Aaeon MAX-Q670A, Installation Manual, Page: 70 / 80

Raptor MicroATX – Installation Guide
60
Differential Transmission
For balanced or differential transmission, a pair of signal lines is
necessary for each channel. On one line, a true signal is transmitted,
while on the second one, the inverted signal is transmitted. The receiver
detects voltage difference between the inputs and switches the output
depending on which input line is more positive. As shown below, there
is additionally a ground return path.
Balanced interface circuits consist of a generator with differential
outputs and a receiver with differential inputs. Better noise
performance stems from the fact that noise is coupled into both wires of
the signal pair in much the same way and is common to both signals.
Due to the common mode rejection capability of a differential
amplifier, this noise will be rejected. Additionally, since the signal line
emits the opposite signal like the adjacent signal return line, the
emissions cancel each other. This is true in any case for crosstalk from
and to neighboring signal lines. It is also true for noise from other
sources as long as the common mode voltage does not go beyond the
common mode range of the receiver. Since ground noise is also
common to both signals, the receiver rejects this noise as well. The
twisted pair cable used in these interfaces in combination with a correct
line termination—to avoid line reflections—allows very high data rates
and a cable length of up to 1200 m.
Advantages of Differential Transmission
Differential data transmission schemes are less susceptible to common-
mode noise than single-ended schemes. Because this kind of
transmission uses two wires with opposite current and voltage swings
compared to only one wire for single-ended, any external noise is
coupled onto the two wires as a common mode voltage and is rejected
by the receivers. This two-wire approach with opposite current and
voltage swings also radiates less electro-magnetic interference (EMI)
noise than single-ended signals due to the canceling of magnetic fields.