Patent ID: 7690256
Filing Date: 2010-04-06
Classification: H03B,H03L

Abstract:
1. A sensing device, comprising: a piezoelectric resonator provided with electrodes on both surfaces of a piezoelectric substrate and an adsorption layer for adsorbing a sensing target on the surface of one electrode; a Colpitts oscillation circuit including the piezoelectric resonator and a transistor amplifier circuit; a means for determining the variation of natural frequency of the piezoelectric resonator created by adsorption of the sensing target to the adsorption layer based on the frequency signal outputted from the Colpitts oscillation circuit; a tuning circuit provided on the output side of said transistor amplifier circuit and the impedance thereof has inductivity at the oscillation frequency; a first capacitive component connected between a base and an emitter of the transistor of said transistor amplifier circuit; and a second capacitive component connected between the emitter and a around of said transistor, wherein the ratio of the impedance of the first capacitive component at the oscillation frequency to the impedance of said second capacitive component at the oscillation frequency of the Colpitts oscillation circuit is 3 or more, and the impedance of the first capacitive component at the oscillation frequency is 300 Ω or more.