Patent ID: 8760233

Claim:
A frequency selection device, comprising: a resonator mass which is connected by a spring arrangement to a substrate; a feedback piezoresistive element for controlling a response of motion of the resonator mass to an input signal connected to the resonator mass and which is arranged such that the strain in the feedback piezoresistive element varies in response to movement of the resonator mass, and a change in strain in the feedback piezoresistive element causes a change in electrical resistance; means for driving a current through the feedback piezoresistive element to control the response of the motion of the resonator mass to force generated from the input signal; an input for coupling the input signal from which a range of desired frequencies is to be selected to the device such as to influence the motion of the resonator mass; a detector exhibiting an impedance (Zout) for detecting an output signal amplified and filtered by the resonator mass by measuring a change in voltage across or current through the feedback piezoresistive element for detecting said change in electrical resistance; a capacitor, electrically connected in series with the detector, for preventing DC current from entering the detector; and an antenna, wherein the input is coupled to the antenna for receiving the input signal, and the input signal is amplitude modulated (AM) or frequency modulated (FM) and needs to be demodulated when being outputted; wherein the means for driving the current through the feedback piezoresistive element generates a dc current with a superposed ac component; and wherein amplitude of the superposed ac component is smaller than 0.3 times of amplitude of the dc current.