Anti aliasing filters

Sampling is an important term in electronics. It is used to convert analog output of an information source into a discrete symbol sequence suitable for transmission over a digital communication system. A sample and hold circuit takes a snapshot of the signal and holds the value. An analog to digital converter is used here which performs precise conversion. The sample and hold system is equivalent to a circuit composed of a switch and a capacitor. Sampling theorem supports accurate reconstruction of any signal from the values sampled at a rate at least twice the highest frequency present in the signal. If the system fails to satisfy this condition, it will result in aliasing. During aliasing, higher frequency components appear with lower values. There exist many methods to tackle this problem. Most effective one is anti aliasing filters where a low-pass filter is applied to the signal before sampling which removes unwanted frequency components. Anti aliasing filters are formed as analog interface chips. These chips convert analog signals into digital form for processing by a digital signal processor. There exist two categories in anti aliasing filters. They are analog and digital. Usage of digital anti aliasing filter avoids noise and drift problems commonly encountered in analog version. MATLAB designed an anti aliasing filter based on Parks-McClellan method. They named it as 204-tap FIR.