High efficiency driver for miniature loudspeakers

• US 7,336,794 B2
• Filed: 12/02/2002
• Issued: 02/26/2008
• Est. Priority Date: 11/30/2001
• Status: Active Grant

• Current Assignee: TDK Corporation
• Original Assignee: Sonion A/S
• Inventors: Thomsen, Henrik, Stenberg, Lars Jorn, Furst, Claus Erdmann, Poulsen, Jens Kristian
• Primary Examiner(s): Mei; Xu
• Application Number:
  US10/307,290
• Publication Number:
  US 20030123681A1
• Time in Patent Office: 1,912 Days
• Field of Search: 381/111, 381/117, 381/116, 330/10, 330/207.A, 330/251
• US Class Current: 381/117
• 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 miniature loudspeaker assembly comprising:

a loudspeaker casing made in an EMI shielding material, the loudspeaker casing comprising;

a digital interface adapted to receive a digital input signal,

a three-level sigma-delta modulator adapted to receive the digital input signal and provide a three-level PDM signal,

a correction circuit comprising a filter adapted to convert the three-level PDM signal into a pattern of pulses with five or more states,

a pattern generator adapted to convert the pattern of pulses into a pattern of pulses with level dependent RTZ states, and

a loudspeaker comprising a motor adapted to receive the pattern of pulses with level dependent RTZ states, the motor further being adapted to drive a diaphragm so as to generate an acoustical signal.

2. The miniature loudspeaker assembly of claim 1, wherein the digital interface is adapted to receive and process signal formats selected from the group consisting of:

SPDIF, AES/EBU, PCM, SSI and I²S.

3. The miniature loudspeaker assembly of claim 2, further comprising a three-level H-bridge comprising at least 4 switches for providing independent control.

4. A mobile device comprising the miniature loudspeaker assembly of claim 3.

5. The mobile device of claim 4, 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.

6. A mobile device comprising the miniature loudspeaker assembly of claim 2.

7. The mobile device of claim 6, 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.

8. The miniature loudspeaker assembly of claim 1, further comprising a three-level H-bridge comprising at least 4 switches for providing independent control.

9. A mobile device comprising the miniature loudspeaker assembly of claim 8.

10. The mobile device of claim 9, 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.

11. A mobile device comprising the miniature loudspeaker assembly of claim 1.

12. The mobile device of claim 11, 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.