Return to Zero (RZ):
Transitions are required by receivers clock to maintain synchronization.
In RZ encoding technique a signal change (transition) for each bit is assured.
But to change with every bit, we need more than just two values.
And here RZ uses three values : positive, negative and zero.
In RZ, the signal changes not between bits but during each bit.
Like NRZóL, a positive voltage means 1 and a negative voltage means 0.
But, unlike NRZóL, halfway through each bit interval, the signal returns to zero.
A 1 bit is actually represented by positive to zero and a 0 bit by negative to zero, rather than by positive and negative alone.
See the bellow figure
The main disadvantage of RZ encoding is that it requires two signal changes to encode one bit and therefore occupies more bandwidth.
The main disadvantage of RZ encoding is that it requires two signal changes to encode one bit and therefore occupies more bandwidth.