Abstract:
A communication system including a plurality of communication devices configured to operate according to a plurality of communication clock signals, respectively, wherein the plurality of communication clock signals are based on a common reference clock signal. The communication system further includes a phase-locked loop configured to generate an output signal in response to the common reference clock signal, wherein the output signal is in phase lock with the common reference clock signal; a signal division controller configured to generate a divider reset signal in response to a binary select signal; and a divider configured to generate one of the plurality of communication clock signals by performing frequency division of the output signal, wherein the divider reset signal controls a start time of the frequency division.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 10/790,689, filed Mar. 3, 2004. The disclosure of the application referenced above is incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates to noise and interference reduction in information communication systems. More particularly, the present invention relates to a system and method for reducing electromagnetic interference and ground bounce in an information communication system by controlling the phase of clock signals among a plurality of information communication devices of the information communication system. 
     A gigabit transceiver chip can, for example, transmit information from several ports simultaneously. Such simultaneous transmission can lead to a condition known as “ground bounce” that can cause unwanted transients in the supply voltage and current on the chip. Ground bounce is a voltage oscillation between the ground pin on a component package and the ground reference level on the component die. Ground bounce is essentially caused by a current surge passing through the lead inductance of the package. More particularly, the output voltage of an IC package can be referenced to the ground on the chip. The bond wire connection between the chip and the lead frame of the package contributes a small amount of inductance in the circuit. When the output voltage goes low, a spike of current flows through this inductance and creates a voltage spike at the ground on the chip. A device connected to the output of the circuit will see a logical low that is the specified low for the device plus the voltage spike across the inductance of the lead frames. This effect is the ground bounce. 
     The effect is most pronounced when all outputs switch simultaneously. Consequently, ground bounce is sometimes referred to as “simultaneous switching noise.” While the inductance is the combined effect of the package lead, the package lead frame, the bond wire and the inductance in the die pad, a majority of the inductance is caused by the bond wire. Ground bounce can cause, for example, signal degradation in the output waveform of the device. 
     For example, in a gigabit transceiver chip, each port can derive its port clock from a common reference clock. Transitions in each port clock can cause a small ground bounce. When all of the port clocks are aligned (i.e., all of the port clocks are in phase), the small ground bounce caused by each port clock can aggregate to produce a large ground bounce. Similarly, each transmitter of the network switch chip can derive its transmitter clock from a common system transmitter clock. Each transmitter clock can generate a tone of electromagnetic interference (EMI) at the transmit frequency. When all of the transmitter clocks are aligned (i.e., all of the transmitter clocks are in phase), the EMI produced by each transmitter clock can aggregate to produce an amplified tone of EMI. Thus, clock alignment can cause increased ground bounce and EMI in, for example, the gigabit transceiver chip. 
     SUMMARY 
     A system and method are disclosed for reducing electromagnetic interference and ground bounce in an information communication system by controlling the phase of clock signals among a plurality of information communication devices of the information communication system. In accordance with exemplary embodiments of the present invention, according to a first aspect, an information communication system can include a plurality of information communication devices. Each of the plurality of information communication devices can be responsive to a respective information communication clock signal. Each information communication clock signal of each of the plurality of information communication devices can be associated with a common reference clock signal. The information communication system can include a phase controller. The phase controller can be responsive to the common reference clock signal. The phase controller can alter a phase of each information communication clock signal of each of the plurality of information communication devices by a predetermined amount. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments, in conjunction with the accompanying drawings, wherein like reference numerals have been used to designate like elements, and wherein: 
         FIG. 1  is a block diagram illustrating a system for controlling phase of clock signals among a plurality of information communication devices of an information communication system, in accordance with an exemplary embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating a system for controlling phase of clock signals among a plurality of information communication devices of an information communication system using a plurality of time delay elements, in accordance with an exemplary embodiment of the present invention. 
         FIG. 3  is a block diagram illustrating a system for controlling phase of clock signals among a plurality of information communication devices of an information communication system using a phase controller comprised of a plurality of time-delayed communication channels, in accordance with an alternative exemplary embodiment of the present invention. 
         FIG. 4  is a block diagram illustrating a system for controlling phase of clock signals among a plurality of information communication devices of an information communication system using a phase controller comprised of a phase locked loop, in accordance with an alternative exemplary embodiment of the present invention. 
