
which it uses to lock to the sampling rate of the
NICAM signal.
When processing FM-stereo the system clock runs
free on the crystal’s 18.432MHz signal.
20.2.3.Demodulation Stage
The digitised I.F. sound signals fed from the A/D
converter are then fed to two Quadrature mixer
circuits. By means of the two programmable
quadrature mixers two different audio signals e.g.
Nicam and FM-mono signals can be input. This
audio information could depending on the selected
standards have a frequency range of 0 to 9MHz.
From the Quadrature mixers the signals are then fed
via a lowpass filter, these filters being programmable
make it possible to process both NICAM standards.
Control of these filters are carried out by the
microprocessor via I
2
C bus 1.
From the output of the low pass filters the signals
are then fed to the Phase and AM Discriminator
stage, from the output of this stage the FM and
Nicam processing follow different paths.
The NICAM signal is fed via the DQPSK decoder,
from the output of the decoder we now have a data
stream of 728k bits/sec which is fed to the NICAM
decoder.
For FM processing the demodulated signals are fed
to two differentiator circuits which differentiate the
phase information output from the demodulator
circuit, this completes the FM demodulation.
20.2.4.NICAM Decoder
Before any NICAM decoding can start, the
MSP3410 IC2101 must first lock to the NICAM
frame structure by searching and synchronizing to
the Frame Alignment Word (FAW).
To reconstruct the original digital sound samples, the
NICAM
- bitstream has to be descrambled,
deinterleaved and rescaled, as well as performing bit
error detection and correction all of which are carried
out in this section.