Method of reducing emission of electromagnetic radiation on high speed communication backplane

1. A method, comprising:

transmitting data to a backplane from a first communication module simultaneously on a first pair of operating frequencies, the first pair of operating frequencies including first and second operating frequencies, wherein

a −3 dB point of a first electromagnetic emission spectrum peak originating from transmission of the data at the first operating frequency is outside a −3 dB point of a second electromagnetic emission spectrum peak originating from transmission of the data at the second operating frequency; and

selecting a pair of reference clocks, from among at least two pairs of reference clocks, where each pair of reference clocks has a center clock frequency and lower and upper clock frequencies, wherein

the first and second operating frequencies respectively correspond to the lower and upper clock frequencies of a selected pair of reference clocks.

2. The method according to claim 1 , further comprising:

receiving, from the backplane at a second communication module, the data from the first communication module at the first pair of operating frequencies.

3. The method according to claim 1 , further comprising:

transmitting the data to the backplane from the first communication module simultaneously on a second pair of operating frequencies, including third and fourth operating frequencies different from the first and second operating frequencies,

wherein a −3 dB point of a third electromagnetic emission spectrum peak originating from transmission of the data at the third operating frequency is outside a −3 dB point of a fourth electromagnetic emission spectrum peak originating from transmission of the data at the fourth operating frequency.

4. The method according to claim 3 , further comprising:

receiving, from the backplane at a third communication module, the data from the first communication module at the second pair of operating frequencies.

5. The method according to claim 4 , further comprising:

selecting to transmit at one of the first pair of operating frequencies and the second pair of operating frequencies,

wherein said selecting is based on a position of a transmitting communication module on the backplane and a position of a receiving communication module on the backplane.

6. The method according to claim 2 , further comprising:

at the first communication module, adding more pad bytes to the data transmitted at the second frequency than to the data transmitted at the first frequency, wherein

the second frequency is higher than the first frequency.

7. The method according to claim 4 , further comprising:

at the first communication module, adding more pad bytes to the data transmitted at the fourth frequency than to the data transmitted at the third frequency, wherein

the fourth frequency is higher than the third frequency.

8. The method according to claim 2 , further comprising:

performing clock data recovery and clock correction to align the data received at the second communication module with a local clock of the second communication module.

9. The method according to claim 4 , further comprising:

performing clock data recovery and clock correction to align the data received at the second communication module with a local clock of the third communication module.

10. The method according to claim 2 , wherein each of the first and second communication modules includes a Multi-Gigabit Transceiver (MGT).

11. A system, comprising:

a backplane;

first and second communication modules connected to the backplane, wherein

the first communication module is configured to transmit data to the backplane simultaneously on a first pair of operating frequencies, the first pair of operating frequencies including first and second operating frequencies,

a −3 dB point of a first electromagnetic emission spectrum peak originating from transmission of the data at the first operating frequency is outside a −3 dB point of a second electromagnetic emission spectrum peak originating from transmission of the data at the second operating frequency, and

each of the first and second communication modules includes

two transceivers, and

two pairs of reference clocks, each reference clock pair having a center clock frequency, a first reference clock pair having a lower center clock frequency than a second reference clock pair, a lower clock frequency of each reference clock pair being connected to a first one of the two transceivers and a higher clock frequency of each reference clock pair being connected to a second one of the two transceivers.

12. The system according to claim 11 , wherein the second communication module is configured to receive data from the first communication module at the first pair of operating frequencies.

13. The system according to claim 11 , wherein

the two transceivers are Multi-Gigabit Transceivers (MGTs), and

each of the first and second communication modules includes a controller connected to each of the MGTs that instructs the MGTs to select either the first reference clock pair or the second reference clock pair.

14. A non-transitory computer-readable medium encoded with instructions that, when executed by a computer, cause the computer to perform a method comprising:

transmitting data to a backplane from a first communication module simultaneously on a first pair of operating frequencies, the first pair of operating frequencies including first and second operating frequencies, wherein

a −3 dB point of a first electromagnetic emission spectrum peak originating from transmission of the data at the first operating frequency is outside a −3 dB point of a second electromagnetic emission spectrum peak originating from transmission of the data at the second operating frequency; and

selecting a pair of reference clocks, from among at least two pairs of reference clocks, where each pair of reference clocks has a center clock frequency and lower and upper clock frequencies, wherein

the first and second operating frequencies respectively correspond to the lower and upper clock frequencies of a selected pair of reference clocks.

15. The medium according to claim 14 , the method further comprising:

transmitting the data to the backplane from the first communication module simultaneously on a second pair of operating frequencies, including third and fourth operating frequencies different from the first and second operating frequencies,

wherein a −3 dB point of a third electromagnetic emission spectrum peak originating from transmission of the data at the third operating frequency is outside a −3 dB point of a fourth electromagnetic emission spectrum peak originating from transmission of the data at the fourth operating frequency.

16. The medium according to claim 15 , the method further comprising:

selecting to transmit at one of the first pair of operating frequencies and the second pair of operating frequencies,

wherein said selecting is based on a position of a transmitting communication module on the backplane and a position of a receiving communication module on the backplane.

17. The medium according to claim 15 , the method further comprising:

at the first communication module, adding more pad bytes to the data transmitted at the fourth frequency than to the data transmitted at the third frequency, or

at the first communication module, adding more pad bytes to the data transmitted at the second frequency than to the data transmitted at the first frequency.

18. The medium according to claim 14 , the method further comprising:

performing clock data recovery and clock correction to align data received at a second communication module with a local clock of the second communication module.

19. The medium according to claim 15 , the method further comprising:

performing clock data recovery and clock correction to align data received at a second communication module with a local clock of a third communication module.

20. The medium according to claim 19 , wherein each of the first and second communication modules includes a Multi-Gigabit Transceiver (MGT).