Digital processing of signals

Abstract

Much of the processing necessary in dealing with signals acquired from transducers involves filtering, since the raw signals consist of a large number of components at different frequencies, some of which may interfere with, or mask, the essential components. With analogue, or continuous, signals this can be achieved by the use of op-amp circuits with appropriate feedback components including inductors and capacitors. There are two main types of filter, the first of which allows low-frequency signals to pass but removes all components above a defined frequency. This is the low-pass filter (LPF). The second operates in the opposite sense and allows the high-frequency signals to pass but removes the components below a defined frequency. This is the high-pass filter (HPF). In theory components within the passband are not attenuated at all and there is a linear relationship between phase shift and frequency, whilst those outside the band are removed completely. As always, in practice these ideals are not met. Two related filter types can be constructed using combinations of low-and high-pass filter sections; when connected in series low-pass and high-pass sections give a bandpass filter in which only the band of frequencies lying between the two defined frequencies is transmitted, and when connected in parallel a bandstop filter is achieved.