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Low pass filter


Himanshu Choudhary

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 = 1/2RC.


Circuit Diagram


Resistor Image

Resistor is a passive component used to control current in a circuit. Its resistance is given by the ratio of voltage applied across its terminals to the current passing through it. Thus a particular value of resistor, for fixed voltage, limits the current through it. They are omnipresent in electronic circuits.

Capacitor image



Capacitor is a passive component used to store charge. The charge (q) stored in a capacitor is the product of its capacitance (C) value and the voltage (V) applied to it. Capacitors offer infinite reactance to zero frequency so they are used for blocking DC components or bypassing the AC signals. The capacitor undergoes through a recursive cycl...

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