Patent Publication Number: US-9847803-B2

Title: Electromagnetic interference reduction by beam steering using phase variation

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure is generally directed toward systems and devices that produce electromagnetic radiation and, in particular, ways to reduce constructive interference produced by multiple radiators. 
     BACKGROUND 
     High speed digital data network equipment must meet international requirements limiting radiated emissions to reduce interference with radio communications systems. For example, in the United States, above 960 MHz, the Federal Communication Commission (FCC) requires unintentional radiators to generate electric fields less than 300 uV/m at a distance of 10 m. As data rates increase, unintentional radiation tends to increase because higher edge rates and symbol rates radiate more efficiently on a given conductor geometry and the fields penetrate through holes in shields more efficiently. Power consumption of leading edge high speed data transceivers is fairly high and is usually cooled with the assistance of air flow, so openings in shielding enclosures are required even though they facilitate unintentional radiation, making it difficult to sufficiently shield emissions. 
     Furthermore, it is common to incorporate 32 or 48 or more transceiver modules per unit of digital switches and related network equipment. Each transceiver modules may include eight or more transmitters and receivers. Generally speaking, the transceiver modules are distributed along rack mounted equipment approximately 19 inches wide. This configuration represents a tightly-grouped array of (unintentional) radiators which spans many wavelengths. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is described in conjunction with the appended figures, which are not necessarily drawn to scale: 
         FIG. 1  is a block diagram depicting a first system of processing devices in accordance with at least some embodiments of the present disclosure; 
         FIG. 2  is a block diagram depicting a second system of processing devices in accordance with at least some embodiments of the present disclosure; 
         FIG. 3  is a block diagram depicting details of a processing device in accordance with at least some embodiments of the present disclosure; 
         FIG. 4  is a graph depicting simulated results of 32 processing devices operating in close proximity with one another where a dither of 2.0 ps is employed to steer the peak emission of the processing devices into a time varying direction in accordance with at least some embodiments of the present disclosure; 
         FIG. 5  is a graph depicting simulated results of 32 processing devices operating in close proximity with one another where a dither of 10.0 ps is employed to steer the peak emission of the processing devices into a time varying direction in accordance with at least some embodiments of the present disclosure; 
         FIG. 6  is a graph depicting simulated results of 32 processing devices operating in close proximity with one another where a dither of 50.0 ps is employed to steer the peak emission of the processing devices into a time varying direction in accordance with at least some embodiments of the present disclosure; 
         FIG. 7  is a graph depicting simulated results of 32 processing devices operating in close proximity with one another where a dither of 1000.0 ps is employed to steer the peak emission of the processing devices into a time varying direction in accordance with at least some embodiments of the present disclosure; and 
         FIG. 8  is a flow diagram depicting a method of managing electromagnetic radiation by an array of processing devices into a common area in accordance with at least some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Further discussing the issues associated with a tightly-grouped array of (unintentional) radiators, depending on the phase relationship between the emission sources and the azimuth angle to the observation antenna, the electric fields created by the source array can be as much as 48 times higher than the fields from one source (in the case of 48 tightly-grouped transceivers). It is quite difficult and time consuming to design fiber optic or wired transceivers at 25 Gbaud and faster which still complies with these international standards of radiation emission. 
     Embodiments of the present disclosure will be described in connection with any type of processing device or collection of processing devices that emit electromagnetic radiation as part of its operation. Processing devices that may particularly benefit from embodiments described herein include an array of transceivers operating at high data rates as discussed above. It should be appreciated, however, that embodiments of the present disclosure are not so limited. 
     The ensuing description provides embodiments only, and is not intended to limit the scope, applicability, or configuration of the claims. Rather, the ensuing description will provide those skilled in the art with an enabling description for implementing the described embodiments. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the appended claims, 
     it is one aspect of the present disclosure to provide a reduced cumulative effect of electromagnetic emission into a common area by a plurality of processing devices. In some embodiments, by employing the techniques described herein, a reduction in emission measurements can be realized on the order of 20*log 10(n) dB, where n is the number of processing devices driven at a fixed frequency. As a non-limiting example, an array of 48 processing device can experience an improvement of 16.8 dB for emissions into a common area that is within proximity of the 48 processing devices. 
