Crystal Oscillators Alex Fertelmes fertelmes@psu.edu 217-2131

High Level Description Crystal If a crystal is placed into the feedback path of an amplifier circuit, it begins to oscillate at a frequency dependent primarily on the dimensions of the crystal The size of the crystal is the primary factor in determining the frequency of the oscillation Example The Earth rotates once and this designates the time period of a day. If the Earth rotated at a different speed (frequency) the amount of time in a day would be different

Piezoelectric Effect

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TTL Crystal Oscillator 50 ns per division About 250 ns in period 1/250 ns = 4 MHz

Crystal 10 ms per division About 16 ms in period 1/16 ms = 62.5 Hz

Frequency Stability Effected by Temperature Time of operation (Aging) Correction Methods Temperature compensated oscillators TCXO (voltage control) VCXO Oven controlled oscillators OCXO