Chapter 1 Line Code Encoder

Chapter 1 Line Code Encoder

1-1: Curriculum Objectives

1. 2. 3. 4. 5.

To understand the theory and applica tions of line code enc encoder. To understand understand the the encode theory theory and and circuit circuit structu structure re of NRZ. NRZ. To understand understand the the encode theory theory and and circuit circuit structu structure re of RZ. RZ. To understand understand the the encode theory theory and and circuit circuit structu structure re of AMI. AMI. To understand the enc ode theory and circ uit structure of Manchester. er.

1-2: Curriculum Theory Line codin is a part of source codin. !efore "#M sinal send to $odulator% &e use certain sinal $ode in certain application. The considerations of selectin the diital sinal $odes to carry the 'inary data are( 1. types of $odulation% 2. types of de$odulation% 3. the li$itation of 'and&idth% and 4 types of recei)er. Line codin can 'e di)ided into t&o types% &hich are return*to*+ero return*to*+ero ,RZ- and nonreturn*to*+ero ,NRZ-. RZ line codin denotes for a sinle 'it ti$e ,nor$ally is half of a sinle sinle 'it ti$e-% ti$e-% the the &a)efor$ &a)efor$ &ill &ill return return to  / 'et&e 'et &e en da ta pu lse s.

 The data strea$ is sho&n in fiure 1*1,c-. NRZ line codin denotes for a sinle sinle 'it ti$e% the &a)efor$ & ill not return to  /. The data strea$ is sho&n in fiure 1*1,a-. As

a result of the characteristics of sinal% line codin also can 'e di)ided into t&o types% &hich are unipolar sinal and 'ipolar sinal. 0nipolar sinal denotes that the sinal a$plitude )aries 'et&een a positi)e )oltae le)el &hich are / and  /. The only different 'et&een 'ipolar sinal and unipolar sinal is the sinal a$plitude )aries  'et&ee n a positi)e and a neati)e )oltae le)el &hich are / and */. iure 1*1 sho&s different types of line code sinals and &e &ill discuss the encodin sinals in net section.

1. 0nipolar Nonreturn*to*+ero inal ncode The data strea$ of unipolar nonreturn*to*+ero ,0NI*NRZ- is sho&n in fuure 1*1,a-. ro$ fiure 1*1,a-% &hen the data 'it is 6 17% the &idth and the ap 'et&een 'its of 0NI*NRZ are e8ual to each others9 &hen the data 'it is 67% then the pulse is represented as /. The circuit diara$ of 0NI*NRZ encoder is sho&n in fiure 1*2. As a result of the data sinal and the NRZ encoder sinal are si$ilar% therefore% &e only need to add a 'uffer in front of the circuit.

iure 1*2 #ircuit diara$ of unipolar nonreturn*to*+ero encoder. 2. !ipolar Nonreturn*to*+ero inal ncode The data strea$ of 'ipolar nonreturn*to*+ero ,!I"*NRZ- is sho&n in fiu re 1* 1,'-. :hen the data 'it of !I"*NRZ is ;1; or ;;% the sinal a$plitude &ill 'e a positi)e or a neati)e )oltae le)el. As for 'it ti$e% no $atter the data 'it is ;1; or ;;% the )oltae le)el re$ain sa$e. iure 1*3 is the circuit diara$ of !I"*NRZ encoder. !y co$parin the data strea$s of 0NI*NRZ a !I" *NRZ% the onl y difference is the sinal a$plitude is a nea ti)e )oltae le )el &hen th e data 'it is ; ;% therefore% &e $ay utili+e a co$parator to encode the data 'it in the circuit.

3. 0nipolar Return*to*+ero inal ncode  The data strea$ of unipolar return*to*+ero ,0NI*RZ- is sho&n in fiure 1*1,c-. :hen the d ata ' it is ; 1;% t he si nal a$plitu de a t 1 sinal. The circuit diara$ of unipolar return*to *+ero encoder is sho&n in fiure 1*4.

iure 1*3 #ircuit diara$ of 'ipolar nonreturn*to*+ero encoder.

iure 1*4 #ircuit diara$ of unipolar return*to*+ero encoder.

4. !ipolar Return*to*+ero inal ncode The data strea$ of 'ipolar return*to*+ero ,!1"*RZ- is sho&n in fiure 1 *1, d-. :hen the data 'it is ;1;% the sinal a$plitude at 1 In)ersion inal ncode Alternate $ar> in)ersion ,AMI- sinal is si$ilar to RZ sinal ecept the al ternate ;1 ; in)erte d. The data strea$ o f AMI sinal is sho& n in fiure 1*1,f-. :hen the data 'it is ;1;% the first sinal a$plitude at 1 sinal% then pass throuh a di)ider circuit 'y utili+in cloc> as s&itch echane. The final sinal is the AMI sinal. The $ini$u$  'a nd&idth of AMI is less than 0NI*RZ and !I"*RZ. An additio nal ad)antae of AMI is the trans$ission errors can 'e detec ted 'y detectin the )iolations of the alternate*one rule.

iure 1*@ #ircuit diara$ of AMI sinal encoder.

@. Manchester inal ncode

Manchester sinal is also >no&n as split*phase sinal. The data strea$ of Manchester  sinal is sho&n in fiure 1*1,e-. :hen the data 'it is ;1;% the sinal a$plitude at first 1 sinal. iure 1*C is the circuit diara$ of Manchester sinal encoder.

iure 1*C #ircuit diara$ of Manchester sinal encoder.

1-3 : Experiment tems Experiment 1: !nipolar and bipolar "#$ si%nal encode Experiment 1-1: !nipolar "#$ si%nal encode

1. To i$ple$ent a unipolar NRZ encode circuit as sho&n in fiure 1*2 or refer to fiure ?#T1*1 on DTT ?#T*@*1 $odule. 2. ettin the fre8uency of function enerator to 1 >=+ TTL sinal and connect this sinal to the ?ata I=+

2.5 >=+

7.5 kHz

4 >=+

utput inal :a)efor$s

#LE I