OPA320-Q1 Datasheet, PDF (21/34 Pages) Texas Instruments – Precision, 20-MHz, 0.9-pA, Low-Noise, RRIO, CMOS Operational Amplifier

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OPA320-Q1, OPA2320-Q1
SLOS884A – SEPTEMBER 2014 – REVISED DECEMBER 2016
8.2.4 Active Filter
The OPAx320-Q1 device is well-suited for active filter applications that require a wide bandwidth, fast slew rate,
low-noise, single-supply operational amplifier. Figure 43 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
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 the following
options:
1. adding an inverting amplifier
2. adding an additional second-order MFB stage
3. using a noninverting filter topology, such as the Sallen-Key
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 Ω
C2
150 pF
R1
549 Ω
R2
1.24 kΩ
V_(V+)
V_I
C1
1 nF
OPA320-Q1
V_O
V_(V–)
Figure 43. Second-Order Butterworth 500-kHz Low-Pass Filter
220 pF
1.8 kΩ
19.5 kΩ 150 kΩ
V_(V+)
V_I = 1 V_RMS
3.3 nF
47 pF ^OPA320-Q1
V_O
V_(V–)
Figure 44. OPAx320-Q1 Configured as a Three-Pole, 20-kHz, Sallen-Key Filter
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