Configurable Computing Array Implementing Math Functions with Multiple Input Variables

Abstract

To implement a math function with multiple input variables, a configurable computing array comprises at least an array of configurable interconnects, an array of configurable logic elements, and an array of configurable computing elements. Each configurable computing element comprises at least a memory for storing a look-up table (LUT) for a math function with a single input variable.

Description

BACKGROUND

1. Technical Field of the Invention

The present invention relates to the field of integrated circuit, and more particularly to configurable gate array.

2. Prior Art

A configurable gate array is a semi-custom integrated circuit designed to be configured by a customer after manufacturing. U.S. Pat. No. 4,870,302 issued to Freeman on Sep. 26, 1989 (hereinafter referred to as Freeman) discloses a configurable gate array. It contains an array of configurable logic elements (also known as configurable logic blocks) and a hierarchy of configurable interconnects (also known as programmable interconnects) that allow the configurable logic elements to be wired together. Each configurable logic element in the array is in itself capable of realizing any one of a plurality of logic functions (e.g. shift, logic NOT, logic AND, logic OR, logic NOR, logic NAND, logic XOR, arithmetic addition “+”, arithmetic subtraction “−”, etc.) depending upon a first configuration signal. Each configurable interconnect can selectively couple or de-couple interconnect lines depending upon a second configuration signal.

Complex math functions are widely used in various applications. A complex math function has multiple independent variables and can be expressed as a combination of basic math functions. On the other hand, a basic function has a single or few independent variables. Exemplary basic functions include transcendental functions, such as exponential function (exp), logarithmic function (log), trigonometric functions (sin, cos, tan, atan) and others. To meet the speed requirements, many high-performance applications require that these complex math functions be implemented in hardware. In conventional configurable gate arrays, complex math functions are implemented in fixed computing elements, which are portions of hard blocks and not configurable, i.e. the circuits implementing these complex math functions are fixedly connected and are not subject to change by programming. Apparently, fixed computing elements would limit further applications of the configurable gate array. To overcome this difficulty, the present invention expands the original concept of the configurable gate array by making the fixed computing elements configurable. In other words, besides configurable logic elements, the configurable gate array comprises configurable computing elements, which can realize any one of a plurality of math functions.

OBJECTS AND ADVANTAGES

It is a principle object of the present invention to extend the applications of a configurable gate array to the field of complex math computation.

It is a further object of the present invention to provide a configurable computing array where not only logic functions can be customized, but also math functions.

It is a further object of the present invention to provide a configurable computing array with more computing power.

It is a further object of the present invention to provide a configurable computing array with smaller die size and lower die cost.

In accordance with these and other objects of the present invention, the present invention discloses a configurable computing array comprising three-dimensional writable memory (3D-W).

SUMMARY OF THE INVENTION

The present invention discloses a configurable computing array comprising three-dimensional writable memory (3D-W). It is a monolithic integrated circuit comprising an array of configurable computing elements, an array of configurable logic elements and an array of configurable interconnects. Each configurable computing element comprises at least a three-dimensional writable memory (3D-W) array, which is electrically programmable and can be loaded with a look-up table (LUT) for a math function. The usage cycle of the configurable computing element comprises two stages: a configuration stage and a computation stage. In the configuration stage, the LUT for a desired math function is loaded into the 3D-W array. In the computation stage, a selected portion of the LUT for the desired math function is read out from the 3D-W array. For a re-programmable 3D-W, a configurable computing element can be re-configured to realize different math functions.

Besides configurable computing elements, the preferred configurable computing array further comprises configurable logic elements and configurable interconnects. During operation, a complex math function is first decomposed into a combination of basic math functions. Each basic math function is realized by programming the associated configurable computing element. The complex math function is then realized by programming the appropriate configurable logic elements and configurable interconnects.

