Abstract:
A rectangular termination ring for a power distribution mesh is placed on the upper two layers of an integrated circuit and may be placed over some I/O circuitry. The strapping connecting the bonding pads to the termination ring are placed on upper levels of the integrated circuit, minimizing the via requirements and freeing space for additional circuitry. Further, the termination ring may be adapted to work in conjunction with L-shaped, as well as other power distribution meshes.

Description:
BACKGROUND OF THE INVENTION 
     a. Field of the Invention 
     The present invention pertains to wiring within integrated circuits and specifically to power distribution circuits within integrated circuits. 
     b. Description of the Background 
     An integrated circuit (IC) typically includes two or more layers dedicated to power distribution. The power distribution layers may have various arrangements for grossly transmitting current throughout the IC to the various cells that require power. 
     Various power distribution meshes are known in the art. Examples are U.S. Pat. No. 6,346,721 entitled “Integrated Circuit Having Radially Varying Power Bus Grid Architecture” by Schultz, U.S. Pat. No. 6,111,310 entitled “Radially Increasing Core Power Bus Grid Architecture” by Schultz, copending and commonly assigned U.S. patent application Ser. No. 09/948,190 entitled “Power Redistribution Bus for a Wire Bonded Integrated Circuit” by Schultz, et al., filed Sep. 7, 2001, copending and commonly assigned U.S. patent application Ser. No. 09/968,286 entitled “Die Power Distribution Bus” by Ali, et al, filed Oct. 1, 2001, all of which are hereby specifically incorporated herein by reference for all they disclose and teach. 
     In general, these distribution meshes address the transmittal of current to the inside portions of a die. However, there is need in the art for an improved termination ring that provides the distributed current to the periphery of the mesh. 
     One type of IC is known as an Application Specific Integrated Circuit (ASIC). The design of ASICs comprises many pre-designed circuits that are connected to create the necessary logic and circuitry for the specific task. One type of pre-designed circuit is an I/O circuit. The I/O circuit is the circuitry that is close to the bonding pad. Recent designs have increased the size of the I/O circuits, known as ‘tall I/O’, referring to the length of the rectangular shape of the I/O circuits. 
     In older ASIC designs, it had been commonplace to place a termination ring for a power distribution mesh inside of the I/O circuits for a number of reasons. However, as the size of some of the I/O circuits has grown, it has become impractical to adhere to this design rule. As such, rectilinear termination rings have been designed to avoid the tall I/O circuits by changing shape to meander around the tall I/O. These types of termination rings may occupy more space on the die than necessary and thus may cause the die to be larger to accommodate the larger termination ring. Further, as the I/O circuits become taller, the termination ring is placed further inward, causing a longer distance for the power to travel from a bonding pad to the termination ring. The increased distance causes the trace or strap from the bonding pad to the termination ring to become wider and may increase the number of bonding pads required for transmitting sufficient current to the termination ring. In some cases, the number of bonding pads required for the specific application may determine the size of the die. In such cases, increases in the number of bonding pads may increase the die size, adding to the cost of the resultant IC. 
     The design convention has been that I/O circuits have been placed in lower metal layers of the IC. Further, the traces from the bonding pads to the termination ring have been commonly incorporated into special I/O circuits known as power I/O. The traces or straps that transfer the current from the outside of the die to the termination ring within the die require vias to transfer the current between layers. The size and depth of the vias necessarily take up space within the die that is otherwise useable. 
     It would therefore be advantageous to provide a system and method for a power termination ring in an integrated circuit that requires a minimum of space on the periphery of the die. It would further be advantageous to provide a termination ring that accommodated tall I/O circuits as well as occupied a minimum amount of space within and integrated circuit so that additional circuitry may be placed in an IC without increasing the size of the IC. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages and limitations of the prior art by providing a system and method for placing a termination ring and straps in the top two layers of an integrated circuit. The termination ring may be placed over I/O circuits so that the distance between a bonding pad and the termination ring is minimized. Further, the termination ring architecture is adapted to L-shaped power distribution meshes as well as other power distribution meshes. 
