Abstract:
A method of transmitting adjacent signals is disclosed. Sensing is performed on signals in the group and adjacent signals are either switched or delayed if the adjacent signals are switching at the same time. The method is used in networks where coupling and capacitance effects are possible.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a method and system using delay signals to reduce or eliminate interference between paths in a communication network, in particular an electronic circuit. 
   2. Description of the Related Art 
   Communication networks, in particular communication networks on integrated circuits, have numerous paths carrying signals from one device to other devices. Multiple paths that are placed near one another can lead to problems related to coupling and capacitative interference. The situation becomes most problematic when multiple paths carrying signals that transition or switch at the same time, run parallel to a single path switching in the opposite direction. 
   Coupling effects do not have a noticeable effect upon signals that are switching in the same direction. In a digital signal transmission, the rise of the signal from a driver connected to a path is not affected by signals from the other paths switching in the same direction. Coupling effects, however, can have an effect upon the paths whose signals switch in the opposite direction. In particular coupling effects lead to slower rise times of path signals. To compensate for slower rise times, path driver power is increased. Path drivers are required to provide additional power to compensate for a slower rise time in order to get signals out and to achieve proper signal level and timing requirements. 
   In certain designs, neutral paths such as ground paths, also known as shield lines, are available and placed between aggressors and victim paths, effectively shielding the opposite switching paths from one another. Shield lines typically serve no function but are merely used to shield the victim path. The use of neutral paths or shield lines also leads to design considerations and network architecture constraints in laying out paths. Adding shield lines further adds to an increase in the space of the network. In an integrated circuit, minimizing size is highly desirable, and adding non-functional shield lines becomes counter productive to meeting the goal of minimizing size. 
   SUMMARY OF THE INVENTION 
   In one embodiment, a method of transmitting a signal is disclosed. The method includes sensing adjacent signals and delaying certain adjacent signals until switching or transition takes place with the other adjacent signal or signals. 
   In certain embodiments, various number signal groups including two-signal, three-signal, and five-signal groups sense and delay for particular signals. Signals that are adjacent to more than one signal are delayed in the event that any or all of the adjacent signals simultaneously switch with the particular signals. 
   In certain embodiments, a separate sensing and delay circuit is provided. Along with buffers, the sensing and delay circuit provides a delay signal to the buffers in the event that adjacent signals switch simultaneously, thus delaying an adjacent signal. 
   In other embodiments, the method assigns priorities to transmitted signals. Signals that have a lower priority compared to signals with a higher priority are delayed until the higher priority signals are switched. In certain embodiments, a delay pulse is sent to by the higher priority signal or signals to the lower priority signal or signals. 
   The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the present invention, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the figures designates a like or similar element. 
       FIG. 1A  is a diagram illustrating the use of inverter delays to avoid coupling interference. 
       FIG. 1B  is a timing diagram illustrating a three-signal group with delay provisioning. 
       FIG. 1C  is a timing diagram illustrating a five-signal group with delay provisioning. 
       FIG. 1D  is a timing diagram illustrating a five-signal group with delay provisioning when three adjacent signals switch simultaneously. 
       FIG. 1E  is a timing diagram illustrating a five-signal group with an extended delay when initial delay results in simultaneously switching with an adjacent signal. 
       FIG. 2  is a block diagram illustrating use of a sensing and delay circuit and buffers to transition a three-signal group. 
       FIG. 3  is a flow diagram illustrating transition of adjacent signals for a three-signal group. 
       FIG. 4  is a block diagram illustrating use of a sensing and delay circuit and buffers to transition a five-signal group. 
       FIG. 5  is a flow diagram illustrating transition of adjacent signals for a five-signal group. 
       FIG. 6  is a block diagram of three and five signal groups with shield lines. 
   

   While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail, it should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present invention as defined by the appended claims. 
   DETAILED DESCRIPTION 
   The following is intended to provide a detailed description of an example of the invention and should not be taken to be limiting of the invention itself. Rather, any number of variations may fall within the scope of the invention which is defined in the claims following the description. 
