OPA3832_07 Datasheet, PDF (19/32 Pages) Burr-Brown (TI) – Triple, Low-Power, High-Speed, Fixed-Gain Operational Amplifier

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50W Source
V_IN
175W
50W
+5V
0.1mF
6.8mF
+
1/3
OPA3832
V_O
150W
0.01mF
400W
400W
6.8mF
+
0.1mF
-5V
Figure 48. DC-Coupled, G = +2, Bipolar Supply
Specification and Test Circuit
SINGLE-SUPPLY ACTIVE FILTER
The OPA3832, while operating on a single +3.3V or
+5V supply, lends itself well to high-frequency active
filter designs. Again, the key additional requirement
is to establish the dc operating point of the signal
near the supply midpoint for highest dynamic range.
Figure 50 shows an example design of a 1MHz
low-pass Butterworth filter using the Sallen-Key
topology.
Both the input signal and the gain setting resistor are
ac-coupled using 0.1µF blocking capacitors (actually
giving bandpass response with the low-frequency
OPA3832
SBOS370 – DECEMBER 2006
pole set to 3.2kHz for the component values shown).
As discussed for Figure 46, this configuration allows
the midpoint bias formed by one 2kΩ and one 3kΩ
resistor to appear at both the input and output pins.
The midband signal gain is set to +2 (6dB) in this
case. The capacitor to ground on the noninverting
input is intentionally set larger to dominate input
parasitic terms. At a gain of +2, the OPA3832 on a
single supply will show 80MHz small- and
large-signal bandwidth. The resistor values have
been slightly adjusted to account for this limited
bandwidth in the amplifier stage. Tests of this circuit,
shown in Figure 49, illustrate a precise 1MHz, –3dB
point with a maximally-flat passband (above the
3.2kHz ac-coupling corner), and a maximum stop
band attenuation of 36dB.
9
6
3
0
-3
-6
-9
-12
-15
-18
100
1k
10k
100k
1M
10M
Frequency (Hz)
Figure 49. 1MHz, 2nd-Order, Butterworth
Low-Pass Filter
0.1mF
V_I
3kW
205W
2kW
866W
300pF
+5V
470pF
1/3
OPA3832
400W
2V_I
1MHz, 2nd-Order
Butterworth Filter
400W
0.1mF
Figure 50. Single-Supply, High-Frequency Active Filter
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