AN IMPROVED TOLERANCE MULTIPLE Vbe VOLTAGE REFERENCE

Publishing Venue

Motorola

Related People

Abstract

Voltage references of one form or another exist in all integrated circuits. These references may be extremely simple or quite complex. Examples of simple voltage references include the base to emitter voltage drop (Vbe) in a Bipolar IC or the Vth in a MOS device. Zener diodes are frequently used reference elements providing stability and high initial tolerance. Where the requirements for a voltage reference include temperature stability and tight tolerance initial value, bandgap references tend to be the configuration of choice. Bandgaps are the only choice if the reference value is to be less than that obtainable in a zener diode.

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@ MOTVROLA

Technical Developments Volume 5 October 1985

AN IMPROVED TOLERANCE MULTIPLE Vbe VOLTAGE REFERENCE

by Robert B. Jarrett

   Voltage references of one form or another exist in all integrated circuits. These references may be extremely simple or quite complex. Examples of simple voltage references include the base to emitter voltage drop (Vbe) in a Bipolar IC or the Vth in a MOS device. Zener diodes are frequently used reference elements providing stability and high initial tolerance. Where the requirements for a voltage reference include temperature stability and tight tolerance initial value, bandgap references tend to be the configuration of choice. Bandgaps are the only choice if the reference value is to be less than that obtainable in a zener diode.

   Bandgap references derive their voltage temperature stability through the addition of a positive temperature coefficient voltage (usually generated by a current which is proportional to absolute temperature) to one or more negative temperature coefficient reference elements (usually a Vbe). The predictability of the bandgap generated voltage reference tends to be limited by the absolute value of the negative voltage component Vbe element. Varia- tions in this Vbe value will be directly reflected to the voltage reference output. Trimming of the output voltage prior to the assembly of the IC is an expensive way to correct for these Vbe nominal variations. If a 2.5 voltage Bandgap reference is to be made, two...