A high-performance autozeroed CMOS opamp with 50 /spl mu/V offset

Bandwidth, DC gain, offset and noise are the major performance parameters that limit the applicability of operational amplifiers (opamps). The design of a general-purpose opamp in a digital CMOS process that offers excellent performance in all these categories is a long-standing challenge for the analog designer. While MOSFET amplifiers have extremely small bias currents, they exhibit much larger offset voltages and low-frequency noise than their BJT counterparts. A high-performance opamp in a 1 /spl mu/m 5 V digital CMOS technology achieves high DC gain, as well as excellent PSRR and CMRR and is capable of driving a 100 /spl Omega/, 1 nF load. It uses a mixed-mode (analog/digital) compensation loop to reduce input offset to <50 /spl mu/V. The loop uses digital offset extraction and storage circuitry, and has an analog current-mode output. Offset cancellation can be performed at power-up or upon request. Unlike existing commercially available low-offset high-precision amplifiers, the opamp needs only a single 5 V low-voltage supply, requires no trimming, and uses no BJTs or JFETs. Thus, although developed as a stand-alone product, it can potentially be used as an on-chip component of larger mixed-mode ICs.