A ventilator includes a sensor to monitor a characteristic associated with thedelivery of gas to the patient, such as pressure. A sensor power supply (100,130) is feeding a sensor in the form of a Wheatstone bridge. A first end (104)of the bridge is coupled to a first positive voltage source (112, 142) and asecond end (116) is coupled to a second positive voltage source (118, 156,180). A capacitor (120) is coupled to the second end of the bridge. Acontroller (50) controls the first and the second positive voltage sources soas to (a) disable the sensor by causing the first positive voltage source toprovide substantially zero voltage to the first end of the Wheatstone bridgeand by causing the second positive voltage source to provide a positivevoltage to the second end of the capacitor, and to (b) enable the sensor bycausing the first positive voltage source to provide a positive voltage to thefirst end of the Wheatstone bridge and by causing the second positive voltagesource to provide a decreasing voltage to the second end of the capacitor.