   Introduction 
   The present invention provides a method and apparatus for avoiding or minimizing coupling interference in adjacent paths in a communication network by sensing transitioning (switching) instances of adjacent paths and delaying a signal from transitioning while adjacent signal(s) transitions. Coupling interference is avoided between the adjacent signal paths by assuring sufficient time differences exist between the transitioning of the adjacent signals. A signal transitions (switches) without coupling interference from a simultaneously switching adjacent signal. 
   Delay Signals 
     FIG. 1A  is a diagram illustrating the use of inverter delays to avoid coupling interference. Signal  1   100  is an adjacent signal to Signal  2   105 . Signal  2   105  is an adjacent signal to Signal  3   110 . In order to avoid coupling interference, in particular when Signal  1   100 , Signal  2   105 , and Signal  3   110  are switching, a delay is provided in the form of an inverter  115  along the path of Signal  2   105 . Switching of a signal takes place on either a rising or falling edge of the signal. In this particular example, the signals are digital signals representing either a “1” or “0” value. Signal  2   105  is restored later along the transmission line is by inverter  120 . In other words, the signal  2   105  is inverted once again to restore the original transmitted value prior to inverter  115 . The path of inverted Signal  2   105  is presented by path length  125 . Because of the delay from inverter  115  and  120 , a non-coupling zone  125  is provided assuming signal  2   105  is not delayed such that signal  2   105  switches at the same time as signal  1   100  and/or signal  3   110 . Within non-coupling zone  130 , there is a small likelihood of coupling interference between signals  100 ,  105  and  110 , assuming that delay to Signal  2   105  would not cause Signal  2   105  to couple with Signal  1   100  and Signal  3   110 . 
     FIG. 1B  is a timing diagram illustrating a three-signal group with delay provisioning. Signal  1   100 , signal  2   105 , and signal  3   110  are part of a three-signal group with signal  2   105  placed between signal  1   100  and signal  3   110 . Whenever signals  100  and  105 , or signals  105  and signal  110  switch simultaneously, in this particular example the three signals  100 ,  105 ,  110  are switching at time T 1   115 , a delay is performed by delay logic  120 . Delay logic  120  provides a sufficient delay to signal  2   105  in order to prevent simultaneous switching with signal  1   100  and/or signal  3   110 . Signal  2   105  switches at time T 2   125 . The delay is a delay d  130 . Delay d  130  can be a predetermined period of time or any amount of time sufficient to prevent simultaneous switching with signal  2   105  and adjacent signal  1   100  and signal  3   110 . The delay avoids any coupling interference in the event that signal  2   105  is an opposite switching signal to either signal  1   100  and/or signal  3   110 . 
     FIG. 1C  is a timing diagram illustrating a five-signal group with delay provisioning. Signal  1   100 , signal  2   105 , signal  3   110 , signal  4   135  and signal  5   140  are adjacent to one another in order. In this particular example, all five signals are switching at the same time, time T 1   115 . In this particular embodiment, delay logic  120  delays signal  1   100 , signal  3   110 , and/or signal  5   140  whenever simultaneous switching occurs with adjacent signal  2   105  and/or signal  4   135 . Signal  2   105  and signal  4   135  are never delayed, and are allowed to switch at their initial switching time, in this case time T 1   115 . In this example, signal  1   100 , signal  3   110 , and signal  5   140  are delayed and switch at time T 2   125 . The delay d  130  can be a predetermined period or any sufficient amount of time that prevents simultaneous switching of signals. The delay avoids any coupling interference between adjacent simultaneously switching signals. 
     FIG. 1D  is a timing diagram illustrating a five-signal group with delay provisioning when three adjacent signals switch simultaneously. In this particular example, signal  1   100  and signal  5   140  simultaneously switch at time T 1   115 . Signal  1   100  and signal  5   140  are far enough apart that simultaneously switching does not affect the respective signals. Signal  2   105 , signal  3   110 , and signal  4   135  simultaneously switch at time T 3   145 . In order to avoid any coupling interference, specifically if signal  3   110  is an opposite switching signal to signal  2   105  and/or signal  4   135 , delay logic  120  delays signal  3   110 . Signal  2   105  and signal  4   135 , in this embodiment, are never delayed and switch at their respective original switch time T 3   145 . Signal  3   110  is switched at time T 4   150 , providing a delay of d  130 . Delay d  130  can be a predetermined period of delay of any amount of delay sufficient to avoid simultaneously switching of adjacent signals. 
