This paper presents novel low-voltage all-MOS analog circuit techniques for the synthesis of oversampling Σ∆ A/D converters. The new approach exploits the possibilities of Log-domain processing by using the MOSFET in subthreshold operation. Based on this strategy, a complete set of very low-voltage (down to 1V) low-power (below 100μW) all-MOS basic building blocks is proposed. The resulting analog circuit techniques allow the integration of Σ∆ A/D converters for low-frequency (below 100KHz) applications in digital CMOS technologies. Examples are given for a standard 0.35μm VLSI process.