Basic low pass filter using capacitor and resistor

To avoid unwanted noise in the output, a filter is required to be placed before it. Such filters are more commonly used in audio circuits. To avoid or retain frequencies which are higher than filter’s cutoff frequency, a low pass filter is employed. It is also known as high-cut filter since it provides a difficult passage to high frequency signals from source to output as shown in this project. Low pass filter is used for signal decoding, audio amplifiers, and demodulators. Also, various consumer electronic gadgets like mobiles, speakers system, gaming consoles, digital image display units apply a low pass filter.

The low pass filter circuit which is the prime part of this project, filters a frequency spectrum or any mix of frequencies. The frequencies above the cut-off frequency of the circuit are bypassed to the ground by the capacitor C. This is a capacitive low pass filter which has a resistor connected in series and a capacitor in parallel with the output. The principle involved: the reactance of the capacitor is inversely proportional to the frequency applied, i.e., Xc = 1/WC . As the frequency increases, the voltage across capacitor C drops down. This means that the output decreases with the increase in frequency. Thus the frequencies above the cutoff frequency are effectively reduced in amplitude. The cutoff frequency is the design parameter of the filter and depends on the value of capacitor C and resistor R according to the relation, f = 1/2