集成电路的数字数据传输--Integrated Circuits for Digital Data Transmission
It is frequently necessary to transmit digital data in a
high-noise environment where ordinary integrated logic circuits
cannot be used because they do not have sufficient
noise immunity. One solution to this problem, of course, is to
use high-noise-immunity logic. In many cases, this approach
would require worst case logic swings of 30V, requiring high
power-supply voltages. Further, considerable power would
be needed to transmit these voltage levels at high speed.
This is especially true if the lines must be terminated to eliminate
reflections, since practical transmission lines have a
low characteristic impedance.
A much better solution is to convert the ground referred digital
data at the transmission end into a differential signal and
transmit this down a balanced, twisted-pair line. At the receiving
end, any induced noise, or voltage due to
ground-loop currents, appears equally on both ends of the
twisted-pair line. Hence, a receiver which responds only to
the differential signal from the line will reject the undesired
signals even with moderate voltage swings from the transmitter.