Pierce oscillator
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The Pierce oscillator is a type of electronic oscillator circuit particularly well-suited for implementing crystal oscillator circuits. Named for its inventor, George W. Pierce, the Pierce oscillator is a derivative of the Colpitts oscillator. Virtually all digital IC clock oscillators are of Pierce type as the circuit can be implemented using a minimum of components: a single digital inverter, two resistors, two capacitors, and the quartz crystal, which acts as a highly selective filter element. The low manufacturing cost of this circuit, combined with the outstanding frequency stability of the quartz crystal, give it an advantage over other designs in many consumer electronics applications.
[edit] Applications
R1 converts the inverter into an amplifier by operating as a feedback resistor. By operating in parallel, the crystal forms a pi network with C1 and C2 which provides phase shift from the output to input. The values of C1 and C2 must be considered, as they are used to calculate the load capacitance which will determine the oscillation frequency. A second resistor could be used between the output of the inverter and the crystal to isolate the inverter from the crystal network. This would also add additional phase shift to C1.
[edit] References
Fairchild Semiconductor Corporation, HCMOS Crystal Oscillators: Fairchild Semiconductor Application Note 340, May 1983, pp. 1-2
