FPGA ARCHITECTURE OF DIFFERENT VENDORS

ABSTRACT:

Field-Programmable Gate Arrays (FPGAs) are integrated circuits which may be programmed to implement virtually any digital circuit. This programmability provides a low-risk, low-turn around time option for implementing digital circuits.  This programmability comes at a price, how

ever.  Typically, circuits implemented on FPGAs are 3 times as slow and have just one tenth the density of circuits implemented using more conventional techniques. Much of this area and speed penalty is thanks to the programmable routing structures contained within the FPGA. 

In this survey, we'll  focus routing structures of various vendors.  First, we specialize in a switch block, which may be a programmable  switch connecting fixed routing tracks.  A typical FPGA contains several hundred switch blocks. Second, we specialize in the logic block Interconnect Matrix, which may be a programmable switch connecting logic elements

INTRODUCTION:

Since their inception in 1985, Field Programmable Gate Arrays (FPGAs) have emerged as a number one  choice of technology for the implementation of the many digital circuits and systems.   New commercial architectures offer sort of features like densities of up to three.2 million system gates,on-chip single or dual port memories, digital phase lock loops for clock management, and system performance up to 311 MHz [19-24], making FPGAs ideal not just for glue logic but also for the implementation of entire systems.

Field Programmable Gate Arrays (FPGAs), Complex Programmable Logic Devices (CPLDs),and Masked Programmable Gate Arrays (MPGAs) are a part of a programmable logic family which provides an alternate way of designing and implementing digital circuits. the normal approach consists of designing a chip to satisfy a group of specific requirements which can't be changed once the planning is complete.  In contrast, a programmable logic device are often programmed “in the field”, resulting in lower time to plug, and lower non-recurring engineering(NRE) costs. additionally many programmable devices are often re-programmed repeatedly, resulting in a faster recovery from design errors, and therefore the ability to vary the planning as requirements change, either late within the design cycle, or in subsequent generations of a product.Of all programmable devices, one among the foremost common is that the Field Programmable Gate Array (FPGA).  Compared to other programmable devices, an FPGA offers the very best logic density, a good speed-area trade-off, and a really general architecture suitable for a good range of applications.  FPGAs are getting used in prototyping of styles, communication encoding and filtering, random logic, video communication systems, real time image processing, device controllers,computer peripherals, pattern matching, high speed graphics, digital signal processing and therefore the list goes on. PLD shipments from various vendors are expected to exceed $3 billion for 1999. The advantages of FPGAs come at a price, however. the character of their architecture, and the abundance of user-programmable switches makes them relatively slow compared to another devices within the programmable logic family.  Regardless, FPGAs have a significant impact on the way a digital circuit design is completed today.

FPGA ARCHITECTURE:

There are many various FPGA architectures available from various vendors including Altera

[19], Xilinx [20], Actel [21], Lucent [22], QuickLogic [23], and Cypress [24].   Although the

exact structure of those FPGAs varies from vendor to vendor, all FPGAs contains three funda

mental components: Logic Blocks, I/O blocks, and therefore the Programmable Routing.  What comprises of a logic block, and the way the programmable routing is organized defines a specific architecture. A logic block is employed to implement alittle portion of the circuit being implemented using an FPGA.  The programmable routing is employed to form all the specified connections among various logic block and therefore the required connections to the I/O (input/output) blocks.  Many commercially available FPGAs use an Island-style architecture during which logic blocks are organized in an array separated by horizontal and vertical programmable routing channel

ROUTING RESOURCES:

The programmable routing in an FPGA consists of two categories: (1) routing within each Logic

Block/Logic Cluster, and (2) routing between the Logic Blocks/Logic Clusters.

For the routing between the logic blocks/logic clusters, the foremost  important structure may be a Switch Block and for routing within each logic block  interconnection matrix is employed

 Each Switch Block programmably connects each incoming track from a channel to number of outgoing tracks in other channels. Clearly the flexibility of every Switch Block may be a key to the general flexibility and therefore the routability of a particular FPGA architecture.   The transistors within the Switch Block add capacitance and resistance loading to the each track during a channel, and hence the Switch Block features a significant effect on the speed of every routable connection and thus a serious impact on the speed of the FPGA as a whole. additionally, since such an outsized portion of an FPGA is dedicated to the routing, the chip area required by each Switch Block will have a significant effect on the achievable logic density of the device.  Thus, the planning of an honest Switch Block is of the utmost importance. There are  four sorts of interconnection technologies used

- Static RAM

- Anti fuse

- EPROM

EEPROM

General Architecture of Xilinx FPGAs:

Basic logic cells CLBs(Configurable Logic Blocks) are bigger and more complex than the Actel or Quick Logic cells. The Xilinx LCA basic cell is an example of a rough grain architecture that has both combinational logic and Flip Flop (FF). The XC3000 has five logic inputs, as common clock, FF, MUXs,……Using programmable MUXs connected to the SRAM programming cells, outputs of two CLBs X and Y can been independently connected to the outputs of FFQx and Qy or to the outputs of the Combinational Logic F& G.

ACTEL FPGA ARCHITECTURE: