Datasheet

OPA890
1.5kW
432W137W
500W
1.87kW
1.87kW
V
I
+5V
DIS
0.1 Fm
150pF
0.1 Fm
100pF
4V
I
5MHz,
2nd-Order,
Butterworth
Filter
15
12
9
6
3
0
-3
-6
Frequency(Hz)
Gain(dB)
100k 1M 10M
OPA890
SBOS369B –MAY 2007–REVISED DECEMBER 2009 www.ti.com
SINGLE-SUPPLY ACTIVE FILTERS The capacitor to ground on the noninverting input is
intentionally set larger to dominate input parasitic
The high bandwidth provided by the OPA890, while
terms. At a gain of +4, the OPA890 on a single
operating on a single +5V supply, lends itself well to
supply shows ~30MHz small- and large-signal
high-frequency active filter designs. Again, the key
bandwidth. The resistor values have been slightly
additional requirement is to establish the dc operating
adjusted to account for this limited bandwidth in the
point of the signal near the supply midpoint for
amplifier stage. Tests of this circuit show a precise
highest dynamic range. See Figure 50 for an example
5MHz, –3dB point with a maximally flat passband
design of a 5MHz low-pass Butterworth filter using
(above the 32kHz ac-coupling corner), and a
the Sallen-Key topology.
maximum stop band attenuation of 24dB at the
amplifier –3dB bandwidth of 30MHz.
Both the input signal and the gain setting resistor are
ac-coupled using 0.1μF blocking capacitors (actually
Note that the dc impedance looking out of each input
giving band pass response with the low-frequency
for this circuit has been set to 1.5kΩ to reduce the
pole set to 32kHz for the component values shown).
output offset voltage retaining maximum signal swing
As discussed for Figure 47, this configuration allows
for a mid supply nominal operating voltage at the
the midpoint bias formed by the two 1.87kΩ resistors
output.
to appear at both the input and output pins. The
midband signal gain is set to +4 (12dB) in this case.
Figure 50. Single-Supply, High-Frequency Active Filter
DESIGN-IN TOOLS
DEMONSTRATION FIXTURES MACROMODELS AND APPLICATIONS
SUPPORT
Two printed circuit boards (PCBs) are available to
assist in the initial evaluation of circuit performance Computer simulation of circuit performance using
using the OPA890 in its two package options. Both of SPICE is often useful when analyzing the
these are offered free of charge as unpopulated performance of analog circuits and systems. This
PCBs, delivered with a user's guide. The summary practice is particularly true for video and RF amplifier
information for these fixtures is shown in Table 2. circuits where parasitic capacitance and inductance
can have a major effect on circuit performance. A
Table 2. Demonstration Board Summary SPICE model for the OPA890 is available through the
Texas Instruments web page (www.ti.com). These
ORDERING LITERATURE
models do a good job of predicting small-signal ac
PRODUCT PACKAGE NUMBER NUMBER
and transient performance under a wide variety of
OPA890ID SO-8 DEM-OPA-SO-1A SBOU009
operating conditions. They do not do as well in
OPA890IDBV SOT23-6 DEM-OPA-SOT-1A SBOU010
predicting the harmonic distortion or dG/dP
characteristics. These models do not attempt to
The demonstration fixtures can be requested at the
distinguish between package types in the small-signal
Texas Instruments web site (www.ti.com) through the
ac performance.
OPA890 product folder.
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Product Folder Link(s): OPA890