Charge pump circuit and methods of operation thereof

• US 20080150621A1
• Filed: 12/13/2007
• Published: 06/26/2008
• Est. Priority Date: 12/22/2006
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Wolfson Microelectronics plc
• Inventors: Frith, Peter J., Lesso, John P., Pennock, John L.
• Granted Patent: US 7,622,984 B2
• Time in Patent Office: Days
• US Class Current: 327/536
• CPC Class Codes: H02M 1/009 having two or more independently controlled outputs for DC-DC converter with intermediate AC H02M3/33561
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps
• CPC Class Codes: H02M 3/071 adapted to generate a negative voltage output from a positive voltage source
• CPC Class Codes: H02M 3/072 adapted to generate an output voltage whose value is lower than the input voltage

Abstract

A charge pump circuit and associated method and apparatuses for providing a plurality of output voltages using a single flying capacitor. The circuit includes a network of switches that are operable in a number of different states and a controller for operating the switches in a sequence of states so as to generate positive and negative output voltages together spanning a voltage approximately equal to the input voltage and centered on the voltage at the common terminal.

Claims

1. A method of generating a split-rail voltage supply from a single input supply received across an input terminal and a common terminal, the split-rail supply being output at first and second output terminals connected to said common terminal via respective first and second loads and also via respective first and second reservoir capacitors, the method comprising connecting a flying capacitor between different ones of said terminals in a sequence of states, so as to transfer packets of charge repeatedly from said input supply to said reservoir capacitors via said flying capacitor thereby generating said split rail supply with positive and negative output voltages together spanning a voltage approximately equal to the voltage of said input supply, and centered on the voltage at the common terminal.

2. A method as claimed in claim 1 comprising interleaving repetitions of at least first and second states, the first state being effective to divide said input voltage between the flying capacitor and first reservoir capacitor in series, the second state being effective to apply the flying capacitor'"'"'s portion of said divided voltage across the second reservoir capacitor.

3. A method as claimed in claim 2 wherein said first state is obtained by connecting said flying capacitor across said input terminal and said first output terminal, and said second state is obtained by connecting the flying capacitor across said common terminal and said second output terminal.

4. A method as claimed in claim 2 comprising including repetitions of a third state within the sequence, said third state being effective to apply the flying capacitor'"'"'s portion of said divided voltage across the first reservoir capacitor.

5. A method as claimed in claim 4 wherein, said third state is obtained by connecting said flying capacitor across said first output terminal and said common terminal.

6. A method as claimed in claim 4 wherein said third state is included less frequently than the first and second states.

7. A method as claimed in claim 1 comprising interleaving repetitions of fourth and fifth states, the fourth state being effective to charge up said flying capacitor to said input voltage, the fifth state being effective to divide the voltage on said flying capacitor between the first reservoir capacitor and second reservoir capacitor in series.

8. A method as claimed in claim 7 wherein said fourth state is obtained by connecting said flying capacitor across said input terminal and said common terminal, and said fifth state is obtained by connecting the flying capacitor across said first output terminal and said second output terminal.

9. A method as claimed in claim 1 wherein sequence of states is varied according to load conditions.

10. A method as claimed in claim 9 wherein said variation in the sequence of states includes lowering the frequency of inclusion of the second state should the load be asymmetrical.

11. A method as claimed in claim 9 wherein said first reservoir capacitor is charged only when the voltage at said first output terminal falls below a first threshold value and said second reservoir capacitor is charged only when the voltage at said second output terminal falls below a second threshold value.

12. A method as claimed in claim 11 wherein said at least one said first and second threshold values is settable by a user therefore allowing control of the voltage levels at said first and second output terminals.

13. A method as claimed in claim 1 further comprising selecting a signal to be input into said input supply terminal and therefore controlling the voltage levels at said first and second output terminals.

14. A method as claimed in claim 1 wherein, depending on the state, one of the terminals of said flying capacitor is connected independently to one of said input terminal, said first output terminal or said common terminal and the other terminal of said flying capacitor is connected independently to one of said first output terminal, said common terminal or said second output terminal.

15. A charge pump circuit for providing a plurality of output voltages, the circuit comprising:

an input terminal and a common terminal for connection to an input voltage,

first and second output terminals for outputting said plurality of output voltages, said output terminals in use being connected to said common terminal via respective first and second loads and also via respective first and second reservoir capacitors,

first and second flying capacitor terminals for connection to a flying capacitor, and

a network of switches that is operable in a plurality of different states for interconnecting said terminals,

the circuit being operable to generate, at said output terminals, positive and negative output voltages together spanning a voltage approximately equal to the input voltage and centered on the voltage at the common terminal, using only said flying capacitor and first and second reservoir capacitors.

32. A circuit as claimed in claim 15 wherein said charge pump circuit is included within an integrated circuit, said reservoir capacitors and flying capacitor not being included within the integrated circuit.

