Method and Apparatus for Reduced Power Consumption Adc Conversion

• US 20080030388A1
• Filed: 04/30/2004
• Published: 02/07/2008
• Est. Priority Date: 04/30/2003
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Labbe, Patrick, de Courville, Marc Bernard, Muck, Markus
• Granted Patent: US 7,432,838 B2
• Time in Patent Office: Days
• US Class Current: 341/138
• CPC Class Codes: H03M 1/1235 Non-linear conversion not otherwise provided for in subgroups of H03M1/12
• CPC Class Codes: H03M 1/664 Non-linear conversion not otherwise provided for in subgroups of H03M1/66

Abstract

A method for analog to digital conversion (ADC) characterised by;

• • applying a non-linear transfer function to an input signal, such that the relation between the quantisation levels of the converter and the input signal vary as a non-linear function of the magnitude of the input signal.

The non-linear transfer function is related to an at least approximate measurement of probability density function ‘p(x)’ of said input signal so that larger quantisation bins of the converter correspond to less probable values of the input signal.

The relation is iteratively updated by updating quantisation levels.

Claims

1. A method for analog to digital conversion (ADC) comprising;

applying a non-linear transfer function to an input signal such that the relation between the quantisation levels of the converter and the input signal vary as a non-linear function of the magnitude of the input signal,

the non-linear transfer function being related to an at least approximate measurement of probability density function ‘

p(x)’

of said input signal so that larger quantisation bins of the converter correspond to less probable values of the input signal,

wherein an application of the non-linear transfer function to the input signal includes iteratively updating the relation between the non-linear transfer function and the measurement of probability density by updating quantisation levels.

2. A method according to claim 1 for analog to digital conversion in a programmable non-linear analog to digital converter, wherein the iterative relation can be ongoing, periodically re-started or used once during an initialisation period.

3. A method according to claim 1, wherein the non-linear transfer function is applied by predefining quantisation levels according to an optimisation process utilising said non-linear transfer function.

4. A method according to claim 3 wherein for analog to digital conversion in a programmable non-linear analog to digital converter, the optimisation process for predefining quantisation levels reduces a global mean squared quantisation error determined by a cost function for the process, J, being a function of input value probability density function p(x) and the quantisation error for a given quantisation level a_i of corresponding quantisation bin {b_i,b_i+1}, N quantisation levels ā

=(a₀, . . . , a<sub>N−

1</sub>)^T so being updated to reduce the global cost J_tot, said global cost being a sum of J over N selected quantisation bins, N quantisation levels ā

=(a₀, . . . , a<sub>N−

1</sub>)^T being taken to define the ADC or DAC quantisation arrangement when global cost J_tot is below a given threshold.

5. A method according to claim 4 wherein a Gaussian function with variance σ

_g² is used as approximation for the input value probability density function.

6. A method according to claim 5 wherein cost function J for a single quantisation bin is substantially equal to

7. A method according to claim 1 wherein for programmable non-linear ADCs, quantisation levels are updated according to the output of an iterative gradient descent process utilising a cost function J, being a function of input value probability density function p(x)and the quantisation error for a given quantisation level a_i of corresponding quantisation bin {b_i,b_i+1}, the calculation of the gradient of cost function J utilising at least first-order terms of a Taylor series expansion of exponential and error functions about the current quantisation level values.

8. A method according to claim 7 wherein values for terms of Taylor series expansions are provided by a look-up table.

9. A method according to claim 7 wherein values for terms of Taylor series expansions are provided by an approximation function.

10. A method according to claim 7 wherein a Gaussian function with variance σ

_g² is used for the input value probability density function.

11. A method according to claim 10 wherein the first bounded quantisation level at iteration step k, a₀^{k}, is updated as

12. A method according to claim 7 wherein convergence of the iterative gradient descent process is only sought once during an initialisation phase.

13. A method according to claim 1 wherein the output of the converter is linearised by application of a nonlinear transfer function being substantially the inverse of the non-linear transfer function applied to the input signal.

14. Apparatus for converting between analog and digital signals comprising;

non-linear transfer function means for applying a non-linear transfer function to an input signal such that the relation between the quantisation levels of the converter and the input signal vary as a non-linear function of the magnitude of the input signal,

the non-linear transfer function means being responsive to an at least approximate measurement of probability density function ‘

p(x)’

of said input signal so as to relate thereto the non-linear transfer function so that larger quantisation bins of the converter correspond to less probable values of the input signal,

wherein the non-linear transfer function means includes means, operative for an application of the non-linear transfer function to the input signal, for iteratively updating the relation between the non-linear transfer function and the measurement of probability density by updating quantisation levels.

15. Apparatus according to claim 14 comprising a communication system.

16. Apparatus according to claim 14 comprising a communication system where signals with high Peak-To-Average-Power Ratio (PAPR) amplitudes occur.

17. Apparatus according to claim 14 comprising a communication system utilising a multi-carrier modulation scheme.

18. Apparatus according to claim 14 comprising a communication system utilising orthogonal frequency division multiplexing.

19. Apparatus according to claim 14 comprising a mobile station.