Abstract: Disclosed are methods, systems, and algorithms for accurately measuring a DC voltage signal (Vin) using a sigma-delta modulator (36). The preferred embodiments disclose determining a fundamental period (Tp) of the pattern noise cycle of sigma-delta modulator output at a given DC input (Vin), and mapping a one-to-one relationship to the ratio of Vin to reference voltage (Vref). Methods, systems, and algorithms according to the invention include the conversion of a DC input (Vin) into a digital bitstream that periodically provides low-resolution high-frequency digital words (D1) representative of the DC input (Vin). The low-resolution high-frequency words (D1) are in turn periodically converted into high-resolution low-frequency words (D2) representative of the DC input (Vin).