Low-delay signal processing based on highly oversampled digital processing

• US 7,365,669 B1
• Filed: 03/28/2007
• Issued: 04/29/2008
• Est. Priority Date: 03/28/2007
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Melanson, John L.
• Primary Examiner(s): JEANGLAUDE, JEAN BRUNER
• Application Number:
  US11/692,906
• Time in Patent Office: 398 Days
• Field of Search: 341/143, 341/144, 341/155, 381/312
• US Class Current: 341/143
• CPC Class Codes: G10K 11/17819 between the output signals and the reference signals, e.g. to prevent howling
• CPC Class Codes: G10K 11/17853 of the filter
• CPC Class Codes: G10K 11/17855 for improving speed or power requirements
• CPC Class Codes: G10K 11/17873 using a reference signal without an error signal, e.g. pure feedforward
• CPC Class Codes: G10K 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: H03M 3/424 the quantiser being a multiple bit one
• CPC Class Codes: H03M 3/452 with weighted feedforward summation, i.e. with feedforward paths from more than one filter stage to the quantiser input
• CPC Class Codes: H03M 7/3024 having one quantiser only
• CPC Class Codes: H03M 7/3033 the modulator having a higher order loop filter in the feedforward path, e.g. with distributed feedforward inputs
• CPC Class Codes: H03M 7/304 with distributed feedback, i.e. with feedback paths from the quantiser output to more than one filter stage
• CPC Class Codes: H04R 25/453 electronically

Abstract

A low-delay signal processing system and method are provided which includes a delta-sigma analog-to-digital converter, an oversampling processor, and a delta-sigma digital-to-analog converter. The delta-sigma analog-to-digital converter receives an input or audio signal and generates a digital sample signal at a high oversampling rate. The oversampling processor is connected to the analog-to-digital converter for processing the digital sample signal at the high oversampling rate with low-delay. The delta-sigma digital-to-analog converter is connected to the oversampling processor for receiving the digital sample signal at the high oversampling rate with low-delay for generating an analog signal. The oversampling processor includes a low-delay filter and a programmable delay element. In this manner, the analog signal is produced with a low delay and high accuracy.

Claims

1. A low-delay audio data processing system comprising:

a first converter for converting sound into an audio signal;

a delta-sigma analog-to-digital converter for receiving the audio signal and for generating a digital sample signal at a high oversampling rate;

a decimation filter responsive to the digital sample signal at the high oversampling rate for generating a downsampled signal;

an audio data processor being connected to said decimation filter for processing the downsampled signal;

an interpolation filter responsive to the processed downsampled signal for generating an upsampled signal;

a delta-sigma digital-to-analog converter for receiving a compensated upsampled signal and for generating an analog signal;

a second converter for converting the analog signal into a sound signal;

an oversampling processor including a low-delay filter interconnected between said analog-to-digital converter and said digital-to-analog converter for processing the digital sample signal at the high oversampling rate with low-delay; and

a summer connected to said oversampling processor and to the output of said interpolation filter for generating the compensated upsampled signal.

2. A low-delay audio data processing system as claimed in claim 1, wherein the high oversampling rate is at least 16 times an audio sampling rate.

3. A low-delay audio data processing system as claimed in claim 1, wherein said oversampling processor further comprises a programmable delay element connected to the output of said low-delay filter.

4. A low-delay audio data processing system as claimed in claim 1, wherein said low-delay filter is formed of a plurality of series-connected second-order IIR filters.

5. A low-delay audio data processing system as claimed in claim 1, wherein said analog-to-digital converter comprises a feedforward analog-to-digital converter which is formed of a plurality of integrators and a quantizer.

6. A low-delay audio data processing system as claimed in claim 5, wherein said analog-to-digital converter is being operated at the high oversampling rate of at least 1.5 MHz.

7. A low-delay audio data processing system as claimed in claim 1, wherein said digital-to-analog converter comprises a plurality of integrators, a quantizer, a pulse-width modulator, and a FIR filter.

8. A low-delay audio data processing system as claimed in claim 1, wherein said first converter for converting the sound consists of a microphone.

9. A low-delay audio data processing system as claimed in claim 1, wherein said second converter for converting the analog signal consists of a speaker.