         FIGS. 5A and 5B  are graphs illustrating how electromagnetic interference can be mitigated, in accordance with an exemplary embodiment of the present invention. 
         FIG. 6  is a flowchart illustrating steps for controlling phase of clock signals among a plurality of information communication devices of an information communication system, in accordance with an exemplary embodiment of the present invention. 
         FIG. 7  is a flowchart illustrating steps for generating information communication clock signals, in accordance with an exemplary embodiment of the present invention. 
         FIG. 8  is a flowchart illustrating steps for altering a phase of a common reference clock signal, in accordance with an exemplary embodiment of the present invention. 
         FIG. 9  is a flowchart illustrating steps for altering a phase of a common reference clock signal, in accordance with an exemplary embodiment of the present invention. 
         FIG. 10  is a flowchart illustrating steps for altering a phase of a common reference clock signal, in accordance with an alternative exemplary embodiment of the present invention. 
         FIG. 11  is a flowchart illustrating steps for altering a phase of a common reference clock signal, in accordance with an alternative exemplary embodiment of the present invention. 
         FIG. 12  is a flowchart illustrating steps for controlling phase of clock signals among a plurality of information communication devices of an information communication system, in accordance with an alternative exemplary embodiment of the present invention. 
         FIG. 13  is a flowchart illustrating steps for altering a phase of a common reference clock signal, in accordance with an exemplary embodiment of the present invention. 
         FIG. 14  is a flowchart illustrating steps for altering a phase of a common reference clock signal, in accordance with an alternative exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A system and method are disclosed for reducing electromagnetic interference and ground bounce in an information communication system by controlling the phase of clock signals among a plurality of information communication devices of the information communication system. The information communication system, such as, for example, a multi-port transceiver or network device compliant with I.E.E.E. 802.3ab, can communicate information on several ports simultaneously. Such simultaneous communication can lead to “ground bounce,” causing unwanted transients in the supply voltage and current in the information communication system. For example, each port of the information communication system can derive its port clock from a common reference clock. Transitions in each port clock can cause a small ground bounce. When all of the port clocks are aligned (i.e., all of the port clocks are in phase), the small ground bounces contributed by each port clock can aggregate to produce a large ground bounce. According to exemplary embodiments of the present invention, the phase of each port clock can be staggered in a deterministic manner relative to all other port clocks so that the port clocks are not aligned (i.e., not in phase). For example, the phase of each port clock can be staggered by 45 or 90 degrees using, for example, a clock divider and combinatorial logic. By staggering the phase of each of the port clocks relative to one another, the small ground bounces contributed by each port clock do not aggregate, thereby reducing the effects of ground bounce in the information communication system. 
     According to an alternative exemplary embodiment, the information communication system can include a plurality of, for example, transmitters. Each transmitter of the information communication system can derive its transmitter clock from a common system transmitter clock. Each transmitter clock can generate a tone of electromagnetic interference (EMI) at the transmit frequency. When all of the transmitter clocks are aligned (i.e., all of the transmitter clocks are in phase), the EMI contributed by each transmitter clock can aggregate to produce an amplified tone of EMI. According to exemplary embodiments of the present invention, the phase of each transmitter clock can be staggered in a deterministic manner relative to all other transmitter clocks, such as, for example, by 45 or 90 degrees. By staggering the phase of each of the transmitter clocks relative to one another, the amplitude of the EMI can be decreased, while the frequency of the EMI can be increased, thereby helping to mitigate the EMI of the information communication system. 
     These and other aspects of the present invention will now be described in greater detail.  FIG. 1  is a block diagram illustrating a system for controlling phase of clock signals among a plurality of information communication devices of an information communication system  100 , in accordance with an exemplary embodiment of the present invention. Information communication system  100  includes a plurality of information communication devices  105 . Information communication system  100  can be comprised of any number N of information communication devices. Each of the plurality of information communication devices  105  is responsive to a respective information communication clock signal. Each information communication clock signal of each of the plurality of information communication devices  105  is associated with a common reference clock signal  122 . In other words, each information communication clock signal can be derived, either directly or indirectly, from a common reference clock signal  122  or several of such reference clock signals (e.g., where the number of common reference clock signals  122  is less than the number of information communication devices  105 ). 
