AD8138
OPERATIONAL DESCRIPTION
Common-mode voltage refers to the average of two node
voltages. The output common-mode voltage is defined as
DEFINITION OF TERMS
C
F
V
OUT, cm = (V+OUT + V−OUT)/2
R
F
R
Balance is a measure of how well differential signals are
matched in amplitude and exactly 180° apart in phase. Balance
is most easily determined by placing a well-matched resistor
divider between the differential voltage nodes and comparing
the magnitude of the signal at the divider’s midpoint with the
magnitude of the differential signal (see Figure 41). By this
definition, output balance is the magnitude of the output
common-mode voltage divided by the magnitude of the output
differential mode voltage:
G
G
+IN
–IN
–OUT
+OUT
+D
IN
V
R
V
OUT, dm
OCM
AD8138
L, dm
–D
IN
R
R
C
F
F
Figure 42. Circuit Definitions
Differential voltage refers to the difference between two node
voltages. For example, the output differential voltage (or
equivalently output differential-mode voltage) is defined as
VOUT, cm
Output Balance Error =
VOUT, dm
V
OUT, dm = (V+OUT − V−OUT)
where V+OUT and V−OUT refer to the voltages at the +OUT and
−OUT terminals with respect to a common reference.
Rev. F | Page 16 of 24
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