Datasheet

Data Sheet ADA4940-1/ADA4940-2
Rev. C | Page 21 of 32
TERMINOLOGY
DEFINITION OF TERMS
ADA4840-1/
ADA4940-2
R
L, dm
V
OUT, dm
R
F
R
F
R
G
R
G
+FB
+IN
+OUT
–OUT
–
+
+D
IN
+V
OCM
–D
IN
–FB
–IN
08452-090
Figure 61. Circuit Definitions
Differential Voltage
Differential voltage refers to the difference between two node
voltages. For example, the differential output voltage (or
equivalently, output differential mode voltage) is defined as
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.
Similarly, the differential input voltage is defined as
V
IN, dm
= (+D
IN
− (−D
IN
))
Common-Mode Voltage (CMV)
CMV refers to the average of two node voltages. The output
common-mode voltage is defined as
V
OUT, cm
= (V
+OUT
+ V
−OUT
)/2
Similarly, the input common-mode voltage is defined as
V
IN, cm
= (+D
IN
+ (−D
IN
))/2
Common-Mode Offset Voltage
The common-mode offset voltage is defined as the difference
between the voltage applied to the V
OCM
terminal and the
common mode of the output voltage.
V
OS, cm
= V
OUT, cm
− V
OCM
Differential V
OS
, Differential CMRR, and V
OCM
CMRR
The differential mode and common-mode voltages each have
their own error sources. The differential offset (V
OS, dm
) is the
voltage error between the +IN and −IN terminals of the amplifier.
Differential CMRR reflects the change of V
OS, dm
in response to
changes to the common-mode voltage at the input terminals
+D
IN
and −D
IN
.
dmOS,
cmIN,
DIFF
ΔV
ΔV
CMRR =
V
OCM
CMRR reflects the change of V
OS, dm
in response to
changes to the common-mode voltage at the output terminals.
dmOS,
OCM
V
ΔV
ΔV
CMRR
OCM
=
Balance
Balance is a measure of how well the differential signals are
matched in amplitude; the differential signals are exactly 180°
apart in phase. By this definition, the output balance is the
magnitude of the output common-mode voltage divided by
the magnitude of the output differential mode voltage.
dmOUT
cm
OUT
V
V
ErrorBalanceOutput
,
,
=