In telecommunication, a paired disparity code is a line code in which at least one of the data characters is represented by two code words of opposite disparity that are used in sequence so as to minimize the total disparity of a longer sequence of digits.
The simplest example of a paired disparity code is Alternate Mark Inversion (AMI). It uses three logical levels corresponding to two bipolar levels: +,-, and zero.
A binary 0 is encoded as absence of power during the bit interval (zero voltage), while a binary 1 is encoded alternately as a positive voltage or a negative voltage. A binary 1 is referred to as a mark, while a binary 0 is known as a space.
General benefits of using a line code with bipolar encoding:
The solution is to add a binary 1 after seven binary zeros to maintain synchronization. On the decoder side, this extra symbol is removed.