Method and apparatus for high-speed multiple channel and line selector switch

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.

BACKGROUND

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.

A switch that allows easy channel selection is a high-speed channel selector switch (HCSS) as disclosed in U.S. Pat. No. 6,933,628 hereby incorporated by reference.

The HCSS typically consists of two units-stationary unit100and rotary200unit as shown inFIGS. 1 and 2, respectively. High speed channel pads120are distributed around circle125in a circular pattern and a high speed channel is electrically coupled to each of high speed channel pads120. Rotary unit200has a pad frame that matches to stationary unit100resulting in a one to one mapping between outer pads220on rotary unit200and high speed channel pads120on stationary unit100when rotary unit200is properly mated to stationary unit100. Placing conductive balls or bumps on stationary unit100allows high speed connections to be made. On rotary unit200, all outer pads220except one are terminated to proper loads or impedances by short segments of transmission lines250. The remaining outer pad220is electrically coupled to pad240at the center by transmission line225. This allows selection of one channel while properly terminating all others to termination impedances275. Note that portions260of rotary unit200are kept at ground. By rotating rotary unit200by the proper amount, any high speed channel is selectable.

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 pads140and240are at the center of stationary unit100and rotary unit200, 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 pads140and240that degrade the high speed performance of the pads because of the increasing pad capacitance associated with increased pad size.

SUMMARY OF INVENTION

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.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment in accordance with the invention is shown inFIG. 3a. HMCSS stationary unit300inFIG. 3aof HMCSS450(seeFIG. 4b) 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.

With reference toFIG. 3a, each of the incoming channels is electrically coupled to one of high speed pads311-319of HMCSS stationary unit300by incoming lines351. High speed pads311-319are typically uniformly distributed on inner circle321in a circular pattern. High speed pads301-309are typically uniformly distributed on outer circle331in a circular pattern. One of outer high speed pads301-309, for example, high speed pad301, is electrically coupled to the outgoing channel by outgoing line352while the remaining outer high speed pads, for example, high speed pads302-309, are properly terminated to a load on outgoing lines353. In accordance with an embodiment of the invention, any one of inner high speed pads311-319can be routed to high speed pad301while the remaining pads of inner high speed pads311-319is routed to one of remaining outer high speed pads302-309.

In accordance with the invention, if inner high speed pads411-419of HMCSS rotary unit400of HMCSS450(seeFIG. 4b) are electrically couple to outer high pads401-409of HMCSS rotary unit400shown inFIG. 4a, it is possible to obtain selective routing on HMCSS stationary unit300by rotation of HMCSS rotary unit400. The electrical coupling that is needed between inner circle421and outer circle431to achieve this is shown inFIG. 4a. Inner high speed pads411,413,415,417and419are electrically coupled to outer high speed pads401,402,403,404,405, respectively, while inner high speed pads412,414,416,418are electrically coupled to outer high speed pads406,407,408,409, 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.

HMCSS rotary unit400is attached to HMCSS stationary unit300such that all pads are mated. The start or 0 degree position of HMCSS rotary unit400is defined as the position when high speed pad311is aligned with high speed pad41land high speed pad301is aligned with high speed pad401. In the start position, the incoming channel on high speed pad311is selected and routed to the outgoing channel on high speed pad301. Rotating HMCSS rotary unit400in 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 pad301. The selection scheme is shown in Table 1 below:

For example, taking a clockwise rotation of 240 degrees, pad317of HMCSS stationary unit300is aligned with high speed pad414of HMCSS rotary unit400and high speed pad301HMCSS stationary unit is aligned with pad407of HMCSS rotary unit400so that an electrical connection is established between high speed pad317and high speed pad301. Although each 40 degree clockwise incremental rotation of HMCSS rotary unit400establishes a connection between one of inner high speed pads311-319to outer high speed pad301, an electrical connection is also established between the remaining high speed pads on inner circle321to the remaining high speed pads on outer circle331. Because outer high speed pads302-309are terminated to loads or impedances, the remaining incoming channels are properly terminated.