     The information communication system  100  includes a phase controller  110 . A single phase controller  110  can be in communication with each of the plurality of information communication devices  105 . Alternatively, each of or groups of the plurality of information communication devices  105  can be in communication with a separate phase controller  110 . The phase controller  110  is responsive to the common reference clock signal  122 . For example, the common reference clock signal  122  can be generated by a reference clock signal generator  120 . 
     According to exemplary embodiments, phase controller  110  alters the phase of each information communication clock signal of each of the plurality of information communication devices  105  by a predetermined amount. In other words, phase controller  110  can stagger the phase of each information communication clock signal of each of the plurality of information communication devices  105  relative to each other. The predetermined amount can be any suitable change in phase in each of the information communication clock signals relative to the other information communication clock signals. According to one exemplary embodiment of the present invention, phase controller  110  alters the phase of each information communication clock signal of each of the plurality of information communication devices  105  by a multiple of 90 degrees. For example, if there are four information communication devices  105 , then the corresponding four information communication clock signals can each be staggered in phase by 90 degrees relative to each other by phase controller  110  according to, for example, (0°, 90°, 180°, 270°), (0°, 180°, 270°, 90°), or any other suitable combination of phases such that the phases of the individual information communication clock signals are not aligned. For example, if there are eight information communication devices  105 , then the corresponding eight communication clock signals can each be staggered in phase by 45 degrees relative to each other by phase controller  110  according to, for example, (0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°) or any other suitable combination of phases. 
     Alternatively, the phase controller  110  alters the phase of the information communication clock signals such that the phase of two or more of the information communication clock signals are substantially identical, so long as the number of information communication clock signals with substantially identical phase is less than the total number of information communication clock signals of the information communication system  100 . For the example of eight information communication devices  105 , the corresponding eight communication clock signals can each be staggered in phase by 90 degrees relative to each other by phase controller  110  according to, for example, (0°, 90°, 180°, 270°, 0°, 90°, 180°, 270°) or any other suitable combination of phase such that the phases of less than all of information communication clock signals are not aligned. However, according to exemplary embodiments, phase controller  110  can alter the phase of each of the information communication clock signals relative to each other by any appropriate amount. 
     According to exemplary embodiments, each of the plurality of information communication devices  105  is responsive to the common reference clock signal  122  altered by phase controller  110 . For example, each of the plurality of information communication devices includes a device clock  115  for generating the respective information communication clock signal from the common reference clock signal  122  altered by phase controller  110 . According to an exemplary embodiment, the device clock  115  of each of the plurality of information communication devices  105  derives the respective information communication clock signal from the common reference clock signal  122 . Thus, to alter the phase of each information communication clock signal of each of the plurality of information communication devices  105  by the predetermined amount, phase controller  110  alters the phase of the common reference clock signal  122  for each of the plurality of information communication devices  105  by the predetermined amount. In other words, by staggering the phase of the common reference clock signal  122  for each of the information communication devices  105 , phase controller  110  can stagger the phases of the information communication clock signals relative to each other. 
     For example, phase controller  110  can include a plurality of time delay elements.  FIG. 2  is a block diagram illustrating a system for controlling phase of clock signals among a plurality of information communication devices  105  of an information communication system  100  using a plurality of time delay elements  205 , in accordance with an exemplary embodiment of the present invention. As illustrated in  FIG. 2 , the plurality of time delay elements  205  are cascaded or otherwise arranged in serial communication with each other to provide varying time delays of the common reference clock signal  122 . 
     According to exemplary embodiments, each of the plurality of information communication devices  105  can be in communication with at least one of the plurality of time delay elements  205 . The time delay introduced by each of the time delay elements  205  is cumulative as the common reference clock signal  122  is propagated along the chain of time delay elements  205 . Consequently, the phase of the common reference clock signal  122  can be altered for each of the information communication devices  105  by delaying the common reference clock signal  122  by the desired amount using an appropriate number of time delay elements  205 . For example, each time delay element  205  introduces a time delay of t d  seconds (where t d  can be any appropriate length of time delay), although each of the time delay elements can introduce the same or different amounts of time delay. For the exemplary embodiment illustrated in  FIG. 2 , the common reference clock signal  122  is delayed by t d  seconds into information communication device  1 , by 2*t d  seconds into information communication device  2 , by 3*t d  seconds into information communication device  3 , and by N*t d  seconds into information communication device N. 
