Filters

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basic filters used in an industries

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Filters

  1. 1. FILTERS…
  2. 2. GENERAL• A Filter is an electrical circuit that is designed to pass a specified band of frequencies while attenuating all the signals outside that band.• It is a frequency selective circuit.• The filters are basically classified as active filters & passive filters.• They are used in circuits which require the separation of signals according to their frequencies.• They are widely use in communication & signal processing.
  3. 3. ADVANTAGES OF ACTIVE FILTERS OVER PASSIVE FILTERS• All the elements alongwith op-amp can be used in the integrated form. Hence there is reduction in size & weight.• The op-amp gain can be easily controlled in the closed loop fashion hence active filter I/P signals is not attenuated.• The op-amp has high I/P impedance & low O/P impedance, hence the active filters using op-amp do not cause loading of the source or load.
  4. 4. LIMITATIONS OF ACTIVE FILTERS• The finite bandwidth of the active devices places a limit on the highest frequency of operation.• A reasonably good filter performance can be achieved approximately upto 500 kHz,as against this passive filters can be used upto 500 MHz.• The active elements are more sensitive to the temperature & environmental changes than the passive elements.• The requirement of d.c power supply is another disadvantage of the active filters.
  5. 5. COMMONLY USED FILTERS• The most commonly used filters are :-• Low Pass Filter• High Pass Filter• Band Pass Filter• Band Reject Filter• All Pass Filter &• Universal Filters.
  6. 6. FREQUENCYRESPONSE OF LOW • A Low Pass Filter has aPASS FILTER constant gain from 0 Hz to aIDEAL & PRACTICAL high cut-off frequency, Fh.RESPONSE • Practically, the gain decreases as the frequency increases & at f=Fh, the gain is down by 3 db & after Fh, it decreases at a higher rate. • After the end of a transition band, the gain becomes zero.
  7. 7. FRQUENCY RESPONSE OF HIGH PASS FILTER • For a High pass Filter, Fl is the low cut-off frequency. • The range of frequency 0<f<Fl is the stop band, while f>Fl is the pass band. • The transition band is not shown in the characteristics as it is very small.
  8. 8. FREQUENCY RESPONSE OF BAND PASS FILTER • The band pass filter has two stop bands. • The range of frequency 0<f<Fl & range of frequency Fh<f<infinity are two stop bands while the range Fl<f<Fh is the pass band. • The bandwidth is thus Fh- Fl.
  9. 9. FREQUENCY RESPONSE OF BAND STOP FILTER • The band elimination filter is also called band rejection filter or band stop filter. • Its characteristics is exactly opposite to that of band pass filter. • There are two pass bands while one stop band. • The two ranges are 0<f<Fl & Fh<f<infinity.
  10. 10. FIRST ORDER LOW PASS FILTER• A first order filter consists of a single RC n/w connected to the i/p terminal of a non-inverting op- amp.• Resistors Ri & Rf determine the gain of the filter in the pass band.
  11. 11. The voltage across the capacitor Let wh= 1/RCin the s-domain is:-The closed loop gain of the To determine the frequency response, putop-amp is:- s=jw in above eq.
  12. 12. At very low frequency, i.e. f<<fh And At very High frequency i.e. f>>fh, we haveIt has the max. gain at f=0 Hz. At fh the gain falls to.707 time the max. gain.Hence gain rolls off at the rate of 20 dB/decade.
  13. 13. SECOND ORDER HIGH PASS FILTERHigh pass filter is the complement of the low pass filter& can be obtained simply by interchanging R & C inthe low pass configuration as shown in the fig. This is the transfer function:
  14. 14. BAND PASS FILTER There are two types of band pass filters which are classified as per Quality factor: 1. Narrow band pass filter (Q>10) 2. Wide band pass filter (Q<10) BW = f2 – f1 Q = f0 / BWAv R1 C2 C1 R2 Rfb Stage 2 Stage 1 R1 response R2 response BW Ri + Vin _ + VO _ f f1 fo f2
  15. 15. BAND REJECT FILETR This can also be either as a Narrow or wide band reject filter. The narrow band reject filter is commonly called a notch filter & is useful for the rejection of a single frequency, such as 50 Hz power line frequency hum. Av(dB) low-pass high-pass C1 {-3dB R1 R1 Rfb R2 Ri + C2 + Vin VO _ _ f f1 f2
  16. 16. ALL PASS FILTER• An all-pass filter passes all frequency components of the i/p signal without any attenuation & provides desired phase shifts at different frequencies of the I/P signal.• When signals are transmitted over transmission lines, such as telephone wires, they undergo change in phase. These phase changes can be compensated by all-pass filters.• Thus, they are also called as delay equalizers or phase correctors
  17. 17. STATE VARIABLE FILTER• The state variable configuration uses two op-amp integrators & one op-amp adder to provide simultaneous second order low-pass, band-pass & high-pass filter responses.• As it is possible to obtain LP,BP,HP & notch filter O/P’s from a state variable filter & therefore these are also known as UNIVERSAL FILTERS

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