Filters
Applications of Operational Amplifiers in Tamil
Filters
- A filter is often used in electronic circuits to block or allow a select frequency to the circuit.
- Filter is a frequency selective circuit that passes signal of specified Band of frequencies and attenuates the signals of frequencies outside the band.
- Filters are classified as
- Analog or digital filters
- Active or passive filters
- Audio(AF) or Radio Frequency(RF)
Filters
Types of Filters
- Active Filters
- Passive Filters
Active Filters
- An active filter is a type of analog circuit implementing an electronic filter using active components, typically an amplifier. Amplifiers included in a filter design can be used to improve the cost, performance and predictability of a filter.
- Active filters used op- amp as the active element.
- By enclosing a capacitor in the feed back loop, inductor less active filters can be obtained
Active Filters
Passive Filters
- Passive filters is the passive implementations of linear filters are based on combinations of resistors (R), inductors (L) and capacitors (C). These types are collectively known as passive filters, because they do not depend upon an external power supply and/or they do not contain active components such as transistors.
- Passive filters works well for high frequencies. But at audio frequencies, the inductors become problematic, as they become large, heavy and expensive.
Passive Filters
Advantages of Active Filters over Passive Filters
- Gain and Frequency adjustment flexibility
- Since the op-amp is capable of providing gain, the i/p signal is not attenuated as it is in a passive filter.[Active filter is easier to tune or adjust].
- No loading problem
- Because of the high input resistance and low o/p resistance of the op-amp, the active filter does not cause loading of the source or load.
- Cost
- Active filters are more economical than passive filter. This is because of the variety of cheaper op-amps and the absence of inductors.
Active Filter Types
- Low Pass Filter
- High Pass Filter
- Band Pass Filter
- Wide Band Pass Filters
- Band Reject Filters
Low Pass Filter
- A low pass filter is used in circuits that only allow low frequencies to pass through.
- It is often used to block high frequencies and AC current in a circuit. Here is a sample low pass filter circuit using op-amp.
Low Pass Filters
- It has a constant gain from 0 Hz to a high cutoff frequency f1. At fH the gain in down by 3db.
- The frequency between 0 Hz and fH are known as the pass band frequencies where as the range of frequencies those beyond fH, that are attenuated includes the stop band frequencies.
- Butterworth , Chebyshev and Cauer filter are some of the most commonly used practical filters.
High Pass Filter
- A high pass filter is used in circuits that only require high frequencies to operate.
- It blocks most low frequencies & DC component. Here is a sample high pass filter circuit using op-amp.
High Pass Filters
Band Pass Filter
- A band pass filter is a combination of a high pass and a low pass filter.
- It allows only a select range of frequencies to pass through. Because cut off frequency of the low pass filter is higher than the cut off frequency of the high pass filter.
Band Pass Filter
Wide Band Pass Filters
- It is connection of a low pass filter and a high pass filter in cascade. The fH of low pass filter and fL of high pass filter are related as fH > fL.
Wide Band Pass Filters
Band Reject Filters
- A band reject or band stop filter also known as notch filter is used in circuits that block only a select range of frequencies and allows others to pass through.
- It would be an inverse of the band pass filter, and can be created by using the same input at a high pass and a low pass filter.
Band Reject Filters
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