Amplifier circuit and methods of operation thereof

• US 7,714,660 B2
• Filed: 12/13/2007
• Issued: 05/11/2010
• Est. Priority Date: 06/30/2006
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Wolfson Microelectronics plc
• Inventors: Frith, Peter J., Lesso, John P., Pennock, John L.
• Primary Examiner(s): Pascal; Robert
• Assistant Examiner(s): Nguyen; Hieu P
• Application Number:
  US12/000,549
• Publication Number:
  US 20080116979A1
• Time in Patent Office: 880 Days
• Field of Search: 330/124, 330/310, 330/98, 330/150, 327/536, 307/109, 381/120
• US Class Current: 330/297
• 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: H03F 1/025 by using a signal derived from the input signal
• CPC Class Codes: H03F 2200/507 A switch being used for switching on or off a supply or supplying circuit in an IC-block amplifier circuit
• CPC Class Codes: H03F 2200/511 Many discrete supply voltages or currents or voltage levels can be chosen by a control signal in an IC-block amplifier circuit
• CPC Class Codes: H03F 3/185 with field-effect devices H03F3/187 takes precedence
• CPC Class Codes: H03F 3/187 in integrated circuits
• CPC Class Codes: H03F 3/68 Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics power amplifiers using a combination of several semiconductor amplifiers H03F3/211; combinations of amplifiers using coupling networks with distributed constants H03F3/602
• CPC Class Codes: H03G 1/0017 the device being at least one of the amplifying solid state elements of the amplifier
• CPC Class Codes: H03G 1/0029 using FETs
• CPC Class Codes: H03G 1/0088 using discontinuously variable devices, e.g. switch-operated
• CPC Class Codes: H03G 1/0094 using switched capacitors

Abstract

A signal amplifying circuit and associated methods and apparatuses, the circuit comprising: a signal path extending from an input terminal to an output terminal, a gain controller arranged to control the gain applied along the signal path in response to a control signal; an output stage within the signal path for generating the output signal, the output stage having a gain that is substantially independent of its supply voltage, and a variable voltage power supply comprising a charge pump for providing positive and negative output voltages, the charge pump comprising a network of switches that is operable in a number of different states and a controller for operating the switches in a sequence of the states so as to generate positive and negative output voltages together spanning a voltage approximately equal to the input voltage.

Claims

1. A signal amplifying circuit comprising:

an input for receiving an input signal;

an output for outputting an output signal;

a signal path extending from the input to the output;

a gain controller arranged to control the gain applied along said signal path in response to a control signal;

an output stage coupled to the gain controller within said signal path for generating said output signal; and

a variable voltage power supply comprising a charge pump circuit for providing a positive output voltage and a negative output voltage for supplying the output stage, the charge pump circuit comprising;

a supply input node and a common node for connection to an input voltage supply;

first and second supply output nodes for connection to first and second reservoir capacitors, said first and second supply output nodes outputting said positive and negative output voltages;

at most first and second flying capacitor nodes;

a network of switches for interconnecting said nodes;

a controller for operating said switches; and

a control signal input for receiving said control signal;

wherein said variable voltage power supply, employing said charge pump circuit with said at most first and second flying capacitor nodes, is arranged for generating either first positive and negative output voltages or second positive and negative output voltages in response to said control signal, wherein said first positive and negative output voltages are each substantially equal in magnitude to the voltage of said input voltage supply and said second positive and negative output voltages are each substantially equal in magnitude to half the voltage of said input voltage supply.

2. An amplifying circuit as claimed in claim 1, wherein said variable voltage power supply comprises an input selector for selecting a voltage to be input into said input supply node of said charge pump circuit, depending on a signal derived from said control signal.

3. An amplifying circuit as claimed in claim 1, wherein said first and second flying capacitor nodes for connection to a flying capacitor.

4. An amplifying circuit as claimed in claim 3, 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.

5. An amplifying circuit as claimed in claim 4, wherein, in said first state said first and second flying capacitor nodes are connected to said supply input node and said first supply output node respectively, and in said second state the first and second flying capacitor nodes are connected to said common node and said second supply output node respectively.

6. An amplifying circuit as claimed in claim 4, 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.

7. An amplifying circuit as claimed in claim 6, wherein, in said third state, said first and second flying capacitor nodes are connected to said first supply output node and said common node respectively.

8. An amplifying circuit as claimed in claim 3, wherein said switch network is operable in at least a first state and a second state, the first state being effective to charge up said flying capacitor to said input voltage, the second 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 first and second states.

9. An amplifying circuit as claimed in claim 8, wherein, in said first state, said first and second flying capacitor nodes are connected to said supply input node and said common node respectively, and in said second state, the first and second flying capacitor nodes are connected to said first supply output node and said second supply output node respectively.

