A crystal oscillator includes a current source that charges a capacitor. A charge on the capacitor is periodically injected into a crystal of the crystal oscillator. A switch couples the capacitor to the crystal and a timing circuit controls the switch to cause the charge to be injected beginning at approximately a peak of a crystal output signal. The timing circuit is configurable into a self-resonant mode for calibration of a delay through the timing circuit by coupling an output of the timing circuit to an input of the timing circuit. A comparator compares a magnitude of the crystal output signal to a reference voltage and supplies compare results to a gain control circuit. The gain control circuit adjusts the current from the current source to adjust the charge being injected into the crystal from the capacitor to thereby control the magnitude of the crystal output signal.