Temperature independent reference circuit

An integrated circuit (IC) fabricated on a semiconductor substrate comprising:

• first and second bipolar transistors, the base and collector of the first bipolar transistor being coupled to the base of the second bipolar transistor;
• first and second resistors coupled in series between the emitter of the second bipolar transistor and a ground potential, the first and second resistors having first and second resistance values, R1 and R2, and third and second temperature coefficients, TC3 and TC2, respectively;
• a third bipolar transistor, the emitter of the third bipolar transistor being coupled to the ground potential, the base of the third bipolar transistor being coupled to the collector of the second bipolar transistor;
• and
• a third resistor coupled between a node and the collector of the second bipolar transistor, the third resistor having a third resistance value, R3, and the third temperature coefficient TC3;
• a current mirror coupled to the first and second bipolar transistors such that a first current flows through each of the first and second bipolar transistors and the third resistor when power is supplied to the IC, the first and second resistance values being such that the first current is substantially constant over temperature.