, PeiYin Chen,

1
FPGA????
Logic Design

• ???, Pei-Yin Chen, ???????????
• pychen_at_csie.ncku.edu.tw

2
Computers and Electricity

• Computers are electronic devices(????) (all
  binary)
• range of 01 volt is low -- binary 0
• range of 25 volt is high -- binary 1
• Gate(???) A device that performs a basic
  operation on electrical signals, accepting one or
  more input signals and producing a single output
  signals
• Circuits(??) A combination of interacting gates
  designed to accomplish a specific logical
  function (the output of a gate often serves as
  an input for one or more other gates)

3
Computers and Electricity

• There are three different, but equally powerful,
  notational methods for describing the behavior of
  gates and circuits
• Boolean expressions (?????)
• logic diagrams (???)
• truth tables (???)

4
Computers and Electricity

• Boolean expressions Expressions in Boolean
  algebra(????), a mathematical notation for
  expressing two-valued logic
• This algebraic notation are an elegant and
  powerful way to demonstrate the activity of
  electrical circuits

X is the output signal A and B are input signals
5
Computers and Electricity

• Logic diagram A graphical representation of a
  circuit
• Each type of gate is represented by a specific
  graphical symbol
• Truth table A table showing all possible input
  combinations and the associated output values

inputs
outputs
6
Gates

• Lets examine the processing of the following
  six types of gates (accept one or more inputs
  and produce a single output)
• NOT
• AND
• OR
• XOR
• NAND
• NOR
• Typically, logic diagrams are black and white,
  and the gates are distinguished only by their
  shape

7
NOT Gate

• A NOT gate (???)accepts one input value and
  produces one output value

left(input) right(output)
A(input) X(output)
input output
or
inversion bubble
negate the input
01 10
Various representations of a NOT gate
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NOT Gate

• By definition, if the input value for a NOT gate
  is 0, the output value is 1, and if the input
  value is 1, the output is 0
• A NOT gate is sometimes referred to as an
  inverter because it inverts the input value

01 10
input signal(s)? output signal?
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AND Gate

• An AND gate (??)accepts two input signals
• If the two input values for an AND gate are both
  1, the output is 1 otherwise, the output is 0

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OR Gate (??)

• If the two input values are both 0, the output
  value is 0 otherwise, the output is 1

Various representations of a OR gate
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XOR Gate

• XOR, or exclusive OR, gate (????)
• An XOR gate produces 0 if its two inputs are the
  same, and a 1 otherwise
• Note the difference between the XOR gate and the
  OR gate they differ only in one input situation
• When both input signals are 1, the OR gate
  produces a 1 and the XOR produces a 0

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XOR Gate
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NAND and NOR Gates

• The NAND (???) and NOR(???) gates are essentially
  the opposite of the AND and OR gates, respectively

NAND gate
NOR gate
415
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Review of Gate Processing

• A NOT gate inverts its single input value
• An AND gate produces 1 if both input values are 1
• An OR gate produces 1 if one or the other or both
  input values are 1

15
Review of Gate Processing

• An XOR gate produces 1 if one or the other (but
  not both) input values are 1
• A NAND gate produces the opposite results of an
  AND gate
• A NOR gate produces the opposite results of an OR
  gate

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Gates with More Inputs

• Gates can be designed to accept three or more
  input values
• A three-input AND gate, for example, produces an
  output of 1 only if all input values are 1

All possible input combinations must be described
in Truth Table
17
Constructing Gates

• Transistor(???) A device that acts, depending on
  the voltage level of an input signal, either as a
  wire (??) that conducts electricity or as a
  resistor(??) that blocks the flow of electricity
• A transistor has no moving parts, yet acts like a
  switch
• It is made of a semiconductor(???) material,
  which is neither a particularly good conductor of
  electricity, such as copper, nor a particularly
  good insulator, such as rubber