39. An audio apparatus including a charge pump circuit as claimed in claim 15, the charge pump having a flying capacitor connected to said first and second flying capacitor terminals and first and second reservoir capacitors connected respectively between said first output terminal and said common terminal and said second output terminal and said common terminal, the audio apparatus further comprising audio output circuitry connected to be powered by the first and second output voltages of said converter.

40. Audio apparatus as claimed in claim 39 in portable form.

41. A communications apparatus incorporating audio apparatus according to claim 39.

42. An in-car audio apparatus incorporating audio apparatus according to claim 39.

43. A headphone apparatus incorporating audio apparatus according to claim 39.

44. A stereo headphone apparatus incorporating audio apparatus according to claim 39.

45. An audio apparatus according to claim 39 further including an audio output transducer connected as a load connected to an output terminal of said audio output circuitry.

16. A charge pump circuit for providing a plurality of output voltages, the circuit comprising:

an input terminal and a common terminal for connection to an input voltage,

first and second output terminals for outputting said plurality of output voltages, said output terminals in use being connected to said common terminal via respective first and second loads and also via respective first and second reservoir capacitors,

first and second flying capacitor terminals for connection to a flying capacitor,

a network of switches that is operable in a plurality of different states for interconnecting said terminals, and

a controller for operating said switches in a sequence of said states, said sequence being adapted repeatedly to transfer packets of charge from said input terminal to said reservoir capacitors via said flying capacitor depending on the state, thereby generating positive and negative output voltages together spanning a voltage approximately equal to the input voltage, and centered on the voltage at the common terminal.

17. A circuit as claimed in claim 16 wherein said switch network is operable in at least a first state and a second state, said controller being adapted to operate said switches in a sequence which interleaves repetitions of said first and second states, the first state being effective to divide said input voltage between the flying capacitor and first reservoir capacitor in series, the second state being effective to apply the flying capacitor'"'"'s portion of said divided voltage across the second reservoir capacitor.

18. A circuit as claimed in claim 17 wherein, in said first state said first and second flying capacitor terminals are connected to said input terminal and said first output terminal respectively, and in said second state the first and second flying capacitor terminals are connected to said common terminal and said second output terminal respectively.

19. A circuit as claimed in claim 17 wherein said switch network is further operable in a third state effective to apply the flying capacitor'"'"'s portion of said divided voltage across the first reservoir capacitor, and wherein said controller is adapted to include repetitions of said third state within the sequence.

20. A circuit as claimed in claim 19 wherein, in said third state, said first and second flying capacitor terminals are connected to said first output terminal and said common terminal respectively.

21. A circuit as claimed in claim 19 wherein said controller is adapted to include said third state less frequently than the first and second states.

22. A circuit as claimed in claim 19 wherein said switch network is operable in at least a fourth state and a fifth state, the fourth state being effective to charge up said flying capacitor to said input voltage, the fifth state being effective to divide the voltage on said flying capacitor between the first reservoir capacitor and second reservoir capacitor in series, and wherein said controller is adapted to operate said switches in a sequence which interleaves repetitions of said fourth and fifth states.

23. A circuit as claimed in claim 22 wherein, in said fourth state, said first and second flying capacitor terminals are connected to said input terminal and said common terminal respectively, and in said fifth state, the first and second flying capacitor terminals are connected to said first output terminal and said second output terminal respectively.

24. A circuit as claimed in claim 16 wherein said controller is adapted to vary the sequence of states according to load conditions.

25. A circuit as claimed in claim 24 wherein said variation in the sequence of states includes lowering the frequency of inclusion of the second state should the load be asymmetrical.

27. A circuit as claimed in claim 24 operable such that said first reservoir capacitor is charged only when the voltage at said first output terminal falls below a first threshold value and said second reservoir capacitor is charged only when the voltage at said second output terminal falls below a second threshold value.

28. A circuit as claimed in claim 27 wherein further comprising at least one comparator for comparing the voltage at each of said output terminals with at least one reference voltage.

29. A circuit as claimed in claim 28 wherein said at least one reference voltage is settable by a user therefore allowing control of the voltage levels at said first and second output terminals.

30. A circuit as claimed in claim 16 further comprising an input selector for selecting a signal to be input into said input supply terminal, depending on a control signal therefore controlling the voltage levels at said first and second output terminals.

31. A circuit as claimed in claim 16 wherein said switch network is operable to connect said first flying capacitor terminal independently to any of said input terminal, said first output terminal and said common terminal and said second flying capacitor terminal independently to any of said first output terminal, said common terminal and said second output terminal.

