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

Claim 1

Stable reference voltage generator comprising, disposed between a voltage supply (V DD ) and an earth connection, 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, a first bipolar transistor (Q1) with its collector connected in series with the primary branch of the current mirror, 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 a second bipolar transistor (Q2), the base of the second transistor (Q2) being connected to the common point of said resistors, the base of the first transistor (Q1) being connected to the collector of the second transistor (Q2), the output of the generator (V REF ) being connected to the terminal of the bridge opposite that connected to the collector of 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) connected 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 means, distinct from said reference voltage generating section, for feeding to the base of the isolation transistor a voltage predetermined to enable conduction in said isolation transistor.