13 - Frequency Response

13 - Frequency Response - EECS 215 Frequency Response J....

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Unformatted text preview: EECS 215 Frequency Response J. Phillips EECS 215 Transfer Function We often want to know how a circuit will respond to changing frequency Transfer function: relates output to input ( ) ( ) ( ) X Y H = ( ) ( ) ( ) gain Voltage = = i o V V H ( ) ( ) ( ) gain Current = = i o I I H ( ) ( ) ( ) Impedance Transfer = = i o I V H ( ) ( ) ( ) Admittance Transfer = = i o V I H J. Phillips EECS 215 Poles And Zeros Separate H( ) into numerator and denominator (Not necessarily input and output) ( ) ( ) ( ) D N H = ( ) zero) to goes (function zero = N Roots of numerator and denominator provide much insight into frequency response ( ) infinite) is (function pole = D For convenience, substitute s = j Frequency response characteristics described by poles and zeros J. Phillips EECS 215 Low Pass RC 0.5 1 1.5 2 x 10 5 0.5 1 Frequency (Hz) M a g n i t u d e 0.5 1 1.5 2 x 10 5-80-60-40-20 Frequency (Hz) P h a s e ( d e g r e e s ) J. Phillips EECS 215 High Pass LC 0.5 1 1.5 2 x 10 5 0.5 1 Frequency (Hz) M a g n i t u d e 0.5 1 1.5 2 x 10 5 20 40 60 80 Frequency (Hz) P h a s e ( d e g r e e s ) J. Phillips EECS 215 Decibels Convenient to describe frequency response on logarithmic scale bels of number log 1 2 10 = = P P G Ratio of two powers For voltage, current, recall relation to power = 1 2 10 log 10 P P G dB dB P P 3 ~ 2 1 2 = dB P P 3 ~ 5 . 1 2 = dB P P 1 2 = = 1 2 10 log 20 V V G dB = 1 2 10 log 20 I I G dB Decibels J. Phillips EECS 215 Bode Plots Convenient and standard technique of plotting frequency response j He H = = H j H + = ln H ln Semilog plots of magnitude (dB) and phase of transfer function Semilog plots are more intuitive, easier to construct H H dB 10 log 20 = Since these are logarithmic, each factor can be...
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13 - Frequency Response - EECS 215 Frequency Response J....

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