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Filter Design
Filters are signal-processing circuits used to modify the frequency spectrum of an electrical signal. They may be used to amplify, attenuate, or reject a certain range of frequencies of their input signals. Filters are pervasive in integrated circuits because of their vast number of applic...

Circuit Sage Tools

Sallen-Key Mathcad filters routine:
Extensive Mathcad routine for designing integrated Sallen-Key filters
Mathcad routine for Butterworth filters:
Mathcad routine for LC Butterworth filters
Mathcad routine for elliptic filters:
Mathcad routine for LC elliptic filters
Mathcad routine for Chebyshev filters:
Mathcad routine for LC Chebyshev filters
2nd Order Low-Q Active Filter Design:
This tool calculates the required resistor and capacitor values for a second order low-Q active filter.
Single Pole Active Filter Design:
This tool calculates the required resistor and capacitor values for a single pole active filter.

Online Tools

Neil Barnes' Filter:
Intuitive filter program for Windows, can process a .WAV file. Windows-95-looking interface
$1500 tool can design almost any filter
FilterCAD (FREE):
Linear Technology's filter design tool
Waveguide filter design tool
Free, Light, and Full versions available
Waveguide coupled-cavity filters
Time- and frequency-domain plots, S-parameters, Monte Carlo, etc. Student edition FREE
Bandpass filter design and analysis program based on the helical resonator
Butterworth filter routine in BASIC:
BASIC code implements different Butterworth filter responses
BASIC filter routines:
Tom Couthbert's BASIC routines for filter design
DrawFilt MATLAB toolbox (FREE):
Schematic capture filter software for MATLAB
Dr. James Kang's list of MATLAB and Mathcad routines:
Over 100 Mathcad and MATLAB routines, many filter-related, both analog and digital
Professor Bernhard Boser's (UC-Berkeley) Mathcad routines for filter design:
Ten Mathcad routines for designing various filter types
Professor Robert Harger's Mathcad book:
Professor Harger's Mathcad book has a lot of information on digital filter design and DSP
MATLAB routines collection for filter design:
Over 100 MATLAB programs related to analog and digital filter design
Butterworth bandpass filter calculator:
Calculates passive LC filter values from center frequency and bandwidth
LC passive filter designer:
Generates LC components based on response type, cutoff frequency, and I/O impedance
Bandpass filter tool:
Computes LC component values based on center frequency, load impedance, and Q-factor
Guided Wave Technologies:
GWT's waveguide filter tool, select one of 3 waveguide filter types
2nd order system Frequency response tool:
Drag poles/zeros with your mouse and watch as the frequency response changes
Tony Fisher:
Design Butterworth or Chebyshev LC filters, many input options, very nice
Uwe Beis online filter tool:
Design low- and high- pass filters, outputs a SPICE netlist
Toshio Iwata:
Digital and analog filter tools collection, very nice
TI's FilterPro:
Design almost any type of active filter
Transmission line and LC-filter synthesis, need to email them to get a copy
PCFILT has a free demo which works only at 833 MHz
Sun OS tool plots frequency response and pole/zero locations
Filter synthesizer and analyzer, demo available
DOS-looking software plus author's book, may not work in Windows XP
Synthesizes Chebyshev filters
RF design tool includes filter synthesis among other things
Professor Bogdan Wilamowski's analog filter synthesizer
Synthesizes passive ladder prototypes for analog and digital filter design
$70, runs Monte Carlo simulations and over temperature
Free if you only need low- or high-pass filters. Outputs a SPICE netlist
Switched-capacitor filter design tool
AADE Filter Design (FREE):
Free tool simulates many filter types over time and frequency, includes statitical analysis
AKtivFilter Tools:
AktivFilter is a software for the design of active filters tuned on the opamp type. Personal, Professional and a free Demo Edition are available.

Toshio Iwata:
Design and simulate digital filters and DSP systems
WinFilter (FREE):
Windows software to design IIR and FIR digital filters, outputs VHDL code and .GIF files of responses
FIR and IIR design tool, $69, demo available
Cool digital filter demo in Java:
Turn on your speakers and hear outputs of many waveforms passed through many different filter types
IIR filter explorer:
Move poles and zeros on the complex plane and watch how the frequency response changes
FIR tool, $10 for student version
IIR filter tool:
U. of Texas - Austin Java tool plots magnitude, phase, and step response of IIR filters
QEDesign from Momentum Data Systems:
IIR/FIR filter tool available at 3 price levels
Introduction to digital filtering using Mathematica:
Learning digital filters fundamentals in Mathematica

