A circuit includes a comparator unit, a capacitive device, and a switching network. The comparator unit is configured to set a control signal at a first logical value when an output voltage reaches a first voltage value from being less than the first voltage value, and to set the control signal at a second logical value when the output voltage reaches a second voltage value from being greater than the second voltage. The capacitive device provides the output voltage. The switching network is configured to charge or discharge the capacitive device based on the control signal.