Abstract:
A high-speed multiple channel and line selector switch allows the simultaneous selection of the two lines of a differential channel and permits the simultaneous selection of multiple channels by introduction of the appropriate high speed pad connectivity.

Description:
BACKGROUND  
       [0001]     In the emerging area of parallel and parallel coarse wavelength division multiplexing (CWDM) optical interconnects, the trend is to increase the number of channels per module while maintaining channel speed at a reasonable level as determined by the available device and integrated circuit technologies. For example, in one system, it may be desired to run a 48 channel module at a speed of up to 10 Gb/s. In such a module, channels are typically arranged into four groups of twelve with each group operating at a different wavelength. The testing and evaluation of a system having many high speed channels presents a problem. Extension of typical conventional approaches where each channel is handled separately requires a test configuration that uses a large number of high-speed cables, connectors, terminations, a large evaluation board and a considerable number of man-hours for testing and evaluation. Hence, it is desirable to transition from the typical conventional approach to a more integrated approach that, for example, uses compact on-board components allowing the selection of a subset of channels at the time of measurement while properly terminating the remaining channels. This allows a significant reduction in the number of high-speed cables and components needed, reducing the complexity of the test configuration. Central to such an integrated test approach is a switch that allows easy selection of one or more channels from a multiplicity of high speed channels.  
         [0002]     A switch that allows easy channel selection is a high-speed channel selector switch (HCSS) as disclosed in U.S. patent application Ser. No. 10/627,317 hereby incorporated by reference. The HCSS typically consists of two units-stationary unit  100  and rotary  200  unit as shown in  FIGS. 1 and 2 , respectively. High speed channel pads  120  are distributed around circle  125  in a circular pattern and a high speed channel is electrically coupled to each of high speed channel pads  120 . Rotary unit  200  has a pad frame that matches to stationary unit  100  resulting in a one to one mapping between outer pads  220  on rotary unit  200  and high speed channel pads  120  on stationary unit  100  when rotary unit  200  is properly mated to stationary unit  100 . Placing conductive balls or bumps on stationary unit  100  allows high speed connections to be made. On rotary unit  200 , all outer pads  220  except one are terminated to proper loads or impedances by short segments of transmission lines  250 . The remaining outer pad  220  is electrically coupled to pad  240  at the center by transmission line  225 . This allows selection of one channel while properly terminating all others to termination impedances  275 . Note that portions  260  of rotary unit  200  are kept at ground. By rotating rotary unit  200  by the proper amount, any high speed channel is selectable.  
         [0003]     However, the HCSS switch allows only one channel to be selected at a time and may be a problem for some test applications. For example, in applications that involve differential signaling and two lines, the use of the HCSS switch allows monitoring of only a single line at a time. Hence, monitoring both lines simultaneously is not possible with the use of one HCSS switch. Additionally, the mechanical tolerances required for the HCSS switch are not easily implemented. Because pads  140  and  240  are at the center of stationary unit  100  and rotary unit  200 , respectively, alignment features such as an alignment pin cannot be located at the center. The mechanical housing typically has several parts, a rotary part, a stationary part and a clamping part. The inability to use the center for alignment of these parts typically degrades the stack-up tolerances. The mechanical housing functions to hold and lock the rotary unit with respect to the stationary unit and when unlocked the mechanical housing allows the rotation of the rotary unit in fixed increments. To allow large stack-up tolerances requires the use of larger pads  140  and  240  that degrade the high speed performance of the pads because of the increasing pad capacitance associated with increased pad size.  
       SUMMARY OF INVENTION  
       [0004]     In accordance with the invention, eliminating the central high speed pad removes the constraint of single channel selection to allow the simultaneous selection of the two lines of a differential channel and permit the simultaneous selection of multiple channels by introduction of the appropriate high speed pad connectivity. Additionally, eliminating the need for a high speed pad at the center of rotary and stationary units by use of a High-speed Multiple Channel and Line Selector Switch (HMCSS) allows for smaller alignment tolerances between the rotary and stationary units. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  shows a HCSS stationary unit from the prior art.  
