Circuits and methods to produce a VPTAT and/or a bandgap voltage

1. A circuit to generate a voltage proportional to absolute temperature (VPTAT), comprising:

a group of X transistors, each of which includes a base and a current path between a collector and an emitter;

wherein a first subgroup of Y of the X transistors are used to produce a first base-emitter voltage (VBE 1 ) indicative of a voltage drop between the base(s) of the Y of the X transistors and the emitter(s) of the Y of the X transistors, where 1≦Y<X;

wherein a second subgroup of Z of the X transistors are used to produce a second base-emitter voltage (VBE 2 ) indicative of a voltage drop between the bases of the Z of the X transistors and the emitters of the Z of the X transistors, where Y<Z<X;

wherein the VPTAT is produced by determining a difference between the first base-emitter voltage (VBE 1 ) and the second base-emitter voltage (VBE 2 ); and

wherein which Y of the X transistors are in the first subgroup and used to produce the first base-emitter voltage (VBE 1 ), and which Z of the X transistors are in the second subgroup and used to produce the second base-emitter voltage (VBE 2 ), selectively changes over time.

2. The circuit of claim 1 , wherein during X periods of time, each of the X transistors is selected in a cyclical manner:

to be in the first subgroup of Y of the X transistors that is/are used to produce the first base-emitter voltage (VBE 1 ); and

to be in the second subgroup of Z of the X transistors that are used to produce the second base-emitter voltage (VBE 2 ).

3. The circuit of claim 1 , further comprising:

a controller; and

a plurality of switches;

wherein the controller controls the switches to select

which Y of the X transistors is/are in the first subgroup and used to produce the first base-emitter voltage (VBE 1 ), and

which Z of the X transistors are in the second subgroup and used to produce the second base-emitter voltage (VBE 2 ).

4. The circuit of claim 3 , wherein:

the controller controls the switches to produce a predictably shaped switching noise that can be filtered; and

one or more of the X transistors may be specified to not be used to produce VBE 1 or VBE 2 .

5. The circuit of claim 3 , wherein:

the controller selects in a random or pseudo-random manner at least one of

which Y of the X transistors is/are selected to be in the first subgroup and used to produce the first base-emitter voltage (VBE 1 ), and

which Z of the X transistors are selected to be in the second subgroup and used to produce the second base-emitter voltage (VBE 2 ); and

one or more of the X transistors may be specified to not be used to produce VBE 1 or VBE 2 .

6. The circuit of claim 1 , wherein Y=1.

7. The circuit of claim 1 , wherein 2≦Y<X/2.

8. The circuit of claim 1 , wherein multiple of the switches are controlled at the same time such that multiple switches can be switched at the same time.

9. A method for generating a voltage proportional to absolute temperature (VPTAT) using a group of X transistors, comprising:

producing a first base-emitter voltage (VBE 1 ) using a first subgroup of Y of the X transistors, wherein the first base-emitter voltage (VBE 1 ) is indicative of a voltage drop between the base(s) of the Y of the X transistors and the emitter(s) of the Y of the X transistors, where 1≦Y<X;

producing a second base-emitter voltage (VBE 2 ) using a second subgroup of Z of the X transistors, wherein the second base-emitter voltage (VBE 2 ) is indicative of a voltage drop between the bases of the Z of the X transistors and the emitters of the Z of the X transistors, where Y<Z<X;

producing the VPTAT by determining a difference between the first base-emitter voltage (VBE 1 ) and the second base-emitter voltage (VBE 2 ); and

changing over time which Y of the X transistors are in the first subgroup that are used to produce the first base-emitter voltage (VBE 1 ), and which Z of the X transistors are in the second subgroup that are used to produce the second base-emitter voltage (VBE 2 ).

10. The method of claim 9 , wherein during X periods of time the changing step includes selecting each of the X transistors in a cyclical manner:

to be in the first subgroup of Y of the X transistors that is/are used to produce the first base-emitter voltage (VBE 1 ); and

to be in the second subgroup of Z of the X transistors that are used to produce the second base-emitter voltage (VBE 2 ).

11. The method of claim 9 , wherein the changing step comprises selectively controlling which Y of the X transistors are in the first subgroup that are used to produce the first base-emitter voltage (VBE 1 ), and which Z of the X transistors are in the second subgroup that are used to produce the second base-emitter voltage (VBE 2 ), to thereby produce a predictably shaped switching noise that can be filtered.

12. The method of claim 11 , wherein the selectively controlling includes not using some of the X transistors to produce VBE 1 or VBE 2 .

13. The method of claim 9 , wherein Y=1.

14. The method of claim 9 , wherein 2≦Y<X/2.

15. A bandgap voltage reference circuit, comprising:

a group of X transistors, each of which includes a base and a current path between a collector and an emitter;

a first circuit portion that generates a voltage complimentary to absolute temperature (VCTAT) using at least one of the X transistors; and

a second circuit portion that generates a voltage proportional to absolute temperature (VPTAT) that is added to the VCTAT to produce a bandgap voltage output (VGO), the second circuit portion comprising:

a first subgroup of Y of the X transistors that are used to produce a first base-emitter voltage (VBE 1 ), where 1≦Y<X;

a second subgroup of Z of the X transistors that are used to produce a second base-emitter voltage (VBE 2 ), where Y<Z<X; and

wherein the VPTAT is produced by determining a difference between the first base-emitter voltage (VBE 1 ) and the second base-emitter voltage (VBE 2 ); and

wherein which at least one of the X transistors is/are used to generate the VCTAT, which Y of the X transistors is/are in the first subgroup and used to produce the first base-emitter voltage (VBE 1 ), and which Z of the X transistors are in the second subgroup and used to produce the second base-emitter voltage (VBE 2 ), changes over time.

