OPA322_1111 Datasheet, PDF (16/34 Pages) Texas Instruments – 20-MHz, Low-Noise, 1.8-V, RRI/O, CMOS Operational Amplifier with Shutdown

OPA322, OPA322S
OPA2322, OPA2322S
OPA4322, OPA4322S
SBOS538C – JANUARY 2011 – REVISED NOVEMBER 2011
APPLICATION EXAMPLES
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ACTIVE FILTER
The OPA322 is well-suited for active filter applications that require a wide bandwidth, fast slew rate, low-noise,
single-supply operational amplifier. Figure 33 shows a 500-kHz, second-order, low-pass filter using the
multiple-feedback (MFB) topology. The components have been selected to provide a maximally-flat Butterworth
response. Beyond the cutoff frequency, roll-off is –40 dB/dec. The Butterworth response is ideal for applications
that require predictable gain characteristics, such as the anti-aliasing filter used in front of an ADC.
One point to observe when considering the MFB filter is that the output is inverted, relative to the input. If this
inversion is not required, or not desired, a noninverting output can be achieved through one of these options:
1. adding an inverting amplifier;
2. adding an additional second-order MFB stage; or
3. using a noninverting filter topology, such as the Sallen-Key (shown in Figure 34).
MFB and Sallen-Key, low-pass and high-pass filter synthesis is quickly accomplished using TI’s FilterPro™
program. This software is available as a free download at www.ti.com.
R₃
549 W
C₂
150 pF
R₁
R₂
549 W 1.24 kW
V_IN
C₁
1 nF
V+
OPA322
V-
V_OUT
Figure 33. Second-Order Butterworth 500-kHz Low-Pass Filter
V_IN = 1 V_RMS
1.8 kW
220 pF
V+
19.5 kW 150 kW
3.3 nF
47 pF ^OPA322
V_OUT
V-
Figure 34. OPA322 Configured as a Three-Pole, 20-kHz, Sallen-Key Filter
16
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