Patent ID: 8552707

Claim:
A bandgap circuit, comprising: a bias current generating circuit, comprising a first node and a second node and arranged to generate a bias current in response to a voltage provided at the first node or a voltage provided at the second node; and a complementary start-up circuit, arranged to start-up the bias current generating circuit and comprising: a first start-up circuit, coupled to the first node; and a second start-up circuit, coupled to the second node, wherein the first and the second start-up circuits operate complementarily, so that the second start-up circuit provides the voltage to the second node when the first start-up circuit is unable to provide the voltage to the first node, and the first start-up circuit provides the voltage to the first node when the second start-up circuit is unable to provide the voltage to the second node, the first start-up circuit comprises at least a first switch coupled to the first node of the bias current generating circuit and a second switch coupled to a third node of the bias current generating circuit, and the second start-up circuit comprises at least a third switch coupled to the second node of the bias current generating circuit and a fourth switch coupled to a fourth node of the bias current generating circuit, and wherein when the second switch is turned off, the first switch is turned on in response to ramping up of a supply power so as to provide the voltage to the first node and start up the bias current generating circuit, and when the second switch is turned on, the first switch and the fourth switch are turned off and the third switch is turned on in response to ramping up of the supply power, so as to provide the voltage to the second node and start up the bias current generating circuit.