MSP3410D datasheet(12/83 Pages) MICRONAS

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MSP 34x0D

PRELIMINARY DATA SHEET

Micronas

4.1.4. Phase and AM Discrimination

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.

4.1.5. Differentiators

FM demodulation is completed by differentiating the

phase information output.

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.

4.1.7. 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.

4.1.8. FM Carrier Mute Function

in the Dual-Carrier FM Mode

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.

4.1.9. 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.

4.1.10. 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).

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

CCU instructions in case of bad NICAM reception.

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