Butterworth third-order lowpass filter

Butterworth Circuit Diagram

Introduction

This circuit demonstrates a Butterworth filter of third order, implemented with two inductors, a capacitor and a resistor. The default parameter values are designed to give a cutoff frequency of 10 MHz, however with experimentation different cutoff frequencies and step responses are achievable.

In this circuit the input is a sinusoidal voltage source (with adjustable frequency) and the output is the filtered output, as shown in the attached circuit diagram.

The circuit netlist is contained within the butterworth.spice file in this directory. To begin running the simulation harness, open the butterworth_transient.jl or butterworth_ac.jl files and begin running statements.

Files

Analyses

Transient

Butterworth Transient Response

Note that here we have a single measure applied (just as in the example) disallowing the voltage to ever peak above the absolute maximum value above 1.1.

AC

The AC response is calculated for a frequency sweep from 10 kHz to 1 GHz. By moving the sliders the influence of each parametere can be understood. L1 is the primary component for controlling the passband ripple.

Butterworth AC Response

Noise

The Noise spectrum is calculated for a frequency from 10 kHz to 1 Ghz. By moving the sliders the influence of each parametere can be understood.

Butterworth Noise Spectrum

API Reference