The REF30xx is a series, CMOS, precision bandgap voltage reference. Its basic topology is shown in the Functional Block Diagram section. Transistors Q1 and Q2 are biased so that the current density of Q1 is greater than that of Q2. The difference of the two base-emitter voltages, Vbe1 – Vbe2, has a positive temperature coefficient and is forced across resistor R1. This voltage is gained up and added to the base-emitter voltage of Q2, which has a negative coefficient. The resulting output voltage is virtually independent of temperature. The curvature of the bandgap voltage, as shown in Figure 3, is due to the slightly nonlinear temperature coefficient of the base-emitter voltage of Q2.