10. An amplifying circuit as claimed in claim 1, wherein said switch network is operable to connect said first flying capacitor node independently to any of said supply input node, said first supply output node and said common node and said switch network is operable to connect said second flying capacitor node independently to any of said first supply output node, said common node and said second supply output node.

11. An amplifying circuit as claimed in claim 1, wherein said switch network comprises:

a first switch for connecting the supply input node to the first flying capacitor node,

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

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

a fourth switch for connecting the second flying capacitor node to said first supply output node,

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

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

12. An amplifying circuit as claimed in claim 1, wherein said controller is operable to control said network to generate said first positive and negative output voltages when operating in a first mode, and said second positive and negative output voltages when operating in a second mode.

13. An amplifying circuit as claimed in claim 12, wherein said variable voltage power supply varies a voltage between said first and second supply output node by having said charge pump circuit switch between said first mode and said second mode in response to said control signal.

14. An amplifying circuit as claimed in claim 12, wherein said controller is adapted in the first mode to operate said switches in a sequence which interleaves repetitions of at least first and second states, the first state being effective to charge the flying capacitor and said first reservoir capacitor substantially to said input voltage, the second state being effective to transfer said voltage from the flying capacitor to the second reservoir capacitor.

15. An amplifying circuit as claimed in claim 14, wherein in said second state, said first and second flying capacitor nodes are connected to said common node and said second supply output node respectively, and in said first state said first flying capacitor node is connected to both said supply input node and said first supply output node and said second flying capacitor node is connected to said common node.

16. An amplifying circuit as claimed in claim 14, wherein said controller is adapted in the first mode to include in said sequence repetitions a third state, said third state being effective to charge the flying capacitor independent of either reservoir capacitor.

17. An amplifying circuit as claimed in claim 16, wherein in said third state said first flying capacitor node is connected to said supply input node only and said second flying capacitor node is connected to said common node.

18. An amplifying circuit as claimed in claim 12, wherein said network includes a switch which is used in the first mode to connect the supply input node to the first supply output node independently of said first flying capacitor node.

19. An amplifying circuit as claimed in claim 18, wherein said switch is always closed when said circuit is operating in a particular implementation of said first mode, thus ensuring that said first reservoir capacitor is always connected between said supply input node and said common node when operating in this particular implementation.

20. An amplifying circuit as claimed in claim 1, wherein said variable voltage power supply further comprises a DC-DC converter, said input voltage supply of said charge pump circuit being derived from the output of said DC-DC converter, and wherein the output of said DC-DC converter depends on a signal derived from said control signal.

21. An amplifying circuit as claimed in claim 1, wherein said variable voltage power supply is arranged to vary a voltage between said first and second supply output nodes such that reductions in the amplitude of said output signal caused by a variation of said control signal are not matched by increases in voltage drop within said output stage.

22. An amplifying circuit as claimed in claim 1, wherein said variable voltage power supply is arranged to vary a voltage between said first and second supply output nodes such that reductions in the amplitude of said output signal caused by a variation of said control signal are not matched by increases in power loss within said output stage.

23. An amplifying circuit as claimed in claim 1, wherein said amplifier circuit comprises a linear amplifier.

24. An amplifying circuit as claimed in any claim 1, wherein said amplifying circuit is of a type adapted for the amplification of audio signals.

25. An amplifying circuit as claimed in claim 24, wherein said control signal is a volume control signal.

26. An audio apparatus incorporating an amplifying circuit according to claim 1.

27. An RF transmitter apparatus comprising an amplifying circuit according to claim 1 having its output stage adapted to drive an antenna.

28. A line driver for driving a signal through a transmission line, the line driver incorporating the signal amplifying circuit according to claim 1 adapted for driving a transmission line.

29. An amplifying circuit of claim 1, the gain controller comprising:

an amplifier; and

at least one resistive element;

wherein the resistance of the at least one resistive element can be varied by the control signal to vary the gain of the amplifier.

30. An amplifying circuit as claimed in claim 29, wherein the at least one resistive element comprises at least one resistor.

31. An amplifying circuit as claimed in claim 30, wherein the resistance of the at least one resistive element is varied by switching in the at least one resistor.

