The device I used is C2000 kit (Micro-controller F28069).
The high resolution PWM (1MHz, 50% duty cycle) is generated shown as blue line in the attached figure. A second order low pass filter with the cutoff frequency 100Hz is used, and the yellow line shows the filtered signal.
By observing the PWM signal, we can see significant oscillations at the transitions between on and off. I am not sure whether this ripple is normal or not.
My second question is about the filtered analog signal. The oscillation of the filtered signal is too high: the biggest error away from the mean is about 100mv. Although the cutoff frequency is very low compared to the frequency of PWM, it looks that the high frequency components are still there. I can not figure out the reason.
Hope anyone can help me.
Thanks a lot.
Check if your probes has a good ground. The best way is to found something grounded very near from your testpoint and connect the probes shield to this ground with some wide conductive thing (screwdriver or knife is a good idea). In case you see significant decreasing of your oscillations it means you probes ground wires is too long and actually there is no oscillations in your system.
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