EECS 105 Spring 2005 Lecture 19 R T Howe EECS 105 Spring 2005 Lecture 19 thin Film Bulk Acoustic Resonator FBAR Lecture 19 RF MEMS Agilent Technologies Last time IEEE ISSCC 2001 Phasor analysis techniques Rapid sketching techniques for Bode Plots N 1000 Thin Piezoelectric Film Brian Otis Jan Rabaey BWRC low noise oscillator 2nd order circuits in the frequency domain MOSFET models Equivalent Circuit C1 University of California Berkeley Dept of EECS EECS 105 Spring 2005 Lecture 19 R T Howe j L Vl R Vc Il Ir Ic C0 Cx Dept of EECS R0 Rx Lx University of California Berkeley R T Howe Simplifying 1 H j 2 1 j RC LC Define parameters 1 j C Vc Vs 1 j C R j L University of California Berkeley C2 Transfer Function 1 j C Impedance divider Sense Electrode EECS 105 Spring 2005 Lecture 19 Phasor Analysis of 2nd Order Circuit Dept of EECS Drive Electrode 2 GHz resonator Today Vs R T Howe o 1 LC RC 1 H j 2 1 o j Dept of EECS University of California Berkeley 1 EECS 105 Spring 2005 Lecture 19 R T Howe EECS 105 Spring 2005 Lecture 19 Limiting Cases Magnitude and Phase Low frequency o R T Howe Inductor Capacitor Tuning At resonance the impedance of the capacitor cancels the impedance of the inductor phasor current is maximum and capacitor voltage peaks High frequency o How sharp or narrow is the resonance Resonant frequency o Define the quality factor Q University of California Berkeley Dept of EECS EECS 105 Spring 2005 Lecture 19 R T Howe o Q 1 o University of California Berkeley Dept of EECS EECS 105 Spring 2005 Lecture 19 Magnitude Bode Plot R T Howe Phase Bode Plot 60 o 0 H dB Phase H 40 o o 45 90 20 o 0 o 135 o 180 20 Dept of EECS University of California Berkeley Dept of EECS University of California Berkeley 2 EECS 105 Spring 2005 Lecture 19 R T Howe Common Source Amplifer Ai j EECS 105 Spring 2005 Lecture 19 R T Howe CS Short Circuit Current Gain Transfer function Ai j g m 1 j C gd g m j C gs C gd DC Bias is problematic what sets VGS University of California Berkeley Dept of EECS EECS 105 Spring 2005 Lecture 19 R T Howe University of California Berkeley Dept of EECS EECS 105 Spring 2005 Lecture 19 R T Howe MOS Unity Gain Frequency Magnitude Bode Plot Since the zero occurs at a higher frequency than pole assume it has negligible effect Transition frequency Current gain 1 gm Cgs Cgd Ai gm 1 j Cgs Cgd T W g m Cox L VGS VT 3 VGS VT 2 2 Cgs L2 WLCox 3 T Performance improves like L 2 for long channel devices For short channel devices the dependence is like L 1 T Dept of EECS T University of California Berkeley Dept of EECS 3 VGS VT 2 L 2 VGS VT Time to Eeff v L cross L channel L L University L of California Berkeley 3
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