OPA4316 Datasheet, PDF (20/46 Pages) Texas Instruments – OPAx316 10-MHz, Low-Power, Low-Noise, RRIO, 1.8-V CMOS Operational Amplifier

OPA316, OPA2316, OPA2316S, OPA4316
SBOS703D – APRIL 2014 – REVISED DECEMBER 2014
8 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 General Configurations
When receiving low-level signals, the device often requires limiting the bandwidth of the incoming signals into the
system. The simplest way to establish this limited bandwidth is to place an RC filter at the noninverting pin of the
amplifier, as Figure 39 shows.
R_G
R_F
R₁
V_IN
V_OUT
C₁
f_{-3 dB} =
1
2pR₁C₁
( ( ^VOUT
V_IN
=
1
+
R_F
R_G
1
1 + sR₁C₁
Figure 39. Single-Pole Low-Pass Filter
If even more attenuation is needed, the device requires a multiple-pole filter. The Sallen-Key filter can be used
for this task, as Figure 40 shows. For best results, the amplifier must have a bandwidth that is 8× to 10× the filter
frequency bandwidth. Failure to follow this guideline can result in phase shift of the amplifier.
C₁
R₁
R₂
V_IN
C₂
R_F
R_G
V_OUT
R₁ = R₂ = R
C₁ = C₂ = C
Q = Peaking factor
(Butterworth Q = 0.707)
f_{-3 dB} =
1
2pRC
R_F
( ^{RG =}
2-
1
Q
Figure 40. Two-Pole, Low-Pass, Sallen-Key Filter
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