Active Filters Name of the Subject :Integrated Circuits Name of the faculty :Mr. Mahesh Navale Name of the Department :EnTC Engg Department Name of the Institute :Smt. Kashibai Navale College of Engg, Vadgaon(Bk), Pune Introduction to Active Filters

Objectives After completing this kapsule, students should able to : State the ways filters can be classified and explain the characteristics of each. Discuss the differences among a Butterworth and Chebyshev Filter Approximation. 2Mr. Mahesh Navale - STES's SKNCOE, Pune

Introduction ► Filters are frequency selective circuit that are capable of passing signals within a specified band of frequencies while rejects or blocks or attenuates signals of frequencies outside this band. ►Depending on the type of elements used in their construction, filters are classified as : Filters Passive Filters Active Filters 3Mr. Mahesh Navale - STES's SKNCOE, Pune

Passive Filters ► Elements used in passive filters are: ▬ Resistors ▬ Capacitors ▬ Inductors 4Mr. Mahesh Navale - STES's SKNCOE, Pune RC FiltersLC Filters

Active Filters Mr. Mahesh Navale - STES's SKNCOE, Pune5 ► Active Filter consists of Transistors or Op-Amps in addition to Resistors and Capacitors.

Advantages of Active Filters ►Active filters can be designed to provide required gain, and hence no attenuation as in the case of passive filters. ►Active filter is easier to tune or adjust. ►No loading problem, because of high input resistance and low output resistance of op-amp. ►Active Filters are cost effective as a wide variety of economical op-amps are available. 6Mr. Mahesh Navale - STES's SKNCOE, Pune

Filter Approximation Mr. Mahesh Navale - STES's SKNCOE, Pune7 Active Filter Butterworth Chebyshev BesselElliptical Source :

►The implementation of the Butterworth active filter guarantees a flat response in the pass band and an ample roll-off. ►This group of filters approximates the perfect filter fit in the pass band. ►This kind of filter is a good, very easy to understand and is excellent for audio processing applications. ►higher the order, the higher the number of cascaded stages and the closer the filter becomes to the ideal “brick wall” response. Mr. Mahesh Navale - STES's SKNCOE, Pune8 Butterworth Filters Source : Also named as flat filter.

►It gives a sharper cutoff than a Butterworth filter in the pass band. ►A disadvantage of the Chebyshev filter is the exterior of gain minima and maxima below the cutoff frequency. ► The implementation of these filters gives a lot steeper roll- off, but has ripple in the pass- band, so it is not used in audio systems. Mr. Mahesh Navale - STES's SKNCOE, Pune9 Chebyshev Filters Source : Also called as an equal ripple filter.

Mr. Mahesh Navale - STES's SKNCOE, Pune10 Filter Parameters Transition region shows the area where the fall-off occurs.

Mr. Mahesh Navale - STES's SKNCOE, Pune11 Filter Parameters Passband of a filter is the range of frequencies that are allowed to pass through the filter with minimum attenuation (usually defined as less than -3 dB of attenuation).

Mr. Mahesh Navale - STES's SKNCOE, Pune12 Filter Parameters Stopband is the range of frequencies that have the most attenuation.

Mr. Mahesh Navale - STES's SKNCOE, Pune13 Filter Parameters Critical frequency, f c, (also called the cutoff frequency) defines the end of the passband and normally specified at the point where the response drops – 3 dB (70.7%) from the passband response.

Mr. Mahesh Navale - STES's SKNCOE, Pune14 Filter Parameters The bandwidth (BW) is defined as the difference between the upper critical frequency (f 2 ) and the lower critical frequency (f 1 ). B.W. = ( f 2 - f 1 ) The bandwidth (BW) is defined as the difference between the upper critical frequency (f 2 ) and the lower critical frequency (f 1 ). B.W. = ( f 2 - f 1 ) Damping Factor (DF) of an active filter determines which response characteristic the filter exhibits. DF is determined by the negative feedback and defined as :

Mr. Mahesh Navale - STES's SKNCOE, Pune15 Filter Parameters The quality factor (Q) can also be expressed in terms of the damping factor (DF) of the filter as : The quality factor (Q) is the ratio of the center frequency to the bandwidth.

Summary In this Kapsule, we discussed … The concept of filtering and its types. Various Filter parameters. Different Filter Approximation.. In the Next Kapsule, we will discuss … Ideal and Practical response of LPF. Design of First and Second order LPF. Frequency Response of First and Second order LPF Mr. Mahesh Navale - STES's SKNCOE, Pune16

References Ramakant A. Gayakwad, “ Op-Amps and Linear Integrated Circuits”, Third Edition-PHI Publication. Mr. Mahesh Navale - STES's SKNCOE, Pune17

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