Single supply amplifier with swing to ground

摘要

An amplifier circuit has a voltage input terminal, for receiving Vin, and a voltage output terminal, for outputting Vout. A feedback circuit controls Vout to match Vin. A differential input stage receives Vin and Vout and generates a first output signal. An output stage comprises a pull down circuit for Vout. A main MOSFET is controlled by the first output signal to pull down Vout to match Vin when Vout is above a threshold voltage Vtrans. An auxiliary MOSFET, in parallel with the main MOSFET, is controlled by the first output signal to pull down Vout to match Vin when Vout is below Vtrans. The main MOSFET is turned substantially off when Vout is below Vtrans. A headroom generator coupled between the Vout terminal and a drain of the auxiliary MOSFET allows the auxiliary MOSFET to operate in its active region and pull Vout to ground.

主权项

1. An amplifier circuit comprising:
a voltage input terminal for receiving an input voltage Vin; a voltage output terminal for outputting an output voltage Vout, the output terminal being coupled to a pull up circuit and a pull down circuit; and a differential input stage connected to receive Vin and a first feedback voltage corresponding to Vout, the differential input stage generating a first signal, the pull down circuit comprising:
a first transistor connected to be controlled by the first signal to pull down the voltage output terminal to generate the first feedback voltage to substantially match Vin when Vout is above a transition voltage Vtrans; anda second transistor, connected in parallel with the first transistor, and connected to be controlled by the first signal to pull down the voltage output terminal to generate the first feedback voltage to substantially match Vin when Vout is below Vtrans,wherein a majority of current from the Vout terminal is conducted by the first transistor when Vout is above Vtrans, and a majority of the current from the Vout terminal is conducted by the second transistor when Vout is below Vtrans, andwherein the second transistor operates in its active region during a time when Vout falls below Vtrans, while the first transistor operates outside of its active region during a time when Vout falls below Vtrans.