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Free spice software

Article-Free spice software

Spice, in this case, is actually S.P.I.C.E, which stands for Simulation Program with Integrated Circuit Emphasis.  SPICE is a program most (all?) E.E.s are familiar with, which is used to simulator electrical circuits.  I was looking for something simple to see the frequency response of a filter circuit and I ran across LTSpice IV, freely available from Linear Technology.

Many freely available SPICE programs will only support a limited number of nets or have other restrictions.  LTSpice is fully functional with no limitations.  Registration is asked for but not required to download the software.  Even better, it comes with a large design library of parts, both from Linear Technology and from other manufacturers.  It includes a schematic capture program so you don’t have to enter a netlist in text format, and it can also display analysis results graphically.

In the photo (click to see the full size version) you can see a simple low pass circuit with a 3dB rolloff at 1.5kHz.  The signal source is V1, and the filter is composed of Rext and Cext.  This filter is attached to the ADC input of an NXP LPC1768 ARM based microcontroller, and the rest of the components model the input to the ADC circuitry, taken from the LPC1768 datasheet.  I included them in the circuit to make the simulation more complete, although they have very little  impact on the circuit.  In the bottom of the photo is the frequency response, from 1 Hz to 5 kHz.  Both the magnitude and the phase of the output are shown.  Nets are added to the graph by clicking on them in the schematic.  Voltages across two nets can be displayed, as can current through components.  Analysis types include AC (frequency response), transient, and others.

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Steve RavetDesign News Gadgeteer

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