Datasheet

OPA690
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
Gain(dB)
Frequency(Hz)
5MHz,2nd-OrderButterworthFilterResponse
100k 1M
10M
15
10
5
0
-5
OPA690
www.ti.com SBOS223F –DECEMBER 2001–REVISED FEBRUARY 2010
SINGLE-SUPPLY ACTIVE FILTERS both the input and output pins. The midband signal
gain is set to +4 (12dB) in this case. The capacitor to
The high bandwidth provided by the OPA690, while
ground on the noninverting input is intentionally set
operating on a single +5V supply, lends itself well to
larger to dominate input parasitic terms. At a gain of
high-frequency active filter designs. Again, the key
+4, the OPA690 on a single supply will show ~80MHz
additional requirement is to establish the dc operating
small- and large-signal bandwidth. The resistor
point of the signal near the supply midpoint for
values have been slightly adjusted to account for this
highest dynamic range. See Figure 42 for an example
limited bandwidth in the amplifier stage. Tests of this
design of a 5MHz low-pass Butterworth filter using
circuit show a precise 5MHz, −3dB point with a
the Sallen-Key topology.
maximally flat passband (above the 32kHz
ac-coupling corner), and a maximum stop band
Both the input signal and the gain setting resistor are
attenuation of 36dB at the amplifier’s −3dB bandwidth
ac-coupled using 0.1mF blocking capacitors (actually
of 80MHz.
giving bandpass response with the low-frequency
pole set to 32kHz for the component values shown).
As discussed for Figure 37, this allows the midpoint
bias formed by the two 1.87kΩ resistors to appear at
Figure 42. Single-Supply, High-Frequency Active Filter
Copyright © 2001–2010, Texas Instruments Incorporated 17
Product Folder Link(s): OPA690