     FIG. 1E  is a timing diagram illustrating a five-signal group with an extended delay when initial delay results in simultaneously switching with an adjacent signal. In this particular embodiment of the invention, signal  2   105  and signal  4   135  are never delayed, and always switch at their respective original switch times, in this example signal  2   105  switches at time T 1   115  and signal  4   135  switches at time T 3   145 . Signal  1   100 , signal  3   110 , and signal  5   140  switch at time T 1   115 , the same time that signal  2   105  switches. Delay logic  120  senses that adjacent signal  1   100  and signal  3   110  switch at the same time as signal  2   105 , therefore a delay is provided to signal  1   100  and signal  3   110 . Signal  1   100  now switches at time T 3   145 , the same time as signal  4   135 , however the two signals are far enough removed from one another to avoid any coupling interference. Signal  3   110  would also be delayed to time T 3   145 , however, this condition would result in signal  3   110  switching at the same time as signal  4   135 . Delay logic  120  therefore provides for signal  3   110  to be further delayed to time T 5   155 . The adjusted delayed timing diagram prevents adjacent signals from switching at the same times and avoids coupling interference when adjacent signals are switching opposite one another. 
   Sensing and Delay Logic 
     FIG. 2  is a block diagram illustrating use of a sensing and delay circuit and tri-state buffers to transition signals. Signals  100 ,  105 , and  110  are monitored by sensing and delay circuit  200 . Sensing and delay circuit  200  receives sense signals  205 ,  210 , and  215  respectively from signal  1   100 , signal  2   105 , and signal  3   110 . Sensing and delay circuit  200  determines if signal  2   105  switches at the same time as signal  1   100  and/or signal  3   110 . If signal  2   105  switches at the same time as either adjacent signal  1   100  or adjacent signal  3   110 , signal  2   105  is delayed. In this example, buffers  220  and  230  are buffers to match the delay of tri-state buffer  225  when there is no simultaneous switching. Tri-state buffer  225  provides for three possible values: a value of 0, 1, or a high impedance value. A signal may be switching on the rising edge, therefore a value of 1 is associated with it. A signal that is switching on the falling edge has a value of 0. A signal that has been delayed or is awaiting transition from sensing and delay circuit  200  maintains its binary signal value. The use of sensing and delay circuit  200  along with buffers  220 ,  225 , and  230  assure that signal  1   100  and  3   110  are always immediately passed through. Signal  2   105  is immediately passed through without delay unless signal  2   105  switches at the same time as Signal  1   100  or Signal  3   110 . Since signal  1   100  is far enough removed from signal  3   110 , possibility of coupling interference between signal  1   100  and signal  3   110  is minimal. 
     FIG. 3  is a flow diagram illustrating transition of adjacent signals for a three signal group. Sensing and delay circuit  200  receives signals  100 ,  105 , and  110 , step  300 . Signals  100  and  105  are sensed at the same time, step  305 . Simultaneously, signals  105  and  110  are also sensed with one another at the same time, step  310 . A determination is made if signals  100  and  105  are switching at the same time, step  315 . A determination is also made whether signals  105  and  110  are switching at the same time, step  320 . If the condition is “yes” for either steps  315  or  320 , then signal  2   105  is delayed, step  325 . If steps  315  and  320  are both determined to be “no,” then signal  2   105  is not delayed, step  330 . 
