Fpga 3u3b34

FIELD PROGRAMMABLE GATE ARRAY • FPGA was first developed in the mid 1970’s as the first non memory programmable logic device. • It is used as a programmable AND array and programmable OR array. • It contains 3 main units : • logic blocks • I/O blocks • Interconnection wires and switches • FPGA contains large number of configurable logic blocks(CLBs) which contain programmable combinational logic and s for sequential circuits. • In FPGA , all the configurable logic block and input/output blocks can be programmed interconnected to implement virtually any logic circuit.

• Each logic block in an FPGA typically has a smaller number of inputs and outputs. • The most commonly used logic block is a look up table (LUT) which contains storage cells that are used to implement a small logic function. • Each cell is capable of holding a single logic value either 0 or 1. The stored value is produced as output of the storage cell. • The figure contains two inputs x1 and x2 and one output f. • The input variables are used to select inputs of three multiplexers depending on the valuation of x1 and x2, select the content of one of the 4 storage cells as output of LUT.

Comparison of SRAM and Anti fuse FPGA

SRAM

ANTI FUSE • Anti fuse provides insulation between two conductors, but when sufficient voltages is applied across it, conducting path forms. • The figure shows and amorphous silicon based FPGA contains two layers of metal are separated by amorphous silicon, it provides electrical insulation. • A programming pulse of 10v to 12v and necessary duration is applied. It creates bidirectional conductive link between two metals. • Once programmed, an anti-fuse element cannot be erased or reprogrammed.

Basic Structure of FPGA • Several different types of structure for FPGAs are available commercially. All of them have basic structures which consists of many logic blocks or logic cells accompanied by large number of connecting lines. • FPGA type of Gate array with routing channels. • FPGA type of sea of gates • FPGA type of row based array • FPGA type of bus based array

1.FPGA type of Gate array with routing channels

2. FPGA type of sea of gate

3. FPGA type of row based array

4. FPGA type of bus based array

FPGA Programming Types • FPGA program sets up the look up table, switching routes and multiplexer addressing to the correct specification. • There are 3 main types of programming in FPGA : 1. Static RAM programming - where interconnected routes are setup using transistors, transmission gates and multiplexers.

2. Anti fuse programming - where interconnection routes are programmed permanently by devices known as anti fuses. 3. EPROM/EEPROM programming - Where transistors are programmed to exist or not. If a transistor exist then it connects in an input to a logic block.

1. Static RAM Programming • SRAM programming uses one or two way switches and multiplexers to define paths. • In the case of switches with single NMOS transistor , then if the RAM cell associated is programmed with 1 then a path will be created for the signal. • For two way switches , then a transmission gate can be used. Advantages: • No need to take FPGA out of the circuit. • We can change the program stored in the non volatile memory Disadvantages: • The main disadvantage of SRAM programming is that it looses the program stored in memory when power is off.

Anti Fuse Programming • Antifuse is a high impedance , when it is applied high voltage to it which turns into a low impedance state. • Anti fused cannot be reprogrammed. • A relative high volatage of 18v is applied across the device. • The current approx. 5mA causes the dielectric to melt and form a conductive link between polysilicon and the diffusion.

EPROM and EEPROM Programming • An EPROM transistor differs from normal NMOS transistor is that it has two gates, a floating gate and a select gate.