         [0006]      FIG. 2  shows a HCSS rotary unit from the prior art.  
         [0007]      FIG. 3   a  shows an HMCSS stationary unit in an embodiment in accordance with the invention.  
         [0008]      FIG. 3   b  shows a cross-section of an HMCSS stationary unit in an embodiment in accordance with the invention.  
         [0009]      FIG. 4   a  shows an HMCSS rotary unit in an embodiment in accordance with the invention.  
         [0010]      FIG. 4   b  shows an exploded view of an HMCSS unit in an embodiment in accordance with the invention.  
         [0011]      FIG. 4   c  shows a cross-section of an HMCSS rotary unit in an embodiment in accordance with the invention.  
         [0012]      FIG. 5  shows an HMCSS stationary unit in an embodiment in accordance with the invention.  
         [0013]      FIG. 6  shows an HMCSS rotary unit in an embodiment in accordance with the invention.  
         [0014]      FIG. 7  shows an HMCSS stationary unit in an embodiment in accordance with the invention.  
         [0015]      FIG. 8  shows an HMCSS rotary unit in an embodiment in accordance with the invention.  
         [0016]      FIG. 9  shows an evaluation board in an embodiment in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     An embodiment in accordance with the invention is shown in  FIG. 3   a . HMCSS stationary unit  300  in  FIG. 3   a  of HMCSS  450  (see  FIG. 4   b ) is shown having nine incoming channels but the number of incoming channels may be more or less than nine. To simplify the discussion, the HMCSS in accordance with the invention is described in the context of choosing one or more lines from a plurality of incoming lines, however, the HMCSS also functions in reverse where one or more incoming lines are routed to lines selected from a plurality of outgoing lines.  
         [0018]     With reference to  FIG. 3   a , each of the incoming channels is electrically coupled to one of high speed pads  311 - 319  of HMCSS stationary unit  300  by incoming lines  351 . High speed pads  311 - 319  are typically uniformly distributed on inner circle  321  in a circular pattern. High speed pads  301 - 309  are typically uniformly distributed on outer circle  331  in a circular pattern. One of outer high speed pads  301 - 309 , for example, high speed pad  301 , is electrically coupled to the outgoing channel by outgoing line  352  while the remaining outer high speed pads, for example, high speed pads  302 - 309 , are properly terminated to a load on outgoing lines  353 . In accordance with an embodiment of the invention, any one of inner high speed pads  311 - 319  can be routed to high speed pad  301  while the remaining pads of inner high speed pads  311 - 319  is routed to one of remaining outer high speed pads  302 - 309 .  
         [0019]      FIG. 3   b  shows cross-section  399  of HMCSS stationary unit  300 . Dielectric layers  374  and  375  are sandwiched between metalized ground planes  371  and  372 . Pads  311  and  301  are electrically coupled to incoming line  351  and outgoing line  352 , respectively, by vias  391  and  381 , respectively. Note that pads  311  and  301  are electrically isolated from ground plane  371 .  
         [0020]      FIG. 4   a  shows two sets of high-speed pads,  401 - 409  and  411 - 419  of HMCSS rotary unit  400  typically distributed uniformly on outer circle  431  and inner circle  421  in a circular pattern, respectively. When HMCSS stationary unit  300  and HMCSS rotary unit  400  are properly aligned and mated, a one-to-one mapping exists between pads  301 - 309  and  311 - 319  on HMCSS stationary unit  300  and pads  401 - 409  and  411 - 419  on HMCSS rotary unit  400  for HMCSS  450  (see  FIG. 4   b ).  
