Abstract:
The method relates to assembling modules for an integrated circuit comprising at least a plurality of modules. The method provides for the formation of at least one module architecture which comprises a plurality of modules and is aligned along one dimension of such modules. The invention also concerns an integrated circuit and a stacked module architecture obtained with the inventive assembling method.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method of assembling modules to form a complex integrated circuit. The invention also relates to an integrated circuit and a module architecture of the stack type. The invention relates in particular, but not exclusively, to a method of assembling modules to form an integrated circuit, and the description which follows makes reference to this field of application for convenience of illustration. 
     BACKGROUND OF THE INVENTION 
     High-complexity integrated circuits, such as a microprocessor integrated in a single chip, for example, are known to include a plurality of sub-circuits, commonly termed modules, which are interfaced by suitable electrical connections carrying system signals. These signals may either be data or control signals which are transmitted under management by a supervisory module, such as a CPU. 
     Each of the modules included in a single integrated circuit is intended to implement a specific function. For example, certain modules may function as analog-to-digital converters, or serial circuits, or logic units, etc. An individual module contains an interface circuit enabling it to communicate with other modules. 
     FIG. 1 shows schematically a portion of a final integrated circuit CIF comprising four modules and being assembled in a conventional manner. In this example, the final integrated circuit CIF portion comprises first  1 , second  2 , third  3  and fourth  4  modules, respectively designated LOGICA — 1, LOGICA — 2, LOGICA — 3 and LOGICA — 4. These four modules have first IF 1 , second IF 2 , third IF 3  and fourth IF 4  interface circuits, respectively, which are respectively designated INTERFACCIA — 1, INTERFACCIA — 2, INTERFACCIA — 3 and INTERFACCIA — 4. 
     It should be noted that the modules in an integrated circuit may come in two general categories: simple modules, which are characterized by having a small number of transistors and a simple interface circuit (the modules  2 ,  3  and  4  in the example of FIG.  1 ); and complex modules, which are characterized by having a large number of transistors and either a simple or complex interface circuit (such as module  1  in the example of FIG.  1 ). 
     When formed on a semiconductor, the layout of each of these modules, whether simple or complex, is usually given an aspect ratio, or length-to-width layout ratio, aimed at producing the densest possible integrated circuit. The different modules are then assembled, either manually or automatically, into the final integrated circuit CIF portion. 
     The schematic presentation of FIG. 1 brings to light some limitations of this conventional assembly method, as specified below. 
     1. A high silicon area requirement, for interfacing the individual modules. The final integrated circuit CIF portion of FIG. 1 includes a number of interface circuits equal to the number of modules, and a complicated pattern of buses  5  must be provided for supplying these interface circuits IF 1 , IF 2 , IF 3  and IF 4 . 
     2. An intensification of the capacitance driven from a common system bus  8 , connected to the complicated pattern of buses  5  and to additional connection buses  6  and  7 , resulting in the speed of the final integrated circuit CIF portion being slowed. 
     3. More complicated assembling of the individual modules  1 ,  2 ,  3  and  4 , resulting in lengthened times for developing the final integrated circuit CIF. 
     An alternative approach would be to make all modules, both simple and complex, with the same length, so as to simplify the assembling procedure. However, even this alternative approach has a serious drawback. In fact, the modules it produces would not be individually optimized, while a large area would be occupied by internal connections commonly known as the connection paths. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing background, it is therefore an object of the present invention to provide a method of assembling modules into an integrated circuit, which has such structural and functional features as to overcome the limitations of prior assembling methods, especially with regard to the silicon area requirement. 
     The present invention is directed to creating module architectures aligned along one dimension, specifically architectures of simple modules having an individually optimized aspect ratio to produce a dense final integrated circuit, having the same width along a direction X, and being aligned in their length direction. Thus, a more efficient aspect ratio is obtained in the respect of both the individual simple modules and the final integrated circuit. 
     The present invention is also directed to a method as previously indicated of assembling modules to form a complex integrated circuit including a plurality of such modules, which method is characterized in that it provides a module architecture which is aligned along one dimension of the modules. The integrated circuit, comprising at least a plurality of modules, preferably comprises at least one portion constructed as a module architecture aligned along one dimension of the modules. 
     The module architecture, comprising a plurality of modules and being adapted for introduction into a complex integrated circuit, is characterized by the plurality of modules being aligned along one module dimension. The module architecture is further characterized in that it comprises a common interface circuit combining all the characteristics of individual interface circuits of the individual modules. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the method, integrated circuit, and module architecture according to the invention will be apparent from the following description of embodiments thereof, given by way of non-limitative examples with reference to the accompanying drawings. In the drawings: 
     FIG. 1 shows schematically an integrated circuit portion as obtained by an assembling method according to the prior art; 
     FIG. 2 shows schematically an aligned architecture of modules, specifically simple modules, according to this invention; 
     FIG. 3 shows schematically the principle of consolidating interface circuits for aligned module architectures according to the invention; 
     FIG. 4 shows the aligned module architecture of FIG. 3 in greater detail; and 
     FIG. 5 shows schematically an integrated circuit as obtained by the assembling method of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The method of assembling modules for an integrated circuit, according to the invention, provides a plurality of module architectures. In particular, the architectures are aligned along a preferred dimension of the modules, and each architecture comprises a plurality of simple modules. It will be appreciated by the skilled person in the art that the problem to be solved by this invention concerns the optimum arrangement of modules on a two-dimensional plane, wherein the overall width and length of the circuit are referenced X and Y. With the two-dimensional plane shown in the figures taken as a reference, and to make the description consistent with such reference, what is normally the length Y of the module will be termed its “height” hereinafter. Based on the above assumption, the alignment of the modules along their length will be referred to as a “stacked arrangement”, and the resulting architecture as a “stacked architecture”, hereinafter. 