     Adding time varying phase delays in each processing device within radiation range of a common area effectively steers the peak emission toward different time varying directions. This reduces the average amount of interference to radio communications equipment and reduces the reported field strengths when measuring compliance to requirements such as FCC Part 15. When an array of processing devices is spaced roughly 30 mm apart in a linear pattern (e.g., as where the processing devices are mounted in a server rack or the like) and when the emissions are primarily at (for example) 25.78125 GHz, the emission pattern vs. azimuth angle is a complex pattern of narrow lobes and deep nulls. By varying the phase of the data signals a few picoseconds, these emission lobes can be moved to different directions over time. If the phase variation frequency is on the order of 10 Hz to 100 Hz, such beam steering will happen rapidly enough to allow averaging over the time frame specified by international standards (e.g., 100 ms for FCC Part 15). Where the processing devices correspond to digital data transceiver modules, this proposed steering scheme will also be slow enough that clock recovery circuits on the receiving end of data links will not be affected (since typical clock recovery loop bandwidths are usually on the order of 10 MHz). 
     Embodiments of the present disclosure are cheaper to implement than solutions like improved shielding and the like and do not negatively impact link performance where the processing devices correspond to digital data transceiver modules. 
     Prior spread spectrum approaches such as clock frequency modulation can also reduce unintentional radiation measurements by spreading the energy over more than 1 MHz (the generally the required resolution bandwidth for measurements above 1 GHz), however these approaches are limited due to finite jitter tolerance of clock recovery circuits on the receiving end of data links. Use of different frequency clocks for each processing device can also reduce unintentional radiation measurements while embodiments of the present disclosure, on the other hand, can provide more reduction than the multiple clock frequency approach because data standards generally require +/−100 ppm frequency accuracy, limiting the amount of spreading to only a small multiple of the 1 MHz resolution bandwidth generally required by international standards. In some embodiments, the disclosed practices can be implemented with firmware changes only. Other solutions generally require hardware changes (electrical and/or mechanical), which are almost sure to be more expensive that firmware updates. 
     With reference now to  FIG. 1 , additional details of a system  100  will be described in accordance with at least some embodiments of the present disclosure. The system  100  is shown to include a first processing device  104   a  and a second processing device  104   b . The first processing device  104   a  and second processing device  104   b  may correspond to the same types of devices or different types of devices. A common feature between the processing devices  104   a ,  104   b  is that both devices are capable of emitting radiation  112   a ,  112   b , respectively. In embodiments where the processing devices  104   a ,  104   b  are co-located or otherwise positioned in close, transmission distance, proximity of one another, the processing devices  104   a ,  104   b  may both contribute to a total electromagnetic radiation for the common area  108 . 
     The common area  108  may correspond to a two or three dimensional space within a predetermined distance of both the processing devices  104   a ,  104   b . In some embodiments, the common area  108  corresponds to an area in which both the first processing device  104   a  and second processing device  104   b  emit a detectable amount of electromagnetic radiation  112   a ,  112   b , respectively. As will be discussed in further detail herein, unless certain measures are taken to steer the peak emission direction of the sum of electromagnetic radiation contributions  112   a  and  112   b  away from the common area, there may be situations where the amount of total (maximum or average) electromagnetic radiation in the common area  108  exceeds a predetermined threshold (e.g., governmental threshold, standard-body threshold, best practice threshold, etc.). 
     As mentioned above, the processing devices  104   a ,  104   b  may be the same type or similar types of devices. As an example, both processing devices  104   a ,  104   b  may correspond to or include one or more digital data transceiver modules that are used in an optical/fiber optic communication system. Other examples of processing devices  104   a ,  104   b  include, without limitation, servers, server blades, server components (e.g., network cards, optical modules, Printed Circuit Boards (PCBs), optical receivers, optical transmitters, modems, gateways, switches, etc. Indeed, any type of computing device having a processor or microprocessor and one or more electrical traces that are capable of emitting electromagnetic radiation (by virtue of alternating current flow) may be referred to as a processing device. 
     With reference now to  FIG. 2 , another example of a system  200  having multiple processing devices  104   a -N will be described in accordance with at least some embodiments of the present disclosure. The number, N, of processing devices included in the plurality of processing devices can be any integer number greater than or equal to two. The processing devices  104   a ,  104   b , . . . ,  104 N may be the same or similar to one another or they may be different types of processing devices. 
     Again, each processing device  104   a -N may contribute a certain amount of electromagnetic radiation  112   a -N to the common area  108  by virtue of their operation. As can be appreciated, when the number of processing devices  104   a -N within a small area becomes larger, then the total amount of electromagnetic radiation contributed to the common area  108  may increase. Furthermore, if the emissions  112  of two or more processing devices  104   a -N happen to arrive in phase, then the total (peak and/or average) amount of electromagnetic radiation in the common area  108  will be greatly increased. This may result in the total electromagnetic radiation exceeding a predetermined threshold for the common area  108 . 
