Lucent Technologies Inc.

Kai-Kit Ngai

Satwant Singh

Barry K Britton

Richard G Stuby, Jr

Carolyn W Spivak

Ho Trong Nguyen

Gary P Powell

William B Andrews

The FPGA has an array of programmable logic cells (PLCs) surrounded by a ring of programmable input/output cells (PICs). In one embodiment, the pads of each pair of adjacent PICs, as well as internal routing resources of each of the two PICs, are programmably connected to a single global-signal spine, and the spine is programmably connected directly to only half of the perpendicular branches. Each of the branches can then connect to the cells in two adjacent rows/columns of the array to provide a global signal to any of the cells in the array while only using a branch per every two rows/columns of the device. The reduced number of spine-to-branch connections reduces the capacitive loading on the spines, thereby increasing the speed at which global signals can be transmitted. In addition, sharing spines between adjacent PICs reduces the number of spines in the FPGA by half, thereby providing additional layout space for other resources. Sharing branches also has the same effect as sharing spines in that the number of branches is reduced by half, also increasing global signal speed. These advantages are achieved without reducing the programming flexibility of the FPGA.

Global signal distribution with reduced routing tracks in an FPGA

The bi-directional (BI-DI) buffers and supplemental logic and interconnect (SLIC) cells are designed to be programmed to operate in different modes in order to implement different kinds of logic circuits. In particular, BI-DI buffers of the present invention support at least five different operational modes. In a first mode (Mode A), the BI-DI buffer generates a logic '1' output, for any input value. In a second mode (Mode B), the BI-DI buffer generates a logic '0' output, for any input value. In a third mode (Mode C), the BI-DI buffer buffers the input signal and generates an output signal equal to the input signal. In a fourth mode (Mode D), the BI-DI buffer buffers the input signal and generates an output signal equal to the inverse of the input signal. In a fifth mode, (Mode E), the BI-DI buffer operates as a conventional tri-state driver. Two or more of the BI-DI buffers can be configured to form more complex logic circuits having two or more inputs. For example, groups of BI-DI buffers can be configured as SLIC cells that are part of the basic logic cells for an FPGA. When used in FPGAs, the BI-DI buffers and SLIC cells make implementation of different kinds of logic circuits more efficient than is the case for conventional FPGAs, including logic circuits like decoders and state machines that have large numbers of inputs. At the same time, the FPGAs retain their efficiencies for implementing logic circuits for which FPGAs have traditionally been very efficient, such as random logic and datapath logic.

Bi-directional buffers and supplemental logic and interconnect cells for

A field programmable gate array includes programmable function units (PFUs) that may function as either a logic block or a random access memory (RAM). Each PFU has a write-port enable input when the PFUs are being used as user RAM units. In addition, each PFU includes a write-strobe input. The write operation is accomplished when both the write-port enable input and the write-strobe input are active. This technique allows a reduction of logic gates and control signal conductors. In many cases, these advantages allow for higher system operating frequencies and more gate capacity at a lower cost.

Field programmable gate array with write-port enabled memory

A field programmable gate array (FPGA) with a programmable function unit (PFU) that includes a look-up table (LUT) for implementing a plurality of functions including first and second RAM cells, and a programmable switching device dedicated to coupling and decoupling the RAM cells. The first and second RAM cells are coupled to respective first and second read/write ports. The RAM cells function individually as single-port RAM cells when decoupled by the switching device. However, the RAM cells share data to function collectively as a dual-port RAM cell when coupled by the switching device. The dual-port RAM cell is accessible by both the first and second read/write ports.

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Campbell, CA, United States of America

Kai-Kit Ngai