Using the 3D-W for configurable computing element offers many advantages. First of all, because it has a large storage density, 3D-W can be used to store a large LUT to provide a better precision for a math function; or, more LUTs for more math functions. Being electrically programmable, the math functions that can be realized by a 3D-W array are essentially boundless. Secondly, because they can be vertically stacked, the 3D-W arrays belonging to different configurable computing elements can be stacked together within a single 3D-W block. This would save substantial die area. Thirdly, because the 3D-W array does not occupy any substrate area, the configurable logic elements and/or the configurable interconnects can be formed underneath the 3D-W arrays. This would further save die area.

Accordingly, the present invention discloses a configurable computing array, comprising: at least a configurable logic element formed on a semiconductor substrate, wherein said configurable logic element selectively realizes a logic function from a logic library; at least a configurable computing element, wherein said configurable computing element comprises a first three-dimensional writable memory (3D-W) array stacked above said semiconductor substrate, said first 3D-W array stores at least a first portion of a first look-up table (LUT) for a first math function; wherein said configurable logic element and said configurable computing element are electrically coupled.

The present invention further discloses another configurable computing array, comprising: at least a configurable interconnect formed on a semiconductor substrate, wherein said configurable interconnect selectively realizes an interconnect from an interconnect library; at least a configurable computing element, wherein said configurable computing element comprises a first three-dimensional writable memory (3D-W) array stacked above said semiconductor substrate, said first 3D-W array stores at least a first portion of a first look-up table (LUT) for a first math function; wherein said configurable interconnect and said configurable computing element are electrically coupled.

The present invention further discloses yet another configurable computing array, comprising: an array of configurable computing elements including a configurable computing element, wherein said configurable computing element stores at least a portion of a look-up table (LUT) for a math function; an array of configurable logic elements including a configurable logic element, wherein said configurable logic element selectively realizes a logic function from a logic library; an array of configurable interconnects including a configurable interconnect, wherein said array of configurable interconnects selectively realizes an interconnect from an interconnect library; wherein said configurable computing array realizes a math function by programming said array of configurable computing elements, said array of configurable logic elements and said array of configurable interconnects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a three-dimensional writable memory (3D-W);

FIG. 2 discloses a symbol for a preferred configurable computing element;

FIG. 3 is a substrate layout view of a preferred configurable computing element;

FIG. 4 discloses two usage cycles of a preferred re-configurable computing element;

FIG. 5A shows an interconnect library supported by a preferred configurable interconnect; FIG. 5B shows a logic library supported by a preferred configurable logic element;

FIG. 6 is a circuit block diagram of a first preferred configurable computing array;

FIG. 7 is a substrate layout view of a first implementation of the first preferred configurable computing array;

FIG. 8A is a cross-sectional view of a second implementation of the first preferred configurable computing array; FIG. 8B is its substrate layout view;

FIG. 9 shows an instantiation of the first preferred configurable computing array implementing a complex math function;

FIG. 10 is a circuit block diagram of a second preferred configurable computing array;

FIGS. 11A-11B show two instantiations of the second preferred configurable computing array.

It should be noted that all the drawings are schematic and not drawn to scale. Relative dimensions and proportions of parts of the device structures in the figures have been shown exaggerated or reduced in size for the sake of clarity and convenience in the drawings. The same reference symbols are generally used to refer to corresponding or similar features in the different embodiments. In the present invention, the terms “write”, “program” and “configure” are used interchangeably. The phrase “a circuit is formed on a substrate” means that the active elements (e.g. diodes/transistors) of the circuit are formed on the substrate, i.e. at least a portion of the active element (e.g. channel/source/drain) is formed in the substrate. The phrase “a circuit is formed above a substrate” means that the active elements (e.g. diodes/transistors) of the circuit are formed above the substrate, i.e. no portion of the active element is formed in the substrate. The symbol “/” means a relationship of “and” or “or”.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Those of ordinary skills in the art will realize that the following description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons from an examination of the within disclosure.

