RZ vs NRZ vs Manchester Code: Digital Signal Encoding Explained

Digital signals often consist of sequential binary information in the form of zeros and ones. Each of these binary digits is represented by a pulse width, which varies depending on the transmission data rate requirements.

There are three common signal types used in digital transmission of binary information: NRZ, RZ, and Manchester codes. Let’s explore the basics of each and highlight the key differences.

NRZ - Non-Return to Zero

In NRZ (Non-Return to Zero) encoding, binary digits switch between a High (H) and Low (L) value, and the signal does not return to a ground or DC potential in between bits.

Let’s assume ‘H’ represents a High voltage level and ‘L’ represents a Low voltage level.

NRZ waveforms can be further categorized into two types:

• Unipolar: Both H and L values are either above zero or below zero potential.
• Bipolar: Binary digits are represented by voltages both above and below zero potential.

The bit time, $T_b$, is the duration for which a single digit of data remains either low or high. Therefore, the pulse width, $T_p$, is equal to $T_b$, where $T_b$ is the bit period. Mathematically:

$T_p = T_b$

RZ - Return to Zero

In RZ (Return to Zero) encoding, the signal returns to zero or ground potential after every binary digit. This is the key difference from NRZ.

Consequently, the pulse width is half of the binary digit bit period. Mathematically:

$T_p = \frac{T_b}{2}$

Manchester Code

In Manchester coding, transitions or edges are sensed, and the direction of these transitions determines the value of the digital data.

• A transition from Low (L) to High (H) typically represents a zero ( ‘0’).
• A transition from High (H) to Low (L) typically represents a one (‘1’).

For more details, refer to Manchester vs. Differential Manchester encoding.

Comparison

The RZ and NRZ line coding methods are used in digital communication and optical Duobinary transmission systems.