crystaloscillator.pdf - APPLICATION NOTE Crystal Oscillator...

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APPLICATION NOTE Crystal Oscillator Circuit Design © 1997 MX COM Inc. Tele: 800 638-5577 910 744-5050 Fax: 910 744-5054 Doc. # 20830065.001 4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies. In this application note we shall discuss our recommended crystal oscillator circuit, explain each component in the circuit and provide some guidelines on selecting values for these components. Finally, we shall give a few precautions to take in order to avoid in-stability and start-up problems. R L C Cp Figure 1. Crystal equivalent Circuit. Anti-Resonance Series Resonance fs Parallel Resonance fa Impedence f Figure 2. Reactance Vs Frequency plot of a crystal. Figure 1. shows the crystal equivalent circuit. R is the effective series resistance, L and C are the motional inductance and capacitance of the crystal. C P is the shunt capacitance due to the crystal electrodes. Figure 2. shows the reactance- frequency plot of the crystal. When a crystal is operating at series resonance it looks purely resistive and the reactances of the inductor and the capacitor are equal (XL = XC). The series resonance frequency is given by the equation fs LC = 1 2 π When the crystal is operating in parallel resonant mode it looks inductive. The frequency of operation in this mode is defined by the load on the crystal. The crystal manufacturer should specify the load capacitance C L for parallel resonant crystals. In this mode the frequency of oscillation is given by the equation.
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  • Winter '18
  • Crystal, Crystal oscillator, Electronic oscillator

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