OPA2890_08 Datasheet, PDF (20/35 Pages) Texas Instruments – Low-Power, Wideband, Voltage-Feedback OPERATIONAL AMPLIFIER with Disable

OPA2890
SBOS364B – DECEMBER 2007 – REVISED MAY 2008.................................................................................................................................................... www.ti.com
DIFFERENTIAL RECEIVER/DRIVER
A very versatile application for a dual operational
amplifier is the differential amplifier configuration
shown in Figure 56. With both amplifiers of the
OPA2890 connected for noninverting operation, the
circuit provides a high input impedance, while the
gain can easily be set by just one resistor, R_G. When
operated in low gains, the output swing may be
limited as a result of the common-mode input swing
limits of the amplifier itself. An interesting modification
of this circuit is to place a capacitor in series with R_G.
Now the dc gain for each side is reduced to +1V/V;
the ac gain follows the standard transfer function of G
= 1 + 2R_F/R_G. This configuration might be
advantageous for applications processing only a
frequency band that excludes dc or very low
frequencies. An input dc voltage resulting from input
bias currents is not amplified by the ac gain and can
be kept low. This circuit can be used as a differential
line receiver, driver, or as an interface to a differential
input ADC.
50W
V_I
1/2
R_O
OPA2890
SINGLE-SUPPLY MFB DIFFERENTIAL
ACTIVE FILTER: 2MHz BUTTERWORTH
CONFIGURATION
The active filter circuit illustrated in Figure 58 can be
easily implemented using the OPA2890. In this
configuration, each amplifier of the OPA2890
operates as an integrator. For this reason, this type of
application is also called an infinite gain filter
implementation. A Butterworth filter can be
implemented using the following component ratios:
f_O =
1
2´p´R´C
R₁ = R₂ = 0.65 ´ R
R₃ = 0.375 ´ R
C₁ = C
C₂ = 2 ´ C
The frequency response for a 2MHz Butterworth filter
is shown in Figure 57. One advantage for using this
type of filter is the independent setting of ω_o and Q. Q
can be easily adjusted by changing the R_{3A, B}
resistors without affecting ω_o.
3
R_F
750W
R_G
R_F
750W
V_DIFF =
1+
2R_F
R_G
V_I - (-V_I)
1/2
R_O
50W _OPA2890
-V_I
Figure 56. High-Speed Differential Receiver
0
-3
-6
-9
-12
10k
100k
1M
10M
Frequency (Hz)
Figure 57. Multiple Feedback Filter Frequency
Response
20
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