Motorola MC92300CG Datasheet
MOTOROLA
SEMICONDUCTOR TECHNICAL DATA
Product Preview
VITERBI Decoder for Digital TV
This product preview describes a high performance device, a Viterbi Decoder, for
Digital-TV applications according to the EBU defined DVB transmission standard for
satellite and cable Set-Top systems.
Viterbi Decoder - Capability Specification
Current Information@www.mot.com/ADC
MC92300
DTVVIT
RESET_N
VC0,VC1[2:0]
VDCLK
SYMCLK
VTSTI[1:0]
BITCLK
VO
VLCK
VFF
VEF
SR[2:0]
• Operates at max. 50MBits/s output rate to work with all present DVB channels
• Implements K=7, (1718,1338) Viterbi decoder for rates 1/2, 2/3, 3/4, 5/6 and 7/8
with a survivor depth of 96
• Code rate and synchronization control programmable via I2C standard serial bus
• Automatic rate selection and signal quality output (qval)
• Full/empty flag generation of input FIFO for system monitoring of VDCLK/BITCLK
ratio
• Simplified system design with internal PLL for the generation of output BITCLK
from the incoming VDCLK for all depuncturing modes
• Available in a 128QFP package
VEF
Depuncturing
Viterbi
Core
VC1[2:0]
VC2[2:0]
VFF
Synchronizer
FIFO
VDCLK
SDA
DSA[6:0]
SCL
Ordering Information
Device
MC92300CG
VO
Package
128QFP
APLL
BIT-
SYMCLK
RESET_N
VLCK
SR
QVAL
2
VTSTI[1:0]
SCL
I2C
Interface
7
DSA
SDA
CLK
Figure 1. Viterbi Decoder Block Diagram
This document contains information on a new product.
Specifications and information herein are subject to change without notice.
MOTOROLA, INC. 1997 5/28/97
Product Description
The Viterbi Decoder contains the Viterbi core logic,
which operates the K=7 convolutional code and generates
a lock indication after successful acquisition. The core
works with the main clock BITCLK, which provides the output data VO (output of the Viterbi). This clock is generated
by the integrated bit clock generator circuit and is adjusted
according to the programmed depuncturing rate.
The input to the chip are 3 bit soft decision data VC0/1
from the QPSK demodulator together with the associated
demodulator clock VDCLK. Rate adjustment in accordance
with the several depuncturing rates is achieved with the input FIFO. The data is read into the depuncturing logic with
the internally generated BITCLK.
Generator Polynomials
The Viterbi decoder is designed to decode bit streams
encoded using the DVB standard generator polynomials
(1718, 1338).
Punctured Codes
The Viterbi Decoder is able to decode a basic rate 1/2
convolutional code and the “standard” punctured codes for
a k=7 constraint length. The punctured codes are shown in
the table below. Specific bits of the original rate 1/2 code sequence are periodically deleted prior to transmission according to the entries in the table, where a 0 means that the
bit is deleted and a 1 means that the bit is transmitted.
Table 1 Deletion Map For Punctured Rate 1/2 Codes
Coding
Rate
Puncture
Map
The Viterbi block employs a method known as Syndrom
Based Node Synchronization to achieve both I & Q symbol
and punctured rate synchronization.
The theory of the Syndrom Based Node Synchronization is
based on the observation that the product of the incoming
data and a syndrom is zero if there are no errors If errors are
present in the data, the probability of 0’s and 1’s in the product increases.
The possible states that the synchronizer has to deal with
are a combination of the following factors:
1.The phasing of the received symbols.
I & Q input streams can either be processed as-is or
can be rotated 90oto account for constellation
rotation in the receiver.
2. Determination of the framing of the I and Q bit
streams so as to extract the correct symbol. There
are four possible ways to frame the two bit stream
and the synchronizer must determine the correct
one.
I2C Interface
The internal registers of the VITERBI are accessible
via the I2C interface. After reset, default values are preprogrammed, so that no more configuration is necessary.
APLL
In order to allow a simple system design, a Analogue
PLL is integrated for generation of the output Bit Clock. The
following output frequencies Ro are generated for a given
DVB transponder Bandwidth TBW respectively for a given
input symbol rate Rs.
1/2
2/3
3/4
1
1
11
10
110
101
TBW[MHz] Rs[MHz] Ro[MHz] for rates
1/2 2/3 3/4 5/6 7/8
36 38.3 28.3 37.7 42.4 47.2 49.5
33
30
27
5/6
7/8
11010
10101
1111010
1000101
26 20.5 20.5 27.3 30.7 34.2 35.9
Rs/R
o
1 4/3 3/2 5/3 7/4
Application
Synchronization
The MC92300 is used in satellite receiver implementa-
Prior to outputting valid data the Viterbi decoder block
must synchronize to the input data stream, i.e. remove any
phase ambiguity in the received symbols and determine the
punctured code rate transmitted
MOTOROLA MC92300
2 Rev.1.3
tion for DVB.
Packaging
The MC92300 is available in a 128-pin Plastic Quad
Flat Pack (128QFP) package.
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