I am trying to extract the DC component out of a PWM signal produced by the MCU using a LPF. I understand that 1st order RC filter is looked upon as being amateurish because the gain in the passband will be still less than 1V/V and because it does not have low enough roll off factor.

However, the PWM frequency of the MCU (Atmega328PB) I will be using can go up to 3.9kHz which means that it is sufficiently far from a designed cut off of lets say 100Hz frequency that the LPF can attenuate it by about -20dB.

Does that justify the use of passive over active filter since I wish not to use the following Sallen-Key filter to reduce cost and area https://hackaday.com/2017/03/08/dont-fear-the-filter-lowpass-edition/

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    $\begingroup$ Whether an attenuation of 20 dB at the first harmonic is good enough depends on your requirements. What do you want to do with the filter's output? Also, note that an active filter is not the only alternative. You can design higher order passive filters. $\endgroup$ – MBaz Nov 12 '18 at 1:35

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