Abstract: Power control circuitry is provided for controlling connection of a power source having a source voltage level to a switched power rail to provide power to an associated circuit block. The power control circuitry comprises a switch block for selectively connecting the switched power rail to the power source, and a switch controller for controlling operation of the switch block. A ring oscillator circuit is powered from the switched power rail and produces an oscillating output signal, and analysis circuitry is then used to analyse change in frequency of the oscillating output signal produced by the ring oscillator circuit during a period of time when the switched power rail is not at the source voltage level. The switch controller is then arranged to control at least one aspect of the operation of the switch block in dependence on the analysis. This technique provides a simple and effective digital technique for observing voltage changes on the switched power rail.

Abstract: Power control circuitry is provided for controlling connection of a power source having a source voltage level to a switched power rail to provide power to an associated circuit block. The power control circuitry comprises a switch block for selectively connecting the switched power rail to the power source, and a switch controller for controlling operation of the switch block. A ring oscillator circuit is powered from the switched power rail and produces an oscillating output signal, and analysis circuitry is then used to analyse change in frequency of the oscillating output signal produced by the ring oscillator circuit during a period of time when the switched power rail is not at the source voltage level. The switch controller is then arranged to control at least one aspect of the operation of the switch block in dependence on the analysis. This technique provides a simple and effective digital technique for observing voltage changes on the switched power rail.