NRZ (Non-Return-to-Zero)
NRZ (Non-Return-to-Zero) is a binary signaling method used in digital communication where the signal maintains a constant voltage level throughout the duration of each bit. Introduced in the mid-20th century, NRZ became a standard for data transmission due to its simplicity and ease of implementation. In this scheme, logical “1” and “0” are represented by two distinct voltage levels, typically high and low, without returning to a baseline (zero voltage) between bits. This approach enables efficient use of bandwidth and is widely utilized in early serial communication protocols and physical layer interfaces.
https://en.wikipedia.org/wiki/Non-return-to-zero
A primary advantage of NRZ is its efficiency in encoding data, as it does not require additional transitions or overhead, making it suitable for high-speed data transmission over short distances. However, NRZ is susceptible to issues like clock synchronization and signal degradation, particularly over long distances or at higher frequencies. These limitations arise because NRZ lacks inherent mechanisms for distinguishing bit boundaries when long strings of identical bits are transmitted, leading to potential loss of synchronization between sender and receiver.
https://www.techopedia.com/definition/24865/non-return-to-zero-nrz
As data rates increased in modern communication systems, NRZ began to be replaced by more advanced signaling methods, such as PAM4 (Pulse Amplitude Modulation with 4 levels), which doubles the data capacity by encoding two bits per signal cycle. NRZ remains foundational in understanding digital communication and is still employed in legacy systems and certain low-speed applications. Its simplicity and historical significance make it a key concept in the evolution of data encoding techniques.
https://www.eetimes.com/nrz-versus-pam4-in-high-speed-interfaces/