Patent ID: 6998902

Claim:
A bandgap reference voltage circuit, comprising: a constant-current circuit receiving a power supply and generating a constant current proportional to a thermal voltage, having first circuit elements defining a lower limit voltage equal to a lowest voltage of the power supply at which the constant-current circuit can operate, and having a starter node controlling a flow of said constant current; a reference voltage output circuit connected to the constant-current circuit, generating a bandgap reference voltage according to said constant current; a power supply voltage detection circuit receiving the power supply, having second circuit elements having electrical characteristics corresponding to electrical characteristics of the first circuit elements in the constant-current circuit, using the second circuit elements to detect whether the power supply has reached the lower limit voltage; and a start-up output circuit connected to the power supply voltage detection circuit, for starting the constant-current circuit, when the power supply is turned on, by supplying a starting potential to the starter node until the power supply has reached the lower limit voltage, then ceasing to supply the starting potential to the starter node, wherein the first circuit elements in the constant-current circuit include a pair of p-channel metal-oxide-semiconductor (MOS) transistors, an n-channel MOS transistor, and a bipolar transistor, the lower limit voltage being defined by a saturation source-drain voltage of one of the p-channel MOS transistors, a threshold voltage of another one of the p-channel MOS transistors, a saturation source-drain voltage of the n-channel MOS transistor, and a base-emitter voltage of the bipolar transistor, and the second circuit elements in the power supply voltage detection circuit include a corresponding pair of p-channel MOS transistors, a corresponding n-channel MOS transistor, and a corresponding bipolar transistor, and wherein the corresponding n-channel MOS transistor, the corresponding bipolar transistor, and one of the corresponding p-channel MOS transistors of the second circuit elements are coupled in series on a detection path conducting current from the power supply, and the other one of the corresponding p-channel MOS transistors has a gate coupled to the detection path, a source coupled to the power supply, and a drain coupled to the start-up output circuit.