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Constructing Gates

• A transistor has three terminals
• A source (feed with 5 volts)
• A base
• An emitter, typically connected to a ground wire
• If the base signal is high (close to 5 volts),
  the source signal is grounded and the output
  signal is low (0). If the base signal is low
  (close to 0 volts), the source signal stays high
  and the output signal is high (1)

5 volts
The connections of a transistor
19
Constructing Gates

• It turns out that, because the way a transistor
  works, the easiest gates to create are the NOT,
  NAND, and NOR gates

V1 V2 Vout 0 0 1 0 1 1 1 0
1 1 1 0
V1 V2 Vout 0 0 1 0 1 0 1 0
0 1 1 0
Vin Vout 0 1 1 0
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Circuits

• Circuits A combination of interacting gates
  designed to accomplish a specific logical
  function
• Two general categories
• In a combinational circuit(????), the input
  values explicitly determine the output
• In a sequential circuit(????), the output is a
  function of the input values as well as the
  existing state of the circuit
• As with gates, we can describe the operations of
  entire circuits using three notations
• Boolean expressions, logic diagrams, truth
  tables

21
Combinational Circuits

• Gates are combined into circuits by using the
  output of one gate as the input for another

22
Combinational Circuits

• Because there are three inputs to this circuit,
  eight rows are required to describe all possible
  input combinations
• This same circuit using Boolean algebra is (AB
  AC)

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Now lets go the other way lets take a Boolean
expression and draw

• Consider the following Boolean expression A(B C)

• Now compare the final result column in this truth
  table to the truth table for the previous example
• They are identical

24
Now lets go the other way lets take a Boolean
expression and draw

• We have therefore just demonstrated circuit
  equivalence(????)
• That is, both circuits produce the exact same
  output for each input value combination
• Boolean algebra allows us to apply provable
  mathematical principles to help us design
  logical circuits

A(B C)ABAC
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Properties of Boolean Algebra
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Adders(???)

• At the digital logic level, addition is performed
  in binary
• Addition operations are carried out by special
  circuits called, appropriately, adders

27
Adders

• The result of adding two binary digits could
  produce a carry value
• Recall that 1 1 10 in base two
• A circuit that computes the sum of two bits and
  produces the correct carry bit(????) is called a
  half adder(???)

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Adders

• Circuit diagram representing a half adder
• Two Boolean expressions
• sum A ? B
• carry AB

one-bit adder How about 8-bit ?
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Combinational Circuits (1/2)
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Combinational Circuits (2/2)
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Sequential Circuits (1/2)

• Combinational circuits
• contains no memory elements
• the outputs depends on the inputs
• Sequential circuits
• a feedback path
• the state of the sequential circuit
• (inputs, current state) Þ (outputs, next state)
• synchronous the transition happens at discrete
  instants of time
• asynchronous at any instant of time

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Sequential Circuits (2/2)
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Integrated Circuits

• Integrated circuit(????) (also called a chip) A
  piece of silicon(?) on which multiple gates have
  been embedded
• These silicon pieces are mounted on a plastic or
  ceramic package with pins along the edges that
  can be soldered onto circuit boards or inserted
  into appropriate sockets

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Integrated Circuits
data sheet
Figure 4.13 An SSI chip contains independent
NAND gates
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Integrated Circuits

• Integrated circuits (IC) are classified by the
  number of gates contained in them

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Integrated Circuits
12 13
1
3
8
1
2
2
1
3
2
Multiple chips (gates) combined to a circuit to
solve a specific problem(??????)
37
Example Alarm
Assume that four persons might come. Alarm is
activated when (1) more than three persons come
or (2) the fourth person come together with other
persons
Out AD BD CD ABC
38
Example Alarm
Out AD BD CD ABC
A B C D
two chips
(from sensors or buttons)
Out (might connect to bell)
and-chip
or-chip (commercial ASIC chips)
A B C D
(from sensors or buttons)
Out (might connect to bell)
one chip (a dedicated chip) -- ASIC
Application Specific Integrated Circuit -- ASIC
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IC Industry in Taiwan
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CPU Chips

