# low pass filter

Topics: Low-pass filter, High-pass filter, Filter Pages: 4 (1351 words) Published: October 6, 2013
﻿Theory:
A low-pass filter is an electronic filter that passes low-frequency signals and attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency. It implemented using a resistor and a capacitor. The actual amount of attenuation for each frequency varies from filter to filter. A low-pass filter is the opposite of a high-pass filter. The below circuit diagram illustrates a simple 'RC' low-pass filter.

The range of frequencies passed by a low pass filter within a specified limit called the band-pass of the filter. The point considered to be the upper end of the band is at the critical frequency (fc). The critical frequency (fc) is the frequency at which the filter’s output is 70.7 % of the maximum. The filter’s critical frequency is called the cut off frequency, break frequency or -3dB frequency. For a RC filter, the cut off frequency (fc) = 1/ (2RC)

Introduction
Basically, an electrical filter is a circuit that can be designed to modify, reshape or reject all unwanted frequencies of an electrical signal and accept or pass only those signals wanted by the circuits designer. In other words they "filter-out" unwanted signals and an ideal filter will separate and pass sinusoidal input signals based upon their frequency. In low frequency applications (up to 100kHz), passive filters are generally constructed using simple RC (Resistor-Capacitor) networks, while higher frequency filters (above 100kHz) are usually made from RLC (Resistor-Inductor-Capacitor) components. Passive filters are made up of passive components such as resistors, capacitors and inductors and have no amplifying elements (transistors, op-amps, etc) so have no signal gain, therefore their output level is always less than the input. Filters are so named according to the frequency range of signals that they allow to pass through them, while blocking or "attenuating" the rest. The most commonly used filter designs are the: 1. The...