Crystal Oscillator

This application note addresses issues commonly raised during the selection of the reference crystal, typically 14.318 MHz, for Chrontel's product line.

Pierce Oscillator
A simplified schematic of the oscillator circuit used in Chrontel products is shown in Figure 1. Note that the typical 2-pin crystal has been replaced by its equivalent circuit model.
• Co is the pin-to-pin capacitance. Its value is associated with the crystal electrode design and the crystal holder.
• Rs is the motion resistance. Its value is specified by the crystal manufacturer.
• Cs is the motion capacitance and Ls is the motion inductance, which are not specified, and are functions of the crystal frequency.
• Rbias is a feedback resistor, implemented on-chip in Chrontel products, which provides DC bias to the inverting amplifier.
• C1 and C2 are total capacitance-to-ground at the input and output nodes of the amplifier, respectively. If external capacitance is not added, the values of the internal capacitance C1 and C2, including pin parasitic capacitance, are each approximately 15pF to 20pF.