Configurable computing array using two-sided integration

Abstract

The present invention discloses a configurable computing array using two-sided integration. It is a monolithic integrated circuit comprising at least a configurable computing element located on one side of the substrate and at least a configurable logic element on the other side of the substrate. Each configurable computing element comprises at least a writable-memory array, which stores at least a portion of a look-up table (LUT) for a math function.

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, a tan) 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 a small size.

It is a further object of the present invention to provide a configurable computing array with a fast computational speed.

In accordance with these and other objects of the present invention, the present invention discloses a configurable computing array using two-sided integration.

SUMMARY OF THE INVENTION

The present invention discloses a configurable computing array. It is a monolithic integrated circuit comprising an array of configurable computing elements and an array of configurable logic elements, which are formed on different sides of a semiconductor substrate. Each configurable computing element comprises at least a writable-memory array, which is electrically programmable and can be loaded with a look-up table (LUT) for a math function. Being electrically programmable, the math functions that can be realized by a writable-memory array are essentially boundless. The preferred configurable computing array further comprises a plurality of configurable interconnect, which are formed on both sides of the semiconductor substrate.

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 writable-memory array. In the computation stage, a selected portion of the LUT for the desired math function is read out from the writable-memory array. For a rewritable-memory array, a configurable computing element can be re-configured to realize different math functions at different time.

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.

Accordingly, the present invention discloses a configurable computing array, comprising: a semiconductor substrate having a first side and a second side; at least a configurable computing element formed on said first side of said semiconductor substrate for storing at least a portion of a look-up table (LUT) for a math function; at least a configurable logic element formed on said second side of said semiconductor substrate for selectively realizing a logic function from a logic library; a plurality of through-substrate vias through said semiconductor substrate for coupling said configurable computing element and said configurable logic element; wherein said configurable computing array realizes a math function by programming said configurable computing element and said configurable logic element.

The present invention further discloses another configurable computing array, comprising: a semiconductor substrate having a first side and a second side; at least a configurable computing element formed on said first side of said semiconductor substrate for storing at least a portion of a look-up table (LUT) for a math function; at least a configurable logic element formed on said second side of said semiconductor substrate for selectively realizing a logic function from a logic library; a plurality of through-substrate vias through said semiconductor substrate for coupling said configurable computing element and said configurable logic element; at least a configurable interconnect for selectively realizing an interconnect from an interconnect library; wherein said configurable computing array realizes a math function by programming said configurable computing element, said configurable logic element and said configurable interconnect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 discloses a symbol for a preferred configurable computing element;

FIG. 2 is a layout view of the preferred configurable computing element;

FIG. 3 discloses two usage cycles of a preferred re-configurable computing element;

FIG. 4A shows an interconnect library supported by a preferred configurable interconnect; FIG. 4B shows a logic library supported by a preferred configurable logic element;

FIG. 5 is a circuit block diagram of a first preferred configurable computing array;

FIG. 6 shows an instantiation of the first preferred configurable computing array implementing a complex math function;

FIG. 7 is a circuit block diagram of a second preferred configurable computing array;

FIGS. 8A-8B show two instantiations of the second preferred configurable computing array;

FIG. 9A is a perspective view of a front side of the preferred configurable computing-array die; FIG. 9B is a perspective view of a back side of the preferred configurable computing-array die; FIG. 9C is a cross-sectional view of the preferred configurable computing-array die.

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 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 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. 2 is a layout view of the preferred configurable computing element 100. The LUT is stored in at least a writable-memory array 110. The configurable computing element 100 further includes the X decoder 15 and Y decoder (including read-out circuit) 17 of the writable-memory array 110. The writable-memory array 110 could be a RAM array or a ROM array. Exemplary RAM includes SRAM, DRAM, etc. On the other hand, exemplary ROM includes OTP (one-time-programmable) and MTP (multiple-time-programmable, including re-programmable), etc. Among them, the MTP further includes EPROM, EEPROM, flash memory, three-dimensional memory, etc.

Referring now to FIG. 3, two usage cycles 620, 660 of a preferred re-configurable computing element 100 are shown. For the re-configurable computing element 100, the writable-memory 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 writable-memory array 110. In the computation stage 630, a selected portion of the LUT for the first desired math function is read out from the writable-memory 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 writable-memory 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. 4A-4B, an interconnect library and a logic library are shown. FIG. 4A 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. 4B 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. 5, 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. 6 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. 4A: 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. 7, 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. 8A-8B disclose two instantiations of the second preferred configurable computing array 400. In the instantiation of FIG. 8A, 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. 8B, 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).

Referring now to FIGS. 9A-9C, a preferred configurable computing-array die 400 using two-sided integration is disclosed. It is a monolithic integrated circuit comprising a semiconductor substrate 0. The substrate 0 has a front side 0F (towards the +z direction) and a back side 0B (towards the −z direction). In this preferred embodiment, the configuration logic elements 200AA-200BB are formed at the front side 0F of the substrate 0 (FIG. 9A), while the configurable computing elements 100AA-100BB are formed at the back side 0B of the substrate 0 (FIG. 9B). They are coupled through a plurality of through-substrate vias 160 (including 160a-160c). Examples of the through-substrate vias include through-silicon vias (TSV). Alternatively, the configurable computing elements 100AA-100BB are formed at the front side 0F, while the configurable logic elements 200AA-200BB are formed at the back side 0B.

