OPA350 Datasheet, PDF (18/40 Pages) Burr-Brown (TI) – High-Speed, Single-Supply, Rail-to-Rail OPERATIONAL AMPLIFIERS MicroAmplifier ™ Series

OPA350, OPA2350, OPA4350
SBOS099D – SEPTEMBER 2000 – REVISED DECEMBER 2015
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
Low pass filters are commonly employed in signal processing applications to reduce noise and prevent aliasing.
The OPAx350 are ideally suited to construct high speed, high precision active filters. Figure 29 illustrates a
second order low pass filter commonly encountered in signal processing applications.
8.2 Typical Applications
8.2.1 Second Order Low Pass Filter
Input
R4
2.94 k
R1
590
R3
499
C2
39 nF
C5
1 nF
±
+
OPAx350
Output
Figure 29. Second Order Low Pass Filter
8.2.1.1 Design Requirements
Use the following parameters for this design example:
• Gain = 5 V/V (inverting gain).
• Low pass cutoff frequency = 25 kHz.
• Second order Chebyshev filter response with 3-dB gain peaking in the passband.
8.2.1.2 Detailed Design Procedure
The infinite-gain multiple-feedback circuit for a low-pass network function is shown in Equation 1. Use Equation 2
to calculate the voltage transfer function.
Output _s
Input
s²
1 R₁R₃C₂C₅
s C₂ 1 R₁ 1 R₃ 1 R₄ 1 R₃R₄C₂C₅
(1)
This circuit produces a signal inversion. For this circuit the gain at DC and the low pass cutoff frequency can be
calculated using Equation 2.
Gain ^R4
R₁
f_C
1
2S
1 R₃R₄C₂C₅
(2)
Software tools are readily available to simplify filter design. WEBENCH® Filter Designer is a simple, powerful,
and easy-to-use active filter design program. The WEBENCH Filter Designer lets you create optimized filter
designs using a selection of TI operational amplifiers and passive components from TI's vendor partners.
Available as a web based tool from the WEBENCH® Design Center, WEBENCH® Filter Designer allows you to
design, optimize, and simulate complete multi-stage active filter solutions within minutes.
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