SLOA049D July 2000 – February 2023

- Abstract
- Trademarks
- 1 Introduction
- 2 Filter Characteristics
- 3 Second-Order Low-Pass Filter Standard Form
- 4 Math Review
- 5 Examples
- 6 Low-Pass Sallen-Key Architecture
- 7 Low-Pass Multiple Feedback (MFB) Architecture
- 8 Cascading Filter Stages
- 9 Filter Tables
- 10Example Circuit Simulated Results
- 11Non-ideal Circuit Operation
- 12Comments About Component Selection
- 13Conclusion
- A Filter Design Specifications
- B Higher-Order Filters
- C Revision History

This report focuses on active low-pass filter design using
operational amplifiers. Low-pass filters are commonly used to implement
anti-aliasing filters in data acquisition systems. Design of second-order filters is
the main topic of consideration.

Filter tables are developed to simplify circuit design based on the idea of cascading lower-order stages to realize higher-order filters. The tables contain scaling factors ( $FSF$ ) for the corner frequency ( ${f}_{\mathrm{c}}$ ) and the required quality factor ( $Q$ ) of each of the stages for the particular filter being designed. The tables enable designers to skip straight to calculating required circuit component values.

To illustrate an actual circuit
implementation, six circuits, separated into three types of filters (Bessel,
Butterworth, and Chebyshev) and two filter configurations (Sallen-Key and
Multiple Feedback), are simulated using a TLV9062 operational amplifier.
Limiting factors in the high-frequency performance of the filters are also
examined. The tables in this document are used in the *Analog Engineer’s
Circuit Cookbook: Amplifiers*.