       FIG. 2  also shows that the plurality of processing devices  104   a -N may be contained in a common fixture or structure  204 , which effectively defines the common area  108  and creates the problem of overlapping radiation into the common area  108  by the processing devices  104   a -N. In some embodiments, the structure  204  corresponds to a server rack or set of racks that are contained within a common room of a building. Other examples of common structures  204  include, without limitation, shelves, hangers, tables, racks, vehicles, boxes, etc. Indeed, any type of mechanical structure that holds or supports two or more processing devices  104   a -N may correspond to a structure  204  without departing from the scope of the present disclosure. 
     With reference now to  FIG. 3 , additional details of a processing device  104  will be described in accordance with at least some embodiments of the present disclosure. The processing device  104  is shown to include a processor  304 , memory  308 , an optional communication interface  238 , one or more radiation emitters  332 , a power source  336 , and other component(s)  340 . 
     The processor  304  may include any type of known or yet-to-be developed processor or collection of processors used in computing devices. The processor  304  may include, without limitation, a microprocessor, a collection of microprocessors, an Integrated Circuit (IC) chip, a collection of IC chips, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a digital processor, an analog processor, or any other collection of circuit elements configured to receive one or more input signals and generate one or more output signals. The processor  304 , in some embodiments, may be configured to receive instructions from the memory  308  and execute the instructions in a parallel or serial-processing fashion. 
     The memory  308  may include any type of computer memory capable of storing data, instructions, collections of instructions, and the like. Suitable examples of memory  308  include, without limitation, ROM, RAM, flash memory (NOR or NAND flash memory), EEPROM, buffer memory, cache memory, variants thereof, combinations thereof, or any other type of computer memory that is known or yet-to-be developed. 
     The memory  308  is shown to contain instructions in the form of operating instructions  312  and emitting instructions  316 . It should be appreciated that these instructions may be combined into a single instruction set or they may be separated into more than two instruction sets. The instructions may be stored as software, firmware, or any other format. The operating instructions  312 , when executed by the processor  304 , may cause the processing device  104  to perform its desired behaviors. For instance, where the processing device  104  corresponds to a digital data transceiver module that is used in an optical/fiber optic communication system, the operating instructions  312  may enable the processing device  104  to send and/or receive optical signals via the optical fiber of the communication system and transform such signals to/from electrical signals. The operating instructions  312  may also include one or more drivers for the various hardware components of the processing device  104 . 
     The emitting instructions  316 , when executed by the processor  304 , may enable the processing device  104  to intelligently steer electromagnetic radiation  112 . More specifically, the emitting instructions  316  may include a phase delay element  320  and a random number generator  324 . The phase delay element  320  may cause the processing device  104  to implement a time-varying phase delay to steer a peak of the net electromagnetic radiation  112  in a particular time-varying direction. For instance, when two processing devices  104   a ,  104   b  are co-located with respect to a common area  108 , a phase delay element  320  of the first processing device  104   a  may cause the first processing device  104   a  to implement a first time-varying phase delay whereas a phase delay element  320  of the second processing device  104   b  may cause the second processing device  104   b  to implement a second time-varying phase delay such that the direction for which the electric fields from electromagnetic radiation  112   a  and  112   b  arrive in phase is steered in a time-varying direction. In some embodiments, enabling the different processing devices  104   a ,  104   b  to steer their net electromagnetic radiation  112  in different directions facilitates a reduction in an average emission of electromagnetic radiation in the common area  108  by the first and second processing devices  104   a ,  104   b . It should be appreciated that the first time-varying phase delay may be different from the second time-varying phase delay. In other embodiments, the first time-varying phase delay can be the same as the second time-varying phase delay but the first time-varying delay may be offset in time relative to the second time-varying phase delay. In other words, both processing devices  104   a ,  104   b  may implement the same time-varying delays, but at different (unsynchronized) times. 
     It may also be possible to utilize the random number generator  324  of the emitting instructions  316  to further ensure that the peak emissions of the processing devices  104   a -N do not overlay in time. More specifically, the time-varying delay produced by the phase delay element  320  may be at least partially driven by the random number generator  324 . This enables the various processing devices  104   a -N near the common area  108  to execute their operating instructions  312  and/or emitting instructions  316  without requiring knowledge of the other processing devices  104   a -N and the time-varying phase delays being implemented thereby. In other embodiments, there may be coordination between the processing devices  104   a -N to ensure that their phase delays are not synchronized and, thus, ensure that the direction of net peak emissions varies with time. Such coordination may be facilitated by direct (e.g., processing device-to-processing device) communications or indirect communications. The indirect coordination may be facilitated by a phase-delay coordinator that is attached and in communication with the various processing devices  104   a -N and is coordinating the various time-varying phase delays of the different processing devices  104   a -N. 
