High efficiency driver for miniature loudspeakers

• US 20030123681A1
• Filed: 12/02/2002
• Published: 07/03/2003
• Est. Priority Date: 11/30/2001
• Status: Active Grant

• Current Assignee: TDK Corporation
• Original Assignee: Sonion A/S
• Inventors: Thomsen, Henrik, Furst, Claus Erdmann, Poulsen, Jens Kristian, Stenberg, Lars Jorn
• Granted Patent: US 7,336,794 B2
• Time in Patent Office: Days
• US Class Current: 381/111
• CPC Class Codes: H04R 1/005 using digitally weighted transducing elements
• CPC Class Codes: H04R 25/505 using digital signal processing
• CPC Class Codes: H04R 3/00 Circuits for transducers , loudspeakers or microphones

Abstract

In a first aspect the present invention provides a compact high efficiency driver suitable for driving a loudspeaker, such as a miniature loudspeaker for mobile phones or hearing aids. The driver comprising an interface for receiving an input signal, a three-level modulator, and a three-level H-bridge. The interface may be adapted to receive a digital input signal. In a preferred embodiment of the driver the H-bridge is controlled by a correction circuit which is operated by a Return-To-Zero scheme. In a further preferred embodiment the driver comprises a supply voltage step-up circuit for increasing a voltage supplied to the H-bridge. In a second aspect the present invention provides a miniature loudspeaker assembly having a built-in driver. In a third aspect the present invention provides a mobile device with a built-in miniature loudspeaker assembly.

Claims

1. A driver suitable for driving a loudspeaker, the driver comprising

an interface adapted to receive an input signal,

a three-level modulator, and

a three-level H-bridge.

2. A driver according to claim 1, wherein the interface is adapted to receive an analog input signal.

3. A driver according to claim 1, wherein the interface is adapted to receive a digital input signal.

4. A driver according to claim 3, wherein the interface is adapted to receive and process signal formats selected from the group consisting of:

SPDIF, AES/EBU, PCM, SSI and I²S.

5. A driver according to claim 1, wherein the three-level modulator is implemented in the digital domain.

6. A driver according to claim 1, wherein the three-level modulator is implemented in the analog domain.

7. A driver according to claim 1, further comprising an interpolator.

8. A driver according to claim 1, wherein the three-level modulator comprises a three-level sigma-delta modulator.

9. A driver according to claim 1, further comprising a power supply voltage regulator.

10. A driver according to claim 1, further comprising a PLL.

11. A driver according to claim 1, wherein the H-bridge is controlled by a correction circuit.

12. A driver according to claim 11, wherein the correction circuit is operated according to a RTZ scheme.

13. A driver according to claim 12, wherein the RTZ scheme is level dependent.

14. A driver according to claim 11, wherein the correction circuit comprises a digital filter.

15. A driver according to claim 14, wherein the digital filter is a 1+Z⁻

1 filter.

16. A driver according to claim 11, wherein the correction circuit comprises a pattern generator.

17. A driver according to claim 11, wherein the correction circuit comprises means for providing a feedback signal.

18. A driver according to claim 11, wherein the correction circuit comprises means for providing pseudo multibit coding.

19. A driver according to claim 1, wherein the three-level H-bridge comprises at least 4 switches for providing independent control.

20. A driver according to claim 1, further comprising a filter having its input terminal connected to an output terminal of the driver.

21. A driver according to claim 20, wherein the filter comprises a low-pass filter section.

22. A driver according to claim 20, wherein the filter comprises a coil.

23. A driver according to claim 1, further comprising a power supply step-up circuit for increasing a level of supply voltage supplied to the three-level H-bridge.

24. A miniature loudspeaker assembly adapted to convert a first electrical signal to an acoustical signal, the miniature loudspeaker assembly comprising

a driver according to claim 1, the driver being adapted to receive the first electrical signal and to generate a modified first electrical signal in response to the first electrical signal, and

a loudspeaker comprising a motor adapted to receive the modified first electrical signal, the motor further being adapted to drive a diaphragm so as to generate the acoustical signal.

25. A miniature loudspeaker assembly according to claim 24, further comprising a control circuit, the control circuit being electrically connected between the driver and the motor.

26. A miniature loudspeaker assembly according to claim 24, wherein the motor comprises a coil and a magnetic circuit.

27. A miniature loudspeaker assembly according to claim 24, wherein the motor comprises a piezo element.

28. A miniature loudspeaker assembly according to claim 27, wherein the control circuit is adapted to charge and to discharge the piezo element.

29. A miniature loudspeaker assembly according to claim 28, wherein charging and discharging is performed by switching a coil between the piezo element and a voltage supply.

30. A miniature loudspeaker assembly according to claim 29, wherein charging and discharging is performed by switching a capacitor between the piezo element and a voltage supply.

31. A miniature loudspeaker assembly according to claim 24, wherein the driver is positioned in a casing fabricated in an EMI shielding material.

32. A mobile device comprising a miniature loudspeaker assembly according to claim 24.

33. A mobile device according to claim 32, wherein the mobile device is selected from the group consisting of:

mobile phones, hearing aids, assistive listening devices, head-sets, palm computers, and laptop computers.