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

Abstract

A stable reference voltage generator using a current mirror circuit comprising a primary branch and a secondary branch, is shown and described. A first bipolar transistor (Q1) has its collector connected in series with the primary branch of the current mirror, and a voltage divider bridge comprising at least two series-connected resistors (R1, R2), is 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) is connected to the common point of the series resistors, the base of the first transistor (Q1) is connected to the collector of the second transistor (Q2), and the output of the generator (V REF ) is connected to the terminal of the bridge opposite that connected to the collector of the second transistor (Q 2 ). The geometry of said transistors being such that the first transistor (Q1) is equivalent to "N" transistors identical to the second transistor (Q2) connected in parallel. An isolation bipolar transistor (Q7) is connected in series between the primary branch of the current mirror circuit and the first transistor, the collector of the latter being connect to the emitter of the isolation transistor.

We 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.   
     
     
       2. .[.Voltage.]. .Iadd.The stable voltage .Iaddend.generator according to claim 1 .[.characterized in that.]. .Iadd.wherein .Iaddend.the current mirror circuit comprises at least two .[.cascade.]. .Iadd.cascode .Iaddend.transistor stages .[.(Q3, Q4 and Q5, Q6).].. 
     
     
       3. .[.Generator.]. The reference voltage generator according to claim 1 .[.characterized in that the transistors are.]. .Iadd.wherein the current mirror circuit comprises first, second, third, and fourth .Iaddend.bipolar transistors .[.in a so-called "Wilson" circuit.]. in which the base of the .[.output.]. .Iadd.third .Iaddend.transistor .[.(Q6).]. of the primary branch .[.of the circuit.]. is connected to .[.the.]. .Iadd.its .Iaddend.collector.[.of this transistor (Q6) whereas.]..Iadd., .Iaddend.the base of the .Iadd.second .Iaddend.transistor .[.(Q3) connected to the supply voltage of the generator (V DD ),.]. .Iadd.of the secondary branch .Iaddend.is connected to .[.the.]. .Iadd.its .Iaddend.collector, .[.of this transistor (Q3),.]. .Iadd.and .Iaddend.the bases of the .Iadd.first and second and the third and fourth .Iaddend.transistors of each stage .[.being.]. .Iadd.are .Iaddend.connected together. 
     
     
       4. .[.Generator.]. .Iadd.The reference voltage generator .Iaddend.according to claim 1 .[.characterised in that it comprises.]. .Iadd.further comprising .Iaddend.a starter capacitor .[.(C1).]. between .[.the collector of.]. the isolation transistor .[.(Q7).]. and .[.earth.]. .Iadd.ground..Iaddend. 
     
     
       5. .[.Generator.]. .Iadd.The reference voltage generator .Iaddend.according to claim 4 .[.characterised in that it comprises.]. .Iadd.wherein .Iaddend.a second starter capacitor .[.(C2).]. .Iadd.is .Iaddend.connected between .[.the collector of the bipolar transistor connected to the generator supply voltage (V DD ).]. .Iadd.an internal connection in the secondary branch of said current mirror circuit .Iaddend.and .[.earth.]. .Iadd.ground .Iaddend.through isolating means adapted to isolate the second starter capacitor .[.(C2).]. from .[.earth.]. .Iadd.ground .Iaddend.when the second .[.bipolar.]. transistor .[.(Q2).]. is .[.not turned on.]. .Iadd.off..Iaddend. 
     
     
       6. .[.Generator.]. .Iadd.The reference voltage generator .Iaddend.according to claim 5 .[.characterised in that.]. .Iadd.wherein .Iaddend.said .Iadd.isolating .Iaddend.means for isolating the second starter capacitor .[.(C2) comprise.]. .Iadd.field-effect transistor .[.(M3).]. connected in series between said second starter capacitor .[.(C2).]. and .[.earth.]. .Iadd.ground.Iaddend., the .[.grid.]. .Iadd.gate .Iaddend.of said field-effect transistor being connected to the output of the secondary branch .[.(12).]. of the current mirror .Iadd.circuit..Iaddend. 
     
