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The frequency delta-sigma modulation (FDSM) technique was applied to the microphone sensors. The FDSM is a superior analogue-to-digital conversion technique, which outputs wide band, large dynamic range digital signals without precision analogue components. In this implementation, a microwave cavity resonator having movable membrane on its one end, together with a gain block consisting of a heterojunction field effect transistor, was used for sound-frequency converter. The output of this converter (frequency modulated intermediate signal) was sampled and converted to 1-bit delta sigma modulated digital signals. The noise shaping behaviour with a clear signal peak was demonstrated for the fabricated devices.
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Delta-sigma modulation microphone sensors using microwave cavity resonator