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.