     The processing device  104  is also shown to include an optional communication interface  328 , which may correspond to any type of wired or wireless communication interface. Examples of communication interfaces  328  may include, without limitation, antennas, network cards, communication ports (e.g., Ethernet ports, optical fiber ports, etc.) and the like. 
     The radiation emitter(s)  332  of the processing device  104  may correspond to any element or collection of elements in the processing device  104  that produce electromagnetic radiation  112 . In some embodiments, the radiation emitter(s)  332  may further correspond to those emitters that respond to the emitting instructions  316 , rather than all emitters in the processing device  104 . The radiation emitter(s)  332  may include the communication interface  328 , the processor  304 , the power source  336 , other components  340 , as well as the circuitry that constitutes these elements of the processing device  104 . 
     The power source  336  may correspond to either an internal or external power source. The power source  336  may provide AC and/or DC power to the other components of the processing device  104 . Examples of suitable power sources include batteries, power converters for conditioning AC power received from an outlet into usable DC power, transformers, etc. The power source  336  may be contained within a common housing with the other components of the processing device  104  or the power source  336  maybe located external to the housing. 
     The other components  340  may include any other type of known components used in a processing device  104 . Examples of other components  340  include, without limitation, user interfaces (e.g., user input and/or output devices), drivers, peripheral devices, filters, amplifiers, and the like. 
     With reference now to  FIGS. 4-7 , additional features and operational behaviors of the emitting instructions  316  will be discussed in accordance with at least some embodiments of the present disclosure.  FIG. 4  depicts a first example where a simulation was performed for 32 processing devices operating in close proximity with one another. The simulation of  FIG. 4  shows a scenario where a dither of 2.0 ps is employed to steer the peak emissions of the processing devices  104  in accordance with at least some embodiments of the present disclosure. As can be seen in this simulation, when each of the 32 processing devices  104  employ emitting instructions  316  that cause a time-varying phase delay of 2.0 ps, then an advantage of 2.1 dB per one switch is achieved. 
     As can be seen in the simulation of  FIG. 5 , if the dither is increased from 2.0 ps to 10.0 ps, then the advantage can be increased to approximately 6.5 dB per switch. Further increasing the dither from 10.0 ps to 50.0 ps is shown to further increase the advantage to 8.6 dB per switch as shown in  FIG. 6 . Lastly, as shown in  FIG. 7 , if the dither is increased to 100.0 ps, then an advantage of approximately 9.4 dB can be achieved. These simulation results were performed for a situation where the processing devices  104   a -N were not coordinated, but rather implemented independently on a time-varying basis. 
     With reference now to  FIG. 8 , a method of managing electromagnetic radiation by an array of processing devices into a common area will be described in accordance with at least some embodiments of the present disclosure. Although the method will be described in connection with operating two processing devices near a common area  108 , it should be appreciated that the concepts disclosed herein can be applied to the operation of N processing devices. 
     The method begins with a first processing device  104   a  begins operating and, as a result of its operation, emits electromagnetic radiation. The first processing device  104   a  utilizes its emitting instructions  316  to adjust the phase of its electromagnetic radiation  112   a  in a first time-varying pattern (step  804 ). 
     The method proceeds with a second processing device  104   b  operating and, as a result of its operation, emitting electromagnetic radiation into the same area as the first processing device  104   a . The second processing device  104   b  adjusts the phase of its electromagnetic radiation  112   b  in a second time-varying pattern (step  808 ). In some embodiments, the phase delays of the first and second processing devices  104   a ,  104   b  may be controlled so as to ensure that they are not synchronized with one another (step  812 ). This may be accomplished by a number of mechanisms. As one example, an optional random number generator  324  can be utilized to randomize one or both of the first and second phase delay (step  816 ). Alternatively or additionally, a coordinator or coordination algorithm can be used to sense for synchronization of the phase delays and if such synchronization is detected, then one or both of the phase delays may be adjusted to avoid further synchronization (step  820 ). 
     In some embodiments, the first and/or second time-varying phase delay may be between 10 Hz and 100 Hz. In some embodiments, the first and/or second time-varying phase delay may be less than 1.0 kHz. In some embodiments, the first time-varying phase delay can be the same as the second time-varying phase delay but the first time-varying phase delay may be offset in time relative to the second time-varying phase delay. In some embodiments, the first time-varying phase delay is different from the second time-varying phase delay and the two delays may be offset in time relative to one another. 
     Specific details were given in the description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that the embodiments may be practiced without these specific details. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. 
     While illustrative embodiments of the disclosure have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art.