     In the exemplary embodiment illustrated in  FIG. 2 , the time delay of the common reference clock signal  122  into each of the plurality of information communication devices  105  is based on the cumulative effect of the cascaded or otherwise serially-arranged time delay elements  205 . However, each of the time delay elements  205  can be affected by slight variations in voltage, process, temperature and the like, which alters the length of time delay introduced by each of the time delay elements  205 . To address this condition, an alternative structure can be used for phase controller  110 . 
       FIG. 3  is a block diagram illustrating a system for controlling phase of clock signals among a plurality of information communication devices  105  of an information communication system  100  using a phase controller  110  comprised of a plurality of time-delayed communication channels, in accordance with an alternative exemplary embodiment of the present invention. According to the alternative exemplary embodiment, the phase controller  110  includes at least one delay locked loop  305 . The at least one delay locked loop  305  is in communication with each of the plurality of information communication devices  105  via an information communication channel  312 . For example, the delay locked loop  305  can be in communication with each of the plurality of information communication devices  105  using a separate information communication channel  312 , or an information communication channel  312  can be in communication with groups of information communication devices  105 . To control the amount of time delay of the common reference clock signal  122  into each of the plurality of information communication devices  105 , each information communication channel  312  includes at least one of the plurality of time delay elements  310 . The amount of time delay introduced through each information communication channel  312  is altered by, for example, changing the number of time delay elements  310  located along an information communication channel  312 , changing the amount of time delay supplied by the one or more time delay elements  310  in the information communication channel  312 , and the like. The embodiment illustrated in  FIG. 3  can also be used to address issues related to clock skew. 
     According to an exemplary embodiment, phase controller  110  alters the phase of each information communication clock signal of each of the plurality of information communication devices  105  by, for example, altering the phase of the common reference clock signal  122  supplied to each of the information communication devices  105  from which each information communication clock signal can be generated. Alternatively, the phase of each information communication clock signal can be directly altered by the phase controller  110 . 
       FIG. 4  is a block diagram illustrating a system for controlling phase of clock signals among a plurality of information communication devices of an information communication system using a phase controller comprised of a phase locked loop, in accordance with an alternative exemplary embodiment of the present invention. Phase controller  110  includes a phase locked loop  405  that is configured to receive the common reference clock signal  122 . For example, phase locked loop  405  includes a phase detector  410 , a loop filter  415 , a voltage-controlled oscillator  420  and a divider  425 . Phase locked loop  405  produces an output signal  440  at any appropriate frequency. The output signal  440  is supplied to a divider  435 . Divider  435  is configured to perform signal division or decimation on output signal  440  to generate an information communication clock signal  460  of equal or lesser frequency than output signal  440 . The output signal  440  is associated with the information communication clock signal  460 . In other words, divider  435  divides the frequency of output signal  440  by any appropriate amount to generate the desired frequency of information communication clock signal  460 . For purposes of illustration and not limitation, if the frequency of output signal  440  is 500 MHz, and if each of the information communication devices  105  uses a 125 MHz information communication clock signal, then divider  435  divides output signal  440  by a factor of four to generate an information communication clock signal  460  of 125 MHz. Other frequencies and division ratios can also be used. 
     To control the phase of each information communication clock signal  460  relative to the other information communication clock signals  460 , the phase controller  110  includes a signal division controller  430 . Signal division controller  430  is configured to control the start time of signal division performed by divider  435  on the output signal  440  of phase locked loop  405 . In other words, signal division controller  430  varies the start time of signal division of the output signal  440  performed by divider  435  to alter the phase of each information communication clock signal  460  generated for each of the plurality of information communication devices  105 . For example, signal division controller  430  can be comprised of combinatorial logic that is responsive to the common reference clock signal  122 , as well as the output signal  440 . Signal division controller  430  can also be responsive to a system reset signal  445  that can be from, for example, a power management system associated with information communication system  100 . For example, when an information communication device(s)  105  is (are) powered up or otherwise activated, the system reset signal  445  can be used as notification to begin controlling signal division to create information communication clock signal(s)  460  for the powered-up device(s). As the system reset signal  445  may not be synchronous with common reference clock signal  122  and/or output signal  440 , system reset signal  445  can be gated so that it is synchronous with common reference clock signal  122  and/or output signal  440 . 
