Help and Documentation


Getting started with DoCircuits


How to run frequency domain analysis?

What is frequency domain analysis?

Frequency domain analysis describes a certain type of simulation. In this analysis you can see as to how the output varies with respect to the given sweep in frequency. That is the frequency is varied according to the given step increment between the set frequency values and the corresponding variation in output is plotted.

How to run frequency domain analysis

1.     After rigging up the circuit, click on RUN menu, select Frequency Domain Analysis or use shortcut key f.

2.     On your left hand side of the screen where the components window was present, the simulation window will appear.


3.     If you are not sure as to what settings to give click on the Run with default settings checkbox. And click the RUN button at top bar or simulation settings window.

What is high and low frequency?

Low frequency and high frequency are the limits set for the range through which the frequency of the input is varied. For example,if the low frequency is set as 1 Hz and high frequency as 10 kHz, then the frequency is varied from 1 Hz till 10 kHz.

What is step increment?

This is the size of the incremental steps of frequency from the low frequency to high frequency. That is, of the step increment is 10Hz the frequency is varied in steps of 10 Hz.

How to set the parameters?

Say, we have a low pass filter designed with cutoff frequency at 1 kHz. So to clearly see the variation of output around it our low frequency should be much less than this and the high frequency value should be greater than this. So if for example you choose 0 Hz to 5 kHz, it would be sufficient.

For example if step increment is 10 Hz, the frequency samples are taken at intervals of 10 Hz, so lower the sample gap higher the number of samples for the given range. And higher the number of samples, smoother would be the graph. So it would be better if the step increment is as small as possible.

How to find cutoff frequency

The cutoff frequency is the frequency at which the output voltage (or current) is 0.707 of the maximum output. This can be easily found by moving the mouse over the curve until the y value is the expected value. The figure below shows the frequency response of a high pass filter.