Patent ID: 7570125
Filing Date: 2009-08-04
Classification: G01N,H03B,H03L

Abstract:
1. An apparatus for oscillating a surface, the apparatus comprising an oscillator circuit having: a) a piezoelectric crystal connected to the surface; b) a variable frequency generator for generating a driving signal which is supplied to the crystal to cause the crystal to oscillate, thereby causing the surface to oscillate; and c) an analyzer for monitoring the phase shift between the voltage across the crystal and the current flowing through it and, in response, generating an adjustment signal which relates to the difference between the oscillation frequency and a resonant frequency of the crystal, the variable frequency generator being responsive to the adjustment signal to vary the frequency of the driving signal to cause the crystal to oscillate at the resonant frequency; wherein the variable frequency generator comprises a frequency synthesizer and additionally generates a quadrature signal that is shifted in phase by 90° from the driving signal.