Referring now to FIG. 1, a preferred three-dimensional writable memory (3D-W) 10 is shown. 3D-W is a type of three-dimensional memory (3D-M) whose memory cells are electrically programmable. Based on the number of programming allowed, a 3D-W can be categorized into three-dimensional one-time-programmable memory (3D-OTP) and three-dimensional multiple-time-programmable memory (3D-MTP). Types of the 3D-MTP cell include flash-memory cell, memristor, resistive random-access memory (RRAM or ReRAM) cell, phase-change memory (PCM) cell, programmable metallization cell (PMC), conductive-bridging random-access memory (CBRAM) cell, and the like.

Based on the orientation of the memory cells, the 3D-W can be categorized into horizontal 3D-W (3D-W_H) and vertical 3D-W (3D-W_V). In a 3D-W_H, all address lines are horizontal and the memory cells form a plurality of horizontal memory levels which are vertically stacked above each other. A well-known 3D-W_H is 3D-XPoint. In a 3D-W_V, at least one set of the address lines are vertical and the memory cells form a plurality of vertical memory strings which are placed side-by-side on/above the substrate. A well-known 3D-W_V is 3D-NAND. In general, the 3D-W_H (e.g. 3D-XPoint) is faster, while the 3D-W_V (e.g. 3D-NAND) is denser.

The preferred 3D-W 10 in FIG. 1 comprises a substrate circuit 0K formed on the substrate 0. A first memory level 16A is stacked above the substrate circuit 0K, with a second memory level 16B stacked above the first memory level 16A. The substrate circuit 0K includes the peripheral circuits of the memory levels 16A, 16B. It comprises transistors 0t and the associated interconnect 0i (including 0M1-0M3). Each of the memory levels (e.g. 16A, 16B) comprises a plurality of first address-lines (i.e. y-lines, e.g. 2a, 4a), a plurality of second address-lines (i.e. x-lines, e.g. 1a, 3a) and a plurality of 3D-W cells (e.g. 1aa, 2aa). The first and second memory levels 16A, 16B are coupled to the substrate circuit OK through contact vias 1av, 3av, respectively.

In a 3D-W, each memory level comprises at least a 3D-W array. A 3D-W array is a collection of 3D-W cells in a memory level that share at least one address-line. Within a single 3D-W array, all address-lines are continuous; between adjacent 3D-W arrays, address-lines are not continuous. On the other hand, a 3D-W die comprises a plurality of 3D-W blocks. Each 3D-W block includes all memory levels in a 3D-W and its topmost memory level only comprises a single 3D-W array, whose projection on the substrate defines the boundary of the 3D-W block.

In this preferred embodiment, the 3D-W cell 1aa comprises a programmable layer 12 and a diode layer 14. The programmable layer 12 could be an OTP layer (e.g. an antifuse layer, used for the 3D-OTP) or an MTP layer (e.g. a phase-change layer, used for the 3D-MTP). The diode layer 14 (also referred to as selector layer or other names) is broadly interpreted as any layer whose resistance at the read voltage is substantially lower than the case when the applied voltage has a magnitude smaller than or polarity opposite to that of the read voltage. The diode could be a semiconductor diode (e.g. p-i-n silicon diode), or a metal-oxide (e.g. TiO₂) diode. In certain embodiments, the programmable layer 12 and the diode layer 14 are merged into a single layer.

Referring now to FIG. 2, a symbol for a preferred configurable computing element 100 is shown. The input port IN includes input data 115, the output port OUT includes output data 135, and the configuration port CFG includes at least a configuration signal 125. When the configuration signal 125 is “write”, the look-up table (LUT) for a desired math function is loaded into the configurable computing element 100; when the configuration signal 125 is “read”, the functional/derivative/other value of the desired math function is read out from the LUT.

FIG. 3 discloses a preferred configurable computing element 100. This figure is a layout view of its substrate circuit 0K. Because the 3D-W arrays are stacked above the substrate 0K and not located in the substrate 0, their projections on the substrate 0, not the 3D-W arrays themselves, are shown in the areas enclosed by dash lines. In this preferred embodiment, the LUT is stored in at least a 3D-W array 110. The substrate circuit 0K includes the X decoder 15, Y decoder (including read-out circuit) 17 and Z decoder 19 for the 3D-W array 110.

