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| THS4140 Datasheet, PDF (17/33 Pages) Texas Instruments – HIGH SPEED FULLY DIFFERENTIAL I/O AMPLIFIERS | |||
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THS4140
THS4141
SLOS320F â MAY 2000 â REVISED JANUARY 2006
PRINCIPLES OF OPERATION (continued)
VIN-
VIN+
VCC+
_
+
_
+
a
+1
VO+
0
VO-
+1
VOD= 1-0 = 1
VOCM
VCC-
0
b
VOD = 0-1 = -1
Figure 31. Fully Differential Amplifier With Two 1-VPP Signals
Similar to the standard inverting amplifier configuration, input impedance of a fully differential amplifier is
selected by the input resistor, R(g). If input impedance is a constraint in design, the designer may choose to
implement the differential amplifier as an instrumentation amplifier. This configuration improves the input
impedance of the fully differential amplifier. Figure 32 depicts the general format of instrumentation amplifiers.
The general transfer function for this circuit is:
Ç Ç VOD
VIN1 â VIN2
+
Rf
R(g)
1
)
2R2
R1
(12)
VIN1
THS4012
+
R(g)
Rf
_
R2
_
R1
+
THS414x
R2
_
VIN2
+ THS4012
R(g)
Rf
Figure 32. Instrumentation Amplifier
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