Analog to digital conversion has become, like many other processes drawn more and more into the digital domain. Delta-Sigma A/D conversion avoids some of the challenges with the digital components of traditional A/D conversion. This thesis presents and analyses the idea of an integrated digital FDSM microphone. FDSM is a branch of Delta-Sigma analog-to-digital converters that are implemented only with the use of standard digital gates. An FDSM takes an FM signal as input, and this can be generated in the circuit itself with a ring oscillator of inverters. The FM signal generated by the oscillator, can be modulated with a plate capacitor that responds to air pressure, and brings an analog signal into the digital domain. The thesis analyzes the circuit components used, providing an extensive explanation of a sinc^2 decimator, with both properties in the time and frequency domain. An analasys on the DC gain of the components, and their relation with quantization noise is also provided. This analasys shows that the idea of the FDSM microphone is worthwhile, and how to optimize the parametres to increase the sensitivity of the microphone. It has been shown that the FDSM microphone has high enough sensitivity to meet the demands of such applications as audio, that need a high maximum passband frequency. A documentation of an implementation in CMOS VLSI is provided, however due to a late discovered error, this implementation did not provide qualified results. The thesis also provides ideas on areas of the FDSM microphone, and it's implementation, that can improve the quality and sensitivity, and thus increase the scope of applications and relax demands on implementation.