4.2 Non Return to Zero
As its name implies Non Return to Zero (NRZ) encodes a signal that is always positive or negative but never zero. If the line is idle, ie: neither positive nor negative, then there is no transmission.
With NRZ the level of signal is determined by the binary digit being sent. Binary 1′s are indicated by positive voltages and binary 0′s by negative voltages.
The graphic shows NRZ in action sending the binary transmission of “11011000100″.
Inverting NRZ (NRZ-I) works by using the inversion of the voltage level to represent the binary 1. Therefore, it is the change in the voltage level rather than the actual polarity that signifies a binary 1. If the next bit is a one there will be a voltage change and if it is a zero then there will be no change.
This type of NRZ can offer some synchronisation or timing because a series of binary ones will result in a series of inversions that can be used by the receiving end to resynchronise its timer.
The graphic shows NRZ-I in action sending the binary transmission of “10110010″.
Next: 4.3 Biphase Encoding