Interconnect circuitry for implementing logic functions in a...

Details Interconnect circuitry for implementing logic functions in a... Interconnect circuitry for implementing logic functions in a...

2001-01-31

2002-11-19

Tokar, Michael (Department: 2819)

Electronic digital logic circuitry

Multifunctional or programmable

Array

C326S038000, C326S047000, C326S039000

Reexamination Certificate

active

06483344

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
The present invention is related to that disclosed in U.S. patent application Ser. No. 09/774,891 filed concurrently herewith, entitled “INTERCONNECT CIRCUITRY FOR IMPLEMENTING BIT-SWAP FUNCTIONS IN A FIELD PROGRAMMABLE GATE ARRAY AND METHOD OF OPERATION”. Patent application Ser. No. 09/774,891 is commonly assigned to the assignee of the present invention. The disclosure of this related patent application is hereby incorporated by reference for all purposes as if fully set forth herein.
TECHNICAL FIELD OF THE INVENTION
The present invention is generally directed to field programmable gate array (FPGA) circuits, a more specifically to an FPGA circuit in which logic functions may be implemented by the interconnect circuitry between logic blocks.
BACKGROUND OF THE INVENTION
The speed, power, and complexity of integrated circuits, such as microprocessor chips, random access memory (RAM) chips, application specific integrated circuit (ASIC) chips, and the like, have increased dramatically in the last twenty years. More recently, these increases have led to development of so-called system-on-a-chip (SoC) devices. A SoC device allows nearly all of the components of a complex system, such as a cell phone or a television receiver, to be integrated onto a single piece of silicon. This level of integration greatly reduces the size and power consumption of the system, while generally also reducing manufacturing costs.
A key component in many highly integrated circuits, including SoC devices, is the field programmable gate array (FPGA). FPGA circuits are a particular class of general purpose integrated circuits (ICs) that can be configured (i.e., programmed) to perform a wide range of tasks. There are a number of different types of FPGA circuit topologies, including symmetrical array, row-based, sea-of-gates, and hierarchical programmable logic device (PLD). Each of these FPGA types has certain advantages over other types, depending on the specific application.
FPGA circuits generally are implemented using one of four technologies: static RAM cells, anti-fuse, EPROM transistors, and EEPROM transistors. In static RAM technology, programmable connections in the FPGA are made using pass transistors, transmission gates, or multiplexers controlled by a static random access memory (RAM) cell. Static RAM cells technology allow fast reconfiguration of a FPGA circuit. Anti-fuse technology uses an anti-fuse that is initially a high-impedance connection path (i.e., open circuit). The anti-fuse is then programmed into a low impedance (i.e., short circuit) or fused state. While anti-fuse technology is simple and less expensive than static RAM technology, an anti-fuse is a “program once” device. EPROM and EEPROM technologies use the same methods that are used in EPROM memories.
There are three primary configurable elements in a FPGA circuit: configurable logic blocks (CLBs), input/output (I/O) blocks, and programmable interconnects. The configurable logic blocks contain a variety of different logic functions, such as look-up tables (LUTs), registers, multiplexer (MUX) gates, programmable logic arrays (PLDs) programmable logic devices (PLDs), and the like. A programmable interconnect generally connects a single output of a CLB to an input of another CLB. An interconnect comprises metal wires and transistors that act as pass gates and signal buffers that preserve the signal integrity. Control of the interconnect transistors may be provided by an SRAM cell, a flash RAM cell, or external pins. The programming of an interconnect is usually done in a static fashion, such as at the power-up of a stand-alone FPGA circuit, especially for flash RAM and SRAM based configurations. The I/O blocks provide the interface between the external pins of the IC package and the internal signals lines, including the programmable interconnects.
Despite the considerable advancements made in field programmable gate array circuits, however, there remains room for improvement. There is a limitation to the complexity of the logic functions that may be implemented in a FPGA circuit of a particular size and density. More complex functions call for still greater FPGA density. However, this greater density must be achieved without incurring larger latencies due to increased propagation times through the FPGA circuit.
Therefore, there is a need in the art for system-on-a-chip (SoC) devices and other large scale integrated circuits that implement improved field programmable gate array (FPGA) circuits. In particular, there is a need for FPGA circuits, including embedded FPGA circuits, that achieve greater density and/or utilization over standard FPGA technologies. More particularly, there is a need for improved FPGA circuits that are capable of performing more complex logical functions while minimizing propagation times.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a field programmable gate array capable of performing in the interconnect matrix selected Boolean logic functions, such as OR gates and NOR gates, that are normally performed in the configurable logic blocks of the FPGA. According to an advantageous embodiment of the present invention, the field programmable gate array comprises: 1) a plurality of configurable logic blocks (CLBs); 2) a plurality of interconnects; 3) a plurality of interconnect switches capable of coupling ones of the plurality of interconnects to each other and to inputs and outputs of the plurality of configurable logic blocks; and 4) an interconnect switch controller capable of controlling the plurality of interconnect switches. The interconnect switch controller in a first switch configuration causes a first interconnect to be coupled to an output of a first CLB, causes a second interconnect to be coupled to an output of a second CLB, causes the first and second interconnects to be coupled to a third interconnect, and causes the third interconnect to be coupled to a pull-up device coupled to a power supply source of the field programmable gate array. The first, second and third interconnects and the pull-up device thereby form a two-input NOR gate.
According to one embodiment of the present invention, the interconnect switch controller comprises a memory capable of storing the first switch configuration.
According to another embodiment of the present invention, the memory comprises a static read only memory.
According to still another embodiment of the present invention, the interconnect switch controller comprises at least one configurable logic block in the field programmable gate array.
According to yet another embodiment of the present invention, the pull-up device is a pull-up transistor.
According to a further embodiment of the present invention, the field programmable gate array further comprises a buffer having an input coupled to the third interconnect and an output coupled to an input of a third CLB.
According to a still further embodiment of the present invention, the buffer is a non-inverting line driver.
According to a yet further embodiment of the present invention, the buffer is an inverting line driver, such that the first, second and third interconnects, the pull-up device, and the buffer thereby form a two-input OR gate.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest fo

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