![]() It contains the 2 simulation files we run. Noise from the power supply circuit can affect peripheral circuits and EMI testing.īy understanding the frequency components using the FFT function, noise countermeasures such as filter design can be studied by simulation. The ripple component of the output voltage is shown below.īy FFT analysis, not only the 1MHz switching frequency component but also the 2x, 3x and even and odd frequency components can be confirmed. FFT analysis requires steady state results, so check the ripple voltage after the power supply is turned on. This time let’s check the frequency component with the FFT function. Previously in the article “Try LTspice - DC-DC converter activity”, we have checked the level of ripple voltage of the output voltage. Look at the output voltage signal of the power supply IC with FFT! options, and I have simulated the default Maximum Time Step.ĭespite the FFT of the composite sine wave, the noise floor of the base is large and peaks are visible at unintended frequencies. ![]() The result is that the output of the analysis is not compressed and the noise floor is reduced.Īlso, when the "Maximum Time Step" of the TRAN command is shorter than 1/100 of the signal's one cycle, results of a good FFT are obtained however, when the short setting is shortened and the simulated time takes a few times, it is adjusted with a balance. When using the FFT function, it is recommended to set the command ". There are peaks at frequencies of 1kHz, 3kHz, and 10kHz, and we were able to grasp the waveform components and size. Then, the box as shown in the following figure will appear, so please press OK normally.Ī logarithmic graph with signal level (dB) on the vertical axis and frequency (Hz) on the horizontal axis was obtained. Only looking at the waveform of the OUT terminal does not reveal the frequency component and size. The results of the TRAN analysis are shown below. This time, as an example, we will confirm the signal waveform, which is a composite of 3 sine waves with different frequencies and magnitudes, by TRAN analysis and confirm the frequency distribution using the FFT display function. The FFT function is built into the Waveform Viewer because it performs calculations based on data obtained from the TRAN analysis (time axis). Like a spectrum analyzer, SPICE displays the frequency components and level (power) of the signal. What is FFT?įFT (Fast Fourier Transform) is a Fast Fourier Transform, which is an algorithm that performs fast computation on a computer. This time, I will introduce this FFT function. ![]() On the other hand, the FFT function is useful when you want to check the frequency component of a signal, and you can check the distortion and noise component of the circuit by simulation. In the TRAN analysis, which is a time axis analysis, you can check the signal level as time changes like an oscilloscope. Try LTspice series introduces the use of LTspice
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