Impact of vlsi on design abstractions

1. VLSI ERA
K. Meenakshi
GRIET

2. VLSI
• Since the 1960’s, the dominant technology for
manufacturing computer logic and memory
circuits has been the integrated circuit.
• This technology is evolved from IC’s containing
just a few transistors to those containing
thousands or millions of transistors. The latter
is termed very large scale integration or VLSI.

3. Advantages of VLSI
• The impact of VLSI on computer design has
profound and VLSI allows to fabricate a CPU,
main memory and all the electronic
components of computer on a single IC that
can be mass produced at low cost.
• This has resulted a new class of machines
ranging from portable personnel computers to
supercomputers that contains thousands of
CPUs.

4. IC packages

5. Integrated circuits
• The IC forms the basic building block of third
generation and subsequent generations.
• The IC’S mainly composed of transistors that is
manufactured in a tiny rectangle known as chip
or semiconductor material.
• The Ics are mounted on a protective plastic or
ceramic package which provides electrical points
called pins or leads that allows Ics to be
connected to other Ics , to input and output
devices like keypad and printer.

6. Integrated circuits
• The IC forms the basic building block of third
generation and subsequent generations.
• Thousands or millions of a transistors
fabricated on a single silicon chip.
• VLSI allows to fabricate a CPU, main memory
or i/o devices on a single silicon chip that is
known as microcomputer.
• A “multichip” is a package that containing
several IC chips that provides m

7. Classification of IC’s based on density
• Based on number of transistors fabricated on
a single silicon chip, IC’s are classified into
• Single scale integration(Fewer than 100 chips)
• Medium scale integration(100-1000)
• Large scale integration(1000-10000)
• Very large scale integration(Millions of
transistors)

8. Moore's law

9. Moore's law
• Moore's law is the observation that the
number of transistors in a dense integrated
circuit (IC) doubles about every two years.

10. IC Families
• Within IC technology several subtechnlogies
exist that are distinguished by the transistor
and circuit types that employ.
• Unipolar is MOS after its physical structure.
• Both bipolar and MOS circuits have transistors
as their basic elements.
• Bipolar circuits use both +ve holes and –ve
electrons carriers.

11. Types of MOSFETS

12. MOSFET
• If the carriers are holes, the MOSFET is known
as PMOS FET.
• If the carriers are electrons, the MOSFET is
known as NMOS FET.
• A combination of PMOS and NMOS FET are
called CMOS FET.

13. CMOS Circuit
• A static CMOS is a combination of two
networks called pull up and pull down
network.
• Pull up circuit provides a connection to the
supply voltage Vdd and the output of logic
gate.
• Pull down circuit provides a connection
between the GND and the output of logic
gate.

14. CMOS circuit
• The pull up and pull down network are
connected in a mutually exclusive fashion that
at any time only one circuit conducts in the
steady state.
• In this way, once the transients have settled, a
path exists between the Vdd and the logic
output as 1.
• A path exists between the Vss and the output
of logic gate.

15. Pull up and pull down transistor
Make a connection from
VDD to F when
F(ln1,ln2..lnn)=1
Make a connection from
Vss to F when
F(ln1,ln2..lnn)=0

16. Pull up and pull down circuits
• PUN is constructed by PMOS.
• PDN is constructed by NMOS.

17. CMOS Inverter

18. Operation of N transistor

19. Operation of P transistor

20. CMOS NOR GATE

21. CMOS NAND gate

22. Levels of abstractions of digital circuit
• There are three levels of abstractions of digital
circuit.
• They are
a) Switch level
b) Register level
c) Processor level

23. Switch level (Zero detector)

24. Zero detector

25. Disadvantage of analyzing circuit at
switch level
• Because many of the Ics contain huge number
of transistors, It is rarely practical to compute
at switch level. Instead we move to higher
levels of abstraction level known as gate level
or logic level.
• In this, we represent certain common sub
circuits by components called logic gates.

26. Representation in register level

27. Gate level representation
• The four logic gates in switch level are
representated by a primitive gate at Gate
level.
• When we treat the entire CPU, memory and
computer as a primitive component we have
involved to the higher level of abstraction
called processor or system level.