 So, today we are going to study introduction to passive filter, learning outcome at the end of this session students will be able to identify passive filters. Before starting with the introduction of passive filter you have to stop this video here and you have to answer for our question and the question is explain or what is working of inductor as well as capacitor. Introduction filter is an electrical circuit which can transfer a signal from a particular frequency band and it will attunate frequency signals except that pass band. So, frequency signal which are to be passed through the filter circuit is to be called as a pass band and frequency signal which are to be suppressed from the filter circuit are to be called as attenuation band. And the frequency signal or frequency which will distinguish pass band and attenuation band is to be called as cutoff frequency. So, generally there is a unique cutoff frequency or in some cases there are two cutoff frequencies. So, if a cutoff frequency is unique it is to be represented by fc and if there are two cutoff frequencies in that case the lower cutoff frequency is to be represented by f1 and higher cutoff frequency is to be represented by f2. So, generally in case of ideal filter frequency signals in pass band are to be passed through the filter circuit there should not be any attenuation or zero attenuation and frequency signal in attenuation band are to be suppressed. So, this type of filter circuit is to be called as a ideal filter, practical filters. So, there is a difference between ideal filter and practical filter. So, all the frequency signals which are present in pass band are not passed through the filter circuit in the practical filters. So, there is a loss in signal power and all the frequency signal in attenuation band are not attenuated. So, this is a practical filter and the passive filters are to be designed with the help of different combinations of inductor and capacitor. First property is characteristic impedance. So, characteristic impedance is to be represented by Z0 and the characteristic impedance should match with the circuit with which it is to be connected throughout the pass band. So, this will remove the reflection losses. So, a filter circuit in which the characteristic impedance is present is to be selected properly. Next characteristic is pass band characteristic. So, generally signal in the pass band should have zero attenuation or minimum attenuation and signals within attenuation band should have maximum or infinite attenuation. Attenuation constant is to be represented by alpha and that can be measured with the unit of neighbor or decibel. So, it will measure degree of attenuation present in attenuation band or pass band. Next property in the filter is cutoff frequency characteristic. So, a filter should able to differentiate between pass band and attenuation band. So, it should be capable of identifying the pass band and attenuation band which is to be used in filter circuit. Now, we will see use of filters. First use is in wise frequency number of band pass filters which will have different pass bands are to be used for multi-channel communication. Next telephony or radio and TV broadcasting. So, in this case the filter circuit is to be used to send information in which attenuation of a carrier signal is to be done and these signals are to be received by utilizing filters. Next is radio receivers. So, intermediate carrier frequency selection is to be performed with the help of filters. Next AM detection. So, in case of AM detection high pass filters are to be used to separate carrier frequency from audio frequency signal. Next use is in various stages in TV receivers to produce combined sound and picture carrier and which is to be separated at the receiver with the help of filter circuit. Next use is for audio amplifiers. So, in audio amplifiers harmonic distortion and wise rejection is to be removed or these errors are to be removed with the help of filter circuit. Next application is in many electronic measuring equipment band of frequencies are to be studied with the help of filter circuit. Last use is in case of electrical circuits low pass filter and high pass filters are to be used to eliminate undesired frequency component from thyristor controlled circuits. So, based on relation between series arm impedance Z1 and shunt arm impedance Z2 filters are categorized as prototype filter or constant K filter. So, product of Z1 and Z2 is to be represented by R0 square and which is constant. So, the alphabet K is to be used. So, if the product of series arm impedance and shunt arm impedance is constant. So, that type of filter is to be called as prototype filter or constant K filter. Next type is MD write filter. So, with the help of prototype filter or constant K filter MD write filters are to be designed. Next categorization is based on identifying the frequency characteristic of filter. So, based on that the type of filters are low pass filter, high pass filter, band pass filter and band stop filter. So, this table represents how the classification of filters is to be done based on the frequency characteristic. So, if it is low pass filter pass band is from 0 to fc that is cutoff frequency and attenuation band is from cutoff frequency to infinite. For high pass filter pass band is fc to infinite means from cutoff frequency to infinite and attenuation band is from 0 to fc that is cutoff frequency. If the filter is band pass filter the pass band is from f2 to f1 and attenuation band is from 0 to f2 means 0 to the first cutoff frequency and f1 to infinite. So, from second cutoff frequency to infinite that is attenuation band. If the filter is band stop filter pass band is 0 to f1. So, 0 to lower cutoff frequency and from f2 to infinite. So, higher cutoff frequency to infinite that is pass band and attenuation band is from f1 to f2. Now, we will see constant k low pass filter. So, these circuits will represent t configuration as well as phi configuration of low pass filter as well as the graph represents LPF attenuation characteristics. So, in t configuration we can see that two inductors are present in series arm and a capacitor is present in shunt arm. So, when signal is applied at the input of this t configuration for low frequency signals that capacitor which is present in the shunt arm will act as a open circuit. So, input signal is to be passed to the output and for high frequency signal the capacitor acts as a short circuit and signal is to be revert. So, signal is not transferred means high frequency signals are not transferred to the filter circuit. So, for that the graph is to be shown on the x axis there is a frequency and on y axis there is a alpha that is attenuation constant. Next constant k high pass filter. So, this is exactly opposite to the low pass filter and again t configuration as well as pi configuration as well as high pass filter characteristic are to be shown. So, in the series arm there are capacitors which are to be represented by the value 2c and in the shunt arm there is a inductor. So, with the properties of capacitor and inductor in this case for low frequency the signal is to be attenuated and for high frequency the signal is to be passed. So, capacitor acts as a short circuit for low frequency signal and it acts as a short circuit for high frequency signal. Now, constant k band pass filter. So, the band pass filter is combination of low pass filter as well as high pass filter. So, L C tuned circuit are to be used to construct band pass filter. So, 0 to f 2 that is a lower cutoff frequency it is a stop band and from f 2 to f 1 this is pass band for band pass filter and again from f 1 to infinite that is from higher cutoff frequency to infinite it is stop band. Now, constant k band stop filter. So, here also the combination of low pass as well as high pass is to be present in the filter circuit. So, here also we can see t configuration as well as pi configuration and the band stop filter characteristic are to be shown. So, from 0 to f 1 that is lower cutoff frequency and from f 2 to infinite that is from higher cutoff frequency to infinite is pass band and from f 1 to f 2 means from lower cutoff frequency to higher cutoff frequency it is stops. So, while preparing this video lecture I have referred circuit theory analysis and synthesis by A Chakrabarty.