MC92314 데이터 시트보기 (PDF) - Motorola => Freescale

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MC92314

DVB-T Single Chip Demodulator Application Note

Motorola => Freescale 

Freescale Semiconductor, Inc.

System Overview

formation Figure 1-1. Possible echo constellation

y In In the well known analog TV transmission systems such echoes appear as ghost pictures on the

r screen, but as long as they don’t get too strong the original information remains visible, at the

a penalty of reduced picture quality.

in 1.2.2 Noise

lim Another impairment on every transmission channel is the addition of noise. Due to many reasons

e (e.g. thermal noise, impulse noise from ignition sources) the signal quality degrades with

r increasing distance from the transmitter. On the analog TV picture the different noise sources

P decrease the quality of the picture, but as long as the synchronisation circuitry remains in lock

even heavily distorted pictures deliver visible information to the viewers.

1.3 Advantages of the OFDM Transmission Scheme

In contrast to this the behaviour of analog systems outlined in the paragraphs above the

behaviour of digital transmission systems is different. The picture contents are mapped into

digital signals, transmission impairments lead to transmission errors, resulting in bit errors of the

received datastream. Due to the high compression ration of the source encoded MPEG-2

transport stream used in the DVB systems even single bit errors may have a severe impact on

the picture quality. Without careful system layout, taking into account the characteristics of the

transmission channel, the performance of a digital transmission system may be very poor.

The problems mentioned above can be circumvented successfully leading to the present system

for digital terrestrial transmission. One of the main points is the Orthogonal Frequency Division

Multiplex (OFDM) scheme. The following list gives a short overview about the key features of the

DVB-T standard:

Single Chip DVB-T Demodulator - Rev. 1.3 (11/30/98)

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