1. Field of the Invention
The present invention relates to reference voltage circuits and, in particular, to a bandgap reference voltage circuit characterized by low power consumption.
2. Related Art
Portable wireless systems have increased the demand for analog circuits which are powered by a low voltage source. Most of these analog circuits use a bandgap reference circuit that generates a constant voltage by summing two currents or voltages, one that is proportional to absolute temperature (PTAT) and another that is complementary to absolute temperature (CTAT). The sum of these currents or voltages can be temperature independent and can be used to obtain a reference voltage, usually referred to as a bandgap reference voltage. This technique usually requires a relatively high power supply voltage of approximately 2.5V-3.3V and a power supply current of about 100 xcexcA. Examples of bandgap reference circuits are described in Widlar, xe2x80x9cA new breed of linear ICs run at 1-volt levels,xe2x80x9d Electronics, Mar. 29, 1979, pp. 115-119, and Brokaw, xe2x80x9cA simple three terminal IC bandgap reference,xe2x80x9d IEEE Journal of Solid-State Circuits, 1974, SC-9 (6), pp.667-670.
Recently, various techniques have been proposed for designing reference voltage circuits that provide precise reference voltages and that operate at low supply voltages. A main emphasis in designing such circuits has been reducing the reference voltage and the power consumption. Such circuit design techniques are described in the following articles: Vittoz et al., xe2x80x9cA Low-Voltage CMOS Bandgap Reference,xe2x80x9d IEEE Journal Of Solid-State Circuits, 1979, SC-14, No. 3, pp.573-577; Gunawan et al., xe2x80x9cA Curvature-Corrected Low-Voltage Bandgap Reference,xe2x80x9d IEEE Journal Of Solid State Circuits, 1993, Vol. 28, No. 6, pp.667-670; Jiang et al., xe2x80x9cDesign Of Low-Voltage Bandgap Reference Using Transimpedance Amplifier,xe2x80x9d IEEE Transactions On Circuits And Systems-II: Analog And Digital Signal Processing, 2000, Vol.47, No. 6, pp.667-670; Banba et al., xe2x80x9cA CMOS Bandgap Reference Circuit With Sub-1-V Operation,xe2x80x9d IEEE Journal Of Solid-State Circuits, 1999, Vol. 34, No. 5, pp.670-674. None of these references, however, disclose a reference voltage circuit that is simple and cost effective, and that has very low power consumption. Therefore, what is needed is a simple and cost effective circuit that provides a precise reference voltage and that has very low power consumption.
In one embodiment of the present invention, a bandgap reference circuit includes a bias current source, a transistor, a first resistor, a second resistor, and a proportional to absolute temperature (PTAT) current source. The transistor has an emitter, a collector, and a base. The collector is coupled to the bias current source and to the first resistor. The first resistor is coupled between the collector and the second resistor. The PTAT current source provides a PTAT current to an output node between the first resistor and the second resistor.