Browse Prior Art Database

LOW CURRENT LOW DROPOUT REFERENCE

IP.com Disclosure Number: IPCOM000008576D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jun-25
Document File: 2 page(s) / 75K

Publishing Venue

Motorola

Related People

Don Zobel: AUTHOR

Abstract

Battery powered systems have current drain as a critical parameter. Battery life is a parameter that directly effects and is noticed by the end user. Smaller and smaller end product packaging means fewer battery cells and therefore lower system voltages, making the ability of circuits to operate at low voltage important. A function needed by many systems is a bandgap reference that can supply modest load currents, draw little supply current, have reasonable supply rejection, and have a low drop out voltage.

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MOTOROLA Technical Developments

8

LOW CURRENT LOW DROPOUT REFERENCE

by Don Zobel

ABSTRACT

  Battery powered systems have current drain as a critical parameter. Battery life is a parameter that directly effects and is noticed by the end user. Smaller and smaller end product packaging means fewer battery cells and therefore lower system voltages, making the ability of circuits to operate at low voltage important. A function needed by many systems is a bandgap reference that can supply modest load currents, draw little supply current, have reasonable supply rejection, and have a low drop out voltage.

DESCRIPTION AND OPERATION

  A simple bandgap reference that accomplishes the above needs is shown in Figure 1 and Figure 2. Figure 1 is a thermal current generator used to provide a known bias current for the collector of

transmitter 46. Because the IPTAT (,current propor- tional to absolute temperature) generated by this circuit is to the first order independent of the current through resistor R2, no other start current is needed to energize the circuit. Resistor R2 could also be a long gate length FET, as its current is not

important to the first order.

  Figure 2 shows the regulator portion of the circuit. Assuming the base current of the transistor Q7 is negligible, Vout rises to a voltage that causes the transistor Q6 to sink IPTAT. Because of the area and current scaling between the transistors 46 and QS, the Vout voltage is determined by the base- emitter voltage (Vbe)...