Patent ID: 7605577

Claim:
A bandgap circuit having a startup circuit, the bandgap circuit comprising: a first PMOS device coupled between a supply voltage and a first diode for providing a first node with a first voltage that is complementary to absolute temperature (CTAT); a second PMOS device coupled between the supply voltage and a first resistor for providing a second node with a second voltage that is proportional to absolute temperature (PTAT), wherein the first resistor is connected to a set of diodes further coupled to a complementary supply voltage; a third PMOS device coupled between the power supply voltage and a second resistor for generating an output voltage, wherein gates of the first, second, and third PMOS devices are connected to a control node; and a controllable current switch connected between the second node and the control node, the controllable current switch being a MOS device whose gate and drain are connected to the second node and whose source is connected to the control node, wherein when the voltage at the second node is floating when starting the bandgap circuit, the controllable current switch biases the control node whereby the second voltage at the second node changes based on a current flowing through the second PMOS device causing the bandgap circuit to start its normal operation.