     
       7. .[.Generator.]. .Iadd.The reference voltage generator .Iaddend.according to claim 4 .[.characterised in that.]. .Iadd.wherein .Iaddend.the .Iadd.current mirror circuit comprises .Iaddend..[.transistors are.]. .Iadd.first, second, third, and fourth .Iaddend.bipolar transistors .[.in a so-called "Wilson" circuit.]. in which the base of the .[.output.]. .Iadd.third .Iaddend.transistor .[.(Q6).]. of the primary branch .[.of the circuit.]. is connected to .[.the.]. .Iadd.its .Iaddend.collector.[.of this transistor (Q6) whereas.]. .Iadd., .Iaddend.the base of the .Iadd.second .Iaddend.transistor .[.(Q3) connected to the supply voltage of the generator (V DD ),.]. .Iadd.in the secondary branch .Iaddend.is connected to .[.the.]. .Iadd.its .Iaddend.collector.[.of the transistor (Q3),.]. .Iadd., and .Iaddend.the bases of the .Iadd.first and second and the third and fourth .Iaddend.transistors .[.of each stage.]. being connected together. 
     
     
       8. .[.Voltage.]. .Iadd.The reference voltage .Iaddend.generator according to claim .[.4 characterised in that.]. .Iadd.5 wherein .Iaddend.the current mirror circuit comprises at least two .[.cascade.]. .Iadd.cascode .Iaddend.transistor stages .[.Q3, Q4 and Q5, Q6).].. 
     
     
       9. .[.Generator.]. .Iadd.The reference voltage generator .Iaddend.according to claim 1 .[.characterised in that it comprises.]. .Iadd.further comprising a .Iaddend.starting means .Iadd.for turning on the transistors of the current mirror circuit, said starting means .Iaddend.comprising.[.in particular.]..Iadd.:.Iaddend. a .[.so-called "starter" field-effect.]. .Iadd.starter .Iaddend.transistor .[.(M4) adapted.]. .Iadd.connected .Iaddend.to turn on the transistors of the current mirror circuit.Iadd., .Iaddend.and   an inverter circuit designed to drive the starter field-effect transistor, .[.in particular.]. to turn .[.it.]. off .Iadd.said starter transistor .Iaddend.when the .Iadd.reference voltage .Iaddend.generator has switched to .[.its.]. .Iadd.a .Iaddend.stable state in which all the .[.bipolar.]. transistors are turned on.   
     
     
       10. .[.Generator.]. .Iadd.The reference voltage generator .Iaddend.according to claim 9 .[.characterised in that.]..Iadd., wherein .Iaddend.the inverter circuit comprises.Iadd.:.Iaddend. a PMOS transistor .[.(M6) the.]. .Iadd.having a .Iaddend.source .[.of which is.]. connected to said voltage supply .[.(V DD ).]..Iadd., .Iaddend.and   an NMOS transistor .[.(M7) the.]. .Iadd.having a .Iaddend.source .[.of which is.]. connected to .[.earth.]..Iadd.ground.Iaddend.,   .[.the drains of.]. said .Iadd.NMOS and PMOS .Iaddend.transistors .[.being.]. .Iadd.having drains .Iaddend.connected together and constituting the output .[.(S).]. of the inverter circuit.[.and the grids of.]..Iadd., and .Iaddend.said .Iadd.NMOS and PMOS .Iaddend.transistors .[.being.]. .Iadd.having gates .Iaddend.connected together and constituting .[.the.]. .Iadd.an .Iaddend.input .[.(E).]. of said inverter circuit.   
     
