Audio amplifier circuit and electronic apparatus including the same

• US 20080159567A1
• Filed: 12/13/2007
• Published: 07/03/2008
• 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 8,363,856 B2
• Time in Patent Office: Days
• US Class Current: 381/120
• 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 1/0211 with control of the supply voltage or current
• CPC Class Codes: H03F 1/56 Modifications of input or output impedances, not otherwise provided for
• CPC Class Codes: H03F 2200/03 the amplifier being designed for audio applications
• 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 3/187 in integrated circuits

Abstract

An electronic audio amplifier circuit, operable in two modes and a battery powered portable audio apparatus incorporating the circuit; and associated apparatuses and methods. When in the first mode the audio apparatus is designed for the direct driving of headphones or a speaker. When in the second mode the audio apparatus is designed to drive a line input of an external amplifying apparatus with a signal that having a higher voltage amplitude for a given signal content than when driving headphone or a speaker. The circuit has common output stage circuitry for use in both modes, and a dual mode power supply circuit, ideally a charge pump circuit, for supplying the output stage in the first mode with a lower supply voltage than in the second mode.

Claims

1. A battery powered portable audio apparatus including an electronic audio amplifier circuit operable in two modes:

a first mode for the direct driving of an audio output transducer and

a second mode to drive a line input of an external amplifying apparatus, an output signal to be provided to said line input in the second mode having a higher voltage amplitude for a given signal content than an output signal driving said audio output transducer;

wherein the circuit comprises common output stage circuitry for use in both modes, and a dual mode power supply circuit for supplying said output stage in the first mode with a lower supply voltage than in the second mode.

2. An apparatus as claimed in claim 1 wherein the supply voltage in the first mode is approximately half that in the second mode.

3. An apparatus as claimed in claim 1 wherein the supply voltage in the second mode spans a voltage in the range 4 to 7 volts.

4. An apparatus as claimed in claim 1 wherein the supply voltage in the first mode is split either side of a ground reference.

6. An apparatus as claimed in claim 1 wherein, in use, the power output of said electronic audio amplifier circuit resultant from a full scale signal driving said audio output transducer in said first mode is in the order of milliwatts or tens of milliwatts RMS.

7. An apparatus as claimed in claim 1 wherein the signal for the external load can be delivered to an output jack which is the same jack as used for the audio output transducer.

8. An apparatus as claimed in claim 1 wherein a dedicated output terminal is provided for line level signals.

9. An apparatus as claimed in claim 1 further comprising means for limiting the output current of said amplifier circuit when operating in said second mode, such that maximum power output in said second mode is less than that in the first mode, in spite of the higher maximum voltage amplitude.

10. An apparatus as claimed in claim 1, the apparatus including said audio output transducer, said transducer having an impedance in the range 7 to 90 ohms.

11. An apparatus as claimed in claim 10 wherein said audio output transducer is a headphone device.

12. An apparatus as claimed in claim 10 wherein said audio output transducer is a loudspeaker built into the portable audio apparatus.

13. An apparatus as claimed in claim 1 wherein said dual mode power supply circuitry includes a dual mode charge pump operable in, at least, said first mode to divide an input supply voltage to provide a dual polarity supply to said output stage, the dual polarity supply spanning in total only the same or less than the input supply voltage, and in said second mode to provide a dual polarity supply to said output stage which spans greater than the input supply voltage.

14. An apparatus as claimed in claim 13 wherein the charge-pump circuit comprises:

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

at least first and second flying capacitor terminals for connection to at least one 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 network of switches in a sequence of said different states,

wherein said controller is operable in first and second modes, and where, in the first of said modes, said sequence is 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 and in the second of said modes generates positive and negative output voltages each up to substantially said input voltage.

15. An apparatus as claimed in claim 14 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 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.

16. An apparatus as claimed in claim 15 wherein said controller is adapted in the first mode to include in said sequence repetitions a third state, the third state being effective to apply the flying capacitor'"'"'s portion of said divided voltage across the first reservoir capacitor.

17. An apparatus as claimed in claim 15 wherein said controller is adapted in the second mode to operate said switches in a sequence which interleaves repetitions of at least second and sixth states, the sixth 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.

18. An apparatus as claimed in claim 17 wherein said controller is adapted in the second mode to include in said sequence repetitions a seventh state, said seventh state being effective to charge the flying capacitor independent of either reservoir capacitor.

19. An apparatus as claimed in claim 17 wherein said network includes a switch which is used in the second mode to connect the input terminal to the first output terminal independently of said first flying capacitor terminal.