21. A low-delay audio data processing system as claimed in claim 4, wherein each of said plurality of series-connected second-order IIR filters comprises an integrator.

10. A low-delay signal data processing system comprising:

a delta-sigma analog-to-digital converter for receiving an audio signal and for generating a digital sample signal at a high oversampling rate;

oversampling processor including a low-delay filter connected to said analog-to-digital converter for processing the digital sample signal at the high oversampling rate with low-delay; and

a delta-sigma digital-to-analog converter connected to said oversampling processor for receiving the digital sample signal at the high oversampling rate with low-delay for generating an analog signal.

11. A low-delay signal processing system as claimed in claim 10, wherein said digital sample signal from said delta-sigma analog-to-digital converter is also fed to a decimation filter for generating a downsampled signal.

12. A low-delay signal processing system as claimed in claim 10, wherein said delta-sigma digital-to-analog converter also receives an unsampled signal from an interpolation filter.

13. A low-delay signal processing system as claimed in claim 10, wherein said low-delay filter is formed of a plurality of series-connected second-order IIR filters.

14. A low-delay signal data processing system as claimed in claim 10, wherein said analog-to-digital converter comprises a feedforward analog-to-digital converter which is formed of a plurality of integrators and a quantizer.

15. A low-delay signal processing system as claimed in claim 14, wherein said analog-to-digital converter is being operated at the high oversampling rate of at least 1.5 MHz.

16. A low-delay signal processing system as claimed in claim 10, wherein said digital-to-analog converter comprises a plurality of integrators, a quantizer, a pulse-width modulator, and a FIR filter.

22. A low-delay signal processing system as claimed in claim 13, wherein at least one of said plurality of series-connected second-order IIR filters comprises an integrator.

17. A low-delay signal processing method comprising the steps of:

generating a digital sample signal at a high oversampling rate from a delta-sigma analog-to-digital converter;

processing the digital sample signal at the high oversampling rate through an oversampling processing path having a low-delay filter to produce a low-delay signal; and

receiving the low-delay signal in a delta-sigma digital-to-analog converter to convert the low-delay signal into an analog signal with low delay.

18. A low-delay signal processing method as claimed in claim 17, wherein the step of processing the digital sample signal at the high oversampling rate through the oversampling processing path includes processing the digital sample signal at the high oversampling rate through the oversampling processing path having a programmable delay element connected to the output of the low-delay filter.

19. A low-delay signal processing method as claimed in claim 17, wherein the step of processing the digital sample signal at the high oversampling rate through the oversampling processing path includes processing the digital sample signal at the high oversampling rate through the oversampling processing path having a plurality of series-connected second-order IIR filters.

20. A low-delay signal processing method as claimed in claim 17, wherein the step of generating the digital sample signal at the high oversampling rate includes the step of oversampling at least 16 times an audio sampling rate.

23. A low-delay signal processing method as claimed in claim 19, wherein at least one of said plurality of series-connected second-order IIR filters comprises an integrator.

24. A low-delay headphone system comprising:

a microphone for converting sound into an audio signal;

a delta-sigma analog-to-digital converter for receiving said audio signal and for generating a digital sample signal at a high oversampling rate;

an oversampling processor including a low-delay filter connected to said analog-to-digital converter for processing said digital sample signal at the high oversampling rate with low-delay;

a delta-sigma digital-to-analog converter connected to said oversampling processor for receiving said digital sample signal at the high oversampling rate with low-delay for generating an analog signal; and

a speaker for converting said analog signal into a sound signal.

25. A low-delay portable audio player adapted to be connected to a headphone and a microphone, said audio player comprising:

the microphone being used to convert sound into an audio signal;

a delta-sigma analog-to-digital converter for receiving said audio signal and for generating a digital sample signal at a high oversampling rate;

an oversampling processor including a low-delay filter connected to said analog-to-digital converter for processing said digital sample signal at the high oversampling rate with low-delay;

a delta-sigma digital-to-analog converter connected to said oversampling processor for receiving said digital sample signal at the high oversampling rate with a low-delay for generating an analog signal; and

a speaker disposed in the headphone for converting said analog signal into a sound signal.