• The most important integrated circuit (IC)in any
  computer is the Central Processing Unit(??????),
  or CPU
• Each CPU chip has a large number of pins(??)
  through which essentially all communication in a
  computer system occurs
• The communication connects the CPU to memory and
  I/O devices

41
Design Entry for VLSI System
Choose the design entry method
Schematic Gate level design Intuitive
easy to debug HDL (Hardware Description
Language) Descriptive portable Easy
to modify Mixed HDL Schematic
always _at_(IN) begin OUT (IN0 IN1)
(IN2 IN3) end
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Hierarchical Components in PCB

• Describe the circuits with
• Hardware Description Language
• (HDL??????)
• 2. Synthesis (??) the circuits
• .

application specific integrated circuit (ASIC??)
IC or chip
43
Circuit Design Process
System Spec.
Partitioning
Fabrication
VLSI Design/Sim/Ver
Wafer Test
Post-Layout Sim/Ver
Packaging
Masking
Final Test
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IC Design flow
IC design flow
Full Custom
Semi Custom (Cell-Based Design)

• Standard Cells
• TSMC, UMC-cells
• b. FPGA or PLD Programmable logic
• Xilinx, Altera, Actel-cells

ASIC
Full (Fully) Custom Design

• For analog circuits and digital circuits
  requiring custom optimization
• Gates, transistors and layout are designed and
  optimized by the engineer

Semi Custom Design

• For larger digital circuits
• Real gates, transistors and layout are
  synthesized and optimized by
• related software tools
• c. Realization with hardware description
  language (HDL) such as VHDL and
• Verilog

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Full Custom Design (??????)
CMOS Inverter
in
out

• Digital circuits requiring custom optimization
  (smaller system)
• Analog circuits
• Long design cycle
• (transistors and wires)
• d. No CPLD or FPGA solutions

done by chip designer
masking
done by TSMC, UMC
Packing, Testing
46
Semi Custom Design (??????)
Semi Custom Design

• Product specification
• Modeling with HDL
• Synthesis (by using suitable standard cell)
• Simulation and verification
• Physical placement and layout
• Tape-out (real chip)
• Testing

-- implemented with suitable tools
-- implemented by suitable Fab companies
-- implemented by suitable tools and mechanisms
more flexible, shorter design cycle, suitable for
smaller production
PLD
Xilinx, Altera
FPGA or CPLD
Two different solutions
Real ASIC chip
Fab (TSMC, UMC, ..)
Standard cell
less flexible, long design cycle, larger-scale
production to reduce price
47
Synthesis Flow of Semi Custom design (1/2)
Behavioral requirement
Verification and analysis Behavioral simulation
Synthesis High level synthesis
Functional design
Behavioral representation Boolean equations and
RTL
Verification and analysis Logic verification,
Logic simulation Testing
Logic design
Synthesis Logic synthesis
Structural representation Logic gates, connections
Synthesis Cell generators
Circuit design
Verification and analysis Circuit simulation,
Circuit analysis
Structural representation Transistors and
connections
Synthesis Floorplanning, Placement, Routing
Physical design
Verification and analysis Design-rule
checking Circuit extraction
Physical representation Mask layout rectangles
48
Synthesis Flow of Semi Custom design (2/2)
49
Synthesis (1/3)

• Synthesis TranslationOptimizationMapping

always _at_() if (ab) if (c1)
df else d1
else d0
Translate into Boolean Representation
f
a
b
d
Optimize Map
HDL Source
c
f
c
d
a
Process of logic synthesis
b
Target Technology
50
Synthesis (2/3)

• Synthesis is constraint-driven
• You set the goals. Design Compiler optimizes
  design toward goals.

Large
Area
Small
Fast
Slow
Speed
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Synthesis (3/3)

• Providing an environment and various tools for
  the designers to produce circuits automatically
  and efficiently to meet the requirements of
• performance
• area
• testability