Introduction To Filter

What is a filter?
A filter is a device that passes electric signals at certain frequencies or frequency ranges while
preventing the passage of others.
Applications:
• Filter circuits are used in a wide variety of applications.
• In the field of telecommunication, band-pass filters are used in the audio frequency
range (0 kHz to 20 kHz) for modems and speech processing.
• High-frequency band-pass filters (several hundred MHz) are used for channel
selection in telephone central offices.
• Data acquisition systems usually require anti-aliasing low-pass filters as well as lowpass
noise filters in their preceding signal conditioning stages.
• System power supplies often use band-rejection filters to suppress the 60-Hz line
frequency and high frequency transients.
• In addition, there are filters that do not filter any frequencies of a complex input
signal, but just add a linear phase shift to each frequency component, thus
contributing to a constant time delay. These are called all-pass filters.
• At high frequencies (> 1 MHz), all of these filters usually consist of passive
components such as inductors (L), resistors (R), and capacitors (C). They are then
called LRC filters.
• In the lower frequency range (1 Hz to 1 MHz), however, the inductor value becomes
very large and the inductor itself gets quite bulky, making economical production
difficult.
• In these cases, active filters become important. Active filters are circuits that use an
operational amplifier (op amp) as the active device in combination with some
resistors and capacitors to provide an LRC-like filter performance at low frequencies.


Application as Interface Circuit:
That connects the real world analog signal to the digital signal processor and provides band
limiting before the signal can be sampled for further processing with the digital technique and
reconstruction back to the analog world.
Why We Use Analog Filter?
• The practical active filter makes use of operated amplifier together with capacitor and
resistor is known as Analog filters.
• Many filtering applications are now handle with digital signal processing techniques
and digital filters.
• Analog continues time filter provides a more economical solution.
• For analog filter we must consider such factors as:
Factor considered while filter designing:
1. Technology derived for the system implementation.
2. Availability of DC supplies for the active devices and power
consumption.
3. Availability of voltage source for Op-Amp.
4. Cost.
5. Range of frequency of operation.
6. Sensitivity to parameter changes and stability.
7. Weight and size of the implemented circuit.
8. Noise and dynamic range of the realize filter.
These factors are to choose an analog or digital filter for a particular application.
Introduction to Filter Design:-
• The filter design is a special case of electric wave’s filter which makes the properties of
the Op-Amp.
• Such filter are sometimes called Active filter, currently called Analog Filter.
• In modern integrated circuits technology both analog and digital filter may be
implemented on the same chip.
Circuit Diagram:-
• If we know the circuit and the form of input then we may determine the output V2, this is
known as Circuit Analysis.
• If we know the input and the output or the ration that is |T| then we found the response in
the circuit is known as Circuit Designing.
• We have to design a circuit therefore we concern with designing in the filter Analysis.
• The circuit that we have design for the variation of the magnitude, phase or related
quantities they are known as Filter.
• In electrical engineering we filter the signal in terms of voltages at a specified frequency.
If a signal is made up of 2 tones, one at high frequencies called Piccolo and other is low
frequency called Tuba, imagine a filtering action by which one tone or the other is
suppressed.