An exchange of the amplitude axis for the time axis offers anpossibility of overcoming resolution problems in analog-to-digitalnconversion in low-voltage CMOS circuits and/or of circumventing specialnresistor options in silicided processes. This exchange can be effectednvia some form of duty-cycle modulation. For its implementation a circuitnconfiguration is described, consisting of an asynchronous sigma-deltanmodulator, followed by a phase-synchronized tapped ring oscillator whichnproduces a poly-phase signal for sampling the asynchronous signal at anrelatively low frequency. A detailed analysis is presented whichnaccurately predicts the properties of the conversion scheme with respectnto aliasing, quantization noise and nonlinear distortion. The resultsnare illustrated with simulations of a design example
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