BiCMOS-Based Compensation: Toward Fully Curvature-Corrected Bandgap Reference Circuits
We present a novel BiCMOS-based temperature compensation technique aiming at complete correction of the curvature in the temperature response of bandgap references. The source of the appearance of this curvature is because the well-known nonlinear term <inline-formula> <tex-math notation="LaTeX">$T\ln (T)$ </tex-math></inline-formula> in the base–emitter voltage (<inline-formula> <tex-math notation="LaTeX">$V_{BE}$ </tex-math></inline-formula>) is not completely canceled across all temperature points. Here, we show that the gate-source voltage (<inline-formula> <tex-math notation="LaTeX">$V_{GS}$ </tex-math></inline-formula>) of a subthreshold-operating MOSFET, biased with a proportional to absolute temperature current, also exhibits the <inline-formula> <tex-math notation="LaTeX">$T\ln (T)$ </tex-math></inline-formula> nonlinear temperature dependence. We leverage the existence of <inline-formula> <tex-math notation="LaTeX">$T\ln (T)$ </tex-math></inline-formula> in the temperature response of <inline-formula> <tex-math notation="LaTeX">$V_{GS}$ </tex-math></inline-formula> to directly cancel the nonlinear term <inline-formula> <tex-math notation="LaTeX">$T\ln (T)$ </tex-math></inline-formula> in <inline-formula> <tex-math notation="LaTeX">$V_{BE}$ </tex-math></inline-formula>. A theoretical analysis of the proposed compensation approach is presented. As a proof of concept, a current-mode voltage reference circuit, utilizing the proposed approach, is designed in IBM’s 8HP Silicon–Germanium (SiGe) BiCMOS technology. Thermal characteristics of the compensation components are examined through extensive simulations and are also experimentally evaluated, for the first time. Measurement results of the reference circuit show that the circuit outperforms the temperature performance of the state-of-the-art SiGe reference circuits. Possible origins of observed temperature dependences and mitigation techniques are discussed. The proposed compensation approach can be realized in any BiCMOS/CMOS technology for implementing either current-mode or voltage-mode high precision reference circuits.