Voltage regulator with power rail tracking

An integrated circuit comprising:

• a first transistor coupled between a first metal rail and a second metal rail;
• and
• a second transistor coupled between the second metal rail and a third metal rail, the third metal rail coupled to one or more functional circuits, the second transistor to:
• sense a change in a difference between a first voltage at a source electrode of the second transistor coupled to the third metal rail and a second voltage at a gate electrode of the second transistor coupled to the first metal rail or the second metal rail, due to the one or more functional circuits, and
• adjust a third voltage at a drain electrode of the second transistor according to the sensed change in the difference.

A method comprising:

• providing, through a drain electrode of a transistor coupled to a first point of a metal rail, a supply voltage;
• sensing, through a gate electrode of the transistor, a voltage at a second point of the metal rail, the drain electrode of the transistor coupled to the first point of the metal rail and a first functional circuit, the gate electrode of the transistor coupled to the second point of the metal rail and a second functional circuit;
• and
• adjusting the supply voltage at the first point of the metal rail, according to the sensed voltage at the second point of the metal rail.