     The present invention may therefore comprise a power distribution system for an integrated circuit die comprising: a first electrically conductive ring about the periphery of the die wherein the first ring is located above at least one I/O circuit; a second electrically conductive ring substantially inwardly offset from the first ring and positioned on the layer below the layer of the first ring; a first connection from the first ring to a first bonding pad wherein at least a continuous electrical connection is located in the same layer as the first ring; and a second connection from the second ring to a second bonding pad wherein at least a continuous electrical connection is located in the same layer as the second ring. 
     The present invention may further comprise an integrated circuit with a power distribution system comprising: a first electrically conductive ring about the periphery of the die of the integrated circuit wherein the first ring is located above at least one I/O circuit; a second electrically conductive ring substantially inwardly offset from the first ring and positioned on the layer below the layer of the first ring; a first connection from the first ring to a first bonding pad wherein at least a continuous electrical connection is located in the same layer as the first ring; and a second connection from the second ring to a second bonding pad wherein at least a continuous electrical connection is located in the same layer as the second ring. 
     The present invention may further comprise an integrated circuit with a power distribution system comprising: a first electrically conductive power distribution means about the periphery of the die of the integrated circuit wherein the first electrically conductive power distribution means is located above at least one I/O circuit; a second electrically conductive power distribution means substantially inwardly offset from the first electrically conductive power distribution means and positioned on the layer below the layer of the first electrically conductive power distribution means; a first connection means from the first electrically conductive power distribution means to a first off-die connection means wherein at least a continuous electrical connection is maintained in the same layer as the first electrically conductive power distribution means; and a second connection means from the second electrically conductive power distribution means to a second off-die connection means wherein at least a continuous electrical connection is maintained in the same layer as the second electrically conductive power distribution means. 
     The advantages of the present invention are that a minimum of space within an integrated circuit is used to transfer current from the bonding pads to a power distribution mesh. Certain critical spaces, such as the area around the periphery of the integrated circuit die and the area from the bonding pads to the termination ring are minimized so that the size of the die may be minimized and additional circuitry may be placed in the integrated circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, 
     FIG. 1 is an illustration of an embodiment of the present invention wherein an integrated circuit die has an outer distribution ring, and inner distribution ring, and an optional third distribution ring. 
     FIG. 2 is an illustration of an embodiment of the present invention wherein an L-shaped mesh is incorporated with the distribution rings. 
     FIG. 3 is an illustration of an embodiment of the present invention wherein an V-shaped mesh is incorporated with the distribution rings. 
     FIG. 4 is a three dimensional representation of an embodiment of a power distribution system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an embodiment  100  of the present invention wherein an integrated circuit die  102  has an outer distribution ring  104 , and inner distribution ring  106 , and an optional third distribution ring  107 . The three rings  104 ,  106 , and  107  are positioned over several tall I/O circuits  108 . The bonding pads  110  connect to the rings  104  and  107  through the strap  118 . 
     The embodiment  100  takes the current provided on the bonding pads  110 ,  112 ,  114 , and  116  and distributes the current around the periphery of the die  102 . The use of a peripheral ring to distribute current allows various meshes known in the art to transfer current throughout the die. 
     In the present embodiment, the outer ring  104  may be placed on the top layer of the die, where the metal traces may be thicker than on other layers. The inner rings  106  and  107  may be placed on the next layer below that of the outer ring  104 . In other embodiments, the outer ring  104  may be on another layer other than the topmost layer. In still other embodiments, the inner rings  106  and  107  may be on the layer above the outer layer  104 . 
     Some mesh designs have a primary layer. For example, an L-shaped mesh has a single layer in which most of the power distribution traces reside. Such a layer would be the primary layer of the mesh. Other mesh designs may require two or more planes, and may not have a singular primary plane. In embodiments with a single primary layer, the primary layer of the mesh will generally be on the same layer as the outermost ring. 
     The straps  118  may be on the same layers as the respective rings to which they are attached. Other traces may exist below or above the layers on which the straps exist. However, the primary current path may be within the layer of the respective distribution ring. For example, the straps associated with bonding pads  110  and  114  may be in the same layer as the outer ring  104 . 