     Signal division controller  430  can also be responsive to a signal select  450 . Signal select  450  can be used to select the phase of the information communication signal  460  to be generated. For purposes of illustration and not limitation, if there are four information communication devices  105 , each information communication device  105  can be assigned one of four unique phases. Thus, a two-bit selection signal can be used for signal select  450  to choose one of the four phases for information communication clock signal  460 . In other words, for a chosen information communication clock signal  460 , signal division controller  430  generates a divider reset signal  455  that resets divider  435  so that division of output signal  440  is begun at the proper time. By beginning division of output signal  440  at different times (e.g., at different rising edges and/or falling edges of output signal  440 ), the phase of the information communication clock signal  460  is varied. The number of bits used for signal select  450  will depend on, for example, the number of information communication clock signals  460  to be generated, the total number of phase values from which an information communication clock signal  460  can be selected, and the like. For example, a three-bit selection signal can be used to select one of eight possible phase values. Other bit widths of signal select  450  are possible. 
     According to an exemplary embodiment, a single phase controller  110  can be used to generate information communication clock signals  460  for all of the plurality of information communication devices  105 . Alternatively, two or more phase controllers  110  can be used to generate information communication clock signals  460  for different groups of information communication devices  105 , or each information communication device  105  can have a separate phase controller  110 . However, according to each of these exemplary embodiments, the signal division controller(s)  430  generates the divider reset signal  455  at the proper time to alter the phase of each information communication clock signal of each of the plurality of information communication devices  105  by a predetermined amount relative to one or more other information communication clock signals. 
     For purposes of illustration and not limitation, according to one exemplary embodiment of the present invention, the information communication system  100  can comprise a multi-port transceiver or network device compliant with, for example, I.E.E.E. 802.3ab. For example, the information communication devices  105  can be the ports of the multi-port transceiver or network device. For example, the information communication devices  105  can be the individual transmitters of the multi-port transceiver or network device, such as, for example, individual class B transmitters. The multi-port network device compliant with I.E.E.E. 802.3ab can be comprised of a plurality of transceivers, where the plurality can be, for example, four or eight or any other number of transceivers. Alternatively, the information communication system  100  can be an Ethernet transceiver, such as an Ethernet transceiver compliant with, for example, I.E.E.E. 802.3ab. However, information communication system  100  can be any suitable information communication system. 
     According to exemplary embodiments, any combination or all of the components of information communication system  100  can be formed on a monolithic substrate. For example, the information communication devices  105  of the information communication system  100  can be formed on the monolithic substrate. Alternatively, information communication system  100  can be comprised of discrete components, including any suitable combination of electrical or electronic components or devices comprised of information communication devices  105 , in which each information communication clock signal of each of the information communication devices  105  is derived, either directly or indirectly, from a common reference clock signal  122  (or a few such reference signals), thereby creating a phase relationship between the information communication devices  105 . According to the alternative exemplary embodiment, each of the information communication devices  105  can be any suitable type of electrical or electronic component or device capable of using an information communication clock signal to communicate information, such as, for example, a transceiver compliant with I.E.E.E. 802.3ab, a transmitter, a receiver, or the like, and in which the information communication clock signal can be derived, either directly or indirectly, from the common reference clock signal  122 . 
     According to exemplary embodiments, the information communication clock signal can be any suitable type of clock signal, of any appropriate amplitude, at any suitable frequency that can be used for communicating information. The common reference clock signal  122  can be any suitable reference clock signal, of any appropriate amplitude, at any suitable frequency that can be used to derive, either directly or indirectly, one or more information communication clock signals. 
     The phase control controller  110  can be formed on the same monolithic as the plurality of information communication devices  105 . Alternatively, the phase controller  110  can be a discrete component comprised of any appropriate type of electrical or electronic component or device that is capable of altering the phase of each information communication clock signal of each of the plurality of information communication devices  105 , either directly (e.g., by altering the phase of the information communication clock signal itself) or indirectly (e.g., by altering the phase of the common reference clock signal  122  to alter the phase of the information communication clock signal). According to the alternative exemplary embodiment, the phase controller  110  can be in communication with each of the plurality of information communication devices  105  using any appropriate type of electrical connection capable of communicating electrical information. 
