A start-up circuit is provided. In one embodiment, the start-up circuit operates as follows. In this embodiment, the start-up circuit includes a depletion-mode PMOS transistor and an NMOS switch. The NMOS switch is coupled between ground and a common gate node of a PMOS current mirror. At start-up, the depletion-mode transistor provides a DC path to pull up the gate of the NMOS switch. Accordingly, at start-up, the NMOS switch pulls the common gate of the PMOS current mirror to ground. After the PMOS current mirror begins generating current, the NMOS switch is turned off.