Method and apparatus for generating a metering pulse

• US 7,991,133 B2
• Filed: 09/29/2005
• Issued: 08/02/2011
• Est. Priority Date: 09/29/2005
• Status: Expired due to Fees

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Whaley, Jeffrey, Mills, Michael, Zhou, Yan, Goldenberg, Marius
• Primary Examiner(s): TRAN, QUOC DUC
• Application Number:
  US11/240,272
• Publication Number:
  US 20070081645A1
• Time in Patent Office: 2,133 Days
• Field of Search: 379/124, 379/114.01, 379/133, 379/141, 379/359, 379/362, 379/387.02, 379/388.03, 379/394, 379/395, 379/399.02
• US Class Current: 379/124
• CPC Class Codes: H04M 15/00 Arrangements for metering, time-control or time indication ; Metering, charging or billing arrangements for voice wireline or wireless communications, e.g. VoIP

Abstract

In one embodiment, a subscriber line interface circuit includes circuitry to generate metering pulses for insertion onto a subscriber line. The circuitry includes an audio path and a pulse metering path, where the pulse metering path includes a metering generator to generate a digital sine wave from a plurality of stored values, a first interpolator to interpolate the digital sine wave, a filter to filter the interpolated digital sine wave, and a second interpolator to interpolate the filtered interpolated digital sine wave.

Claims

1. A method comprising:

generating a digital sine wave based on a plurality of samples stored in a storage;

converting the digital sine wave into a metering pulse via a digital-to-analog converter (DAC) circuit having a multiple level structure including a global portion to receive and convert the digital sine wave to a first analog signal, a ramp portion to receive and multiply a digital ramp value with the first analog signal to generate a second analog signal, and a gain portion to receive and multiply a digital gain value with the second analog signal to generate the metering pulse; and

controlling the ramp portion of the DAC circuit to reach a maximum value during the metering pulse.

2. The method of claim 1, further comprising calibrating the DAC circuit to an impedance level of a subscriber line to which the DAC circuit is coupled.

3. The method of claim 2, further comprising dynamically adjusting a gain portion of the DAC circuit based on the impedance level.

4. The method of claim 2, wherein calibrating the DAC circuit comprises:

setting the gain portion of the DAC circuit to a maximum value; and

detecting whether the ramp portion reaches the maximum value before a peak value of the metering pulse is reached.

5. The method of claim 4, further comprising adjusting the gain portion downwardly if the ramp portion reaches the maximum value before the peak value.

6. The method of claim 4, further comprising setting a ramp rate for the ramp portion to a lowest setting outside of an audio band.

7. The method of claim 1, further comprising adjusting the ramp portion at a zero crossing of the metering pulse.

8. The method of claim 1, further comprising processing the generated digital sine wave before its input into the DAC circuit.

9. The method of claim 8, wherein processing the generated digital sine wave comprises:

interpolating the digital sine wave;

filtering the interpolated digital sine wave; and

interpolating the filtered interpolated digital sine wave.

10. The method of claim 2, wherein calibrating the DAC circuit further comprises comparing an echo of the metering pulse to a predetermined threshold, the predetermined threshold compensated from a predetermined amplitude for the metering pulse based on the plurality of samples.

11. A method comprising:

setting a gain value for a digital-to-analog (DAC) structure of a subscriber line interface circuit (SLIC) to a maximum level, the DAC structure including a first portion to receive and convert a digital signal to a first analog signal, a ramp portion to receive and multiply a digital ramp value with the first analog signal to generate a second analog signal, and a gain portion to receive and multiply the gain value with the second analog signal to generate the metering pulse; and

determining whether the ramp portion of the DAC structure reaches a maximized level before the metering pulse reaches a ramp envelope value.

12. The method of claim 11, further comprising adjusting the gain value downwardly if the ramp portion does not reach the maximum level.

13. The method of claim 11, further comprising setting a ramp rate corresponding to the digital ramp value for the ramp portion to a slowest non-audible value.

14. The method of claim 11, further comprising:

adjusting the gain value to a value of less than half of the maximum level; and

disabling at least part of the gain portion of the DAC structure.

15. The method of claim 11, further comprising adjusting the ramp portion at a zero crossing of the metering pulse.

16. An apparatus comprising:

an audio path to transmit and receive audio signals to and from a subscriber line;

a pulse metering path to generate a metering pulse for transmission via the subscriber line, the pulse metering path including;

a metering generator to generate a digital sine wave from a plurality of stored values;

a digital signal processor (DSP) including;

a first interpolator to interpolate the digital sine wave;

a filter to filter the interpolated digital sine wave; and

a second interpolator to interpolate the filtered interpolated digital sine wave; and

a digital-to-analog converter (DAC) coupled to an output of the second interpolator.

17. The apparatus of claim 16, wherein the pulse metering path further comprises:

a detector to detect an amplitude of a reflection of the metering pulse; and

a controller coupled to the detector to receive the detected amplitude and to control the DAC based on the detected amplitude.

18. The apparatus of claim 16, wherein the DAC includes a gain portion coupled to receive an output of a ramp portion of the DAC.

19. The apparatus of claim 18, wherein the audio path includes at least one DAC having a greater resolution than a resolution of the gain portion and the ramp portion.

20. The apparatus of claim 18, wherein the ramp portion is to be controlled by a first-on-first-off scheme.

21. The apparatus of claim 18, wherein the ramp portion is to be controlled at a zero crossing of the metering pulse.

22. The apparatus of claim 18, wherein the apparatus is to be calibrated to a subscriber line to which it is coupled using a maximum gain for the gain portion of the DAC.

23. The apparatus of claim 16, wherein the DSP and the audio path are integrated within a single substrate.

24. The apparatus of claim 23, wherein the single substrate comprises a subscriber line interface circuit (SLIC), and the apparatus comprises a modem.