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Active Low-Pass Filter Design and Dimensioning

New: Simplify Stages 1 and 2 if Pole Numbers are Odd

This utility written in Javascript shall help you to quickly design and dimension your active Sallen-Key or Multiple Feedback topology low-pass filter. Enter the desired filter parameters and find the resulting circuit diagrams and component values below. In this utility great importance is attached to the possibility of automatic selection of capacitors out of the E6- or E12-series. New: If your filter is odd ordered (i. e. 3-pole, 5-pole etc.) you may save one op-amp by combining both stages into one (provided it is of Sallen-Key topology, the stage gain of stages 1 and 2 is one and, in case of Chebychev, the ripple factor is 0.5, 1.0, 2.0 or 3.0 dB). Refer to Dimensioning of Active 3-Pole Single Stage Low-Pass Filters.

This page is not intended to teach the basics of filter design. Look at the TI-website for an in-depth article. Links to more filter design software can be found on the New Wave Instruments company website. Also you may have a look at my homepage. You likely won't be able to understand it - it's German.

You also may go to Active Filter Design and Dimensioning (overview) or directly to Active High Pass Filter Design and Dimensioning.

No responsibility for any kind of errors or bugs is taken from anybody. This page has been tested with MSIE 6 and Netscape 6.2.

To abbreviate atto, femto, pico, nano, micro, milli, kilo, mega, giga and tera use a, f, p, n, u, m, k, M, G and T


Desired Filter Parameters

Filter Characteristics

Filter
Order

Cutoff
Frequency

Stage Gain

Desired RX

CX Selection

Bessel (almost no Overshoot
     and constant Group Delay)
Butterworth (no Ripple)
Chebychev dB Ripple
Hz

Stage Gain:  
In Stage(s) Nr:  1
2
3
4
5

Note: Stage Gain < 1 is
not available for Sallen-Key

Ohm

Sallen-Key:
RA = RB = RX

Multiple Feedback:
(RA || RB) = RC = RX

CX from E6-Series
CX from E12-Series

Sallen-Key component values    Multiple Feedback component values    Spice netlist generator


Sallen-Key Topology Filter



 
 CX using RX

 CX Selection and Resulting RX

 
Stage
CA CB
CA CB RA RB
Q GBW
1
2
3
4
5

 RC, RD if Gain > 1 
RC
RD

Different values for CA and CB may entered in the shaded area, RA and RB will be recalculated.

Return to parameter entry


Multiple-Feedback Topology Filter


 
 CX using RA = RX
 CX Selection and Resulting RX
 
Stage
CA CB RA RB RC
CA CB RA RB RC
Q GBW
1
2
3
4
5

Different values for CA and CB may entered in the shaded area, RA, RB and RC will be recalculated.

Return to parameter entry


Spice Simulation Netlist Generator

Spice Netlist Generator Options
Enable AC-Sweep Analysis
FStart: Hz
FStop: Hz
Enable Transient Analysis
TPulse: s
TStop: s
Enable Monte Carlo Analysis
Steps:
R-Tolerance: %
C-Tolerance: %
Use Ideal Op-Amps
Use Real Op-Amps

Type:

Generate Netlist

Netlist Output

Return to parameter entry


Last update: April, 22nd, 2005 Questions? Suggestions? Email Me! Uwe Beis