EE40 Lecture 18 Venkat Anantharam 3 07 08 Reading Chap 6 Filters twoterminal elements Bode plots EE40 Spring 2008 Slide 1 Venkat Anantharam Transfer Function Transfer function is a function of frequency Complex quantity Both magnitude and phase are functions of frequency Vin Two Port filter network Vout Vout Vout H f out in Vin Vin H f H f EE40 Spring 2008 Slide 2 Venkat Anantharam Frequency Response The shape of the frequency response of the complex ratio of phasors VOUT VIN i e both the magnitude and the phase is a convenient means of classifying a circuit behavior and identifying key parameters We will soon discuss quick and dirty ways of approximating this shape via a piecewise linear approximation based on asymptotes as in the magnitude plot approximations below Magnitude of VOUT VIN Magnitude of Gain Break point Low Pass VOUT VIN Break point Gain High Pass Frequency Frequency Only positive frequencies need be considered since the plots for negative frequencies can be inferred from this FYI These are usually log of the ratio vs log frequency plots EE40 Spring 2008 Slide 3 Venkat Anantharam Example Circuit R2 VIN R1 VT AVT C VOUT TransferFunction VIN VOUT AZ c VIN Z R Zc VOUT A 100 R1 100 000 Ohms R2 1000 Ohms C 10 uF VOUT A 1 jwC A VIN R2 1 j C 1 j R2C EE40 Spring 2008 Slide 4 Venkat Anantharam Filters Filters are circuits designed to retain a certain frequency range and discard others Low pass pass low frequencies and reject high frequencies High pass pass high frequencies and reject low frequencies Band pass pass some particular range of frequencies reject other frequencies outside that band Notch reject a range of frequencies and pass all other frequencies EE40 Spring 2008 Slide 5 Venkat Anantharam Common Filter Transfer Function vs Freq Magnitude of Magnitude of H f H f Low Pass Frequency Magnitude of High Pass Magnitude of Frequency H f H f Band Reject Band Pass Frequency EE40 Spring 2008 Frequency Slide 6 Venkat Anantharam
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