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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	1 2 3 4 5 6 7 8 9 10	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

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 C_A and C_B may entered in the shaded area, R_A and R_B will be recalculated.

Return to parameter entry