Patent ID: 7012416

Claim:
A bandgap reference voltage circuit configured to reduce the Early effect, the circuit including a first amplifier having first and second inputs and providing a buffered voltage reference at the output thereof, the amplifier being coupled at its first input to a first bipolar transistor and at the second input to a second bipolar transistor, the second transistor having an emitter area larger than that of the first transistor, and wherein: the second transistor is coupled at its emitter to a load resistor, the load resistor providing, in use, a measure of the difference in base emitter voltages between the first and second transistors, ΔVbe, for use in the formation of the bandgap reference voltage, the bases of each transistor are commonly coupled such that the base of the first and second transistor is at the same potential, one of the first and second transistors is provided in a diode connected configuration, and the base collector voltage of the other of the first and second transistors is maintained at zero by the amplifier which is coupled in a feedback loop to the collector of each of the transistors, and the circuit further includes a third transistor and a fourth transistor, the third transistor being coupled to the emitter of the first transistor and the fourth transistor being coupled via the load resistor to the emitter of the second transistor, the emitter area of the fourth transistor being greater than that of the first or third transistor, such that the first and third transistors operate at a higher current density than the second and fourth transistors and wherein a PTAT voltage is provided via a resistor, in the feedback loop, at the second input to the amplifier such that the voltage provided at the output of the amplifier is a combination of the base-emitter voltages of the first and third transistors plus the PTAT voltage.