This type of integration, i.e. forming the configurable logic elements 100AA-100BB and the configurable computing elements 200AA-200BB on different sides of the substrate, is referred to as two-sided integration. The two-sided integration can improve computational density and computational complexity. With the conventional 2-D integration, the die size of configurable computing array is the sum of those of the configurable computing elements and the configurable logic elements. With the two-side integration, the configurable computing elements are moved from aside to the other side. This leads to a smaller die size and a higher computational density. In addition, because the memory transistors in the configurable computing elements and the logic transistors in the configurable logic elements are formed on different sides of the substrate, their manufacturing processes can be optimized separately.

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. A configurable computing-array die, comprising: a semiconductor substrate having a first side and a second side;an array of configurable computing elements including first and second configurable computing elements disposed on said first side of said semiconductor substrate, wherein said first configurable computing element comprises a first memory for storing a first look-up table (LUT) for a first math function; and, said second configurable computing element comprises a second memory for storing a second LUT for a second math function;an array of configurable logic elements including a configurable logic element disposed on said second side of said semiconductor substrate, wherein said configurable logic element selectively realizes a logic function from a logic library;a plurality of through-substrate vias through said semiconductor substrate for coupling said configurable computing elements and said configurable logic elements;whereby said configurable computing-array die realizes a complex math function by programming said configurable computing elements and said configurable logic elements, wherein said complex math function is a combination of at least said first and second math functions.

2. The configurable computing-array die according to claim 1, wherein: said first side is a front side of said semiconductor substrate; and,said second side is a back side of said semiconductor substrate.

3. The configurable computing-array die according to claim 1, wherein: said first side is a back side of said semiconductor substrate; and,said second side is a front side of said semiconductor substrate.

4. The configurable computing-array die according to claim 1, wherein said through-substrate vias are through-silicon vias (TSV).

5. The configurable computing-array die according to claim 1, further comprising an array of configurable interconnects including a configurable interconnect, wherein said configurable interconnect selectively realizes an interconnect from an interconnect library.

6. The configurable computing-array die according to claim 5, wherein selected ones of said configurable interconnects are located on said first side.

7. The configurable computing-array die according to claim 5, wherein selected ones of said configurable interconnects are located on said second side.

8. The configurable computing-array die according to claim 5, wherein said configurable interconnects are located on said first and second sides.

9. The configurable computing-array die according to claim 1, wherein each of said configurable computing elements comprises a re-programmable memory, whereby each of said configurable computing elements can be re-configured to realize a different math function by loading the LUT for said different math function into said re-programmable memory.

10. The configurable computing-array die according to claim 1, further comprising at least one multiplier.

11. A configurable computing-array die, comprising: a semiconductor substrate having a first side and a second side;an array of configurable computing elements including first and second configurable computing elements disposed on said first side of said semiconductor substrate, wherein said first configurable computing element comprises a first memory for storing a first look-up table (LUT) for a first math function; and, said second configurable computing element comprises a second memory for storing a second LUT for a second math function;an array of configurable logic elements including a configurable logic element disposed on said second side of said semiconductor substrate, 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 configurable interconnect selectively realizes an interconnect from an interconnect library;a plurality of through-substrate vias through said semiconductor substrate for coupling said configurable computing elements and said configurable logic elements;whereby said configurable computing-array die realizes a complex math function by programming said configurable computing elements, said configurable logic elements and said configurable interconnects, wherein said complex math function is a combination of at least said first and second math functions.

12. The configurable computing-array die according to claim 11, wherein: said first side is a front side of said semiconductor substrate; and,said second side is a back side of said semiconductor substrate.

13. The configurable computing-array die according to claim 11, wherein: said first side is a back side of said semiconductor substrate; and,said second side is a front side of said semiconductor substrate.

14. The configurable computing-array die according to claim 11, wherein said through-substrate vias are through-silicon vias (TSV).

15. The configurable computing-array die according to claim 11, wherein selected ones of said configurable interconnects are located on said first side.

16. The configurable computing-array die according to claim 11, wherein selected ones of said configurable interconnects are located on said second side.

17. The configurable computing-array die according to claim 11, wherein said configurable interconnects are located on said first and second sides.

18. The configurable computing-array die according to claim 11, wherein each of said configurable computing elements comprises a re-programmable memory, whereby each of said configurable computing elements can be re-configured to realize a different math function by loading the LUT for said different math function into said re-programmable memory.

19. The configurable computing-array die according to claim 18, wherein the usage cycle of said configurable computing elements includes: a configuration stage during which the LUT for a math function is loaded into said re-programmable memory;a computation stage during which a selected portion of the LUT for said math function is read out from said re-programmable memory.

20. The configurable computing-array die according to claim 11, further comprising at least one multiplier.