     Reference clock signal generator  120  can be formed on the same monolithic substrate as phase controller  110  and the plurality of information communication devices  105 . Alternatively, the reference clock signal generator  120  can be a discrete component comprised of any suitable type of electrical or electronic component or device that is capable of generating a reference clock signal of any appropriate amplitude at any suitable frequency. According to the alternative exemplary embodiment, phase controller  110  can be in communication with reference clock signal generator  120  using any suitable type of electrical connection that is capable of communicating electrical information. 
     Each device clock  115  can be formed on the same monolithic substrate as phase controller  110 , the plurality of information communication devices  105 , and the reference clock signal generator  120 . Alternatively, each device clock  115  can be a discrete component comprised of any suitable type of electrical or electronic component or device that is capable of generating an information communication clock signal from a common reference clock signal  122 . According to the alternatively exemplary embodiment, the device clock  115  can be in communication with the respective information communication device  105  using any suitable type of electrical connection capable of communicating electrical information, or the device clock  115  can form a component internal to the respective information communication device  105 . 
     The plurality of time delay elements  205  that can comprise phase controller  110 , as illustrated in  FIG. 2 , can be formed on the same monolithic substrate as the other elements of information communication system  100 . Alternatively, time delay elements  205  can be discrete components comprising any suitable type of electrical or electronic component or device that is capable of delaying an electrical signal in time. According to the alternative exemplary embodiment, the plurality of time delay elements  205  can be in communication with each other using any suitable type of electrical connection capable of communicating electrical information. According to either embodiment, time delay elements  205  can comprise, for example, delay locked loops or the like. 
     The delay locked loop  305 , as illustrated in  FIG. 3 , can be any suitable type of delay locked loop. The delay locked loop  305 , and the associated time delay elements  310 , and can be formed on the same monolithic substrate as other elements of information communication system  100 . Each information communication channel  312  illustrated in  FIG. 3  can be formed on the same monolithic substrate as the other elements of information communication system  100 . Alternatively, each information communication channel  312  can be any suitable type of electrical connection capable of communicating electrical information. 
     The phase locked loop  405 , and its associated components, can be formed on a monolithic substrate, such as the same monolithic substrate as other elements of information communication system  100 . Alternatively, phase locked loop  405  can be any suitable type of electrical or electronic component or device that is capable of controlling an oscillator so that it maintains a constant phase angle relative to a reference signal, such as, for example, common reference clock signal  122 . According to the alternative exemplary embodiment, phase detector  410 , loop filter  415 , voltage-controlled oscillator  420  and divider  425  can be discrete components, and can be in communication with each other using any appropriate type of electrical connection capable of communicating electrical information. 
     Divider  435  can be formed on the same monolithic substrate as phase locked loop  405  and the other elements of information communication system  100 . Alternatively, divider  435  can be a discrete component in communication with phase locked loop  405  using any suitable type of electrical connection capable of communicating electrical information. 
     Signal division controller  430  can be formed on the same monolithic substrate as phase locked loop  405 , divider  435 , and the other elements of information communication system  100 . Alternatively, signal division controller  430  can be a discrete component in communication with phase locked loop  405  and divider  435  using any suitable type of electrical connection capable of communicating electrical information. 
     Those of ordinary skilled will recognize that the information communication system  100  can include any additional electrical or electronic components or devices in any suitable combination that can be used for communicating information signals, depending upon the nature and type of information signals to be communicated and the environment in which the information communication system  100  is to be used. For example, the information communication system  100  can be connected to additional components, such as, for example, any type of processor, including any type of microprocessor, microcontroller, digital signal processor (DSP), application-specific integrated circuit (ASIC), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically-erasable programmable read-only memory (EEPROM), or the like. For example, the information communication system  100  can also be connected to any type of computer memory or any other type of electronic storage medium that is located either internally or externally to the processor such as, for example, read-only memory (ROM), random access memory (RAM), cache memory, compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, or the like. The processor and memory can be used, for example, to perform additional processing on information signals that have been or are to be communicated by information communication system  100 , for controlling any part of the information communication system  100 , or the like. 
