Third overtone crystal oscillator

A third overtone crystal oscillator, comprising:

• an oscillator IC;
• and
• a crystal element,
• wherein the oscillator IC comprises:
• an transistor for oscillation which is grounded at an emitter thereof, a bias resistor being connected between a collector and a base of the transistor, and a constant current being supplied from a constant current source to a junction point between the collector and the bias resistor;
• a first capacitor for oscillation connected to the base via a dc blocking capacitor and to a ground potential;
• and
• a second capacitor for oscillation connected between the collector and the ground potential,
• wherein one end of the crystal element is connected to a non-grounded end of the first capacitor while the other end of the crystal element is connected to a non-grounded end of the second capacitor,
• wherein an inductor, which forms a parallel resonant circuit with the first capacitor, is provided as a discrete element separated from the oscillator IC, and
• wherein a parallel resonance frequency of the parallel resonant circuit formed by the first capacitor and the inductor is set higher than an oscillation frequency of a fundamental wave of the crystal element and lower than an oscillation frequency of a third overtone of the crystal element.