Online Articles

Sallen-Key Butterworth 5th order LPF design:
Design and implementation of a 10-kHz, 5th order active filter
LPF tutorial:
Design of a low sensitivity Sallen Key LPF
Ian Purdie LC filter tutorial:
Scroll down to Section 5
TI"s analysis of the Sallen-Key arquitecture:
Analysis and lab data of low- and high-pass Sallen Key filters
TI's Filters for data transmission:
Analysis of what happens when digital signals are filtered
TI Active Low-Pass Filter Design:
Butterworth, Chebyshev, Bessel, Sallen-Key, and MFB active filter design
U. of San Diego's overview of microwave filters:
Goes over distributed and lumped implementations of microwave filters
Queens University's wiki page on microwave filters:
Discusses prototyping and going from lumped to distributed implementations
ARRL RF Filters page:
Links to ARRL articles and a picture of commonly used RF filter topologies
National's Introduction to filters:
Goes over active, passive, and switched-capacitor filter types
National's Designing high-speed active filters:
Discusses low- and high-pass Sallen Key filters, how to select an op-amp and other practical matters
National's Low sensitivity LPF design:
How to design a Sallen-Key LPF insensitive to comp. variation
National's Low sensitivity HPF design:
How to design a Sallen-Key HPF insensitive to comp. variation, how to compensate for parasitic op-amp cap.
National's Pre-distortion for Sallen Key filters:
Shows how to compensate for an op-amp's finite BW by modifying nominal component values
National's BPF design with low sensitivity:
How to design a Sallen-Key BPF insensitive to comp. variation
Swarthmore's switched-capacitor filters page:
Introduction of SC filters and how to implement one using a National Semiconductor IC
Maxim's filter app notes and primers page:
Primers on con-time and SC filters as well as application notes using Maxim's Ics
Frequency Devices' filter design page:
Analog and digtal filter design performance metrics described, topology overviews
Professor Gordon Roberts' published papers on filt:
Log-domain filtering and switch-capacitor filters
Julius Smith's Introduction to Digital Filters:
Very nice, includes some MATLAB routines
gm-C BPF paper from U. of Oulu-Finland:
6th order elliptic gm-C BPF for biomedical applications, 18 uA from 3.0V supply
Agilent's eeosf filter software page :
Filter design examples with Agilent's sofware
Maxim Analog Filter Design Demystified:
Analog filter fundamentals and design procedure for active Butterworth and Chebyshev filters
Bessel crossover design for pro audio applications:
How to design Bessel filter crossovers and comparison with Butterworth and LR crossovers
Linkwitz-Riley Crossovers: A Primer:
Fundamentals of Linkwitz-Riley crossovers for pro audio applications
Bessel filter response:
Bessel filters' responses and comparisons with Butterworth and Chebyshev types
Group delay paper from Applied Radio Labs:
Group delay and how it affects RF filter performance
UC-Berkeley filter lectures:
A few lectures on integrated filter design
RF/Microwave Filters lecture notes:
LC and microstrip line microwave filters. Nice.
RF Filtering Phd thesis:
Bandpass filter integrated in 0.25-um CMOS
Sensitivity Analysis of Analog Filters presentation from TI:
How to efficiently design an analog filter taking into account the sensitivities of the filter's response to component variations.
gm-C filters presentation from Texas A&M:
Very good presentation on OTA's for gm-C filters from 0.1-Hz to 2.0-GHz
Simulating switched capacitor filters using SpectreRF :
Simulating switched-capacitor filters in Spectre using periodic steady-state, AC, noise analysis
Integrated RF Interference Suppresion Filter paper from UC San Diego:
2.1 GHz RF-interference-suppression filter using on-chip metal capacitors and bondwires in 0.18 micron CMOS
22-GHz integrated filter using selectively-etched inductors: paper from National Taiwan University:
22-GHz BPF implemented in 0.18-micron CMOS using inductors enhanced by selectively etching the silicon from underneath them using standard CMOS processing techniques.
Shrinking Microwave Filters: paper from U. of Waterloo:
Introduces low-loss adaptive pre-distortion technique, demonstrates by implementing filters in C (4 GHz) and Ku (12 GHz) bands
Mixed-signal approach to tune the BW of analog LPF's paper from UC - Davis:
Uses an ADC and a digital filter as part of a tuning loop to fine-tune the BW of 2nd and 4th order LPF's.

