The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 13, 2002
Filed:
Mar. 23, 2001
Don R. Sauer, San Jose, CA (US);
National Semiconductor Corporation, Santa Clara, CA (US);
Abstract
A method and apparatus is directed to a rail-to-rail MOS amplifier that operates with a very low power supply. An input stage amplifier operates over rail-to-rail common-mode voltages. The input stage amplifier includes two differential input stages that steer current to loads in a class AB turnaround stage. The class AB turnaround stage converts the differential signals into a single signal that is driven into an output stage amplifier. The output stage amplifier includes level shifting buffer amplifiers that are arranged to bias a pair of MOS output transistors. Each level shifting buffer amplifier is arranged to bias a MOS transistor in a sub-threshold operating region such that the MOS transistor operates as a resistor. The MOS resistor works in conjunction with a MOS diode to provide an AB bias voltage to a gate of a respective one of the output transistors. The level shifting buffer amplifiers are also arranged such that the gate of each output transistor is selectively switched to a power supply voltage, providing maximum gate drive to the output transistor when the output transistor drives a maximum current to an external load. A single capacitor may be employed to provide compensation between the output of the amplifier and the output of the class AB turnaround stage. The sub-threshold operation of the level shifting buffer amplifiers permits the output stage amplifier to operate on power supplies down to roughly a single transistor threshold voltage.