Referring now to FIG. 4, two usage cycles 620, 660 of a preferred re-configurable computing element 100 are shown. For the re-configurable computing element 100, the 3D-W array 110 is re-programmable. The first usage cycle 620 includes two stages: a configuration stage 610 and a computation stage 630. In the configuration stage 610, the LUT for a first desired math function is loaded into the 3D-W array 110. In the computation stage 630, a selected portion of the LUT for the first desired math function is read out from the 3D-W array 110. Being re-programmable, the re-configurable computing element 100 can realize different math functions during different usage cycles 620, 660. During the second usage cycle 660 (including two stages 650, 670), the LUT for a second desired math function is loaded and later read out. The re-configurable computing element 100 is particularly suitable for single-instruction-multiple-data (SIMD)-type of data processing. Once the LUTs are loaded into the 3D-W arrays 110 in the configuration stage, a large amount of data can be fed into the re-configurable computing element 100 and processed at high speed. SIMD has many applications, e.g. vector processing in image processing, massively parallel processing in scientific computing.

Referring now to FIGS. 5A-5B, an interconnect library and a logic library are shown. FIG. 5A shows the interconnect library supported by a preferred configurable interconnect 300. An interconnect library is a collection of all interconnects supported by a configurable interconnect. This interconnect library includes the followings: a) the interconnects 302/304 are coupled, the interconnects 306/308 are coupled, but 302/304 are not connected with 306/308; b) the interconnects 302/304/306/308 are all coupled; c) the interconnects 306/308 are coupled, but the interconnects 302, 304 are not coupled, neither are 302, 304 connected with 306/308; d) the interconnects 302/304 are coupled, but the interconnects 306, 308 are not coupled, neither are 306, 308 connected with 302/304; e) interconnects 302, 304, 306, 308 are not coupled at all. As used herein, the symbol “/” between two interconnects means that these two interconnects are coupled, while the symbol “,” between two interconnects means that these two interconnects are not coupled. More details on the configurable interconnects are disclosed in Freeman.

FIG. 5B shows the logic library supported by a preferred configurable logic element 200. A logic library is a collection of all logic functions supported by a configurable logic element. In this preferred embodiment, the inputs A and B include input data 210, 200, and the output C includes the output data 230. The logic library includes the following logic functions: C=A, NOT A, A shift by n bits, AND(A,B), OR(A,B), NAND(A,B), NOR(A,B), XOR(A,B), A+B, A−B. To facilitate pipelining, the configurable logic element 200 may comprise sequential logic such as flip-flops and registers. More details on the configurable logic elements are disclosed in Freeman.

Referring now to FIG. 6, a first preferred configurable computing array 400 is disclosed. It comprises first and second configurable slices 400A, 400B. Each configurable slice (e.g. 400A) comprises a first array of configurable computing elements (e.g. 100AA-100AD) and a second array of configurable logic elements (e.g. 200AA-200AD). A configurable channel 320 is placed between the first array of configurable computing elements (e.g. 100AA-100AD) and the second array of configurable logic elements (e.g. 200AA-200AD). The configurable channels 310, 330, 350 are also placed between different configurable slices 300A, 300B. The configurable channels 310-350 comprise an array of configurable interconnects 300. For those skilled in the art, besides configurable channels, sea-of-gates may also be used.

FIG. 7 shows a first implementation of the first preferred configurable computing array 400 is shown. Because it does not occupy any substrate area, the 3D-W array 110 can be stacked above the configurable logic element 200 and at least partially cover the configurable logic element 200. Similarly, the 3D-W array 110 can be stacked above the configurable interconnect 300 and at least partially cover the configurable interconnect 300. Apparently, this would save die area.

