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Line codes
The document discusses various line coding schemes used to convert digital data into digital signals, highlighting types such as unipolar, polar, bipolar, and Manchester encoding. It explains the advantages and disadvantages of different encodings, including non-return to zero (NRZ), alternate mark inversion (AMI), and differential Manchester coding. Additionally, it addresses techniques like bipolar with zero substitution (B8ZS) and high-density bipolar (HDB3) to maintain synchronization in the presence of long sequences of zeros.
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Introduction to digital data and line codes, emphasizing the conversion of digital data into digital signals.
Explains line coding types: Unipolar (single voltage), Polar (multiple voltages), and Bipolar (three levels: +, -, 0) for binary representation.
Describes NRZ-L signaling where 0 signifies no signal and 1 signifies a signal on. It highlights benefits and synchronization issues.
Details NRZ-I signaling, where no transition represents 0 and transition indicates 1, along with advantages and disadvantages.
Details AMI signaling using three levels (+V, 0, -V) for 1s, advantages of no DC voltage and issues with long strings of 0.
Explains pseudo ternary modulation which is opposite of AMI, detailing its method and drawbacks regarding long strings of 1s.
Discusses Manchester coding with transitions in the middle of bit periods, benefits including sync maintenance and bandwidth impact.
Specifies Differential Manchester coding, providing improved reliability against noise with similar advantages as Manchester coding.
Describes B8ZS to maintain synchronization by replacing 8 continuous zeros with a new sequence, based on previous pulses.
Explains HDB3 method to avoid sync loss for long zeros, replacing sequences carefully to ensure maintaining DC balance.
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Line codes
- 1. Prof. Madhumita Tamhane DIGITALDATA – DIGITAL SIGNAL LINE CODES
- 2. Prof. Madhumita Tamhane 2 LineCodes •Line Coding is the process for converting digital data into digital signal. . •Digital data is found in binary format. •It is represented (stored) internally as series of 1s and 0s. •Digital signal is denoted by discreet signal, which represents digital data. •There are three types of line encoding schemes available: •Unipolar encoding: single voltage level to represent data. •Binary 1, high voltage •Binary 0, no voltage is transmitted. •E.g. Unipolar-Non-return-to-zero.
- 3. Prof. Madhumita Tamhane 3 LineCodes •Polar encoding: Polar encoding scheme uses multiple voltage levels to represent binary values. •E.g. polar NRZ, RZ, Manchester, Differential Manchester. •Bipolar encoding: Bipolar encoding scheme uses three voltage levels to represent binary values, positive, negative and zero. •Zero voltage represents binary 0 and bit 1 is represented by altering positive and negative voltages. •E.g. AMI,
- 4. Prof. Madhumita Tamhane Non-returnto zero-level (NRZ-L) ! ! ! ! ! • 0 = no signal • 1 = signal on • The reverse is also in use.
- 5. Prof. Madhumita Tamhane Non-returnto zero-level (NRZ-L) • Advantage: • Easy to generate. • Disadvantage: • DC component development during long strings of 0 or 1 result in “baseline wander”. • Loss of synchronization during long strings of 0 or 1, as no transition available.
- 6. Prof. Madhumita Tamhane Non-returnto zero-Invert on 1 (NRZ-I) ! ! • 0 = No transition . • 1 = Transition at beginning of interval • Can be generated by F/F in toggle mode. • Can be decoded by comparing adjacent bits. EX-OR Delay T
- 7. Prof. Madhumita Tamhane Non-returnto zero-Invert on 1 (NRZ-I) • Advantage: • No DC component during long strings of 1. • No loss of synchronization for long strings of 1. • More reliable to detect a transition in presence of noise than the level • Disadvantage: • Presence of DC component resulting in “baseline wander” during long strings of 0. • Loss of synchronization during long strings of 0 as no transition available.
- 8. Prof. Madhumita Tamhane Bipolar-AlternateMark Inversion (AMI) ! ! ! ! ! • Uses 3 signal levels: +V, 0, -V • 0 = No line signal. • 1 = alternating +V and –V on every 1. !
- 9. Prof. Madhumita Tamhane Bipolar-AlternateMark Inversion (AMI) • Advantage: • No DC voltage for long strings of 1or 0. • No loss of synchronization for long strings of 1. • Alternate +V and –V on 1 provide simple means of error detection. • Disadvantage: • Loss of synchronization during long strings of 0 as no transition available.
- 10. Prof. Madhumita Tamhane Pseudoternary ! • Opposite to AMI. • 0 = Alternating +V and –V on every 0. • 1 = No line signal. • Uses 3 signal levels: +V, 0, -V • Disadvantageous for long strings of 1.
- 11. Prof. Madhumita Tamhane ManchesterCoding ! ! ! ! ! • Always transition in middle of bit period. • 0 = low-to-high transition. • 1 = high-to-low transition. • IEEE802.3 for Ethernet follows the opposite. • 1 = low-to-high transition. • 0 = high-to-low transition. • Both have same advantages.
- 12. Prof. Madhumita Tamhane ManchesterCoding • Advantage: • No loss of sync for long strings of 0 or 1. • Transition in middle of bit period provided synchronization. • Called self clocking codes. • No DC component. • Error detection if noise hampers transition. • Disadvantage: • Bandwidth is doubled.
- 13. Prof. Madhumita Tamhane DifferentialManchester Coding ! ! ! ! • Always transition in middle of bit period. • 0 = transition at beginning of bit. • 1 = No transition at beginning of bit. • More reliable to detect a transition in presence of noise than the level as in Manchester coding. • Other advantages and disadvantages are same as Manchester coding.
- 14. Prof. Madhumita Tamhane Bipolarwith 8 – zero substitution (B8ZS)! ! ! ! • Done on AMI to avoid sync loss for long string of 0. • 8 continuous zeros replaced by new sequence. • If the immediate preceding pulse is of (-) polarity, then 8 zeros replaced as 000 - + 0 + - . • If the immediate preceding pulse is of (z) polarity, then 8 zeros replaced as 000 + - 0 - + . • Violation indicates presence of replacement.
- 15. Prof. Madhumita Tamhane HighDensity Bipolar – 3 zeros ( HDB3) • Done on AMI to avoid sync loss for long string of 0. • 4 continuous zeros replaced by new sequence. • Successive violation should be of alternating polarity for no additional DC. • Violations should be self balancing. Preceding pulse No of 1’s since last substitution ODD EVEN - ve 0 0 0 - + 0 0 + + ve 0 0 0 + - 0 0 -