Datasheet

V
OUT
V = 1V
IN RMS
OPA320
150kW19.5kW
220pF
1.8kW
3.3nF 47pF
V+
V-
C
1nF
1
C
150pF
2
R
549W
3
R
549W
1
R
1.24kW
2
V+
V
OUT
V
IN
V-
OPA320
OPA320, OPA2320
OPA320S, OPA2320S
www.ti.com SBOS513E –AUGUST 2010–REVISED JUNE 2013
ACTIVE FILTER MFB and Sallen-Key, low-pass and high-pass filter
synthesis is quickly accomplished using TI’s
The OPA320 is well-suited for active filter applications
FilterPro™ program. This software is available as a
that require a wide bandwidth, fast slew rate, low-
free download at www.ti.com.
noise, single-supply operational amplifier. Figure 45
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;
Figure 45. Second-Order Butterworth 500kHz
2. adding an additional second-order MFB stage; or
Low-Pass Filter
3. using a noninverting filter topology, such as the
Sallen-Key (shown in Figure 46).
Figure 46. OPA320 Configured as a Three-Pole, 20kHz, Sallen-Key Filter
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