06_Lecutre

06_Lecutre - EE114 Lecture 6 R Dutton B Murmann 1 Lecture 6...

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Unformatted text preview: EE114 Lecture 6 R. Dutton, B. Murmann 1 Lecture 6 Intrinsic Capacitance Bandwidth-Supply Current Tradeoff R. Dutton, B. Murmann Stanford University R. Dutton, B. Murmann 2 Common Source Amplifier Revisited • Interesting question – How fast can this circuit go? • R i models finite resistance in the driving circuit – Needed for a realistic discussion v i V I R i “Transducer” V o V B R I B EE114 Lecture 6 R. Dutton, B. Murmann 3 Circuit Speed • There are two perspectives on “how fast” a circuit can go – Somewhat dependent on the application which one of the two matters more • Time domain – Apply a transient at the input (e.g. a voltage step), measure how fast the output settles • Frequency domain – Apply a sinusoid at the input, measure the gain and phase of the circuit transfer function across frequency • Knowing the time domain response, we can estimate the frequency domain response, and vice versa • In EE114 we will mostly work with frequency domain analyses to argue about the useful frequency range of a circuit R. Dutton, B. Murmann 4 Application Perspective • Frequency ranges for various applications – Audio ~20Hz to 20kHz – Video signals ~50MHz – Cable TV ~100-800MHz – Radios • AM ~500kHz–1700kHz • FM ~100MHz • Wireless LAN ~2.4GHz or 5GHz • Cellular phones ~1GHz • GPS ~1227 and 1575 MHz – … EE114 Lecture 6 R. Dutton, B. Murmann 5 The Culprit • In practical circuits, the presence of capacitance prevents us from building circuits that can run “infinitely” fast – Sometimes inductors can be used improve the situation • See EE314 i C + v C-dt dv C i C C = • Intuition – High frequency results in large dv C /dt and large i C – Capacitor becomes a “short” for high frequencies R. Dutton, B. Murmann 6 RC Low-pass i C + v C =v o-+ v i-R dt dv C i C C = ) s ( sCv ) s ( i C C = Laplace domain (ignoring initial condition) p s sRC R sC sC ) s ( v ) s ( v ) s ( H o o ! = + = + = = 1 1 1 1 1 1 sC Z ) s ( i ) s ( v C C C 1 = = RC p 1 ! = “Pole” ! + " = j s EE114 Lecture 6 R. Dutton, B. Murmann 7 1 2 3 1 2 3 1 2 3 !-" | H ( s ) | Pole RC=1-1/RC j ! " s R. Dutton, B. Murmann 8 Magnitude and Phase • Evaluate H(s) for s=j ω – Steady-state phasor analysis ( ) ( ) RC tan ) j ( H RC RC j ) j ( H ! " = ! # ! + = ! + = ! " 1 2 1 1 1 1 • Magnitude and phase of the transfer function are commonly illustrated using Bode plots – Simply a log-log plot of the magnitude along with a log-angle plot for the phase (note red dashed curve on Slide 7) EE114 Lecture 6 R. Dutton, B. Murmann 9 Bode Plot 10-2 10-1 10 10 1 10 2-40-20 | H ( j ! ) | [ d B ] 10-2 10-1 10 10 1 10 2-100-50 ! *RC A n g l e [ H ( j !...
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06_Lecutre - EE114 Lecture 6 R Dutton B Murmann 1 Lecture 6...

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