Voltage generator for generating a stable voltage independent of variations in the ambient temperature and of variations in the supply voltage

Claim 1

.[.Stable.]. .Iadd.A stable .Iaddend.reference voltage generator .[.comprising, disposed.]. .Iadd.for connection .Iaddend.between a voltage supply .[.(V DD ).]. and .[.an earth connection,.]. .Iadd.a ground potential, comprising: a reference voltage generating section including: a current mirror circuit comprising a primary branch and a secondary branch which, in operation, carries a current with characteristics at least comparable with .[., and if possible identical to,.]. those of the current in the primary branch.[.,.]..Iadd.; a first .[.bipolar.]. transistor .[.(Q1) with its collector connected.]. in series with the primary branch of the current mirror.[.,.]..Iadd.; .Iadd.an isolation transistor in series between the primary branch of the current mirror circuit and the first transistor; a voltage divider .[.bridge.]. comprising .[.at least.]. two .[.series-connected.]. resistors .[.(R1, R2) said bridge being connected in series between the secondary branch of the current mirror and the collector of.]. .Iadd.interconnected at a common point; a second .[.bipolar.]. transistor .[.(Q2), the base of the second transistor (Q2) being.]. .Iadd.in series between the resistors and the ground potential, and having a current control element .Iaddend.connected to the common point of said resistors, .[.the base.]. .Iadd.a current control element .Iaddend.of the first transistor .[.(Q1).]. being connected to .[.the collector of.]. .Iadd.a node between .Iaddend.the second transistor .[.(Q2), the.]. .Iadd.and the resistors; said voltage divider being connected in series between the secondary branch of the current mirror circuit and the second transistor; .Iadd.an .Iaddend.output of the .Iadd.reference voltage .Iaddend.generator .[.(V REF ).]. being .[.connected to the terminal.]. derived from one of the .[.bridge opposite that connected to the collector of.]. .Iadd.resistors with respect .Iaddend.the second transistor.[.(Q2), the geometry of said transistors being such that the first transistor (Q1) is equivalent to "N" transistors identical to the second transistor (Q20) connected in parallel, the reference voltage (V REF ) being given by the equation: ##EQU2## in which: T: Ambient temperature V BE2 : Base-emitter voltage of the second transistor (Q2), in turn given (neglecting other than first order terms) by the equation: V.sub.BE2 =V.sub.CO2 +αT in which α and V CO2 are constants related to the design of the second transistor R1: Value of the resistor of the bridge connected to the collector of the second transistor (Q2) R2: Value of the second resistor of the bridge connected in series with R1 k,q: Universal constants R1, R2 and N being chosen so that the sum of the terms αT and ##EQU3## is null, characterised in that it further comprises an isolation bipolar transistor (Q7) connect in series between the primary branch of the current mirror circuit and the first transistor, the collector of the latter being connected to the emitter of the isolation transistor,.].and .Iadd.the characteristics of the first and second transistors and the magnitudes of the first and second resistors having been selected such that a reference voltage provided at the output of the reference voltage generator is substantially independent of variation in ambient temperature; and .Iaddend. means, distinct from said reference voltage generating section, for .[.feeding to the base of.]. .Iadd.biasing .Iaddend.the isolation transistor .[.a voltage predetermined.].to enable conduction in said isolation transistor.