Switched-current sigma-delta modulation for A/D conversion

The authors present the design of a switched-current (SI) double-integrator sigma-delta modulator (DISDM) for analog-to-digital (A/D) conversion that is intended for voiceband (4-kHz) telecommunication applications. With the creation of several new SI signal processing building blocks, a SI DISDM has been designed and laid out in Northern Telecom´s 1.2-μm CMOS process having an area of 0.5 mm² and a predicted power consumption of 2.5 mW. Transistor-level simulation (SPICE) of the SI DISDM design shows that the circuit performs reasonably well, rating it at 12 b of linear resolution. In comparison with corresponding switched-capacitor DISDM designs, the SI version provides a dramatic reduction in both power and area requirements; but, more importantly, the SI design does not utilize linear capacitors and can be fabricated using a standard digital CMOS process