Digital FIR crossovers for loudspeakers:
Method for linear phase FIR crossovers presented, with examples
Comb filters introduction:
Primer on comb filters
IIR filter design:
From BORES Introduction to DSP
Classic paper on FFT windows:
Discusses various types and metrics to compare to each other
FFT on LabView:
Comprehensive overview of FFT-based signal analysis in LabView
LabView windows:
Characteristics of various FFT windows available in LabView
Window choices for high dynamic range FFT processing:
Fundamental trade-offs involved in selecting a window type
Analog versus digital signal processing:
Digital versus analog filters
Dr. Fred DePiero's class notes:
Notes from various signal processing courses at Cal Poly - San Luis Obispo
Digital filter lecture notes and videos from Boise State:
Mixed-signal course notes and videos includes 5 or 6 lectures on digital filters
Interpolation filters presentation:
Presentation with implementation examples in MATLAB. Scroll down, presentation no. 9. Associated MATLAB file also available
Digital filter lectures from Stanford course:
Click on lectures on left frame
FIR's for receiver equalization paper from UT-Dallas:
Presents issues introduced at high frequencies by noisy channels and crosstalk, discusses methods to overcome
How to send Cadence output to MATLAB for post-processing:
If you have a small data set (a few hundred points) then use the "printvs" button in the Cadence calculator. For thousands of points you'd better use ocean (unless you are in the mood to wait a loooong time for your text file)
Search over 1 million articles

Filtering in the Time and Frequency Domains by H. Blinchikoff and A. Zverev:
Re-print of a 1976 book considered a classic by many
Generalized Filter Design by Computer Optimization:
CAD techniques for RF/microwave filter optimization
Passive, Active, and Digital Filters by Wai-Kai Chen:
Compilation of both analog and digtal filters
Mathematics for Circuits and Filters by Wai-Kai Chen:
from back cover: "...stresses the fundamental theory behind professional applications, making an excellent, flexible resource that enables easy access to the information needed to deal with circuits and filters..."
The Circuits and Filters Handbook by Wai-Kai Chen:
Compilation of articles by many authors, almost 3000 pages.
Electronic Filter Analysis and Synthesis by Michael Ellis:
1994 book, from description: "...helps you save time and effort in writing CAD and analysis programs for electronic filters, and provides explicit details on how to synthesize lowpass, bandpass, bandstop, and highpass realizations for passive, active, digital and switched capacitors...."
Modern Filter Design: Active Rc and Switched Capacitor by Mohammed Shuaib Ghausi:
Re-print of 1981 book. From description: "...the authors discuss the design of continuous-time, second order active sections (biquads), various measures of sensitivity, and the basic properties and classification of continuous-time and sampled data systems, together with filter transfer functions and approximations..."
Active Filter Cookbook by Don Lancaster:
From description: "...It gives you everything you need to know to build active lowpass, bandpass, and highpass filters...."
Design and Analysis of Analog Filters by Larry D. Paarmann:
Analog filter design with an eye on system/signal processing issues, MATLAB disc with example included. From description: "...A valuable relationship between analog filter theory and analysis and modern digital signal processing is made by the application of MATLAB to both the design and analysis of analog filters..."
High Frequency CMOS Continuous-Time Filters by S. Pavan and Y. Tsividis:
from description: "...addresses the theoretical and practical problems encountered in the design of robust, programmable continuous-time filters with very high bandwidths, implemented in low-cost digital CMOS technologies.A high performance programmable filter architecture, called `constant-capacitance scaling', is discussed in detail..."
HF Filter Design and Computer Simulation by Randall W. Rhea:
from: "...'HF Filter Design and Computer Simulation' is a complete design guide for printed and L-C filters for RF and microwave applications..."
Design of Analog Filters by R. Schaumann and M. E. Van Valkenberg:
from description: "...Topics covered include fundamental concepts; opamps; first- and second-order filters; second-order filters with arbitrary transmission zeros; filters with maximally flat magnitude, with equal ripple (Chebyshev) magnitude, and with inverse Chebyshev and Cauer response functions; frequency transformation; cascade designs; delay filters and delay equalization; sensitivity; LC ladder filters; ladder simulations by element replacement and by operational simulation; transconductance-C filters; and switched-capacitor filters...."
Analog Filters by K. L. Su:
from description: "...covers four major fundamental types of analog filters - passive, op amp-RC, switched-capacitor, and operational transconductance amplifier-capacitor (OTA-C)..."
Analog and Digital Filter Design by S. Winder:
from description: "...does not start from a position of mathematical complexity. It is written to show readers how to design effective and working electronic filters. The background information and equations from the first edition have been moved into an appendix to allow easier flow of the text while still providing the information for those who are interested..."
Handbook of Filter Synthesis by A. Zverev:
1967 classic re-print. From description: "...originally published in 1967 is the classic reference for continuous time filter design...."
Tables for Active Filter Design by M. Biey:
From 1985. Based on Multiple Critical Pole Equal Ripple (MCPER) approximating functions.