     FIG. 4  is a block diagram illustrating use of a sensing and delay circuit and buffers to transition a five-signal group. Buffer  400  is used for signal  1100 . Buffer  405  is used for signal  2   105 . Buffer  410  is used for signal  3   110 . Buffer  415  is used for signal  4   135 . Buffer  420  is used for signal  5   140 . Buffers  400 ,  410 , and  420  are tn-state buffers that receive delay signals from sensing and delay circuit  425 . A received delay signal to the respective buffer tri-states the respective signals. In this particular example delay signal  430  is provided to buffer  420 . Delay signal  435  is provided to buffer  410 . Delay signal  440  is provided to buffer  400 . Sensing and delay circuit  425 , in this embodiment, includes three separate circuit or logic blocks: sensing and delay circuit A  445 ; sensing and delay circuit B  450 ; and sensing and delay circuit C  455 . The respective sensing and delay circuits can include digital, analog, and/or combined circuits that sense and hold signals and trigger respective tri-state buffers  400 ,  405 ,  410 ,  415 , and  420 . In this particular embodiment, sensing and delay circuit A  445  senses signal  1100  through sense signal  460  and signal  2   105  through sense signal  465 . Sensing and delay circuit B  450  senses signal  2   105  through sense signal  470 , signal  3   110  through sense signal  475 , and signal  4   135  through sense signal  480 . Sensing and delay circuit C  455  senses signal  4   135  through sense signal  485  and signal  5   140  through sense signal  490 . The use of sensing and delay circuit  425 , in particular sensing and delay circuit  450  and tri-state buffer  410  to delay signal  3 , provides a uninterrupted continuous delay. Delay signal  435  is provided to tri-state buffer  410  whenever the delay actually is required to take place. This prevents separate delay glitches that can cause aberrations in signal transmission. 
     FIG. 5  is a flow diagram illustrating transition of adjacent signals for a five-signal group.  FIG. 5  specifically illustrates the logic involved in the block diagram and the sensing and delay circuits of  FIG. 4 . As in a three-signal group, contention is provided for a five-signal group using a sensing and delay circuit or similar logic. Other multiple signal groups can also make use of such logic and similar sensing and delay circuit (logic). In this example, the sensing and delay circuit receives five signals, signals  1 ,  2 ,  3 ,  4  and  5 , step  500 . Signals  1 ,  2 ,  3 ,  4 , and  5  in order are adjacent to one another in the group. In other words, signal  1  is adjacent to signal  2 ; signal  2  is adjacent to signal  3 ; signal  3  is adjacent to signal  4 ; and signal  4  is adjacent to signal  5 . Signals  1  and  2  are sensed with one another, step  505 . Signals  2  and  3  are sensed with one another, step  510 . Signals  3  and  4  are sensed with one another, step  515 . Signals  4  and  5  are sensed with one another, step  520 . A determination is made as to whether signals  1  and  2  are transitioning (switching) at the same time, step  525 . If step  525  is determined to be “yes” then signal  1  is delayed, step  530 . If step  525  is determined to be “no” then signal  1  is not delayed, step  535 . A determination is made as to whether adjacent signals  4  and  5  are transitioning at the same time, step  540 . If step  540  is determined to be “yes” then signal S is delayed, step  545 . Since signal  3  is the middle signal of the five-signal group and is directly adjacent to signals  2  and  4 , signal  3  is delayed if signal  3  transitions at the same time as either signal  2  or signal  4 . A separate determination is made as to whether signals  2  and  3  are transitioning at the same time, step  555 . Another determination is made as to whether signals  3  and  4  are transitioning at the same time, step  560 . If either step  555  or step  560  is “yes,” signal  3  is delayed, step  565 . If both step  555  and step  560  are “no” then signal  3  is not delayed, step  570 . 
     FIG. 6  is a block diagram of three and five signal groups with shield lines. Sensing and delay circuits can be placed before, after, or in signal drivers. The signal drivers transmitting the signal after delay is provided to the signal. In order to maximize the use of sensing and delay circuits, signals are grouped together and use a single sensing and delay circuit. Signal group  600  is a group of three signals. Signal group  605  is another group of three signals. Groups  600  and  605  can be placed near one another; however, to prevent any coupling between the adjacent signals of the two groups, a shield line  610  is added. Signals in groups  600  and  605  can be placed relatively near one another through the use of the sensing and delay circuits, however some protection and spacing is provided by way of shield line  610 . In a similar manner groups of five-signal groups can be provided as illustrated by signal groups  615  and  620 , and separated by shield line  625 . Other multiple number signal groups can be provided, and variations are possible in the use of various groupings of signals and shield lines. Groupings and use of shield lines are dependent on the circuit or network architecture that is desired. 
   Although the present invention has been described in connection with several embodiments, the invention is not intended to be limited to the specific forms set forth herein, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as can be reasonably included with in the scope of the invention as defined by the appended claims.