16. The circuit of claim 15 , wherein during X periods of time each of the X transistors is selected in a cyclical manner:

to be at least one of the X transistors that is/are used to generate the VCTAT;

to be in the first subgroup of Y of the X transistors that is/are used to produce the first base-emitter voltage (VBE 1 ); and

to be in the second subgroup of Z of the X transistors that are used to produce the second base-emitter voltage (VBE 2 ).

17. The circuit of claim 15 , further comprising:

a controller; and

a plurality of switches;

wherein the controller controls the switches to select

which at least one of the X transistors is/are used to generate the VCTAT;

which Y of the X transistors is/are in the first subgroup and used to produce the first base-emitter voltage (VBE 1 ), and

which Z of the X transistors are in the second subgroup and used to produce the second base-emitter voltage (VBE 2 ).

18. The circuit of claim 17 , wherein:

the controller controls the switches to produce a predictably shaped switching noise that can be filtered; and

one or more of the X transistors may be specified to not be used to produce VBE 1 or VBE 2 .

19. The circuit of claim 15 , wherein:

the first base-emitter voltage (VBE 1 ) is indicative of a voltage drop between the base(s) of the Y of the X transistors and the emitter(s) of the Y of the X transistors; and

the second base-emitter voltage (VBE 2 ) is indicative of a voltage drop between the bases of the Z of the X transistors and the emitters of the Z of the X transistors.

20. A method for producing a bandgap voltage using a group of X transistors, comprising:

producing a voltage complimentary to absolute temperature (VCTAT) using at least one of the X transistors;

producing a first base-emitter voltage (VBE 1 ) using a first subgroup of Y of the X transistors, wherein the first base-emitter voltage (VBE 1 ) is indicative of a voltage drop between the base(s) of the Y of the X transistors and the emitter(s) of the Y of the X transistors, where 1≦Y<X;

producing a second base-emitter voltage (VBE 2 ) using a second subgroup of Z of the X transistors, wherein the second base-emitter voltage (VBE 2 ) is indicative of a voltage drop between the bases of the Z of the X transistors and the emitters of the Z of the X transistors, where Y<Z<X;

producing a voltage proportional to absolute temperature (VPTAT) by determining a difference between the first base-emitter voltage (VBE 1 ) and the second base-emitter voltage (VBE 2 ); and

producing the bandgap voltage by adding the VCTAT to the VPTAT to produce the bandgap voltage; and

changing over time which Y of the X transistors is/are in the first subgroup that are used to produce the first base-emitter voltage (VBE 1 ), and which Z of the X transistors are in the second subgroup that are used to produce the second base-emitter voltage (VBE 2 ).

21. The method of claim 20 , wherein the changing step comprises selectively controller which Y of the X transistors are in the first subgroup that are used to produce the first base-emitter voltage (VBE 1 ), and which Z of the X transistors are in the second subgroup that are used to produce the second base-emitter voltage (VBE 2 ), to thereby produce a predictably shaped switching noise that can be filtered.

22. The method of claim 21 , wherein the selectively controlling includes not using some of the X transistors to produce VBE 1 or VBE 2 .

23. The method of claim 20 , wherein one or more of the following are selected in a random or pseudo-random manner:

which Y of the X transistors is/are selected to be in the first subgroup and used to produce the first base-emitter voltage (VBE 1 );

which Z of the X transistors are selected to be in the second subgroup and used to produce the second base-emitter voltage (VBE 2 ); and

which at least one of the X transistors is/are used to produce the VCTAT.

24. The method of claim 20 , wherein Y=1.

25. The method of claim 20 , wherein 2≦Y<Z/2.

26. The method of claim 20 , further comprising changing over time which at least one of the X transistors is/are used to produce the VCTAT.

27. A method for producing a bandgap voltage using a group of X transistors, comprising:

producing a voltage complimentary to absolute temperature (VCTAT) using at least one of the X transistors;

producing a first base-emitter voltage (VBE 1 ) using a first subgroup of Y of the X transistors, where 1≦Y<X;

producing a second base-emitter voltage (VBE 2 ) using a second subgroup of Z of the X transistors, where Y<Z<X;

producing a voltage proportional to absolute temperature VPTAT by determining a difference between the first base-emitter voltage (VBE 1 ) and the second base-emitter voltage (VBE 2 );

producing the bandgap voltage by adding the VCTAT to the VPTAT to produce the bandgap voltage;

changing over time which Y of the X transistors is/are in the first subgroup that are used to produce the first base-emitter voltage (VBE 1 ), and which Z of the X transistors are in the second subgroup that are used to produce the second base-emitter voltage (VBE 2 ); and

changing over time which at least one of the X transistors is/are used to produce the VCTAT.