Fig. 1 is an elementary application of the above principle. Neglecting for the moment the variation of IC with VCe and the effects of base current, this circuit will conduct a current proportional to absolute temperature for any voltage greater than two Vbe across the device. Transistors Q1 and Q2 constrain the collector currents of Q3 and Q4 to be equal. Since the emitter area ratio of Q3 and Q4 is r, the difference in their Vbe’s is Vt in (3). For r = 8,