A bootstrap circuit for a sampling transistor. A circuit includes a MOS transistor having a source terminal coupled to an input for receiving an input voltage; an output at a drain terminal of the MOS transistor coupled to one plate of a sampling capacitor; a first switch coupling the input voltage to a gate terminal of the MOS transistor responsive to an initial phase control signal; a bootstrap capacitor having a top plate coupled to the gate terminal of the MOS transistor and coupled to the first switch; a second switch coupling a bottom plate of the bootstrap capacitor to a first low voltage supply responsive to the initial phase control signal; a third switch coupling the bottom plate of the bootstrap capacitor to a positive voltage supply greater than the first low voltage supply responsive to a first phase periodic control signal. Additional circuits and systems are disclosed.