Pattern biasing for look-ahead delta sigma modulators

• US 20050162286A1
• Filed: 01/26/2005
• Published: 07/28/2005
• Est. Priority Date: 01/26/2004
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Melanson, John L.
• Granted Patent: US 7,138,934 B2
• Time in Patent Office: Days
• US Class Current: 341/50
• CPC Class Codes: H03M 3/366 in feed-forward mode, e.g. using look-ahead circuits
• CPC Class Codes: H03M 3/458 Analogue/digital converters using delta-sigma modulation as an intermediate step
• CPC Class Codes: H03M 7/3011 of non-linear distortion, e.g. by temporarily adapting the operation upon detection of instability conditions avoiding instability by structural design H03M7/3035

Abstract

Look-ahead delta sigma modulators of a signal processing system can selectively bias one or more output candidate vectors to alter the probability of selecting a biased output candidate vector(s) for determination of a quantization output value. The probability, within a range of error, of certain output candidate vectors being selected by a quantizer of the look-ahead delta sigma modulator can be determined. The output candidate vectors determine the quantization output values. Thus, altering the probability of selecting a certain output candidate(s) alters the probability of occurrence of a certain quantization output value(s). Detection of the altered probability allows an output signal to be identified. Identifying an output signal allows for many interesting operations including identifying a specific signal processing system source of the output signal and modifying processing of the output signal. Additionally, some quantization output values can be compressed more densely than others.

Claims

1. A signal processing system comprising:

a pattern biasing look-ahead delta sigma modulator, the pattern biasing look-ahead delta sigma modulator comprising;

a quantizer to determine a quantization output value from a selected output candidate vector, wherein the output candidate vector is selected from a set of output candidate vectors and at least one member of the set of output candidate vectors is biased to alter a probability of the biased output candidate vectors being selected by the quantizer.

2. The signal processing system of claim 1 wherein the quantizer comprises a best match generator to determine a best match between an input signal vector and a set of output candidate vectors, wherein at least one of the output candidate vectors is biased to alter a probability of the biased output candidate vector(s) being selected as the best match to the input signal vector.

3. The signal processing system of claim 2 further comprising:

a filter to filter the input signal vector and each output candidate vector; and

wherein the best match between the input signal vector and a set of output candidate vectors is determined from the lowest power between a filtered input signal vector and each respective filtered output candidate vector.

4. The signal processing system of claim 1 further comprising:

a quantizer to quantize the input signal vector using the output candidate vector that best matches the input signal vector.

5. The signal processing system of claim 1 wherein each biased output candidate vector is biased using a bias factor multiplier.

6. The signal processing system of claim 1 wherein each biased output candidate vector is biased using a biasing factor, and a value of the bias factor is chosen to alter the probability of a selected biased output candidate vector sufficiently to allow detection of the altered probability while causing at most an insignificant change in signal-to-noise ratio.

7. The signal processing system of claim 1 further comprising:

a detector to detect biasing of an output signal derived from the quantized input signal, wherein the output signal is biased in accordance with selection by the quantizer of at least one biased output candidate vector.

8. The signal processing system of claim 1 wherein at least one of the biased output candidate vectors is chosen for biasing on the basis that each output candidate vector chosen for biasing is more densely compressible than substantially similar output candidate vectors.

9. The signal processing system of claim 1 wherein at least one biased output candidate vector has a known probability of selection by the quantizer relative to a probability of selection of another output candidate vector.

10. The signal processing system of claim 1 wherein to alter a probability of the biased output candidate vector(s) being selected comprises to increase the probability of the biased output candidate vector(s) being selected.

11. The signal processing system of claim 1 further comprising:

signal processing and recording equipment to process output data from the quantizer and record the processed output data on storage media.

12. The signal processing system of claim 1 wherein the input signal comprises audio input signal data.

13. The signal processing system of claim 1 wherein each output candidate vector includes a potential current quantization output value and at least one potential future quantization output value.

14. A method of processing an input signal with a look-ahead delta sigma modulator using at least one biased output candidate vector, wherein the look-ahead delta sigma modulator has a look-ahead depth greater than or equal to 2, the method comprising:

biasing at least one output candidate vector with a bias factor that alters a probability of each biased output candidate vector being selected by a quantizer to generate quantization output data.

15. The method of claim 14 wherein biasing at least one output candidate vector further comprises:

biasing output candidate vectors on the basis that each output candidate vector chosen for biasing is more densely compressible than substantially similar output candidate vectors.

16. The method of claim 14 wherein biasing at least one output candidate vector further comprises:

biasing an output candidate vector having a known probability of selection by the quantizer relative to a probability of selection of another output candidate vector.

17. The method of claim 14 wherein biasing at least one output candidate vector using a bias factor comprises multiplying each biased output candidate vector by the bias factor.

18. The method of claim 14 wherein the bias factor is chosen to alter the probability of a selected biased output candidate vector sufficiently to allow detection of the altered probability while causing at most an insignificant change in signal-to-noise ratio.

19. The method as in claim 14 wherein the input signal data sample comprises audio input signal data.

20. The method of claim 14 further comprising:

quantizing the input signal using a set of output candidate vectors that includes the biased output candidate vector.

21. The method as in claim 20 further comprising:

recording quantized input signal data on storage media.

22. A signal processing system comprising:

a detector to receive a first signal and to detect an outcome probability of prescribed bit patterns, wherein the outcome probability of the prescribed bit patterns is determined by biasing prescribed output candidate patterns used by a look-ahead delta sigma modulator to generate a second signal from which the first signal is derived.

23. The signal processing system as in claim 22 wherein the first signal includes audio data content.

24. An apparatus to process an input signal, the apparatus comprising:

means for biasing at least one output candidate vector with a bias factor that alters a probability of each biased output candidate vector being selected by a quantizer to generate quantization output data, wherein each output candidate vector includes a potential current output value and at least one future quantization output value; and

means for quantizing the input signal using a set of output candidate vectors that includes the biased output candidate vector.