overview of VLSI DESIGN

1. EC8095-VLSI DESIGN
INTRODUCTION AND FUNDAMENTALS
Prepared by
Mrs.T.G.RAMABHARATHI
ASSISTANT PROFESSOR
ECE DEPARTMENT
KARPAGAM INSTITUTE OF TECHNOLOGY,COIMBATORE.

2. UNIT-I INTRODUCTION TO MOS TRANSISTOR
• An MOS (Metal-Oxide-Silicon) structure is created by superimposing several layers
of conducting, insulating, and transistor forming materials.
• After a series of processing steps, a typical structure might consists of levels
called diffusion, polysilicon, and metal that are separated by insulating layers.
• CMOS technology provides two types of transistors, an n-type transistor (n MOS)
and a p-type transistor (p MOS). These are fabricated in silicon by using either
negatively doped silicon that is rich in electrons (negatively charged) or positively
doped silicon that is rich in holes (the dual of electrons and positively charged).
• For the n-transistor, the structure consists of a section of p-type silicon separating
two diffused areas of n-type silicon.
• The area separating the n regions is capped with a sandwich consisting of an
insulator and a conducting electrode called the GATE. Similarly, for the p-
transistor the structure consists of a section of n-type silicon separating two p-type
diffused areas.

3. Contd…
• The p-transistor also has a gate electrode. The gate is a control input and it affects
the flow of electrical current between the drain and source. The drain and source
may be viewed as two switched terminals.
• The design considerations for a simple inverter to address the synthesis of arbitrary
digital gates such as NOR, NAND and XOR is discussed.
• The focus is on combinational logic (or non-regenerative) circuits; this is, circuits
that have the property that at any point in time, the output of the circuit is related to
its current input signals by some Boolean expression (assuming that the transients
through the logic gates have settled).

4. UNIT II COMBINATIONAL MOS LOGIC CIRCUITS
• This is in contrast to another class of circuits, known as sequential or
regenerative, for which the output is not only a function of the current input
data, but also of previous values of the input signals.
• This is accomplished by connecting one or more outputs intentionally back
to some inputs. Consequently, the circuit “remembers” past events and has
a sense of history.
• A sequential circuit includes a combinational logic portion and a module that
holds the state. Example circuits are registers, counters, oscillators, and
memory.

5. Contd…
• There are numerous circuit styles to implement a given logic function. As
with the inverter, the common design metrics by which a gate is evaluated
are area, speed, energy and power.
• Depending on the application, the emphasis will be on different metrics. For
instance, the switching speed of digital circuits is the primary metric in a
high-performance processor, while it is energy dissipation in a battery
operated circuit.
• In addition to these metrics, robustness to noise and reliability are also very
important considerations. We will see that certain logic styles can
significantly improve performance, but are more sensitive to noise.
• Recently, power dissipation has also become a very important requirement
and significant emphasis is placed on understanding the sources of power
and approaches to deal with power.

6. UNIT III SEQUENTIAL CIRCUIT DESIGN
• The design of a synchronous sequential circuit starts from a set of
specifications and culminates in a logic diagram or a list of Boolean
functions from which a logic diagram can be obtained.
• In contrast to a combinational logic, which is fully specified by a truth
table, a sequential circuit requires a state table for its specification.
The first step in the design of sequential circuits is to obtain a state
table or an equivalence representation, such as a state diagram.

7. UNIT IV-DESIGN OF ARITHMETIC BUILDING
BLOCKS AND SUBSYSTEM
• This Unit deals with Arithmetic unit - Bit-sliced data path (adder ,
multiplier, shifter, comparator, etc.) and Memory - RAM, ROM,
Buffers, Shift registers.
• A synchronous sequential circuit is made up of flip-flops and
combinational gates. The design of the circuit consists of
choosing the flip-flops and then finding the combinational
structure which, together with the flip-flops, produces a circuit
that fulfils the required specifications. The number of flip-flops is
determined from the number of states needed in the circuit.

8. UNIT-V IMPLEMENTATION
STRATEGIES
• This unit provides the basic concept of the technologies available in the
Integrated Circuits (ICs). Improvements in Large Scale Integration (VLSI)
technology have brought chips with millions of transistors into our offices
and homes.
• The chips may also be designed for the own applications and these chips
are called Application Specific Integrated circuits (ASICs).
• ASIC design methodology use chips with array of prefabricated gates (gate
arrays) or chips based on libraries of standard function cells (standard cell
design).
• Full custom IC have maximum density and performance for high-volume
standard products. Application Specific Standard Products (ASSPs)
incorporated the value added features for specific market segments such as
complete controllers for workstations.

9. Thank you