     
       11. .[.Generator.]. .Iadd.The reference voltage generator .Iaddend.according to claim 9 .[.characterised in that the.]. .Iadd.wherein .Iaddend.the .[.transistors are.]. .Iadd.current mirror circuit comprises first, second, third, and fourth .Iaddend.bipolar transistors .[.in a so-called "Wilson" circuit.]. in which the base of the .[.output.]. .Iadd.third .Iaddend.transistor .[.(Q6).]. of the primary branch .[.of the circuit.]. is connected to .[.the.]. .Iadd.its .Iaddend.collector.[.of this transistor (Q6) whereas.]..Iadd., .Iaddend.the base of the .Iadd.second .Iaddend.transistor .[.(Q3) connected to the supply voltage of the generator (V DD ),.]. .Iadd.in the secondary branch .Iaddend.is connected to .[.the.]. .Iadd.its .Iaddend.collector.[.of the transistor (Q3),.]. the bases of the .Iadd.first and second and the third and fourth .Iaddend.transistors .[.of each stage.]. being connected together. 
     
     
       12. .[.Voltage.]. .Iadd.The reference voltage .Iaddend.generator according to claim 9 .[.characterised in that.]. .Iadd.wherein .Iaddend.the current mirror circuit comprises at least two cascode transistor stages.[.(Q3, Q4 and Q5, Q6).].. 
     
     
       13. .[.Generator.]. .Iadd.The reference voltage generator .Iaddend.according to claim 1 .[.characterised in that it comprises.]. .Iadd.further comprising a starter circuit comprising:.Iaddend. a .[.so-called "starter".]. .Iadd.starter .Iaddend.field-effect transistor (M4) between the collector of.]. .Iadd.connected to .Iaddend.the isolation transistor .[.(Q7).]. and .[.earth.]. .Iadd.ground; .Iaddend.and   an inverter circuit between said voltage supply .[.(V DD ).]. and .[.earth.]. .Iadd.ground.Iaddend., .[.the.]. .Iadd.an .Iaddend.output .[.(S).]. of said inverter circuit being connected to .[.the grid.]. .Iadd.a gate .Iaddend.of the starter transistor .[.(M4).]. and .[.the.]. .Iadd.an .Iaddend.input .[.(E).]. of the inverter circuit being connected to the output of the secondary branch .[.(12).]. of the current mirror circuit.   
     
     
       14. .[.Generator.]. .Iadd.The reference voltage generator .Iaddend.according to claim 13 .[.characterised in that the transistors are.]. .Iadd.wherein the current mirror circuit comprises first, second, third, and fourth .Iaddend.bipolar transistors .[.in a so-called "Wilson" circuit.]. in which the base of the .[.output.]. .Iadd.third .Iaddend.transistor .[.(Q6).]. of the primary branch .[.of the circuit.]. is connected to .[.the.]. .Iadd.its .Iaddend.collector.[.of this transistor (Q6) whereas.]..Iadd., .Iaddend.the base of the .Iadd.second .Iaddend.transistor .[.(Q3) connected to the supply voltage of the generator (V DD ),.]. .Iadd.in the secondary branch .Iaddend.is connected to .[.the.]. .Iadd.its .Iaddend.collector.[.of this transistor (Q3),.]..Iadd., and .Iaddend.the bases of the first and second and the .Iadd.third and fourth .Iaddend.transistors .[.of each stage.]. being connected together. 
     
     
       15. .[.Voltage.]. .Iadd.The reference voltage .Iaddend.generator according to claim 13 .[.characterised in that.]. .Iadd.wherein .Iaddend.the current mirror circuit comprises at least two cascode transistor stages.[.(Q3, Q4 and Q5, Q6).].. .Iadd.16. The voltage generator of claim 1 wherein the geometry of said first and second transistors is such that the first transistor is equivalent to "N" transistors identical to the second transistor connected in parallel..Iaddend. .Iadd.17. The reference voltage generator according to claim 16 wherein the magnitudes of the first and second resistors are determined by the following equations: ##EQU4##.Iaddend. in which: T: Ambient temperature   V BE2  : Base-emitter voltage of the second transistor, 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   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: ##EQU5##   
     
     
        .Iadd.18.  A reference voltage generator according to claim 1 wherein the first transistor, the second transistor and the isolation transistor are bipolar transistors..Iaddend.