--- title: "Line coding: polar RZ and bipolar AMI" subject: "Data Communication" chapter: 5 key: "semester_5/data_communication:line-coding-polar-rz-ami" source: https://www.bctengineer.com/q/semester_5/data_communication/line-coding-polar-rz-ami site: BCT Engineering --- # Line coding: polar RZ and bipolar AMI Data Communication · Chapter 5: Data Encoding and Modulation - Asked in: 2078 Kartik, 4+3+3 marks - Video: [Line Coding Techniques | RZ, NRZ, Unipolar, Polar, Bipolar & Manchester | Digital Communication](https://www.youtube.com/watch?v=daf9F9NC7zQ) — Engineering Funda - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/data_communication/line-coding-polar-rz-ami - Whole chapter: https://www.bctengineer.com/md/semester_5/data_communication/chapter-5 ## Question Define line coding. Explain polar RZ and bipolar AMI line coding schemes with example and compare them. ## Short answer Line coding converts bits to digital signals. Polar RZ: 1 = +V for half-bit then 0, 0 = -V then 0; good sync but wide bandwidth. Bipolar AMI: 0 = 0V, 1s alternate +V/-V; zero DC, error detection, but sync lost on long zeros. For 1011001: Polar RZ: +0-0+0+0-0-0+0; AMI: +0-+00-+. ## Answer **Line coding** is the process of converting a sequence of binary data (bits) into a digital signal (voltage levels) that can be sent over a medium. #### Polar RZ (Return to Zero) Uses three voltage levels. A 1 is +V and a 0 is -V for the first half of the bit; the signal then returns to 0 V for the second half. Every bit therefore has a transition, which gives self-synchronisation. It needs twice the bandwidth of NRZ. #### Bipolar AMI (Alternate Mark Inversion) A 0 is 0 V. The 1s (marks) are represented by pulses of alternating polarity (+V, -V, +V, ...). Alternating polarity gives zero DC component and a simple error check (two successive pulses of the same sign is a violation). A long string of 0s gives no transitions, so synchronisation can be lost. #### Example: 1 0 1 1 0 0 1 ```text Polar RZ 1 0 1 1 0 0 1 +V --| |-| |-| |-| 0 |-| |-| |-| |-| |-| |-| |- -V |-| |-| |-| ``` ```text Bipolar AMI 1 0 1 1 0 0 1 +V ----| |---| 0 |---| | |-------| -V |---| |--- ``` #### Comparison | Point | Polar RZ | Bipolar AMI | |---|---|---| | Levels | +V, -V, 0 | +V, -V, 0 | | Sending a 1 | +V then 0 | +V and -V alternately | | Sending a 0 | -V then 0 | 0 V | | Synchronisation | Good for both 0 and 1 | Good for 1s, poor for long 0s | | DC component | Near zero if 0s and 1s balance | Zero | | Bandwidth | Wide (2 × NRZ) | Narrower than RZ | | Error detection | No | Yes (violation) | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In polar RZ a 1 is: A. -V then 0 B. 0 V C. +V then return to 0 D. Alternating Answer: C. Return to zero. (Key point: Polar RZ) 2. AMI 1s are: A. Always +V B. 0 V C. -V only D. Alternating +V and -V Answer: D. Alternating. (Key point: AMI) 3. AMI weakness: A. Long 0s give no transitions B. No DC zero C. No error detection D. Needs 2x bandwidth Answer: A. Sync loss. (Key point: Weakness) 4. Polar RZ bandwidth: A. Half NRZ B. Twice NRZ C. Same as NRZ D. Zero Answer: B. Wide. (Key point: Bandwidth) ## Related in Data Communication - [Encode 1001101110 with unipolar, polar, bipolar codes](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-1001101110) — Data Communication, chapter 5, asked 3× - [Encode 10110001110 with unipolar, polar, bipolar codes](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-10110001110-68c) — Data Communication, chapter 5, asked 3× - [Line coding: properties; encode 01001100011](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-01001100011) — Data Communication, chapter 5 - [Encode 10101111000011 with NRZ, RZ, AMI, Manchester](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-10101111000011) — Data Communication, chapter 5 - [Encode 1101001 with polar NRZ, AMI, Manchester](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-1101001) — Data Communication, chapter 5, asked 3× - [Polar, unipolar, bipolar, Manchester; encode 101000111011](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-101000111011) — Data Communication, chapter 5 ## Related in other subjects - [Line coding 100111010 (Polar RZ, bipolar NRZ, AMI, Manchester)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-100111010) — Communication Systems, chapter 6 - [Line coding 1011001010 (polar NRZ, polar RZ, Manchester, AMI)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-1011001010) — Communication Systems, chapter 6, asked 8× - [Line coding 1001001101 (polar NRZ, polar RZ, Manchester, AMI)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-1001001101) — Communication Systems, chapter 6, asked 8× - [Line coding 1001101101 (unipolar NRZ, polar RZ, AMI, Manchester)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-1001101101) — Communication Systems, chapter 6, asked 8×