3020-dda.ib.rev0.doc
Page 7 of 17
09/03/2006
Characteristics of signal types
Definition of CMI
CMI is a 2-level non-return-to-zero code in which binary 0 is coded so that both amplitude levels, A
1
and A
2
, are
attained consecutively, each for half a unit time interval (T/2).
Binary 1 is coded by either of the amplitude levels A
1
or A
2
, for one full unit time interval (T), in such a way that
the level alternates for successive binary 1s.
An example is given in Figure A.1.
NOTE 1 – For binary 0, there is always a positive transition at the midpoint of the binary unit time
interval.
NOTE 2 – For binary 1:
a) there is a positive transition at the start of the binary unit time interval if in the preceding time interval
the level was
A
1
;
b) there is a negative transition at the start of the binary unit time interval if the last binary 1 was encoded
by level
A
2
.
Level A
1
Level A
1
Binary
0
1
0
0
1
1
1
T
T
T
2
T
2
Example of CMI coded binary signal
IRT
Communications
www.irtcommunications.com
