Abstract: A modulation circuit arranged to modulate a first voltage from a first power supply grid to produce a desired second voltage not greater than the first voltage on a second power supply grid is provided. A digital register is operatively connected to the modulation circuit to determine the desired second voltage on the second power supply grid. Furthermore, the digital register maintains a value representative of an activity level or an anticipated activity level of a circuit connected to the second power supply grid. The modulation circuit maintains the desired second voltage for the circuit connected to the second power supply grid by transferring charge between capacitances.