Supplying voltage in a circuit using a first voltage source and an adjustable second voltage source

A circuit comprising:

• a regulated first voltage source configured to provide a supply voltage at an output of the first voltage source for a subcircuit;
• an adjustable second voltage source configured to provide an output voltage to supply the subcircuit;
• and
• an evaluation circuit connectable to an output of the second voltage source, to a control input of the second voltage source, and to the output of the first voltage source,
• wherein the evaluation circuit is configured to adjust the output voltage of the second voltage source via a control signal at the control input of the second voltage source,
• wherein the evaluation circuit is configured to adjust the output voltage based on an evaluation of the supply voltage at the output of the first voltage source,
• wherein one or more of the evaluation circuit and the second voltage source has a memory configured to store values of the adjustment by the evaluation circuit,
• wherein the subcircuit is configured to have an operating mode with an operating current through the subcircuit and a sleep mode with a quiescent current that is reduced in comparison to the operating current through the subcircuit, the first voltage source being activated in the operating mode, the first voltage source being deactivated and the second voltage source being activated in the sleep mode, and the evaluation circuit being configured for adjustment in the operating mode.