     In some embodiments, the straps may comprise traces on a plurality of layers. For example, a strap  118  may comprise a trace on the top layer and a substantially identical trace on the layer below. A series of vias may be present to connect the top trace with the bottom trace, effectively making a thicker connection to handle increased currents with less resistance. 
     The embodiment  100  shows two bonding pads associated with each distribution ring. In different embodiments, those skilled in the art will appreciate that more or less bonding pads and straps may be required depending on the amount of current to be supplied to the mesh. 
     The outer ring  104  is shown placed above the tall I/O circuits  108 . The placement of the rings  104 ,  106 , and  107  over the I/O circuits  108  means that the rings  104 ,  106 , and  107  may be further toward the edges of the die  102 . By moving the current distribution rings  104 ,  106 , and  107  outward, the distance between the bonding pad  110  and the ring  104  is minimized. This means that the width and thickness of the straps may be lessened because the straps induce less resistance when they are shorter in length. In some designs, moving the rings outward may eliminate the need for one or more straps, freeing up some space for an additional I/O circuit or causing the integrated circuit to be designed on a smaller die. 
     The third ring  107  is an optional ring. In some embodiments, the third ring  107  may not be present, and the outer ring  104  may be sufficient to carry the current load. 
     FIG. 2 illustrates an embodiment  200  of the present invention wherein an L-shaped mesh is shown. The integrated circuit die  202  has an outer distribution ring  204 , an inner distribution ring  206 , and an optional third ring  208 . As with embodiment  100 , bonding pads  210 ,  212 ,  214 , and  216  are connected to the various rings. The traces  218  and  219  represent traces connected to the outer distribution ring  204 . The trace  220  is likewise connected to the inner ring  206 . The layer for the mesh traces  218  and  220  may be the same layer as the outermost ring  204 . The trace  220  may be connected to the inner ring  206  with vias  220  and  224 . 
     In the embodiment  200 , the primary layer of the mesh is the layer in which the traces  218  and  220  reside. The primary layer is also the layer in which the outer ring  204  resides. 
     The interior of the third ring  208  is free for other trace routing. In some embodiments, the area within the third ring  208  may be necessary for the normal connections amongst the circuitry of the integrated circuit. As the power distribution design frees up more area, more functionality may be incorporated into the integrated circuit while maintaining the same die size. 
     FIG. 3 illustrates an embodiment  300  of a power distribution system utilizing a V-shaped mesh. The integrated circuit die  302  contains an outer ring  304 , an inner ring  306 , and an optional third ring  308  in a similar fashion to embodiments  100  and  200  discussed above. The bonding pads  310  are similar to those of embodiments  100  and  200 . 
     The trace  312  is connected to the outer ring  304  and the third ring  308  by vias  314 ,  316 ,  318 , and  320 . Trace  322  is connected to the inner ring  306  by vias  324  and  326 . The other traces shown are alternatively connected to the inner ring  304  and the outer ring  306  to distribute power throughout the chip. 
     Embodiment  300  illustrates how different mesh designs may be used with multiple distribution rings. Those skilled in the art may envision many different mesh designs that may be similarly incorporated into the present multiple ring design. 
     FIG. 4 illustrates a three dimensional representation of an embodiment  400  of a power distribution system. The outer ring  402  is located on an upper level whereas the inner ring  404  and optional third ring  406  are located on a lower level, typically the next layer below that of the outer ring  402 . The rings  402 ,  404 , and  406  are located over I/O circuitry that is represented by boxes  408  and  410 . 
     The pad strap  412  connects a bonding pad (not shown) to the inner ring  404 . The pad strap  412  may comprise an upper trace  414  with vias  416  to form a sandwich capable of carrying more current than one trace  412  alone. Pad strap  416  connects from a bonding pad (not shown) to the inner trace  402  and is similarly constructed. The strap  416  comprises a lower trace  418  and vias  420  to form a sandwich. 
     The mesh connection  422  is connected to the inner ring  404  through via  424 . The mesh connection  426  is connected to the outer ring  402  and the inner ring  408  through via  428 . 
     The present illustration is schematic in nature, but was chosen to best illustrate the connections of the various elements. In practice, the physical shape and proximity of the components may be substantially different while maintaining within the spirit and intent of the present invention. 
     The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.