Design of ΣΔ modulators with reduced number of operational amplifiers

A method that reduces the number of operational amplifier used in sigma delta modulators is described. The approach together with the double sampling method permits the designer to obtain very low figure of merits (and low power) as required by portable wireless applications. The proposed technique is applied to second and third order architectures. The limits due to capacitor mismatches make the approach useful for medium resolution and low over-sampling ratios. A case study meeting typical WCDMA specification is given.