FIGS. 8A-8B show a second implementation of the first preferred configurable computing array 400. This implementation corresponds to the configurable slice 400A of FIG. 6. For the configurable computing elements 100AA-100AD, their 3D-W arrays 110AA-110AD can be vertically stacked in a single 3D-W block. To be more specific, the substrate circuit 0K comprises the configurable logic elements 200AA-200AD; the 3D-W array 110AA for the configurable computing element 100AA (storing the LUT A for a first math function) is placed in the first memory level 16A and stacked above the substrate 0K (along the +Z direction), the 3D-W array 110AB for the configurable computing element 100AB (storing the LUT B for a second math function) is placed in the second memory level 16B and stacked above the 3D-W array 110AA (along the +Z direction), the 3D-W array 110AC for the configurable computing element 100AC (storing the LUT C for a third math function) is placed in the third memory level 16C and stacked above the 3D-W array 110AB (along the +Z direction), and the 3D-W array 110AD for the configurable computing element 100AD (storing the LUT D for a fourth math function) is placed in the fourth memory level 16D and stacked above the 3D-W array 110AC (along the +Z direction). This arrangement becomes more apparent in the substrate layout view of FIG. 8B. The projections of the 3D-W arrays 110AA-110AD (storing the LUTs A-D) overlap each other on the substrate 0. This would save substantial die area and lead to a compact configurable computing array 400.

FIG. 9 discloses an instantiation of the first preferred configurable computing array implementing a complex math function e=a·sin(b)+c·cos(d). The configurable interconnects 300 in the configurable channel 310-350 use the same convention as FIG. 5A: the interconnects with dots mean that the interconnects are connected; the interconnects without dots mean that the interconnects are not connected; a broken interconnect means that two broken sections are disconnected. In this preferred implementation, the configurable computing element 100AA is configured to realize the function log( ), whose result log(a) is sent to a first input of the configurable logic element 200A. The configurable computing element 100AB is configured to realize the function log[sin( )], whose result log[sin(b)] is sent to a second input of the configurable logic element 200A. The configurable logic element 200A is configured to realize arithmetic addition “+”, whose result log(a)+log[sin(b)] is sent the configurable computing element 100BA. The configurable computing element 100BA is configured to realize the function exp( ), whose result exp{log(a)+log[sin(b)]}=a·sin(b) is sent to a first input of the configurable logic element 200BA. Similarly, through proper configurations, the results of the configurable computing elements 100AC, 100AD, the configurable logic elements 200AC, and the configurable computing element 100BC can be sent to a second input of the configurable logic element 200BA. The configurable logic element 200BA is configured to realize arithmetic addition “+”, whose result a·sin(b)+c·cos(d) is sent to the output e. Apparently, by changing its configuration, the configurable computing array 400 can realize other complex math functions.

Referring now to FIG. 10, a second preferred configurable computing array 400 is shown. Besides configurable computing elements 100A, 100B and configurable logic element 200A, this preferred embodiment further comprises a multiplier 500. The configurable channels 360-380 comprise a plurality of configurable interconnects. With the addition of the multiplier 500, the preferred configurable computing array 400 can realize more math functions and its computational power will become more powerful.

FIGS. 11A-11B disclose two instantiations of the second preferred configurable computing array 400. In the instantiation of FIG. 11A, the configurable computing element 100A is configured to realize the function exp(f), while the configurable computing element 100B is configured to realize the function inv(g). The configurable channel 370 is configured in such a way that the outputs of 100A, 100B are fed into the multiplier 500. The final output is then h=exp(f)*inv(g). On the other hand, in the instantiation of FIG. 11B, the configurable computing element 100A is configured to realize the function sin(f), while the configurable computing element 100B is configured to realize the function cos(g). The configurable channel 370 is configured in such a way that the outputs of 100A, 100B are fed into the configurable logic element 200A, which is configured to realize arithmetic addition. The final output is then h=sin(f)+cos(g).

