A low-voltage CMOS rail-to-rail class-AB input/output opamp with slew-rate and settling enhancement

Abstract

A low-voltage CMOS rail-to-rail op amp with high slew-rate and fast-settling is presented. The input stage is composed of the complementary differential pairs, a pair of modified current-mode maximum selecting circuits (Maximum Current Selecting Circuit II) and a class-AB feedback loop circuit. It achieves rail-to-rail operation, constant-g/sub m/, high slew-rate and fast-settling. With this opamp topology, the design can be easily performed for a wide-range of capacitive loads with a large bandwidth-to-power-consumption ratio. With 2 /spl mu/m and 0.5 /spl mu/m technology respectively, the op amp has a high DC gain (/spl ges/84 dB), and has a bandwidth-to-power-consumption ratio of 13.6 MHz/mW and 25.8 MHz/mW with capacitive loads of 20 pF, 86 V//spl mu/s, S0 V//spl mu/s slew-rate and 159 ns, 36 ns settling-time.