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388 IEEE JOURNAL OF SOLID-STATECIRCUITS,VOL.SC-9,NO. 6, DECEMBER 1974 A Simple Three-Terminal IC Bandgap Reference A. PAUL BROKAW, MEMBER, IEEE A?r.sfrac f—A new configuration for realization of a stabilized bandgap voltage is described, The new two-transistor circuit uses collector current sensing to eliminate errors due to base current. Because the stabilized voltage appears at a high impedance point, the application to circuits with higher output voltage is simplified. Incorporation of the new two-transistor cell in a three-terminal 2.5-V monolithic reference is described. The complete circuit is outlined in functional detail together with analytical methods used in the design. The analytical results include sensitivity coefficients, gain and frequency response parameters, and biasing for optimum temperature performance. The performance of the monolithic cir- cuit, which includes temperature coefficients of 5 ppm/ “C over the military temperature range, is reported. I. INTRODUCTION T HE REQUIREMENT for a stable reference volt- age is almost universal in electronic design. The temperature-compensatecl avalanche breakdown diode fills many of the needs, but cannot be used with low voltage supplies and often suffers from long-term stability problems. Use of a transistor base emitter diode temperature compensated to the bandgap voltage of silicon is a technique which overcomes some of the avalanche cliode limitations. Bandgap circuits can be operated from low voltage sources and depend mainly upon subsurface effects which tend to be more stable than the surface breakdowns generally obtained with avalanche diodes. The conventional three-transistor bandgap cell works well for very low voltage two-terminal or ‘synthetic Zener cliocle” requirements. The tlmee-transistor cell is less flexible in three-terminal applications and in cir- cuits where the desired output is not an integral multiple of the bandgap voltage. The two-transistor cell presented here is simpler, more flexible in three-terminal applications, and elim- inates sources of error inherent in the three-transistor cell. The two-transistor cell offers separate control over output voltage and temperature coefficient in a circuit using only a single control loop. The new bandgap circuit has been used as the basis of a monolithic three-terminal reference circuit sup- plying a stable 2.5-V output and operating down to 4-V input. 11, CONVENTIONAL CIRCUIT Conventional bandgap circuits are based on the con- cept illustrated in Fig. 1. The transistors QI and Qz are Manuscript received May 6, 1974; revised July 25, 1974. This p~per was presented at the International Solid-State Circuits Con- ference, Philadelphia, Pa., February 1974. The author is with the Semiconductor Division, Analog De- vices, Inc., Wilmington, Mass.
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