         [0021]     In accordance with the invention, if inner high speed pads  411 - 419  of HMCSS rotary unit  400  of HMCSS  450  (see  FIG. 4   b ) are electrically couple to outer high pads  401 - 409  of HMCSS rotary unit  400  shown in  FIG. 4   a , it is possible to obtain selective routing on HMCSS stationary unit  300  by rotation of HMCSS rotary unit  400 . The electrical coupling that is needed between inner circle  421  and outer circle  431  to achieve this is shown in  FIG. 4   a . Inner high speed pads  411 ,  413 ,  415 ,  417  and  419  are electrically coupled to outer high speed pads  401 ,  402 ,  403 ,  404 ,  405 , respectively, while inner high speed pads  412 ,  414 ,  416 ,  418  are electrically coupled to outer high speed pads  406 ,  407 ,  408 ,  409 , respectively. The electrical connectivity required may be achieved by using, for example, a multilayer circuit board. The number of layers on the circuit board typically depends on the type of transmission lines used. For strip transmission lines, the minimum number of layers is typically five whereas for coplanar waveguides the minimum number of layers is typically two. The circuit board is typically made from glass-ceramic, ceramic, PTFE, polyimide, FR4 epoxy or similar materials.  
         [0022]     HMCSS rotary unit  400  is attached to HMCSS stationary unit  300  such that all pads are mated. The start or 0 degree position of HMCSS rotary unit  400  is defined as the position when high speed pad  311  is aligned with high speed pad  41  land high speed pad  301  is aligned with high speed pad  401 . In the start position, the incoming channel on high speed pad  311  is selected and routed to the outgoing channel on high speed pad  301 . Rotating HMCSS rotary unit  400  in increments of 40 degrees clockwise from the 0 degree position selects the respective next incoming channel which is routed to the outgoing channel at high speed pad  301 . The selection scheme is shown in Table 1 below:  
                                         TABLE 1                                   Clockwise Rotation               (degrees)   Pad Connectivity                                        0   311→411→401→301           40   312→413→402→301           80   313→415→403→301           120   314→417→404→301           160   315→419→405→301           200   316→412→406→301           240   317→414→407→301           280   318→416→408→301           320   319→418→409→301                      
 
         [0023]     For example, taking a clockwise rotation of 240 degrees, pad  317  of HMCSS stationary unit  300  is aligned with high speed pad  414  of HMCSS rotary unit  400  and high speed pad  301  HMCSS stationary unit is aligned with pad  407  of HMCSS rotary unit  400  so that an electrical connection is established between high speed pad  317  and high speed pad  301 . Although each 40 degree clockwise incremental rotation of HMCSS rotary unit  400  establishes a connection between one of inner high speed pads  311 - 319  to outer high speed pad  301 , an electrical connection is also established between the remaining high speed pads on inner circle  321  to the remaining high speed pads on outer circle  331 . Because outer high speed pads  302 - 309  are terminated to loads or impedances, the remaining incoming channels are properly terminated.  
         [0024]     Because neither HMCSS stationary unit  300  nor HMCSS rotary unit  400  has a high speed pad at the center, alignment pin  445  can be placed at the center as shown in  FIG. 4   b . The alignment tolerance is determined by the size and positional tolerances of alignment pin hole  446  and the alignment pin hole (not shown) in HMCSS rotary unit  400 . A tolerance of less than  10  percent of the pad size can be typically achieved by using conventional techniques such as, for example, drilling or etching to make the alignment pin holes.  
         [0025]      FIG. 4   c  shows cross-section  499  of HMCSS rotary unit  400 . Dielectric layers  474  and  475  are sandwiched between metalized ground planes  471  and  472  while dielectric layers  476  and  477  are sandwiched between metalized ground planes  472  and  473 . Pads  411  and  401  are electrically coupled to connecting line  420  by vias  491  and  481 , respectively. Note that pads  411  and  401  are electrically isolated from ground plane  471 . Connecting lines  422 ,  424  are located on dielectric layer  475  while connecting lines  429 ,  427  are located on dielectric layer  477  so that connecting line  422  may cross over connecting line  429  and connecting line  424  may cross over connecting line  427 . In accordance with the invention, any connecting lines that cross in  FIG. 4   a  are in different dielectric layers.  
