This invention includes a square wave signal generating circuit 20 for
generating a square wave signal whose frequency changes; a MOS transistor 12
which is turned on/off on the basis of the square wave signal to supply a driving
current to a vibrator 14; and a frequency shift detecting circuit 24
for detecting a frequency shift between the square wave signal from the square
wave generating circuit and a resonance frequency of the vibrator. The shift in
the frequency generated by the square wave generating circuit is trimmed by a signal
detected by the frequency shift detecting circuit.
