Dual mode supply circuit and method

A circuit comprising:

• a power supply node;
• a reference node;
• a signal portion comprising first and second inverters configured to generate respective first and second complementary signals;
• and
• a power portion comprising:
• an output node;
• an amplifier coupled between the power supply and reference nodes;
• a first branch extending from the power supply node to the reference node, coupled to a non-inverting input terminal of the amplifier, and comprising a first switching device coupled between the first input terminal and the reference node;
• a second branch extending from the power supply node to the reference node, coupled to an inverting input terminal of the amplifier, and comprising a p-type transistor coupled to an output terminal of the amplifier and the output node, and a second switching device coupled between the output node and the second input terminal;
• and
• a third switching device coupled between the power supply and output nodes,
• wherein the power portion is configured to
• responsive to the first and second signals having first logic levels corresponding to the power supply node having a first voltage level, switch off each of the first and second switching devices and switch on the third switching device, and
• responsive to the first and second signals having second logic levels corresponding to the power supply node having a second voltage level on the power supply node greater than the first voltage level, switch on each of the first and second switching devices and switch off the third switching device.

A method of operating a dual mode circuit, the method comprising:

• receiving a power supply voltage at a power supply node;
• in response to the power supply voltage having a first voltage level:
• using a first switching device to decouple a first input terminal of an amplifier from a reference node, the amplifier being configured to control an output voltage on an output node,
• using a second switching device to decouple a second input terminal of the amplifier from the output node, and
• using a third switching device to couple the output node to the power supply node;
• and
• in response to the power supply voltage having a second voltage level greater than the first voltage level:
• using the first switching device to couple the first input terminal to the reference node,
• using the second switching device to couple the second input terminal to the output node, and
• using the third switching device to decouple the output node from the power supply node.