20. An apparatus as claimed in claim 19 operable such that said switch is always closed when said circuit is operating in a particular implementation of said second mode, thus ensuring that said first reservoir capacitor is always connected between said input terminal and said common terminal when operating in this particular implementation.

21. An apparatus as claimed in claim 1 wherein the controller is adapted to detect automatically the type of load connected and to select the first or second mode of operation automatically.

22. An apparatus as claimed in claim 21 operable such that said detection is made implicitly by reference to a volume setting input of the amplifier.

23. An apparatus as claimed in claim 22 wherein the first mode is selected when said volume is at or near a maximum.

24. Communications apparatus incorporating audio apparatus as claimed in claim 1.

25. Headphone driving apparatus incorporating audio apparatus according to claims 1, and a headphone jack connected to the output stage at least in said first mode.

26. The headphone apparatus as claimed in claim 25 further including a separate output connector for outputting line level signals in said second mode.

27. The headphone apparatus as claimed in claim 25 wherein the amplifier circuit is operable to drive line level signals through said headphone jack in said second mode.

5. An apparatus as claimed in 4 wherein the supply voltage in the second mode is also split either side of said ground reference.

28. A method of, on occasion, direct driving an audio output transducer having a relatively low impedance with signals in a first range of voltages, while, on separate occasions, driving a higher impedance line input of an external amplifying apparatus with signals in a higher range of amplitudes for a given signal content, using common output stage circuitry, the method comprising using a dual mode power supply to supply said common output stage circuitry in first and second modes, such that a lower supply voltage is supplied in said first mode, when said audio output transducer is being driven, than in said second mode when said higher impedance line input of an external amplifying apparatus is being driven.

29. A method as claimed in claim 28 wherein, when driving said audio output transducer with a full scale signal in said first mode, the power output from said output stage circuitry is orders of magnitude greater than when driving said line input of an external amplifying apparatus with a full scale signal in said second mode.

30. A method as claimed in claim 28 wherein the power output of said electronic audio amplifier circuit resultant from a full scale signal driving said audio output transducer in said first mode is in the order of milliwatts or tens of milliwatts RMS.

31. A method as claimed in claim 28 wherein a common output terminal is used for connection to said transducer and said line input.

32. A method as claimed in claim 28 wherein a dedicated output terminal is used for driving said line input.

33. A method as claimed in claim 28 wherein said supply voltage is provided by 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 at 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 directly or via said flying capacitor and thereby to generate, when operating in said first mode, said split rail supply with positive and negative output voltages either together spanning a voltage approximately equal to the input voltage, and centered on the voltage at the common terminal, or, when operating in said second mode, positive and negative output voltages each up to substantially said input supply, depending on a chosen mode of operation.

34. A method as claimed in claim 33 comprising, when operating in a first mode, 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.

35. A method as claimed in claim 33 wherein said sequence in said first mode includes repetitions of a third state, the third state being effective to apply the flying capacitor'"'"'s portion of said divided voltage across the first reservoir capacitor.

36. A method as claimed in claim 33 comprising, when operating in a second mode, interleaving repetitions of at least second and sixth states, the sixth 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.

37. A method as claimed in claim 36 wherein said sequence in said second mode includes repetitions of a seventh state, said seventh state being effective to charge the flying capacitor independent of either reservoir capacitor.

38. A method as claimed in claim 33 wherein, when operating in a particular implementation of a second mode, a connection is maintained between the input terminal and the first output terminal independent of said flying capacitor thus ensuring that said first reservoir capacitor is always connected between said input terminal and said common terminal when operating in this particular implementation.

39. A method as claimed in claim 28 wherein the current at said signal output is limited when operating in said second mode, such that maximum power output in said second mode is less than that in the first mode, in spite of the higher maximum voltage amplitude.

40. A method as claimed in claim 28 wherein the type of load connected is detected automatically and the first or second mode of operation selected accordingly automatically.

41. A method as claimed in claim 40 wherein said detection is made implicitly by reference to a volume setting input of the amplifier.

42. A method as claimed in claim 41 wherein the first mode is selected when said volume is at or near a maximum.

43. An electronic audio amplifier circuit operable in two modes:

a first mode for the direct driving of an audio output transducer and

a second mode to drive a line input of an external amplifying apparatus, an output signal to be provided to said line input in the second mode having a higher voltage amplitude for a given signal content than an output signal driving said audio output transducer;

wherein the circuit comprises;

common output stage circuitry for use in both modes, and a dual mode power supply circuit for supplying said output stage in the first mode with a lower supply voltage than in the second mode; and

means for limiting the circuit'"'"'s output current when operating in said second mode, such that maximum power output in said second mode is less than that in the first mode, in spite of the higher maximum voltage amplitude.