A device for controlling a power supply for a functional block in an integrated circuit, the device comprising: a signal generator configured to provide a clock signal to the functional block, an antenna comprising a transistor, and being located proximate to the functional block, the antenna being configured to receive the clock signal from the signal generator, and wherein the transistor of the antenna receives electrical power from the same power source that delivers power to the functional block, means to measure the clock signal output from the antenna, and output a control signal, and feedback means to control the voltage of the power supply to the functional block on the basis of the control signal.