THS4140 Datasheet, PDF (17/24 Pages) Texas Instruments – HIGH SPEED FULLY DIFFERENTIAL I/O AMPLIFIERS

THS4140, THS4141
HIGHĆSPEED FULLY DIFFERENTIAL I/O AMPLIFIERS
SLOS320E − MAY 2000 − REVISED JANUARY 2004
PRINCIPLES OF OPERATION
theory of operation (continued)
VIN−
VIN+
VCC+
_
+
_
+
VO+
VO−
a
+1
0
+1
VOD= 1−0 = 1
VOCM
VCC−
0
b
VOD = 0−1 = −1
Figure 31. Fully Differential Amplifier With Two 1-V_PP 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. The following schematic depicts the general format of
instrumentation amplifiers.
The general transfer function for this circuit is:
ǒ Ǔ ^VOD
VIN1 – VIN2
+
Rf
R(g)
1
)
2R2
R1
VIN1
THS4012
+
R(g)
Rf
_
R2
_
R1
+
THS414x
R2
_
VIN2
+ _{THS4012 R(g)}
Rf
Figure 32. Instrumentation Amplifier
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