Communication system and method for sample rate converting data onto or from a network using a high speed frequency comparison technique

• US 20040032350A1
• Filed: 08/14/2002
• Published: 02/19/2004
• Est. Priority Date: 08/14/2002
• Status: Active Grant

• Current Assignee: Standard Microsystems Corporation (Microchip Technology Incorporated)
• Original Assignee: Standard Microsystems Corporation (Microchip Technology Incorporated)
• Inventors: Knapp, David J., Gaalaas, Joseph B., Maddox, John G.
• Granted Patent: US 7,106,224 B2
• Time in Patent Office: Days
• US Class Current: 341/61
• CPC Class Codes: H04J 3/0647 Synchronisation among TDM nodes
• CPC Class Codes: H04L 7/0029 interpolation of received data signal

Abstract

A communication system, source and destination ports of the communication system, and methodology is provided for transporting data in one of possibly three different ways. Data is transported across the network at a frame sample rate that can be the same as or different from the sample rate or master clock within the source port or the destination port. If the sample rate of the source port is known, the sample rate of the destination port can be created using a PLL within the destination port and simply employing a phase comparator in the source port. The phase comparator forwards the phase or frequency difference of the network transfer rate and the source sample rate to the destination port, which then generates a local clock equivalent to the source which then compiles audio data being played at the same rate in which it was sampled at the source. Where economically feasible, sample rate conversion can be used at the source. However, sample rate conversion at the destination is preferred if the source sample rate is forwarded across the network relative to the frame transfer rate of the synchronous network. The sample rate converter simply produces a play rate from the transmitted information at the destination. Again, however, sample rate conversion compares relative phase difference changes similar to the phase difference compared in the digital PLL mode. As a further alternative, sample rates within the source and destination ports can be derived from the network frame rate using fractional dividers in the source and destination ports.

Claims

1. A destination port of a communication network, comprising a sample rate converter coupled to receive phase or frequency difference information between a transfer clock used to transfer data across the network and a sampling clock local to a source port coupled to the destination port via the network.

2. The destination port as recited in claim 1, wherein the transfer clock comprises a cycle equal in duration to a frame of data sent across the network.

3. The destination port as recited in claim 1, wherein the transfer clock transitions at a frequency synchronous with a rate at which a plurality of frames are sent across the network.

4. The destination port as recited in claim 1, wherein the sampling clock transitions at a rate equal to a sample rate of streaming data sent from a multimedia device onto the network.

5. The destination port as recited in claim 1, wherein the frequency difference information is calculated on successive cycles of the transfer clock or the sampling clock such that a first phase difference on one cycle is compared to a second phase difference on the successive cycle.

6. The destination port as recited in claim 1, wherein the frequency difference information is calculated as a difference measured on a first cycle of the transfer clock or the sampling clock and a Nth cycle of the transfer clock or the sampling clock such that a first phase difference on the first cycle is compared to a second phase difference on the Nth cycle.

7. The destination port as recited in claim 1, wherein the phase difference information comprises two values, a first value corresponding to a first phase difference measured at one transition of the transfer clock or the sampling clock and a second value corresponding to a second phase difference measured at another transition of the transfer clock or the sampling clock.

8. The destination port as recited in claim 1, wherein the phase difference information comprises a value corresponding to a first phase difference measured at a first transition of the transfer clock or sampling clock subtracted with a second phase difference measured at a second transition of the transfer clock or sampling clock.

9. The destination port as recited in claim 1, wherein the phase difference information comprises a value corresponding to a frequency difference between the transfer clock and the sampling clock.

10. The destination port as recited in claim 1, wherein the converter is adapted to change coefficients of a digital filter local to the destination port to match a frequency of the sampling clock.

11. The destination port as recited in claim 1, wherein the source port sources streaming data onto the network.

12. The destination port as recited in claim 1, wherein the source port includes a multimedia device selected from the group consisting of a digital video device (DVD), compact disk (CD) and digital video broadcast (DVB) receiver.

13. The destination port as recited in claim 1, further comprising a multimedia device selected from the group consisting of an amplifier and a digital-to-analog converter.

14. The destination port as recited in claim 1 is embodied upon a single, monolithic substrate.

15. A communication network, comprising:

a source port;

a destination port coupled to the source port by the network;

a plurality of frames of data, each of which are transferred across the network at a frame transfer rate;

a comparator coupled to produce;

a first compare result during a first clock cycle of a phase difference between a transfer clock transitioning at the frame transfer rate and a sampling clock used to sample data at the source port;

a second compare result during a second clock cycle of a phase difference between the transfer clock and the sampling clock; and

a sample rate converter at the destination port coupled to receive a frequency difference corresponding to the first and second compare results for changing coefficients of a digital filter local to the destination port.

16. The communication network as recited in claim 15, further comprising an adder local to the source port that combines the first and second compare results in the source port and forwards the frequency difference across the network to the sample rate converter.

17. The communication network as recited in claim 15, further comprising an adder local to the destination port that combines the first and second compare results in the destination port and forwards the frequency difference to the sample rate converter.

18. The communication network as recited in claim 15, wherein the first and second clock cycles are clock cycles of the transfer clock or the sampling clock.

19. The communication network as recited in claim 15, wherein the second clock cycle succeeds the first clock cycle.

20. The communication network as recited in claim 15, wherein the second clock cycle is the next clock cycle after the first clock cycle.

21. The communication network as recited in claim 15, wherein the second clock cycle is Nth clock cycle after the first clock cycle.

22. The communication network as recited in claim 15, wherein the sample rate converter changes a sample rate local to the destination port proportional to a ratio by which the second compare result is dissimilar from the first compare result.

23. The communication network as recited in claim 15, wherein the network forwards the plurality of frames synchronously across the network.

24. A method for generating a sampling rate local to a destination node of a communication network, comprising:

calculating a frame transfer rate of a plurality of data sent across the network;

comparing the frame transfer rate to a transition rate of a sampling clock at a source node by determining either a phase difference or a change in phase difference between the frame transfer rate and a rate of the sampling clock; and

forwarding the phase difference or the change in phase difference across a network;

changing a sample rate of the data at a destination port using a clock local to the destination port that is transitioning dissimilar from the transition rate of the sampling clock.

25. The method as recited in claim 24, wherein said changing comprises changing coefficients of a digital filter local to the destination port.

26. The method as recited in claim 24, wherein said comparing occurs on rising or falling edges of successive cycles of the sampling clock or a frame transfer clock transitioning at the frame transfer rate.