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alternate mark inversion (AMI)

The AMI coding, Alternate Mark Inversion (AMI), is a bipolarline coding. It is a pseudo-ternary method developed from Non Return to Zero (NRZ): two binary states are represented by three potentials: 0, +1 and -1. The binary 0 is coded as 0, the first binary 1 has a level of +1 and the following binary 1 one of -1, the next one again has a 1 and so on. The duration of the state is 50% of the clock time, and for the remaining 50% the level is pulled to zero.

In this procedure, two signals with the same polarity must never follow each other. This has the advantage of producing a DC-free digital signal. AMI coding is used, among other things, with DS-1 and is applied in modified form with ISDN at the S0 interface.

Coding according to the AMI method

Coding according to the AMI method

In the modified form of bipolar AMI coding, the binary state 1 is represented by the signal level 0 volts, the binary state 0 is assigned either a negative or a positive signal polarity, whereby the polarity changes between two successive 0 signals. The first 0 is always assigned a negative level. Two consecutive binary zeros are represented by an alternating signal of positive and negative level or vice versa. This code makes it possible to transmit any bit sequence without DC components.

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Englisch: alternate mark inversion - AMI
Updated at: 01.04.2015
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