Patent ID: 7236048

Claim:
A current source for generating a current proportional to absolute temperature (PTAT) comprising: a first bipolar transistor having an emitter terminal connected to a first power supply voltage, a base terminal coupled to a first node, and a collector terminal coupled to a second node, the first bipolar transistor having a first emitter area; a second bipolar transistor having an emitter terminal connected to the first power supply voltage, a base terminal and a collector terminal coupled to a third node, the second bipolar transistor having a second emitter area being A times the first emitter area; a first resistor coupled between the first node and the second node, the first resistor having a resistance value indicative of the emitter resistance r e of the first or second bipolar transistor at a preselected temperature T 0 and a preselected collector current I C ; a second resistor coupled between a fourth node and the third node, the second resistor having a resistance value satisfying the equation r e *(lnA−1); a current mirror electrically coupled to a second power supply voltage, the current mirror having a first current output terminal coupled to the first node to provide a first current and a second current output terminal coupled to the fourth node to provide a second current; and an operational amplifier having an inverting input terminal coupled to the second node, a non-inverting input terminal coupled to the fourth node and an output terminal providing an output signal being coupled to control the current mirror, wherein the second current provided at the second current output terminal of the current mirror and flowing through the second resistor is the current proportional to absolute temperature and the preselected collector current I C is equal to the second current.