Rail-to-rail opamp with large sourcing current and small quiescent current

A CMOS operational amplifier coupled between a first and a second power supply rail, and having differential inputs and an output, comprising:

• an input circuit including:
• a differential pair input stage having a pair of input transistors coupled to the operational amplifier differential inputs, respectively, and a pair of diode-connected load transistors,
• a folded rail-to-rail second stage having a pair of current mirroring transistors coupled to said diode-connected load transistors, respectively, and a pair of current mirroring pull-up transistors;
• a negative slew detector including:
• a source follower transistor having a gate terminal coupled to an output of said input circuit,
• a current source load transistor coupling a source terminal of said source follower transistor to the first power supply rail,
• a diode-connected transistor coupling a drain terminal of said source follower transistor to the second power supply rail,
• a current mirroring transistor having a gate terminal coupled to a gate and drain of said diode-connected transistor, and
• a load transistor having a gate terminal coupled to a gate terminal of said current source load transistor, and coupling said detector output at a drain of said current mirroring transistor to the first power supply rail;
• a buffer circuit having an input coupled to said negative slew detector output and coupled to a plurality of inverters, with said plurality of inverters coupled in series, said buffer circuit having a pair of inverting and non-inverting outputs;
• and
• an output stage including:
• a first pull-up transistor having a gate terminal coupled to said source follower transistor source terminal, and a drain terminal coupled to the operational amplifier output, and
• a pull-down transistor having a gate terminal coupled to said buffer circuit non-inverting output, and a drain terminal coupled to the operational amplifier output.