OPA4314AIPWR Datasheet, PDF (17/36 Pages) Texas Instruments – 3-MHz, Low-Power, Low-Noise, RRIO, 1.8-V CMOS Operational Amplifier

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APPLICATION EXAMPLES
OPA314
OPA2314
OPA4314
SBOS563F – MAY 2011 – REVISED AUGUST 2013
GENERAL CONFIGURATIONS
When receiving low-level signals, limiting the bandwidth of the incoming signals into the system is often required.
The simplest way to establish this limited bandwidth is to place an RC filter at the noninverting terminal of the
amplifier, as Figure 36 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 36. Single-Pole Low-Pass Filter
If even more attenuation is needed, a multiple pole filter is required. The Sallen-Key filter can be used for this
task, as Figure 37 shows. For best results, the amplifier should have a bandwidth that is eight to 10 times 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 37. Two-Pole Low-Pass Sallen-Key Filter
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