Return-to-zero

For other uses, seeReturn to Zero (disambiguation).

The binary signal is encoded using rectangularpulse-amplitude modulationwith polar return-to-zero code

Return-to-zero(RZorRTZ) describes aline codeused intelecommunicationssignalsin which the signal drops (returns) to zero between eachpulse.This takes place even if a number of consecutive 0s or 1s occur in the signal. The signal isself-clocking.This means that a separate clock does not need to be sent alongside the signal, but suffers from using twice the bandwidth to achieve the same data-rate as compared tonon-return-to-zeroformat.

The "zero" between each bit is a neutral or rest condition, such as a zero amplitude inpulse-amplitude modulation(PAM), zerophase shiftinphase-shift keying(PSK), or mid-frequencyinfrequency-shift keying(FSK). That "zero" condition is typically halfway between thesignificant conditionrepresenting a 1 bit and the other significant condition representing a 0 bit.

Although return-to-zero (RZ) contains a provision for synchronization, it still has aDC componentresulting in “baseline wander” during long strings of 0 or 1 bits, just like the line codenon-return-to-zero.

Return-to-zero in optical communication

Return to zero, inverted

Return-to-zero, inverted (RZI) is a method of mapping for transmission. The two-level RZI signal has apulse(shorter than aclock cycle) if the binary signal is 0, and no pulse if the binary signal is 1. It is used (with a pulse 3/16 of a bit long) by theIrDAserial infrared (SIR) physical layer specification. Required bandwidth for this kind of modulation is: BW = R(data rate).

Bipolar return-to-Zero (bipolar RZ)

Main article:bipolar encoding

For bipolar return-to-zero (bipolar RZ), a binary one is encoded as +V volts, a binary zero is encoded as −V volts, and 0 volt is used to provide padding and separation between bits.

Bipolar return-to-zero encoding is used by theARINC 429bus.

See also

Other line codes that have 3 states:

• Hybrid ternary code
• Bipolar encoding
• MLT-3 encoding
• 4B3T

Further reading

• Savard, John J. G. (2018) [2006]."Digital Magnetic Tape Recording".quadibloc.Archivedfrom the original on 2018-07-02.Retrieved2018-07-16.