Class AB enhanced transconductance source follower

A high band width, enhanced transconductance class AB source follower amplifier output circuit, comprising:

• a first CMOS device of a first type, connected as a source follower having an output load;
• a first CMOS device of a second type, complementary to said first type, connected as a current source;
• and
• a second CMOS device of said second type, connected as a current sensor capable of sensing the drain current of said CMOS source follower, and capable of using said sensed current to control the current in the current source and of multiplying said sensed current and feeding said multiplied current to the output load.

A method of performing class AB amplification with enhanced transconductance, said method comprising the steps of:

• providing an input signal to a control terminal of a source follower, said source follower having coupling to an output load;
• providing a current from a first current supply to a current flow terminal of said source follower, said first current supply having a maximum operating current;
• sensing current through said source follower by means of a folded cascode device;
• multiplying said sensed current and feeding said multiplied current to the output load via a first common source device of the same type as said source follower;
• and
• sensing an over-limit current condition when the current through said source follower exceeds said maximum operating current of said first current supply and, on sensing said over-limit current condition being capable of acting as a second current supply, supplying current to said output load by means of a second common source device of the opposite type as said source follower.

A method of providing a high bandwidth, enhanced transconductance class AB source follower amplifier output circuit, comprising the steps of:

• providing a signal to a first NMOS device, connected as a source follower having an output load;
• providing a current from a first PMOS device, connected as a current source;
• sensing the drain current of said NMOS source follower using a second PMOS device, connected as a current sensor;
• using said sensed current to control the current in the current source;
• and multiplying said sensed current and feeding said multiplied current to the output load.