The preferred configurable computing arrays shown in the figures are field-programmable computing array (FPCA). For an FPCA, all manufacturing processes are finished in factory. The function of the FPCA can be electrically defined in the field of use. The concept of FPCA can be extended to mask-programmed computing array (MPCA). For a MPCA, wafers containing the configurable computing elements and the configurable logic elements are prefabricated and stockpiled in factory. However, certain interconnects on these wafers are not fabricated until the function of the MPCA is finally defined.

While illustrative embodiments have been shown and described, it would be apparent to those skilled in the art that many more modifications than that have been mentioned above are possible without departing from the inventive concepts set forth therein. The invention, therefore, is not to be limited except in the spirit of the appended claims.

Claims

1-20. (canceled)

21. A configurable computing array, comprising: at least an array of configurable interconnects including a configurable interconnect for selectively realizing an interconnect from an interconnect library; andat least an array of configurable computing elements including a configurable computing element for realizing a selected one of a plurality of math functions;wherein said configurable computing array realizes a math function with multiple input variables by programming said array of configurable interconnects and said array of configurable computing elements.

22. The configurable computing array according to claim 21, wherein said configurable computing element comprises at least a memory for storing a look-up table (LUT) for said selected math function.

23. The configurable computing array according to claim 22, wherein said memory is a three-dimensional memory.

24. The configurable computing array according to claim 21, wherein said array of configurable computing elements further comprises another configurable computing element for realizing another selected one of said plurality of math functions.

25. The configurable computing array according to claim 21, wherein said array of configurable interconnects and said array of configurable computing elements are disposed on different surfaces.

26. The configurable computing array according to claim 21, further comprising at least an array of configurable logic elements including a configurable logic element for selectively realizing a logic function from a logic library.

27. The configurable computing array according to claim 21, further comprising at least one multiplier.

28. A configurable computing array, comprising: at least an array of configurable interconnects including a configurable interconnect, wherein said configurable interconnect selectively realizes an interconnect from an interconnect library; andat least an array of configurable computing elements including a configurable computing element, wherein said configurable computing element comprises at least a memory for storing a look-up table (LUT) for a math function with a single input variable;wherein said configurable computing array realizes a math function with multiple input variables by programming said array of configurable interconnects and said array of configurable computing elements.

29. The configurable computing array according to claim 28, further comprising at least another memory for storing another LUT for another math function with another single input variable.

30. The configurable computing array according to claim 28, wherein said array of configurable interconnects and said array of configurable computing elements are disposed on different surfaces.

31. The configurable computing array according to claim 28, wherein said memory is a three-dimensional memory.

32. The configurable computing array according to claim 28, further comprising at least an array of configurable logic elements including a configurable logic element, wherein said configurable logic element selectively realizes a logic function from a logic library.

33. The configurable computing array according to claim 28, further comprising at least one multiplier.

34. A configurable computing array, comprising: at least an array of configurable interconnects including a configurable interconnect, wherein said configurable interconnect selectively realizes an interconnect from an interconnect library; andat least an array of configurable computing elements including a configurable computing element, wherein said configurable computing element can be re-configured to realize different math functions;wherein said configurable computing array realizes a math function with multiple input variables by programming said array of configurable interconnects and said array of configurable computing elements.

35. The configurable computing array according to claim 34, wherein said configurable computing element comprises at least a re-programmable memory for storing a look-up table (LUT) for at least a math function.

36. The configurable computing array according to claim 35, wherein said re-programmable memory is loaded with a first LUT for a first math function during a first usage cycle and loaded with a second LUT for a second math function during a second usage cycle.

37. The configurable computing array according to claim 35, wherein said re-programmable memory is a three-dimensional writable memory.

38. The configurable computing array according to claim 34, wherein said array of configurable interconnects and said array of configurable computing elements are disposed on different surfaces.

39. The configurable computing array according to claim 34, further comprising at least an array of configurable logic elements including a configurable logic element, wherein said configurable logic element selectively realizes a logic function from a logic library.

40. The configurable computing array according to claim 34, further comprising at least one multiplier.