         [0026]     Furthermore, because no high speed pads are positioned at the center of HMCSS stationary unit  300  and HMCSS rotary unit  400 , a differential channel switch configuration may be implemented.  FIG. 5  shows differential HMCSS stationary unit  500  and  FIG. 6  shows differential HMCSS rotary unit  600  where each high speed pad on HMCSS stationary unit  300  and HMCSS rotary unit  400  has been replaced by a pair of pads. On HMCSS stationary unit  500  in  FIG. 5 , high speed pad pairs  501   a,b - 509   a,b  replace high speed pads  301 - 309 , respectively, while high speed pad pairs  511   a,b -  519   a,b  replace high speed pads  311 - 319 , respectively. On HMCSS rotary unit  600  in  FIG. 6 , high speed pad pairs  601   a,b - 609   a,b  replace high speed pads  401 - 409 , respectively, while high speed pairs  611   a,b - 619   a,b  replace high speed pads  411 - 419 , respectively.  
         [0027]     In the above discussion, only one of the outer high speed pads in the HMCSS switch was electrically coupled to an outgoing channel while the remaining outer high speed pads are terminated to loads or impedances. However, the remaining outer high speed pads need not be terminated to a load. In accordance with an embodiment of the invention, a plurality of incoming channels may be selected. Multiple outer high speed pads may be electrically coupled to multiple inner high speed pads with the remaining high speed pads being terminated. For an embodiment in accordance with the invention, Table 2 shows an example of how two incoming channels may be selected at the same time with reference to  FIGS. 3   a  and  4   a .  
                                         TABLE 2                                   Clockwise Rotation               (degrees)   Pad Connectivity                                        0   311→411→401→301               312→412→406→306           80   313→415→403→301               314→416→408→306           160   315→419→405→301               316→411→401→306           240   317→414→407→301               318→415→403→306           320   319→418→409→301               311→419→407→306           400   312→413→402→301               313→414→407→306           480   314→417→404→301               315→418→409→306           560   316→412→406→301               317→413→402→306           640   318→416→408→301               319→417→404→306                      
 
 As shown in Table 2, high speed outer pads  301  and  306  are electrically coupled to the outgoing channels. By rotating rotary unit  400  in increments of 80 degrees the incoming channels may be selected. 
 
         [0028]     In accordance with an embodiment of the invention, Table 3 shows the connectivity for the selection of three incoming channels at a time. In this embodiment, high speed outer pads  301 ,  306  and  302  are electrically coupled to the outgoing channels. By rotating rotary unit  400  in increments of 120 degrees the three incoming channels may be selected.  
                                         TABLE 3                                   Clockwise Rotation               (degrees)   Pad Connectivity                                        0   311→411→401→301               312→412→406→306               313→413→402→302           120   314→417→404→301               315→418→409→306               316→419→405→302           240   317→414→407→301               318→415→403→306               319→416→408→302                      
 
         [0029]     In the embodiments in accordance with the invention presented above, the incoming channels have been electrically coupled to high speed pads on inner circles  321  or  521  of HMCSS stationary unit  300  or  500 , respectively while one or more high speed pads on outer circles  331  or  531  of HMCSS stationary unit  300  or  500 , respectively are electrically coupled to outgoing channels. However, in accordance with the invention, the HMCSS switches may be configured so that the incoming channels are electrically coupled to high speed pads on outer circle  731  of stationary unit  700  and the outgoing channels are electrically coupled to high speed pads on inner circle  721  of stationary unit  700  of  FIG. 7 .  FIG. 8  shows HMCSS rotary unit  800  with the required connectivity. High speed pads  801 ,  803 ,  805 ,  807  and  809  are electrically coupled to high speed pads  811 ,  812 ,  813 ,  814  and  815 , respectively. High speed pads  802 ,  804 ,  806  and  808  are electrically coupled to high speed pads  816 ,  817 ,  818  and  819 , respectively. Table 4 below shows the connectivity for the selection of one incoming channel at a time. High speed pad  711  is electrically coupled to the outgoing channel.  
