Electronic – Differences between parallel resistor-capacitor filters and series resistor-capacitor filters

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I've only worked with series resistor-capacitor filters before, so I'm not very clear about the operation of parallel resistor-capacitors filters. Can somebody explain to me what are the differences between them and series resistor-capacitor circuits in terms of operation? Any help will be much appreciated.

Best Answer

It's not clear what exactly you mean by series versus parallel resistor-capacitor filters. Posting a schematic of each would clarify this.

You probably mean series is something the signal passes thru, and parallel is something that works as a shunt. Note that the same thing that is a low pass filter in series is a high pass filter as a shunt, and vice versa.

Basically a capacitor will block low frequencies and short high ones. If you put it in series with a signal then it is a high pass filter. If you put it accross a signal, it will short the high frequencies thereby making a low pass filter. The value of the capacitance and the resistance it is working against tell you the -3dB rolloff frequency of the filter, whether high pass or low pass. This frequency is:

\$ f = \dfrac{1}{2 \cdot \pi \cdot R \cdot C} \$

When R is in Ohms and C in Farads, then f is in Hertz.