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A LOW POWER SUPPLY AND LOW OUTPUT IMPLEMENTATION OF A BANDGAP REFERENCE VOLTAGE

IP.com Disclosure Number: IPCOM000016731D
Publication Date: 2003-Jul-11
Document File: 8 page(s) / 382K

Publishing Venue

The IP.com Prior Art Database

Abstract

ABSTRACT OF THE DISCLOSURE

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A LOW POWER SUPPLY AND LOW OUTPUT IMPLEMENTATION

OF A BANDGAP REFERENCE VOLTAGE

Background

The publication describes a bandgap reference invention relates to implantable devices, and more particularly to a bandgap reference circuit that may be used within the circuitry of an implantable device.

A bandgap reference circuit works as follows: first, it generates two voltages, a forward biased PN junction voltage called VBE, and a temperature related voltage referred to as KT/q.  These two voltages have an opposite temperature coefficient.  Thus, when they are added together with a proper scale constant, a zero temperature coefficient bandgap reference voltage is obtained.  The typical value of a bandgap reference voltage is 1.2 volts (V).

In view of the dual-source nature of a bandgap reference voltage, a circuit that implements the bandgap reference voltage typically consists of two portions: a first portion that provides the term VBE, and a second portion that provides the term KT/q.  These two portions are connected in series between a power supply source and ground.  Since the configuration has two portions in series, the power supply voltage needed for the circuit must be at least 1.2 V, plus any necessary overhead.  Typically, a power supply voltage of 1.5 V or more is needed to power a bandgap reference voltage.

In a device that utilizes a rechargeable battery, the battery may discharge to zero volts.  As the battery discharges, there is a need to monitor the battery voltage as low as possible.  This requires both a low bandgap reference voltage (less than 1.2 V) and a low power supply voltage. 

The above needs and others are addressed by a device that provides a bandgap reference voltage that uses a parallel configuration instead of a series configuration in order to lower the power supply voltage.  Moreover, instead of adding two voltages in series in order to obtain the zero temperature coefficient bandgap reference voltage, the present invention generates two currents which are proportional to VBE and KT/q.  These two currents are then summed (added) together and converted to a voltage, e.g., through a resistor, in order to obtain a desired bandgap reference voltage that is less than 1.2 V.

The following describes a bandgap reference voltage circuit that provides a temperature compensated reference voltage that is significantly lower than current bandgap reference voltage circuits.

Further, the bandgap reference voltage circuit described herein may operate from a power supply voltage VDD that is significantly lower than is possible with current bandgap reference voltage circuits.

Detailed Description

FIG. 1 illustrates a known method of generating a bandgap reference voltage VREF.  As seen in FIG. 1, a first voltage source V1, where V1 is proportional to KT/q (and therefore has a positive temperature coefficient), is connected in series with a second voltage source V2, where V2=VBE, where VBE is a PN junction voltage (and therefore ha...