Quartz Crystal Microbalance Digital Controller

18 Theory, Operation and Calibration Chapter 2AGCAmpR mL mC 0R LC mC vFigure 18. Oscillator Circuit with Varactor Nulling of C 0 .With C o canceled the circuit simplifies to that shown in Figure 19. For this circuit, thezero phase condition is achieved at series resonance where the reactance of C m and L mcancel. At series resonance R m and R L form a resistive attenuator requiring an AGC gainof A v = (R m + R L )/R L to sustain oscillation. By knowing the AGC gain 6 , A v , required tosustain oscillation, we can determine R m = R L • ( A v - 1).AGCAmpL mC mR mZ Lm + Z Cm = 0R LFigure 19. Oscillator Circuit Model with C 0 cancelled by C v .QCM200 Quartz Crystal Microbalance