Digital Signal Encoding Format

Nonreturn to Zero-Level (NRZ-L)

Two different voltages for 0 and 1 bits

Voltage constant during bit interval

• 0 = high level

• 1 = low level

Nonreturn to Zero Inverted (NRZI)

• Binary ‘1’ → Transition

  • The single changes state (from high to low or low to high)

  • This inversion indicates a binary 1

• Binary ‘0’ → No Transition

  • The signal remains the same as the previous bit

  • No change in voltage level means a binary 0

Bipolar - AMI

• 0: no line signal

• 1: positive or negative pulse

• pulses for 1’s alternate in polarity

• No loss of sync if a long string of ones (zeros still a problem)

• No net dc component 

• Lower bandwidth

• Easy error detection

Pseudo-ternary

• 1: absence of line signal

• 0: alternating positive and negative

• No advantage or disadvantage over bipolar-AMI

Manchester Encoding

• has transition in middle of each bit period

• transition serves as clock and data

• low to high represents 1

• high to low represents 0

• used by IEEE 802.3 (Ethernet)

Differential Manchester

• Midbit transition is clocking only

• 0: transition at start of a bit period

• 1: no transition at start of a bit period

• Used by IEEE 802.5 (Token Ring)