Bipolar encoding

The AMI code (Alternate Mark Inversion ) is a pseudoternary line code to transmit data.

Ternary means that this code, three signal values ​​( -, 0, ) may be used to encode the two states of a bit. A logic 0 is transmitted as a physical 0, a 1 alternately by - or . Wherein a direct current component is avoided. But with long zero sequences he has only a low clock information, so that a clock recovery is difficult for the receiver. That is why it is mostly used in this form with a scrambler. B8ZS and HDB3 are modifications of the AMI code, where use of intentional code violations, the timing information is preserved.

The AMI code process was especially needed to send signals over existing transformers in the public telephone network can - so as to obtain pure alternating current, which transform you and can transmit in the existing network.

If a logic 1 is transmitted by the same state as the previous one, it is called a code violation. Through specific code violations, different frames can be separated in a frame- based transmission.

The Modified AMI code is a variant of the AMI code with the reverse assignment of bits to be encoded. The logical 1 is transmitted here as a physical 0, while the logic 0 alternately - is transmitted or . This variant is used, among other things, on the S0 bus in ISDN.

• Line code