In recent years, filters have come to play an ever increasing role in signal processing. Filters have found applications in such areas as the analysis of seismic data and adaptive filtering of signals from noisy communication channels. Filters are essential building blocks in many systems, particularly in communication and instrumentation systems. A filter passes one band of frequencies while rejecting another. Typically implemented in one of two technologies: passive RLC filters and active RC filters.
Television signal splitter, consisting of a hi- and lo-pass filter. wikimedia
Passive and Active Filters
Passive filters work well at high frequencies, however, at low frequencies the required inductors are larges, bulky and non-ideal. Furthermore, inductors are difficult to fabricate in monolithic from and are incompatible with many modern assembly systems. Active RC filters utilize op-amps together with resistors and capacitors and are fabricated using discrete, thick film and thin-film technologies. The performance of these filters is limited by the performance of the op-amps.
Passive filters are a key component, which links power electronics based generation or electrical loads with the power system. For example, a voltage-source converter needs an output filter inductor in order to be able to be operated and controlled. The size of the inductance dictates the amount of current harmonics and thereby influence on the cost, size and efficiency of the overall converter system. A very large inductance, results in an efficient, but a bulky and costly passive filter. On the other hand, a lower inductance implies increased power losses (as a result of increased harmonic current), but at reduced size and cost.
Proper performance specifications of voltage distortion limits has a consequent impact on the on filter design. Stringent harmonic specifications could demand for bulky and costly passive filters, while more permissible specifications could turn into harmonic stability problems, as result of not sufficient filtering and reduced damping. Harmonic stability problems are caused by series and parallel resonances that exist in the passive filters and the grid impedance. It is found that the inappropriate selection of the passive filter parameters and the processing delay in the control system are the key aspects that may lead to harmonic instability.
In realizing a filter, one or more elements must be varied, in order to vary the frequency response of the filter. Elements such as resistors and low-valued capacitors can be varied mechanically or by using specialized de- vices such as resistors and varicap diodes. These methods present practical problems, especially where high accuracy is important.
Electrocarrdiogram (ECG). pixabay
Filters application are mainly in telecommunication and biomedical fields. The telecommunications market requirements and continuous technology development impose. On the transceiver side, the filtering part (active and passive) had an important contribution to the transceiver configurability and smaller size.
In the field of biomedical, biomedical signals are the recorded signals of the biomedical actions through special devices. ECG (Electrocardiogram), EMG (Electromyogram), EEG (Electroencephalogram), EOG (Electro-oculogram) etc. are some examples of these measuring devices. These signals are generated by electrochemical operation of excitable cells such as nervous, muscular and glandular tissue. Electric potentials are developed when millions of such cells are generated. On a larger part, filters play a big role in the development of technology.
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