B&B Electronics 4 Channel Input Buffer Board SDAIBB User Manual
Page 13
SDAIBB1300 Manual
11
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104
Maximum Gain
The maximum gain for a known differential voltage and common
mode voltage can easily be determined using the following set of equations.
Equation 5 calculates the maximum gain based on the positive internal rail
of the amplifier. Equation 6 gives the maximum gain based on the negative
internal rail of the amplifier. Equation 7 calculates the maximum gain
without overflowing the output range of the SDAIBB. The smallest
maximum gain value calculated using these equations is the maximum gain
that may be used.
G is the gain, V
cm
is the common mode voltage, and V
diff
is the
differential voltage.
Equation 2:
(
)
DIFF
CM
MAX
V
V
V
G
−
=
4
.
4
2
Equation 3:
(
)
DIFF
cm
V
V
V
G
59
.
0
2
max
+
=
Equation 4:
InputRange
V
G
MAX
94
.
4
=
Equation 5
(
MAX
Gain
=
4
2
Equation 6
(
c
V
Gain
2
max
=
Equation 7
Gain
MAX
94
.
4
=
Example: Find the maximum allowable gain for a differential voltage of
±10 mV and a common mode voltage of 2.5 V.
From Equation 5:
(
)
380
01
.
0
5
.
2
4
.
4
2
=
−
=
MAX
G
From Equation 6:
(
)
618
01
.
0
59
.
0
5
.
2
2
max
=
+
=
G
From Equation 7:
247
02
.
0
94
.
4
=
=
MAX
G
The minimum value calculated is 247, so the maximum allowable gain is
247.