An Undersampling Digital Microphone

As negative feedback in control systems is often not applicable and/or produces undesirable effects, this paper presents the analysis and simulation of a digital microphone using a sigma delta A/D converter comprising of a voltage controlled oscillator (VCO) and sampling D-FF to digitize data. The sigma delta modulator (SDM) is analyzed mathematically and then used in a digital microphone application. A new approach is taken utilizing undersampling to convert the high frequency bandpass signal to lower frequency digital signal and also to increase the frequency modulation with respect to the center frequency. The combination of high frequencies and undersampling can easily be implemented on a completely integrated circuit.