Because neither HMCSS stationary unit300nor HMCSS rotary unit400has a high speed pad at the center, alignment pin445can be placed at the center as shown inFIG. 4b. The alignment tolerance is determined by the size and positional tolerances of alignment pin hole446and the alignment pin hole (not shown) in HMCSS rotary unit400. A tolerance of less than10percent 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.

FIG. 4cshows cross-section499of HMCSS rotary unit400. Dielectric layers474and475are sandwiched between metalized ground planes471and472while dielectric layers476and477are sandwiched between metalized ground planes472and473. Pads411and401are electrically coupled to connecting line420by vias491and481, respectively. Note that pads411and401are electrically isolated from ground plane471. Connecting lines422,424are located on dielectric layer475while connecting lines429,427are located on dielectric layer477so that connecting line422may cross over connecting line429and connecting line424may cross over connecting line427. In accordance with the invention, any connecting lines that cross inFIG. 4aare in different dielectric layers.

Furthermore, because no high speed pads are positioned at the center of HMCSS stationary unit300and HMCSS rotary unit400, a differential channel switch configuration may be implemented.FIG. 5shows differential HMCSS stationary unit500andFIG. 6shows differential HMCSS rotary unit600where each high speed pad on HMCSS stationary unit300and HMCSS rotary unit400has been replaced by a pair of pads. On HMCSS stationary unit500inFIG. 5, high speed pad pairs501a,b-509a,breplace high speed pads301-309, respectively, while high speed pad pairs511a,b-519a,breplace high speed pads311-319, respectively. On HMCSS rotary unit600inFIG. 6, high speed pad pairs601a,b-609a,breplace high speed pads401-409, respectively, while high speed pairs611a,b-619a,breplace high speed pads411-419, respectively.

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 toFIGS. 3aand4a.

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 pads301,306and302are electrically coupled to the outgoing channels. By rotating rotary unit400in increments of 120 degrees the three incoming channels may be selected.

In the embodiments in accordance with the invention presented above, the incoming channels have been electrically coupled to high speed pads on inner circles321or521of HMCSS stationary unit300or500, respectively while one or more high speed pads on outer circles331or531of HMCSS stationary unit300or500, 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 circle731of stationary unit700and the outgoing channels are electrically coupled to high speed pads on inner circle721of stationary unit700ofFIG. 7.FIG. 8shows HMCSS rotary unit800with the required connectivity. High speed pads801,803,805,807and809are electrically coupled to high speed pads811,812,813,814and815, respectively. High speed pads802,804,806and808are electrically coupled to high speed pads816,817,818and819, respectively. Table 4 below shows the connectivity for the selection of one incoming channel at a time. High speed pad711is electrically coupled to the outgoing channel.

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 unit400where N=4, 2N+1, pairs of pads are evenly distributed on two circles of different radii, for example, circles421and431. Both high speed pads of a pair, for example high speed pads401and411, may lie on a radial line from the alignment pin hole of the rotary unit, for example, rotary unit400but 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 unit300, has 2N+1 pairs of matching high speed pads. Note that for stationary unit300and rotary unit400, 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 inFIG. 4a, assign j=1 . . . 9 to high speed pads401. . .409, respectively and assign k=1 . . . 9 to high speed pads411. . .419. Hence, inFIG. 4a, taking j=2 which corresponds to high speed pad402, high speed pad402is electrically coupled to k=3 which corresponds to high speed pad413.

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.

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.

FIG. 9is a top view of evaluation board900for testing a device under test such as highly parallel optoelectronic module950, for example a receiver or transmitter, in accordance with the invention. HMCSS units901,902,903and904are electrically coupled to optoelectronic module950using input lines910. One or more output lines971a-(n),972a-(n),973a-(n) and974a-(n) provide one or more channels from HMCSS units901,902,903and904, respectively, to evaluation equipment940. In accordance with the invention, multiple channels may be simultaneously sampled from each HMCSS unit by evaluation equipment940while allowing rapid switching between channel configurations.

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.