Apparatus and method to reduce quantization error

• US 20040008791A1
• Filed: 07/15/2002
• Published: 01/15/2004
• Est. Priority Date: 07/15/2002
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: DSPC Technologies Limited
• Inventors: Pick, Kobby, Perets, Yoni
• Granted Patent: US 7,324,598 B2
• Time in Patent Office: Days
• US Class Current: 375/243
• CPC Class Codes: H03M 7/3002 Conversion to or from differential modulation

Abstract

An apparatus includes a quantizer to generate a quantized signal from an input signal and a function unit may be included to generate an output signal by applying a predetermined function to the quantized signal. The apparatus further may include a correction unit to compensate for distortion in the output signal.

Claims

1. An apparatus, comprising:

a quantizer to generate a quantized signal from an input signal;

a function unit to generate an output signal by applying a predetermined function to the quantized signal; and

a correction unit to compensate for distortion in the output signal.

2. The apparatus of claim 1, further comprising an error calculator to generate an error signal in response to distortion between the input signal and the quantized signal.

3. The apparatus of claim 1, wherein the correction unit is able to generate a distortion compensated output signal by calculating a Taylor series approximation of the output signal.

4. The apparatus of claim 1, where the correction unit is able to generate a distortion compensated output signal by subtracting at least a first order term of a Taylor series approximation of the output signal from the output signal.

5. The apparatus of claim 1, wherein a selected number of higher order terms of a Taylor series approximation of the output signal are subtracted from the output signal in the correction unit to provide a predetermined increase in compensation for distortion in the output signal.

6. The apparatus of claim 1, wherein one of the function unit or the correction unit is adapted to generate at least one derivative term by applying a first derivative of the predetermined function to the quantized signal.

7. The apparatus of claim 6, wherein the correction unit compensates for distortion in the output signal by subtracting at least a product of the error signal and the at least one derivative term from the output signal.

8. The apparatus of claim 1, wherein the function unit or the correction unit is adapted to generate more than one derivative terms, the derivative terms being respectively generated by applying a respective higher order derivative of the predetermined function to the quantized signal.

9. The apparatus of claim 8, wherein the correction unit compensates for distortion in the output signal according to the equation:

f(a)≈

f(a+Δ

)−

f′

(a)·

Δ

−

f″

(a)·

Δ

²/2!−

(Σ

_N=2f^(N)(a)·

(Δ

)^N/N!),

wherein Δ

corresponds to the error signal, f′

(a) correspond to the first order derivation of the predetermined function for a value “

a” and

f^(N)(a) correspond to an N'"'"'th order derivative of the predetermined function for the value “

a.”

10. A system, comprising:

a circuit to generate an input signal;

a quantizer to generate a quantized signal from the input signal;

an error calculator to generate an error signal in response to distortion between the sampled analog signal and the quantized signal;

a function unit to generate an output signal by applying a predetermined function to the quantized signal; and

a correction unit to compensate for distortion in the output signal in response to the error signal; and

one of a digital signal processor, central processing unit or storage device to receive the output signal compensated for distortion.

11. The system of claim 10, wherein the correction unit generates a distortion compensated output signal by calculating a Taylor series approximation of the output signal.

12. The system of claim 10, wherein the correction unit generates a distortion compensated output signal by subtracting at least a first order term of a Taylor series approximation of the output signal from the output signal.

13. The system of claim 10, wherein a selected number of higher order terms of a Taylor series approximation of the output signal are subtracted from the output signal in the correction unit to provide a predetermined increase in compensation for distortion in the output signal.

14. The system of claim 10, wherein the function unit or the correction unit is adapted to generate at least one derivative signal by applying a first derivative of the predetermined function to the quantized signal.

15. The system of claim 14, wherein the correction unit compensates for distortion in the output signal by subtracting at least a product of the error signal and the at least one derivative signal from the output signal.

16. A method, comprising:

quantizing an input signal to generate a quantized signal;

generating an output signal by applying a predetermined function to the quantized signal; and

compensating for distortion in the output signal.

17. The method of claim 16, wherein compensating for distortion in the output signal comprises calculating a Taylor series approximation of the output signal.

18. The method of claim 16, wherein compensating for distortion in the output signal comprises subtracting at least a first order term of a Taylor series approximation of the output signal from the output signal.

19. The method of claim 16, further comprising generating at least one derivative term by applying a first derivative of the predetermined function to the quantized signal.

20. The method of claim 19, wherein compensating for distortion in the output signal comprises subtracting at least a product of an error signal and the at least one derivative term from the output signal.

21. A method, comprising:

generating an output signal by calculating a predetermined function using a quantized signal with a reduced number of bits; and

compensating for distortion in the output signal caused by calculating the predetermined function using the reduced number of bits.

22. The method of claim 21, wherein compensating for distortion in the output signal comprises calculating a Taylor series approximation of the output signal.

23. The method of claim 22, wherein calculating the Taylor series approximation of the output signal comprises determining a difference between the quantized signal and an input signal.

24. The method of claim 21, wherein compensating for distortion in the output signal comprises subtracting at least a first order term of a Taylor series approximation of the output signal from the output signal.

25. A computer-readable medium having computer-executable instructions for performing a method comprising:

generating an output signal by calculating a predetermined function using a quantized signal with a reduced number of bits; and

compensating for distortion in the output signal caused by calculating the predetermined function using the reduced number of bits.

26. The computer-readable medium having computer-executable instructions for performing the method of claim 25, wherein compensating for distortion in the output signal comprises calculating a Taylor series approximation of the output signal.

27. The computer-readable medium having computer-executable instructions for performing the method of claim 26, wherein calculating the Taylor series approximation of the output signal comprises determining a difference between the quantized signal and an input signal.

28. The computer-readable medium having computer-executable instructions for performing the method of claim 25, wherein compensating for distortion in the output signal comprises subtracting at least a first order term of a Taylor series approximation of the output signal from the output signal.