Transcription of Crystal Oscillators (XTAL)
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Crystal Oscillators (XTAL)
EECS 142 Crystal Oscillators ( xtal )Prof. Ali M. NiknejadUniversity of California, BerkeleyCopyrightc 2009 by Ali M. NiknejadA. M. NiknejadUniversity of California, BerkeleyEECS 242 p. 1/28 p. 1/28 Crystal ResonatorC0L1C1R1R2R3L2C2L3C3tquartzQuar tz Crystal is a piezoelectric material. An electric fieldcauses a mechanical displacement and vice versa. Thus it is aelectromechanical equivalent circuit contains seriesLCRcircuits thatrepresent resonant modes of the xtal . The capacitorC0is aphysical capacitor that results from the parallel platecapacitance due to the M. NiknejadUniversity of California, BerkeleyEECS 242 p. 2/28 p. 2/28 Fundamental Resonant ModeAcoustic waves through the Crystal have phase velocityv= 3 103m/s. For a thicknesst= 1mm, the delay time throughthe xtal is given by =t/v= (10 3m)/(3 103m/s) = 1/3 corresponds to a fundamental resonant frequencyf0= 1/ =v/t= 3 MHz =12 quality factor is extremely high, withQ 3 106(invacuum) and aboutQ= 1 106(air).
Fundamental Resonant Mode Acoustic waves through the crystal have phase velocity v = 3×103m/s.For a thickness t = 1mm, the delay time through the XTAL is given by τ = t/v = (10−3m)/(3×103m/s) = 1/3µs. This corresponds to a fundamental resonant frequency
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