Patent ID: 7443226
Filing Date: 2008-10-28
Classification: G05F

Abstract:
1. 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 and a collector terminal coupled to a first 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 second node, the second bipolar transistor having a second emitter area being A times the first emitter area; a first resistor coupled between a third node and the second node; 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 third node to provide a second current; an operational amplifier having an inverting input terminal coupled to the first node, a non-inverting input terminal coupled to the third 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 a plurality of bipolar transistors having gradually increasing emitter areas and being switchably connected in parallel with the second bipolar transistor in response to a plurality of programming signals, wherein one or more of the plurality of programming signals are asserted to connect one or more of the plurality of bipolar transistors in parallel with the second bipolar transistor to modify the effective emitter area of the second bipolar transistor, the base terminals of at least the one or more connected bipolar transistors being connected to the respective collector terminals and to the collector terminal of the second transistor, the emitter terminals of at least the one or more connected bipolar transistors being connected to the first power supply voltage.