Method and apparatus for implementing a class D driver and speaker system

• US 7,058,463 B1
• Filed: 02/27/2001
• Issued: 06/06/2006
• Est. Priority Date: 12/29/2000
• Status: Expired due to Fees

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Ruotsalainen, Tarmo, Ruha, Antti, Tervaluoto, Jussi-Pekka
• Primary Examiner(s): Chin, Vivian
• Assistant Examiner(s): Chau, Corey
• Application Number:
  US09/794,599
• Time in Patent Office: 1,925 Days
• Field of Search: 330/251, 330/10, 330/207.A, 341/143, 700/94, 381/120
• US Class Current: 700/94
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers
• CPC Class Codes: H03F 3/2175 using analogue-digital or digital-analogue conversion H03F3/2173 takes precedence
• CPC Class Codes: H04R 1/005 using digitally weighted transducing elements
• CPC Class Codes: H04R 3/00 Circuits for transducers , loudspeakers or microphones

Abstract

An audio path is constructed to include a multi-bit sigma-delta converter for converting an N-bit digital input to an n-bit output representing an over-sampled, lower resolution n-bit version of the N-bit digital input; a formatter for converting the n-bit output to an m signal output (e.g., as a thermometer code, a SDM format or a PWM format); an m-by-m switching matric for receiving the m output signals and for reordering the m output signals, m class-D drivers individual ones of which are driven by one of the reordered m output signals for driving one of m speakers; and a dynamic element matching (DEM) block coupled to the switching matric for controlling the reordering of the m output signals driving the m class-D drivers for spreading the distortion due at least to driver-speaker pair mismatch to wide band noise. The DEM may operate to generate white noise, or it may generate shaped (colored) noise.

Claims

1. An audio path, comprising:

a multi-bit sigma-delta modulator for converting an N-bit digital input to an n-bit output representing an over-sampled, lower resolution n-bit version of the N-bit digital input;

a formatter for converting the n-bit output to an m signal output;

m class-D drivers individual ones of which are driven by one of said m output signals for driving one of m speakers; and

a dynamic element matching (DEM) block for controlling the reordering of the m output signals driving the m class-D drivers for spreading the distortion due at least to driver-speaker pair mismatch to wide band noise.

2. An audio path as in claim 1, wherein said m output signals form a thermometer code format.

3. An audio path as in claim 1, wherein said m output signals are in a pulse width modulated (PWM) format.

4. An audio path as in claim 1, wherein said m output signals are in a sigma-delta modulated (SDM) format.

5. An audio path as in claim 1, wherein m≦

2ⁿ.

6. An audio path as in claim 1, wherein said speakers comprise one or more speaker membranes.

7. An audio path as in claim 1, wherein said speakers comprise speaker coils.

8. An audio path as in claim 1, wherein said speakers comprise an array of speakers.

9. An audio path as in claim 1, wherein said speakers comprise one of piezoelectric or EMF speaker elements.

10. An audio path as in claim 1, wherein said class-D drivers are comprised of differential class-D drivers.

11. An audio path as in claim 1, and further comprising an m-by-m switching matrix interposed between said m output signal of said formatter and said m class-D drivers, said switching matrix being controlled by an output of said DEM block.

12. A method of operating an audio path, comprising steps of:

operating a multi-bit sigma-delta converter for converting an N-bit digital input to an n-bit output representing an over-sampled, lower resolution n-bit version of the N-bit digital input;

converting said n-bit output to an m signal output;

driving m speakers with m class-D drivers individual ones of which are driven by one of said m output signals; and

reordering the m output signals driving the m class-D drivers for spreading the distortion due at least to driver-speaker pair mismatch to wide band noise.

13. A method as in claim 12, wherein said m output signals form a thermometer code.

14. A method as in claim 12, wherein said m output signals are in a pulse width modulated (PWM) format.

15. A method as in claim 12, wherein said m output signals are in a sigma-delta modulated (SDM) format.

16. A method as in claim 12, wherein m≦

2ⁿ.

17. A method as in claim 12, wherein said speakers comprise at least one speaker membrane.

18. A method as in claim 12, wherein the step of reordering comprises a step of operating an m-by-m switching matrix, said switching matrix being controlled by an output of a Dynamic Element Matching (DEM) block for spreading the distortion to white noise or shaped noise.

19. An audio path, comprising:

a multi-bit sigma-delta modulator for converting an N-bit digital input to an n-bit output representing an over-sampled, lower resolution n-bit version of the N-bit digital input;

a formatter for converting said n-bit output to an m signal output;

an m-by-m switching matrix for receiving said m output signals and for reordering the m output signals;

m class-D drivers individual ones of which are driven by one of said reordered m output signals for driving one of m speakers; and

a dynamic element matching (DEM) block coupled to said switching matrix for controlling the reordering of the m output signals driving the m class-D drivers for spreading the distortion due at least to driver-speaker pair mismatch to wide band noise comprised of one of white noise or shaped noise.

20. An audio path as in claim 19, wherein m≦

2ⁿ.

21. An audio path as in claim 19, wherein said audio path, less the speakers, is integrated into one audio path integrated circuit.