     Exemplary embodiments of the present invention can be used to mitigate the effects of ground bounce and EMI in information communication systems.  FIGS. 5A and 5B  are graphs illustrating how EMI can be mitigated, in accordance with an exemplary embodiment of the present invention. For purposes of illustration and not limitation, the plurality of information communication devices  105  can comprise two transmitters (e.g., two class B transmitters) of the information communication system  100 , each using an information communication clock signal of 125 MHz. Each information communication clock signal can be derived from a common reference clock signal. Each transmitter can have a center-tapped current into a respective output transformer, I CT1  and I CT2 , respectively. In  FIG. 5A , the information communication clock signals for the two transmitters are in phase. Graph ( 1 ) of  FIG. 5A  illustrates the current waveform of I CT1 , with an amplitude of I o  and a period of 8 nanoseconds, corresponding to a frequency of 125 MHz. Graph ( 2 ) of  FIG. 5A  illustrates the current waveform of I CT2 , with an amplitude of I o  and a period of 8 nanoseconds, corresponding to a frequency of 125 MHz. As the waveforms of I CT1  and I CT2  are in phase, the addition of the individual waveforms can result in a combined waveform I CT1 +I CT2  that is the same frequency, but twice the amplitude, of I CT1  and I CT2 , as shown in Graph ( 3 ) of  FIG. 5A . Graph ( 4 ) of  FIG. 5A  illustrates the frequency spectrum of the combined waveform I CT1 +I CT2 . As the resulting generated signals of I CT1  and I CT2  are in phase, an EMI frequency component can be created at 125 MHz. 
     In  FIG. 5B , however, the information communication clock signals for the two transmitters are out of phase by 180 degrees, in accordance with an exemplary embodiment of the present invention. Graph ( 1 ) of  FIG. 5B  illustrates the current waveform of I CT1 , with an amplitude of I o  and a period of 8 nanoseconds, corresponding to a frequency of 125 MHz. Graph ( 2 ) of  FIG. 5B  illustrates the current waveform of I CT2 , with an amplitude of I o  and a period of 8 nanoseconds, corresponding to a frequency of 125 MHz. However, as the information communication clock signals used for the two transmitters are 180 degrees out of phase, I CT1  is also 180 degrees out of phase with I CT2 . As the waveforms of I CT1  and I CT2  are out of phase by 180 degrees, the addition of the individual waveforms can result in a combined waveform I CT1 +I CT2  that is twice frequency (e.g., 250 MHz or a period of four nanoseconds) of either I CT1  and I CT2 , as shown in Graph ( 3 ) of  FIG. 5B , and half the amplitude of the combined waveform illustrated in Graph ( 3 ) of  FIG. 5A . Graph ( 4 ) of  FIG. 5B  illustrates the frequency spectrum of the combined waveform I CT1 +I CT2 . As the resulting generated signals of I CT1  and I CT2  are out of phase by 180 degrees, an EMI frequency component can be created at 250 MHz, twice the frequency of the EMI frequency component in Graph ( 4 ) of  FIG. 5A . Additionally, the EMI frequency component at 250 MHz is half the amplitude of the frequency component of Graph ( 4 ) of  FIG. 5A . Thus, exemplary embodiments of the present invention can reduce EMI by creating a EMI frequency component that is of lower amplitude and higher frequency when the information communication clock signals are staggered in phase relative to each other. 
       FIG. 6  is a flowchart illustrating steps for controlling phase of clock signals among a plurality of information communication devices of an information communication system, in accordance with an exemplary embodiment of the present invention. In step  605 , a common reference clock signal is generated. In step  610 , the common reference clock signal is received in each of the plurality of information communication devices. In step  615 , an information communication clock signal is generated in each of the plurality of information communication devices. According to exemplary embodiments, each information communication clock signal of each of the plurality of information communication devices is associated with the common reference clock signal. In step  620 , the phase of each information communication clock signal for each of the plurality of information communication devices is altered by a predetermined amount. According to an alternative exemplary embodiment, the phase of at least two of the information communication clock signals can be substantially identical. However, the number of information communication clock signals with substantially identical phase can be less than the total number of information communication clock signals of the information communication system. The method can be compliant with any suitable communication standard, such as, for example, I.E.E.E. 802.3ab. 
