OPA320 Datasheet, PDF (18/31 Pages) Texas Instruments – Precision, 20MHz, 0.9pA, Low-Noise, RRIO, CMOS Operational Amplifier with Shutdown

OPA320, OPA2320
OPA320S, OPA2320S
SBOS513D – AUGUST 2010 – REVISED NOVEMBER 2011
ACTIVE FILTER
The OPA320 is well-suited for active filter applications
that require a wide bandwidth, fast slew rate,
low-noise, single-supply operational amplifier.
Figure 41 shows a 500kHz, 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 –40dB/dec. The
Butterworth response is ideal for applications
requiring 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 42).
www.ti.com
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
549W
C₂
150pF
R₁
R₂
549W 1.24kW
V_IN
C₁
1nF
V+
OPA320
V-
V_OUT
Figure 41. Second-Order Butterworth 500kHz
Low-Pass Filter
220pF
V_IN = 1V_RMS
1.8kW
19.5kW 150kW
3.3nF
V+
47pF ^OPA320
V_OUT
V-
Figure 42. OPA320 Configured as a Three-Pole, 20kHz, Sallen-Key Filter
18
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