National Semiconductor Corporation

Wade Leitner

Paul Michael Henry

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.

Apparatus and method for start-up circuit without a start-up resistor

A reference circuit includes a band-gap core, two current sources, and an amplifier circuit that are arranged in cooperation. The band-gap core circuit is biased by current that is supplied from a local power supply via the first current source. The second current source shunts the excess away from the band-gap core circuit in response to a control signal. The control signal is provided by the amplifier circuit, which is arranged to monitor the signals in the band-gap core circuit. The feedback loop that is formed with the amplifier circuit is compensated with a capacitor that is not referenced to the local power supply. The first current source can be further improved by cascading. The reference circuit has excellent characteristics for use in switching applications, where the local supply is perturbed by fast switching transients.

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Tucson, AZ, United States of America

Wade Leitner