Ternary data transmission system

DETAILED DESCRIPTION According to the invention, direct current wander of a duobinary data signal is compensated for by subtracting the data signal from a delayed version thereof to derive a ternary change representative signal, which exhibits substantially no direct current wander.
The direct current wander is in effect cancelled by the subtraction, while the information content of the data signal is preserved, albeit in a different form.
Specifically, a source of a data signal in ternary form has a high level, a low level, and an intermediate level.
The high and low levels represent a first binary value, and the intermediate level represents a second binary value.
The data signal follows an encoding rule in which the data signal assumes different levels for successive occurrences of the first binary value separated by an odd number of bit time periods and assumes the same level for successive occurrences of the first binary value separated by zero or an even number of bit time periods.
The data signal has a bit time period equal to the minimum duration of each level.
The data signal source is connected to a remote point by a transmission line.
The coupling transformer network at the input to the transmission line has a high pass characteristic.
The data signal received at the remote point is subtracted from a delayed version thereof to derive the change representative signal, which is utilized at the remote point to regenerate and/or detect code violations of the data signal.
Preferably, the received data signal is subtracted from a version thereof delayed by one bit time period.
A feature of the invention is circuitry for detecting violations of the encoding rule by utilizing the change representative signal.
Specifically, an indication of a violation is generated when, after assuming one extreme level, i.
e.
high or low, in a given bit time period, the change representative signal again assumes the same level before assuming the other extreme level during a bit time period separated by an odd number of bit time periods from the given bit time period