A circuit comprises a first switch, a second switch, a third switch, and a fourth switch. Each has a first end and a second end. The circuit also comprises a capacitive device having a first capacitive end and a second capacitive end, and a voltage source. A first node having a first voltage is coupled to the first fourth-switch end, to the first second-switch end, and to the first capacitive end. A second node having a second voltage is coupled to the voltage source, to the second fourth-switch end, and to the second third-switch end. A third node is coupled to the second second-switch end, and to the first first-switch end. The first switch and the second switch are controlled such that the first node and the voltage source selectively provide the second voltage.
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