MSP 34x0D
PRELIMINARY DATA SHEET
4.1.4. Phase and AM Discrimination
4.1.8. FM Carrier Mute Function
in the Dual-Carrier FM Mode
The filtered sound IF signals are demodulated by
means of the phase and amplitude discriminator block.
On the output, the phase and amplitude is available for
further processing. AM signals are derived from the
amplitude information, whereas the phase information
serves for FM and NICAM (DQPSK) demodulation.
To prevent noise effects or FM identification problems
in the absence of one of the two FM carriers, the
MSP 34x0D offers a carrier detection feature, which
must be activated by means of AD_CV[9]. If no FM
carrier is available at the MSPD channel 1, the corre-
sponding channel FM2 is muted. If no FM carrier is
available at the MSPD channel 2, the corresponding
channel FM1 is muted.
4.1.5. Differentiators
FM demodulation is completed by differentiating the
phase information output.
4.1.9. DQPSK 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 bit-
stream.
4.1.6. Low-pass Filter Block
for Demodulated Signals
The demodulated FM and AM signals are further low-
pass filtered and decimated to a final sampling fre-
quency of 32 kHz. The usable bandwidth of the final
baseband signals is about 15 kHz.
4.1.10. NICAM Decoder
Before any NICAM decoding can start, the MSP must
lock to the NICAM frame structure by searching and
synchronizing to the so-called frame alignment words
(FAW).
4.1.7. High-Deviation FM Mode
By means of MODE_REG [9], the maximum FM devi-
ation can be extended to approximately ±360 kHz.
Since this mode can be applied only for the MSP
sound IF channel 2, the corresponding matrices in the
baseband processing must be set to sound A. Apart
from this, the coefficient sets 380 kHz FIR2 or 500 kHz
FIR2 must be chosen for the FIR2. In relation to the
normal FM mode, the audio level of the high-deviation
mode is reduced by 6 dB. The FM prescaler should be
adjusted accordingly. In high-deviation FM mode, nei-
ther FM-Stereo nor FM identification nor NICAM pro-
cessing is possible simultaneously.
To reconstruct the original digital sound samples, the
NICAM bitstream has to be descrambled, deinter-
leaved, and rescaled. Also, bit-error detection and cor-
rection (concealment) is performed in this block.
To facilitate the Central Control Unit CCU to switch the
(e.g.) TV set to the actual sound mode, control infor-
mation on the NICAM mode and bit error rate are sup-
plied by the NICAM decoder. It can be read out via the
I2C bus.
An automatic switching facility (AUTO_FM) between
NICAM and FM/AM reduces the amount of
CCU instructions in case of bad NICAM reception.
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Micronas
MICRONAS [ MICRONAS ]