     In particular, a stacked architecture of simple modules is generally shown schematically at  9  in FIG.  2 . The stacked architecture  9  of this invention is advantageously assembled without introducing individual interface circuits. A common interface circuit  10  is provided instead, which combines all the characteristics of the individual interface circuits provided in the prior art for the individual simple modules. The consolidating principle of such interface circuits is illustrated schematically in FIG. 3. A stacked architecture  11  thus formed has a height Y which is preset originally at the designing stage of the integrated circuit. 
     Advantageously in this invention, the common interface circuit  10  involves only a trivial increase in the silicon area occupied. This is so especially when compared to the overall saving in silicon area brought about by the use of stacked module architectures, and which saving is to be ascribed to the presence of a single interface circuit. 
     Either of two assembling procedures, according to whether a so-called semi-custom or full-custom design is involved, can be adopted. With a semi-custom design, automatic layout tools are used. In this case, once the common interface circuit  10  is defined, a stacked architecture  11  can be created automatically which has a layout height Y and includes the logics of a number of simple modules, and the common interface circuit  10 . In particular, the stacked architecture  11  has system terminals TS provided at the bottom of the architecture for convenient connection to a system bus  13  via a bus  12 . 
     With a full-custom design, the layouts of the modules and the final integrated circuit are instead defined manually. In this case, it is necessary to abide by certain designing rules, for best utilization of the inventive assembling method, as specified below. 
     1. The layout of each simple module should have the same width x. 
     2. The data transfer logic, commonly referred to as the data path, should be separated, even physically, from the random logic. In particular, the width of such logics should be the same in each simple module, for greater ease of “stacking” the modules. This design stage can be simplified by the use of a layout library, easily selected from those available commercially. 
     3. The layout of each simple module should contain all the signals generated by the common interface circuit  10 , and fully or partly utilized by the module for supplying the other modules included in the same stacked architecture  11 . 
     In the light of the foregoing, it is necessary for the system terminals TAi, TBi, arranged to transfer the signals generated by the common interface circuit  10 , to be located at the same coordinates in the upper and lower portions of the layout of each simple module in the stacked architecture  11  and of the layout of the common interface circuit  10 . 
     FIG. 4 shows in greater detail the stacked architecture  11  of FIG. 2 as produced in compliance with the above rules. The stacked architecture  11  comprises first  14 , second  15  and third  16  modules (in particular simple modules), and the common interface circuit  10  connected to the system bus  13 . In particular, the separation of the Random logic circuits Ai from the Data Path logic circuits Bi is brought out. These are interconnected by internal buses  17 ,  18  and  19  at each of the modules  14 ,  15  and  16  (horizontal connection) and have corresponding system terminals TA 14 , TA 15 , TA 16  and TB 14 , TB 15 , TB 16 , for connection to the common interface circuit  10  (vertical connection), generated by the same from two final system terminals TA and TB of the system bus  13 . Advantageously in this invention, the Random Ai and Data Path Bi logic circuits of the various modules  14 ,  15 ,  16  have corresponding widths for an architecture  11  rightly stacked. 
     Lastly, FIG. 5 shows schematically a final integrated circuit, generally indicated at  20 , which comprises a complex module  21  provided with an interface circuit  22  and a stacked architecture  11  of simple modules, obtained by the method of this invention and having a common interface circuit  10 . In particular, it should be noted that, connected to the system bus  13 , are now only two bi-directional buses  23  and  24 , respectively, for transferring signals between interface circuits  22  and  10  of the complex module  21  and the stacked architecture  11 . In this way, a complicated bus pattern, such as the supplying path  5  to the modules  3  and  4  of the final integrated circuit CIF provided conventionally as shown schematically in FIG. 1, is no longer required. 
     To summarize, this method of assembling modules to form an integrated circuit has the following advantages: 
     1) the silicon area occupied by the final integrated circuit can be optimized by the use of a single interface circuit; 
     2) the silicon area occupied by the final integrated circuit can be optimized by the use of a system bus limited to a single direction; in particular, no complicated bus pattern for supplying the various simple modules in the final integrated circuit is required; 
     3) the capacitive load connected to the common system bus can be reduced, thereby improving the speed of the final integrated circuit as a whole; and 
     4) the assembling time for the individual modules or module architecture in the final integrated circuit can be shortened.