26. A circuit as claimed in 24 wherein said charge pump circuit is arranged to operate in a closed loop configuration.

33. A charge pump circuit for providing a plurality of supply voltages from an input voltage, the charge pump circuit having first and second output terminals and a common terminal for connection to first and second reservoir capacitors and one pair of flying capacitor terminals for connection to a flying capacitor, and a switch network comprising:

a first switch for connecting the input terminal to the a first one of said flying capacitor terminals,

a second switch for connecting the first flying capacitor terminal to the first output terminal,

a third switch for connecting the first flying capacitor terminal to said common terminal,

a fourth switch for connecting the second one of said flying capacitor terminals to said first output terminal,

a fifth switch for connecting the second flying capacitor terminal to said common terminal, and

a sixth switch for connecting the second flying capacitor terminal to the second output terminal.

48. A circuit as claimed in claim 33 further comprising a controller for operating said switches so as to generate positive and negative output voltages across said reservoir capacitors, said output voltages together spanning a voltage approximately equal to the input voltage, and centered on a voltage at the common terminal.

34. A charge pump circuit for providing a plurality of output voltages, the circuit comprising:

an input terminal and a common terminal for connection to an input voltage,

first and second output terminals for outputting said plurality of output voltages, said output terminals in use being connected to said common terminal via respective first and second loads and also via respective first and second reservoir capacitors,

one or more pairs of flying capacitor terminals, each pair comprising first and second flying capacitor terminals for connection to one or more flying capacitors, the number of flying capacitors equalling n,

a network of switches that is operable in a plurality of different states for interconnecting said terminals, and

a controller for operating said switches in a sequence of said states, said sequence being adapted repeatedly to transfer packets of charge from said input terminal to said reservoir capacitors and via said flying capacitors depending on the state thereby generating positive and negative output voltages each of a magnitude up to substantially a fraction of said input voltage, said fraction of said input voltage equalling 1/(n+1), where n is an integer equal to or greater than one.

35. A circuit as claimed in claim 34 wherein n=1 and said fraction of said input voltage is substantially a half.

36. A circuit as claimed in claim 34 wherein n>

1 and s aid fraction of said input voltage is substantially 1/(n+1).

37. A circuit as claimed in claim 36 wherein said circuit is able to generate output voltages of magnitudes at different fractions of said input voltage.

38. A circuit as claimed in claim 37 wherein said different fractions of said input voltage include the inverse of some or all of each integer between 2 and (n+1).

46. A charge pump circuit for providing a plurality of output voltages, the circuit comprising:

an input terminal and a common terminal for connection to an input voltage,

first and second output terminals for outputting said plurality of output voltages, said output terminals in use being connected to said common terminal via respective first and second loads and also via respective first and second reservoir capacitors,

first and second flying capacitor terminals for connection to a flying capacitor,

a network of switches that is operable in a plurality of different states for interconnecting said terminals, including at least a first state and a second state, the first state being effective to divide said input voltage between the flying capacitor and first reservoir capacitor in series, the second state being effective to apply the flying capacitor'"'"'s portion of said divided voltage across the second reservoir capacitor, and

a controller for operating said switches in a sequence of said states said controller being adapted to operate said switches in a sequence which interleaves repetitions of said first and second states, thereby generating positive and negative output voltages together spanning a voltage approximately equal to the input voltage, and centered on the voltage at the common terminal.

47. A circuit as claimed in claim 46 wherein said switch network is further operable in a third state effective to apply the flying capacitor'"'"'s portion of said divided voltage across the first reservoir capacitor, and wherein said controller is adapted to include repetitions of said third state within the sequence.

49. A charge pump circuit, comprising:

an input terminal for receiving a single input supply voltage;

first and second output terminals;

a plurality of capacitor terminals for connecting said charge pump circuit to a plurality of capacitors, including a single flying capacitor; and

a switch network connected to said input terminal, said first and second output terminals, and said plurality of capacitor terminals, said switch network being operable in a plurality of states for interconnecting said input supply voltage to said plurality of capacitors, including said single flying capacitor, and to said first and second output terminals, to provide split-rail voltages at said first and second output terminals.

50. A charge pump circuit as recited in claim 49 wherein said switch network comprises a plurality of switches, and said circuit further comprises a controller for controlling said plurality of switches to provide said split-rail voltages at said first and second output terminals.

51. A method of generating split-rail voltages from a single input supply voltage, comprising connecting a plurality of capacitors, including a single flying capacitor, to the single input supply voltage using a switch network operable in a plurality of different states to provide said split rail voltages at a respective pair of output terminals, said split rail voltages together spanning a voltage approximately equal to the voltage of said input supply.

52. A method of generating a split-rail voltage supply from a single input supply voltage received across an input terminal and a common terminal, the split-rail supply being output at first and second output terminals connected to said common terminal via respective first and second loads and also via respective first and second reservoir capacitors, the method using a single flying capacitor to generate said split rail supply with positive and negative output voltages together spanning a voltage approximately equal to the voltage of said input supply, and centered on the voltage at the common terminal.