Full Form of AMI:
Alternate Mark Inversion
AMI Full Form is Alternate Mark Inversion. Alternate Mark Inversion (AMI), also called as bipolar signaling, is a synchronous clock encoding technique that uses voltages of alternating polarity to represent logical values. The signal uses 3 voltage levels +V, 0, -V to represent binary symbols. The zeros are unipolar i.e. represented by nonappearance of a pulse while ‘1’s are represented by pulses / voltages of alternate polarity.
Thus, a binary code 101 will be represented as +V, 0, -V on the bipolar signal. The signal occupies lesser bandwidth than unipolar signals. Because there are actually three signal states, one bit per signal, it is sometimes referred to as a pseudo-ternary line code. There are a balanced positive and negative polarity signals in AMI. Hence, this line code is DC balanced and so the signal can be transmitted on an AC line as well. This signal is pseudo self-clocking.
As long as there are an adequate number of one-bits in the stream, the code is self-clocking due to ample of signal transitions. The only drawback of this signal is that a long series of zeroes cannot be distinguished from a failed circuit.The popularly used HDB3 code is a bipolar signaling technique. Such signals are also term as duobinary signals.