pseudockb
Member level 5
pulse-width modulated sine wave
Hi, I read it from "The Designer's Guide to Spice and Spectre", that we are able to find the THD of a pulse-width modulated sine wave using the Fourier Integral method by Spectre. The book also mentioned that Fourier integral is not subjected to aliasing.
Now, I am designing a class D amplifier. I am trying to obtain the THD from simulation. I observe the THD at two points, i.e. the output of the class D amplifier ( which is a pulse width modulated sinewave) and the point after a low pass filter to the output ( to remove the clock harmonics).
I am getting ~0.1% THD at the filtered output vs ~3%THD at the unfiltered output. Could anyone explain to me what went wrong? For your information, my input frequency is 1kHz while the clock frequency is 1MHz. In my THD calculation, the bandwidth of interest is from 20Hz ~ 20kHz. The corner frequency of the low pass filter is 40kHz. I was expecting that both THD would give similar result but I was proven wrong. Is the discrepancy due to aliasing or some other effects? Thanks!
Hi, I read it from "The Designer's Guide to Spice and Spectre", that we are able to find the THD of a pulse-width modulated sine wave using the Fourier Integral method by Spectre. The book also mentioned that Fourier integral is not subjected to aliasing.
Now, I am designing a class D amplifier. I am trying to obtain the THD from simulation. I observe the THD at two points, i.e. the output of the class D amplifier ( which is a pulse width modulated sinewave) and the point after a low pass filter to the output ( to remove the clock harmonics).
I am getting ~0.1% THD at the filtered output vs ~3%THD at the unfiltered output. Could anyone explain to me what went wrong? For your information, my input frequency is 1kHz while the clock frequency is 1MHz. In my THD calculation, the bandwidth of interest is from 20Hz ~ 20kHz. The corner frequency of the low pass filter is 40kHz. I was expecting that both THD would give similar result but I was proven wrong. Is the discrepancy due to aliasing or some other effects? Thanks!