                                         TABLE 4                                   Clockwise Rotation               (degrees)   Pad Connectivity                                        0   701→801→811→711           40   702→803→812→711           80   703→805→813→711           120   704→807→814→711           160   705→809→815→711           200   706→802→816→711           240   707→804→817→711           280   708→806→818→711           320   709→808→819→711                      
 
         [0030]     Whereas the discussion so far has focused on the specific case of nine channels to illustrate embodiments in accordance with the invention, embodiments in accordance with the invention may have 2N+1 channels where N=1, 2, 3 . . . . For the rotary unit, such as, for example, rotary unit  400  where N=4, 2N+1, pairs of pads are evenly distributed on two circles of different radii, for example, circles  421  and  431 . Both high speed pads of a pair, for example high speed pads  401  and  411 , may lie on a radial line from the alignment pin hole of the rotary unit, for example, rotary unit  400  but in accordance with the invention there may be a fixed circumferential offset between the high speed pads of each pair as long as the high speed pads are evenly distributed on the two circles of different radii. The stationary unit, such as stationary unit  300 , has 2N+1 pairs of matching high speed pads. Note that for stationary unit  300  and rotary unit  400 , N=4. The requisite connectivity for 2N+1 pairs of high speed pads can be determined as follows. Label both the outer high speed pads and inner high speed pads consecutively from 1 to 2N+1, counterclockwise. Let j be the number for the outer high speed pad and k be the number for the inner high speed pad. Then in accordance with the invention, any outer pad j is uniquely electrically coupled to the inner high speed pad k where k=(2j-1) modulus 2N+1 or any inner high speed pad k is uniquely electrically coupled to the outer high speed pad j where j=(2k-1) modulus 2N+1. For example in  FIG. 4   a , assign j=1 . . . 9 to high speed pads  401  . . .  409 , respectively and assign k=1 . . . 9 to high speed pads  411  . . .  419 . Hence, in  FIG. 4   a , taking j=2 which corresponds to high speed pad  402 , high speed pad  402  is electrically coupled to k=3 which corresponds to high speed pad  413 .  
         [0031]     The fixed rotation increment in degrees necessary to operate the HMCSS is an integer multiple of  360 /(2N+1) degrees. As 2N+1 becomes larger, the size of the HMCSS increases to accommodate the added electrical connections. The required size for HMCSS can be determined from considerations of board layout and tolerances.  
         [0032]     In accordance with the invention, if an even number of channels is desired, an extra channel is added to make the total number of channels an odd number and the extra channel is not used.  
         [0033]      FIG. 9  is a top view of evaluation board  900  for testing a device under test such as highly parallel optoelectronic module  950 , for example a receiver or transmitter, in accordance with the invention. HMCSS units  901 ,  902 ,  903  and  904  are electrically coupled to optoelectronic module  950  using input lines  910 . One or more output lines  971   a -( n ),  972   a -( n ),  973   a -( n ) and  974   a -( n ) provide one or more channels from HMCSS units  901 ,  902 ,  903  and  904 , respectively, to evaluation equipment  940 . In accordance with the invention, multiple channels may be simultaneously sampled from each HMCSS unit by evaluation equipment  940  while allowing rapid switching between channel configurations.  
         [0034]     While the invention has been described in conjunction with specific embodiments, it is evident to those skilled in the art that many alternatives, modifications, and variations will be apparent in light of the foregoing description. Accordingly, the invention is intended to embrace all other such alternatives, modifications, and variations that fall within the spirit and scope of the appended claims.