A multi-stage noise-shaping (MASH) A/D converter combining an RC-integrator and a digital correction technique for high accuracy is described. Using 1.2-µm BiCMOS technology, we developed an A/D converter for digital audio with an S/N ratio of over 100 dB. This paper discusses the principles of MASH technology with an RC-integrator, the technique for correcting RC variation, and the experimental results obtained with a fabricated chip.