Compact fully differential folded cascode operational amplifier for high-resolution sigma-delta modulators

This paper presents the design of a fully differential folded-cascode operational amplifier with separated current sources of input transistors for improving layout matching to be used in switched-capacitor, high-resolution sigma-delta modulators. Using a standard CMOS 0.5-μm technology, an experimental operational amplifier with 2.7 V supply has obtained 560 ns of settling time, 1.25 V/μs of slew rate and 62 dB of dc gain in single-ended test configuration using 16 pF of load capacitance. The active die area occupies 420 x 290 μm 2 excluding bonding pads.