LOGARITHMICAL CURVATURE-CORRECTED VOLTAGE REFERENCES WITH IMPROVED TEMPERATURE BEHAVIOR

Abstract

Two voltage reference circuits will be presented. For the first circuit, the linear compensation of V GS (T) for an MOS transistor in subthreshold region will be realized using an original offset voltage follower block as PTAT voltage generator, with the advantages of reducing the silicon area and of increasing accuracy by replacing matched resistors with matched transistors. A new logarithmic curvature-correction technique will be implemented using an asymmetric differential amplifier for compensating the logarithmic temperature dependent term from V GS (T). Because of the operation in weak inversion of all MOS transistors, the circuit will have a very small current consumption, making it compatible with low-power low-voltage designs. The simulated temperature coefficient of the reference voltage for V DD = 2.5 V and a temperature range 0 < t < 30° C is 36.5 ppm/K, confirming the theoretical estimations. The variation of the reference voltage with respect to the supply voltage is 1.5 mV/V for 2–4 V. The circuit current consumption is about 1 μA and the minimal supply voltage is 2 V. The main goal of the second proposed voltage reference is to improve the temperature behavior of a previous reported bipolar voltage reference, by replacing the bipolar transistors with MOS transistors working in weak inversion, with the advantage of obtaining the compatibility with CMOS technology. The new proposed curvature-correction technique will be based on the compensation of the nonlinear temperature dependence of the gate-source voltage for a subthreshold operated MOS transistor by a correction current obtained by taking the difference between two gate-source voltages for MOS transistors biased at drain currents with different temperature dependencies. The circuit is implemented in 0.35 μm CMOS technology. The SPICE simulation confirms the theoretical estimated results, reporting a temperature coefficient of 4.23 ppm/K for the commercial temperature range, 0 < t < 70° C and a small supply voltage, V DD = 2.5 V . The variation of the reference voltage with respect to the supply voltage is 0.9 mV/V for 2–4 V.