Non return-to-zero-level (NRZ-L): Non return-to-zero-level (NRZ-L) is a data encoding scheme in which a negative voltage is used to represent binary one and a positive voltage is used to represent binary zero.

NRZ-L appears as raw binary bits without any coding. Here typically binary 1 maps to logic-level high, and binary 0 maps to logic-level low. Inverse logic mapping is also a type of NRZ(L) code. NRZ-L is also classified as Polar NRZ-L or Non-polar NRZL.

Polar NRZ-L: In Polar NRZ-L type of Polar signaling, a High in data is represented by a positive pulse, while a Low in data is represented by a negative pulse.

Major disadvantage of this data encoding approach is:

• Presence of low frequencies may cause drop in the signal waveforms.
• No error correction is done.
• Long string of ones and zeros lead to loss of synchronization between clocks of transmitter and receiver.