A curvature-compensation technique based on the difference of Si and SiGe junction voltages for bandgap voltage circuits
This paper presents a novel curvature-compensation technique for bandgap reference circuits implemented in Silicon-Germanium (SiGe) BiCMOS technology. The technique utilizes the designer's access to both Si-based and SiGe-based p-n junctions. Temperature compensation is achieved in two steps: first, by weighted subtraction of two Complementary to Absolute Temperature (CTAT) currents, one proportional to the base-emitter junction of a Si BJT, and the other proportional to that of SiGe HBTs, the non-linear temperature dependent terms are compensated; and second, by adding a Proportional to Absolute Temperature (PTAT) current, the remaining linear temperature dependent terms are canceled. As a result, an almost complete temperature compensation is achieved. Based on this concept, a circuit is designed and simulated in IBM's SiGe BiCMOS 8HP technology. With a power supply of 2.5 V, simulation results show that the circuit generates an output voltage of 978.5 mV with a temperature coefficient (TC) of 1.0 ppm/°C over the temperature range of -25 °C to 125 °C.