THS4150 Datasheet, PDF (20/27 Pages) Texas Instruments – HIGH-SPEED DIFFERENTIAL I/O AMPLIFIERS

THS4150, THS4151
HIGHĆSPEED DIFFERENTIAL I/O AMPLIFIERS
SLOS321D − MAY 2000 − REVISED JANUARY 2004
PRINCIPLES OF OPERATION
theory of operation (continued)
Figure 40 illustrates the increase in dynamic range. The gain factor should be considered in this scenario. The
THS415x fully differential amplifier offers an improved CMRR and PSRR due to its symmetrical input and output.
Furthermore, second harmonic distortion is improved. Second harmonics tend to cancel because of the
symmetrical output.
VIN−
VIN+
VCC+
_
+
_
+
VO+
VO−
a
+1
0
+1
VOD= 1−0 = 1
VOCM
VCC−
0
b
VOD = 0−1 = −1
Figure 40. 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
+
THS415x
R2
_
VIN2
+
THS4012
R(g)
Rf
Figure 41. Fully Differential Instrumentation Amplifier
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