       FIG. 7  is a flowchart illustrating steps for step  610  of  FIG. 6  of generating information communication clock signals, in accordance with an exemplary embodiment of the present invention. In step  705 , each information communication clock signal for each of the plurality of information communication devices is generated using the common reference clock signal. 
       FIG. 8  is a flowchart illustrating steps for step  620  of  FIG. 6  of altering a phase of a common reference clock signal, in accordance with an exemplary embodiment of the present invention. In step  805 , the phase of the common reference clock signal for each of the plurality of information communication devices is altered by the predetermined amount to alter the phase of each information communication clock signal of each of the plurality of information communication devices by the predetermined amount.  FIG. 9  is a flowchart illustrating steps for step  805  of  FIG. 8  of altering a phase of a common reference clock signal, in accordance with an exemplary embodiment of the present invention. In step  905 , the common reference clock signal supplied to each of the plurality of information communication devices is time delayed by the predetermined amount. 
       FIG. 10  is a flowchart illustrating steps for step  620  of  FIG. 6  of altering a phase of a common reference clock signal, in accordance with an alternative exemplary embodiment of the present invention. In step  1005 , the phase of each information communication clock signal of each of the plurality of information communication devices is altered by a multiple of 90 degrees. However, the phase of each information communication clock signal can be altered by any appropriate amount relative to the other information communication clock signals. 
       FIG. 11  is a flowchart illustrating steps for step  620  of  FIG. 6  of altering a phase of a common reference clock signal, in accordance with an alternative exemplary embodiment of the present invention. In step  1105 , the start time of signal division of an output signal of a phase locked loop is controlled. According to exemplary embodiments, the output signal can be associated with the information communication clock signal. In step  1110 , the start time of signal division of the output signal is varied to alter the phase of each information communication clock signal of each of the plurality of information communication devices. 
       FIG. 12  is a flowchart illustrating steps for controlling phase of clock signals among a plurality of information communication devices of an information communication system, in accordance with an alternative exemplary embodiment of the present invention. In step  1205 , a common reference clock signal is generated. In step  1210 , the common reference clock signal is received. According to exemplary embodiments, each of the plurality of information communication devices is responsive to the common reference clock signal. In step  1215 , the phase of the common reference clock signal for each of the plurality of information communication devices is altered by a predetermined amount. In step  1220 , an information communication clock signal is generated for each of the plurality of information communication devices using the respective phase-altered common reference clock signal. Consequently, the phase of each information communication clock signal of each of the plurality of information communication devices is altered by the predetermined amount. According to an alternative exemplary embodiment, the phase of at least two of the information communication signals can be substantially identical. However, the number of information communication clock signals with substantially identical phase can be less than the total number of information communication clock signals of the information communication system. The method can be compliant with any suitable communication standard, such as, for example, I.E.E.E. 802.3ab. 
       FIG. 13  is a flowchart illustrating steps for step  1215  of  FIG. 12  of altering a phase of a common reference clock signal, in accordance with an exemplary embodiment of the present invention. In step  1305 , the common reference clock signal supplied to each of the plurality of information communication devices is time delayed by the predetermined amount.  FIG. 14  is a flowchart illustrating steps for step  1215  of  FIG. 12  altering a phase of a common reference clock signal, in accordance with an alternative exemplary embodiment of the present invention. In step  1405 , the phase of each information communication clock signal of each of the plurality of information communication devices is altered by a multiple of 90 degrees. However, the phase of each information communication clock signal can be altered by any appropriate amount relative to the other information communication clock signals. 
     Any or all of the steps of a computer program as illustrated in  FIGS. 6-14  for controlling phase of clock signals among a plurality of information communication devices of an information communication system can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. As used herein, a “computer-readable medium” can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a non-exhaustive list) of the computer-readable medium can include the following: an electrical connection having one or more wires, a portable computer diskette, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, and a portable compact disc read-only memory (CDROM). 
     Exemplary of the present invention can be used in any device or system that communicates information, including both wired and wireless communication systems, particularly in systems and devices where multiple channels of information can be communicated simultaneously and the information communication clock signals used to communicate that information are derived from a common reference clock signal. 
     It will be appreciated by those of ordinary skill in the art that the present invention can be embodied in various specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalence thereof are intended to be embraced. 
     All United States patents and applications, foreign patents, and publications discussed above are hereby incorporated herein by reference in their entireties.