RFIC circuit MW Stuff (Englis...

RFIC Circuit TutoralSheet 1 of 16

Bandgap reference The schematic diagram of the bandgap voltage reference is shown in Figure 1. The bandgap reference has largely independent of temperature and the supply rails and is therefore used as the controlling current source for mirroring throughout a circuit eg an opamp. As shown in the diagram there are two voltage sources, one generated across a diode junction ie VBE (eg the base-emitter junction on a bipolar transistor) and the other a thermal voltage Vt. VBE = -2.2mV/C and Vt = +0.085mV/C Thus if multiply Vt by a constant K and combine with VBE it is possible to cancel the temperature effects of each voltage source to leave a stable reference voltage VREF ie VREF = VBE + K.Vt

VDD

VDD

Sum

K
VBE

Vref K.Vt

Vt

Figure 1 Schematic diagram of a bandgap reference