IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 34, NO. 7, JULY 1999 949 Low-Power Bandgap References Featuring DTMOST’s Anne-Johan Annema Abstract—This paper describes two CMOS bandgap reference circuits featuring dynamic-threshold MOS transistors. The first bandgap reference circuit aims at application in low-voltage, low- power IC’s that tolerate medium accuracy. The circuit runs at supply voltages down to 0.85 V while consuming only 1 W; the die area is 0.063 mm in a standard digital 0.35- m CMOS process. The second bandgap reference circuit aims at high- accuracy operation ( %) without trimming. It consumes approximately 5 W from a 1.8-V supply voltage and occupies 0.06 mm in a standard 0.35- m CMOS process. Index Terms— Analog integrated circuits, bandgap reference circuits, CMOS integrated circuits, DTMOST’s. I. INTRODUCTION M OST of today’s CMOS IC’s consist of a large digital core and some analog peripheral functions. These ana- log functions typically include reference circuits used, among other things, for analog blocks, for supply voltage regulation, and for digital circuitry (power-on-reset circuits). The most widely used implementation of voltage reference circuits with a low temperature coefficient is the bandgap-reference circuit [1], [2]. In CMOS systems-on-a-chip, two important system trends can be distinguished: one focusing at low-power operation and the other at high-performance operation [6]. With the systems trend on low-power operation, the supply voltage is typically much lower than the nominal supply voltage for the process and is often dictated by the minimum voltage of a battery. With the system trend toward high performance, the system typically operates on the nominal supply voltage, while all the circuits in the system must reach high performance. In this paper, two new bandgap reference circuits are presented. One focuses on low-voltage, low-power operation and is intended for application in portable equipment, such as hearing instruments. The other aims at high accuracy and low-power operation. Both bandgap reference circuits use dynamic-threshold MOS transistors (DTMOST’s) [3]–[5] and are probably the first to exploit the advantages of these devices. II. TYPICAL CMOS BANDGAP REFERENCE CIRCUITS A typical CMOS implementation of a bandgap reference circuit is shown in Fig. 1. For this type of circuit, the output voltage is the sum of a diode voltage and the voltage drop Manuscript received November 3, 1998; revised January 11, 1999. The author is with Philips Research Laboratories, Eindhoven 5656 AA The Netherlands. Publisher Item Identifier S 0018-9200(99)04722-8. Fig. 1. Typical CMOS bandgap reference circuit. across the upper resistor. The diodes are typically imple- mented by diode-connected vertical PNP’s (parasitic devices in CMOS), lateral PNP’s, or both. The current-voltage relation of these transistors, assuming a of at least a few hundred millivolts, is given by [2] where: a process- and size-dependent constant; a mobility-related constant; the temperature in K; the bandgap extrapolated to K. In the remainder of this paper, the factor “1” in the current- voltage relation is neglected for simplicity reasons. Assuming that the two “diodes” in the bandgap circuit differ only by their emitter area and are operated at the same and temperature, the difference in diode voltage of the two “diodes” equals , where is the ratio of the emitter areas. With the circuit in Fig. 1, this is copied and scaled by a factor across the upper resistor. The output voltage of the circuit is then In this relation, the term denotes the current through the diodes in the bandgap reference circuit as a function of temperature. In most bandgap references, this diode bias current is proportional to the absolute temperature (PTAT) but it also may be independent of temperature; both situations can be described by . Substitution of this 0018–9200/99$10.00  1999 IEEE