This document discusses three options for implementing digital designs: microcontrollers, ASICs, and FPGAs. It provides details on the differences between FPGAs and microcontrollers, and between FPGAs and ASICs. FPGAs offer reconfigurable hardware, faster speeds than microcontrollers due to parallel processing, and more flexible I/O. However, ASICs are best for high volume manufacturing due to lower costs. The document also provides information on the internal architecture of FPGAs, including configurable logic blocks, look up tables, programmable interconnects, and I/O blocks.

1.  Three generally available options to implement a Digital
Design:
 Microcontroller
 ASIC
 FPGA
Digital System: Implementation
Spectrum
Microcontroller FPGA ASIC
Reconfigurable Software
Fixed Hardware
Reconfigurable
Hardware
Fixed Hardware

2. FPGA vs Microcontroller
FPGA Microcontroller
Faster speed due to
concurrent behavior of
hardware
Slow Speed due to sequential instructions
execution
Can be used to build
customized hardware
Only software can be used to complete the
required task. Fixed hardware
Processing speed up to 100’s
of MHz
Processing speed limited to few MHz only
100’s of I/O pins available Limited I/O Pins (32 in 89c51)
Each I/O can be used to
perform any operation
Dedicated pins to perform operation e.g. Serial
Comm, Timers, SPI, Interrupts

3. FPGA vs ASIC
FPGA ASIC
General Purpose Application Specific
Reconfigurable Hardware Fixed Hardware
Suitable for Testing /
verification/Prototyping
Suitable for Large manufacturing quantities
(costs about 1 million US$)
No mask charges, no
Minimum Order Qty (MOQ)
Huge setup/mask costs. MOQ exists for ASIC
production
Hardware design is rapidly
available to market
Can take several months to produce first chip
out of a production lot

4. Digital Logic

5. FPGA: Field Programmable Gate Array
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 FPGA is a form of programmable logic device introduced
in 1985 by Xilinx, Inc.
 An FPGA consists of an array of configurable logic
blocks; surrounded by programmable I/O blocks, and
connected with programmable interconnects.
 Also, there will be clock circuitry
for driving the clock signals to
each logic block.
 FPGA Technologies
 Antifuse : One Time Programmable
 SRAM: Reprogrammable FPGAs,
use SRAM configuration cell
 Flash: Reprogrammable and
Nonvolatile FPGAs

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 These blocks contain the logic for the FPGA.
 The block contains RAM for creating combinatorial logic
functions, also known as lookup tables (LUTs).
 It also contains flip-flops for clocked storage elements,
and multiplexers to route the logic within the block and to
and from external resources.
 The multiplexers also allow
polarity selection and reset
and clear input selection.
Configurable Logic Blocks (CLBs)
2 LUTs in a CLB
of Xilinx XC4000

7.  Gates are combined to
create complex circuits
 Multiplexer Example
 If S=0, Z=A
 If S=1, Z=B
 Very Common Digital
Circuit
 Heavily Used in FPGA
 S input is controlled by
Configuration memory bit
Combinational Logic Functions
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0
0
1
1
1
0
1
Z
A
0
B
0
0
0
0
S
0
1
1
0
0
0
1
1
1
0
1
0
1
1
1
1
1
0
1
0

8. Programmable Interconnect
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 Local interconnects are fast and short
 Horizontal and vertical interconnects are of various lengths

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 IOB is used to bring signals onto the chip and send them
back off again.
 It consists of an input buffer and an output buffer with
three-state and open collector output controls.
 Typically there are pull up resistors on the outputs.
 The polarity of the output can
usually be programmed for
active high or active low output,
and often the slew rate of the
output can be programmed for
fast or slow rise and fall times.
Configurable I/O Block (IOBs)

10. Logic Block CLB

11. Look Up Tables

12. Clocked Logic

13. Circuit Compilation

14. Advantages of FPGA

15. Major FPGA Vendors