POWER MANAGEMENT CIRCUIT

One example discloses a power management circuit, including: an ultrasonic transmitter configured to generate an ultrasonic signal having a set of transmitted ultrasonic signal attributes; an ultrasonic receiver configured to detect the ultrasonic signal having a set of received ultrasonic signal attributes; wherein the power management circuit is configured to cause a device to be operated at a first power level and a second power level; and a proximity detection circuit configured to transition the device from the first power level to the second power level in response to a preselected difference between the transmitted set of ultrasonic signal attributes and the received set of ultrasonic signal attributes.