32. An amplifying circuit as claimed in claim 1, wherein the gain controller controls the gain digitally.

33. A method of amplifying an input signal to generate a gain controlled output signal, said method comprising:

generating a positive output voltage and a negative output voltage from a single input supply received across a supply input node and a common node, the positive and negative output voltages being output at first and second supply output nodes connected to said common node via respective first and second reservoir capacitors, the method comprising connecting a flying capacitor to at most first and second flying capacitor nodes, said at most first and second flying capacitor nodes being connected between different ones of said supply nodes in a sequence of states to generate either first positive and negative output voltages or second positive and negative output voltages, wherein said first positive and negative output voltages are each substantially equal in magnitude to the voltage of said input supply and said second positive and negative output voltages are each substantially equal in magnitude to half the voltage of said input supply;

the method further comprising;

applying said positive and negative output voltages to an output stage of an amplifier circuit;

receiving said input signal;

receiving a control signal; and

applying a gain to said input signal in response to said control signal to produce said gain controlled output signal at an amplifier output node of said output stage of said amplifier circuit wherein said gain is independent of said positive and negative output voltages of said output stage.

34. A method as claimed in claim 33, further comprising varying said positive and negative output voltages applied to said output stage in response to said control signal.

35. A method as claimed in claim 34, wherein the voltage applied to said output stage by said positive and negative output voltages is varied by having said control signal control said single input supply received across said supply input node and a common node.

36. A method as claimed in claim 33, comprising interleaving repetitions of at least first and second states in order to generate said second positive and negative output voltages, 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.

37. A method as claimed in claim 36, 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.

38. A method as claimed in claim 33, wherein said control signal controls which states are used to generate said positive and negative output voltages, such that said first positive and negative output voltages are generated when said control signal is within a first range of values and said second positive and negative output voltages are generated said control signal is within a second range of values.

39. A method as claimed in claim 38 comprising, when said control signal is within said first range of values, interleaving repetitions of at least first and second states in order to generate said positive and negative output voltages, the second state being effective to charge the flying capacitor and said first reservoir capacitor substantially to said input voltage, the first state being effective to transfer said voltage from the flying capacitor to the second reservoir capacitor.

40. A method as claimed in claim 39, wherein said sequence in said first mode includes repetitions of a third state, said third state being effective to charge the flying capacitor independent of either reservoir capacitor.

41. A method as claimed in claim 39, wherein, a connection is maintained between the supply input node and the first supply output node independent of said flying capacitor thus ensuring that said first reservoir capacitor is always connected between said supply input node and said common node when operating in this particular implementation.

42. A method as claimed in claim 33, said amplifier circuit being used to drive a load in response to said input signal, wherein

the positive and negative output voltages applied to said output stage is varied in response to variations in said control signal, such that reductions in the amplitude of the output signal caused by variation of said control signal are not matched by increases in voltage drop within the output stage

43. A method as claimed in claim 33, wherein said positive and negative output voltages applied to said output stage varies between a plurality of discrete voltage levels in response to said control signal.

44. A method as claimed in claim 33, wherein said control signal is a volume control signal.

45. A circuit comprising:

an input for receiving an input signal;

an output for outputting an output signal;

a signal path extending from the input to the output;

an output stage along said signal path for generating said output signal; and

a variable voltage power supply comprising a charge pump circuit for providing a positive output voltage and a negative output voltage for supplying the output stage, the charge pump circuit comprising;

a supply input node and a common node for connection to an input voltage supply;

first and second supply output nodes for connection to first and second reservoir capacitor via said common node, said first and second supply output nodes outputting said positive and negative output voltages;

at most first and second flying capacitor nodes;

a network of switches for interconnecting said nodes;

a controller for operating said switches; and

a control signal input for receiving a control signal;

wherein said variable voltage power supply, employing said charge pump circuit with said at most first and second flying capacitor nodes, is arranged for generating either first positive and negative output voltages or second positive and negative output voltages in response to said control signal, wherein said first positive and negative output voltages are each substantially equal in magnitude to the voltage of said input voltage supply and said second positive and negative output voltages are each substantially equal in magnitude to half the voltage of said input voltage supply.

46. A circuit as claimed in claim 45, wherein the output stage is arranged to control the gain applied along said signal path in response to said control signal.

47. A circuit as claimed in claim 46, the output stage comprising:

an amplifier; and

at least one resistive element;

wherein the resistance of the at least one resistive element can be varied by the control signal to vary the gain of the amplifier.

48. A circuit as claimed in claim 45, wherein said switch network comprises:

a first switch for connecting the supply input node to the first flying capacitor node,

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

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

a fourth switch for connecting the second flying capacitor node to said first supply output node,

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

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

49. A circuit as claimed in claim 45, wherein said controller is operable to control said network to generate said first positive and negative output voltages when operating in a first mode, and said second positive and negative output voltages when operating in a second mode.

50. A circuit as claimed in claim 49, wherein said variable voltage power supply varies a voltage between said first and second supply output nodes by having said charge pump circuit switch between said first mode and said second mode in response to said control signal.