28-12-2012, 05:14 PM
VLSI COURSE MATERIAL
[attachment=45638]
Introduction
The quantities that are to be measured, monitored, recorded, processed and
controlled are analog and digital, depending on the type of system used. It is important
when dealing with various quantities that we be able to represent their values efficiently
and accurately. There are basically two ways of representing the numerical value of
quantities: analog and digital.
Analog Representation
Systems which are capable of processing a continuous range of values varying
with respect to time are called analog systems. In analog representation a quantity is
represented by a voltage, current, or meter movement that is proportional to the value of
that quantity. Analog quantities such as those cited above have an important
characteristic: they can vary over a continuous range of values.
Digital Representation
Systems which process discrete values are called digital systems. In digital
representation the quantities are represented not by proportional quantities but by
symbols called digits. As an example, consider the digital watch, which provides the
time of the day in the form of decimal digits representing hours and minutes (and
sometimes seconds). As we know, time of day changes continuously, but the digital
watch reading does not change continuously; rather, it changes in steps of one per
minute (or per second). In other words, time of day digital representation changes in
discrete steps, as compared to the representation of time provided by an analog watch,
where the dial reading changes continuously.
Digital Techniques
· Easier to design. Exact values of voltage or current are not important, only the
range (HIGH or LOW) in which they fall.
· Information storage is easy.
· Accuracy and precision are greater.
· Operations can be programmed. Analog systems can also be programmed, but
the available operations variety and complexity is severely limited.
· Digital circuits are less affected by noise, as long as the noise is not large enough
to prevent us from distinguishing HIGH from LOW (we discuss this in detail in
an advanced digital tutorial section).
· More digital circuitry can be fabricated on IC chips.
Limitations of Digital Techniques
Most physical quantities in real world are analog in nature, and these
quantities are often the inputs and outputs that are being monitored, operated on, and
controlled by a system. Thus conversion to digital format and re-conversion to analog
format is needed.
Numbering System
Many number systems are in use in digital technology. The most common
are the decimal, binary, octal, and hexadecimal systems. The decimal system is clearly
the most familiar to us because it is a tool that we use every day. Examining some of its
characteristics will help us to better understand the other systems. In the next few pages
we shall introduce four numerical representation systems that are used in the digital
system. There are other systems, which we will look at briefly.
· Decimal
· Binary
· Octal
· Hexadecimal
[attachment=45638]
Introduction
The quantities that are to be measured, monitored, recorded, processed and
controlled are analog and digital, depending on the type of system used. It is important
when dealing with various quantities that we be able to represent their values efficiently
and accurately. There are basically two ways of representing the numerical value of
quantities: analog and digital.
Analog Representation
Systems which are capable of processing a continuous range of values varying
with respect to time are called analog systems. In analog representation a quantity is
represented by a voltage, current, or meter movement that is proportional to the value of
that quantity. Analog quantities such as those cited above have an important
characteristic: they can vary over a continuous range of values.
Digital Representation
Systems which process discrete values are called digital systems. In digital
representation the quantities are represented not by proportional quantities but by
symbols called digits. As an example, consider the digital watch, which provides the
time of the day in the form of decimal digits representing hours and minutes (and
sometimes seconds). As we know, time of day changes continuously, but the digital
watch reading does not change continuously; rather, it changes in steps of one per
minute (or per second). In other words, time of day digital representation changes in
discrete steps, as compared to the representation of time provided by an analog watch,
where the dial reading changes continuously.
Digital Techniques
· Easier to design. Exact values of voltage or current are not important, only the
range (HIGH or LOW) in which they fall.
· Information storage is easy.
· Accuracy and precision are greater.
· Operations can be programmed. Analog systems can also be programmed, but
the available operations variety and complexity is severely limited.
· Digital circuits are less affected by noise, as long as the noise is not large enough
to prevent us from distinguishing HIGH from LOW (we discuss this in detail in
an advanced digital tutorial section).
· More digital circuitry can be fabricated on IC chips.
Limitations of Digital Techniques
Most physical quantities in real world are analog in nature, and these
quantities are often the inputs and outputs that are being monitored, operated on, and
controlled by a system. Thus conversion to digital format and re-conversion to analog
format is needed.
Numbering System
Many number systems are in use in digital technology. The most common
are the decimal, binary, octal, and hexadecimal systems. The decimal system is clearly
the most familiar to us because it is a tool that we use every day. Examining some of its
characteristics will help us to better understand the other systems. In the next few pages
we shall introduce four numerical representation systems that are used in the digital
system. There are other systems, which we will look at briefly.
· Decimal
· Binary
· Octal
· Hexadecimal