19-10-2012, 01:21 PM
An Introduction To Digital Signal Processors
[attachment=36679]
INTRODUCTION
COMPUTERS AND MICROPROCESSORS
Charles Babbage invented the concept of computer in the mid 19th century, but the
concept had to wait for the development of vacuum tube electronics in the 1930s to
achieve its full potential.
John W. Mauchly and J. Presper Eckert at University of Pennsylvania’s Moore School of
Electrical Engineering developed one of the first electronic computers between 1942
and 1946. Called ENIAC (Electronic Numerical Integrator and Computer), it was
originally used to calculate ballistic tables for the military. With 17 468 vacuum tubes
and 100 feet of front panel, this 30 tons mighty machine was capable of doing 5000
additions and 300 multiplications a second. Although it is less than 1/10 000th the
computational speed found in a modern cellular phone, due to its “all electronic” design,
it was the fastest computer in use at the time. Later models were used for nuclear
physics and aerodynamics research, two fields where the super-computer is still a tool
of the trade today.
Although not publicised at the time, the first electronic computer was actually built by
Tommy Flowers, an electronics engineer in the British secret service, during the Second
World War. This computer called Colossus was used by the British secret service to
decipher German military codes. Because of the secrecy that surrounded these
operations it was not recognized as the first electronic computer until recently.
Initially computers were used to carry out numerical computations, but nowadays they
are used in many applications from music players to flight control systems.
A computer performs its task by the sequential execution of elementary binary
operations called “instructions”. These elementary instructions may represent the
addition of two numbers for instance, or a comparison between two numbers, or the
transfer of a binary word from one memory location to another. They are assembled in a
complete “program” that defines the global task carried out by the computer.
The part of the computer that executes the instructions is called the Central Processing
Unit (CPU).
APPLICATION AREAS OF THE MICROPROCESSOR
The most obvious application of the microprocessor is the computer. From the supercomputer
used for scientific computation to the pocket personal computer used for word
processing or Internet browsing, computers have become an essential tool in our
everyday life.
The world of computer systems however accounts only for a small fraction of the total
number of microprocessors deployed in applications around the world. The vast majority
of microprocessors are used in embedded systems. Embedded systems are electronic
devices or sub-systems that use microprocessors for their operation. The low cost of
microprocessors, combined to the flexibility offered by programming makes them
omnipresent in areas ranging from customer electronics to telecommunication systems.
Today, it is actually very difficult to find electronic devices or sub-systems that do not
incorporate at least one microprocessor. Needless to say, the vast majority of the
engineering and design activity related to microprocessor systems is in the area of
embedded systems.
By contrast to computer systems, the program of an embedded system is fixed, usually
unique, and designed during the development of the device. It is often permanently
stored in a Read Only Memory and begins its execution from the moment the device
powered on. Because it is fixed and usually resides in a Read Only Memory, the
software of an embedded system is often called firmware.
EXAMPLES OF EMBEDDED SYSTEMS
At home, the microprocessor is used to control many appliances and electronic devices:
microwave oven, television set, compact-disk player, alarm system are only a few
examples. In the automobile microprocessors are used to control the combustion of the
engine, the door locks, the brake system (ABS brakes) and so on… Microprocessors
are used in most measuring instruments (oscilloscopes, multi-meters, signal
generators…etc). In telecommunication systems microprocessors are used in systems
ranging from telephone sets to telephone switches. In the aerospace industry they are
used in in-flight navigation systems and flight control systems.
Microprocessors are even used in very low-cost applications such as wristwatches,
medical thermometers and musical cards.
Even in computer systems, embedded microprocessors are used in pointing devices,
keyboards, displays, hard disk drives, modems… and even in the battery packs of
laptop computers!
Cost of a microprocessor
Like many other electronic components, microprocessors are fabricated from large disks
of mono-crystalline silicon called “wafers”. Using photolithographic processes hundreds
of individual microprocessor chips are typically fabricated on a single wafer. The cost of
processing a wafer is in general fixed, irrespective of the complexity of the
microprocessors that are etched onto it.
The silicon surface occupied by a microprocessor on the wafer is dependant on several
factors. The most important factors being its complexity (number of gates, or
transistors), and the lithographic scale indicating how small a gate can be.
At first glance, for a given fabrication process and a given lithographic scale, it would
seem that the cost of a microprocessor is roughly proportional to its surface area,
therefore to its complexity.
However things are a little bit more complex. In practice the wafers are not perfect and
have a number of defects that are statistically distributed on their surface. A
microprocessor whose area includes the defect is generally not functional. There are
therefore always some defective microprocessors on the wafer at the end of the
process. The ratio of good microprocessors to the total number fabricated on the wafer
is called the “fabrication yield”. For a fixed number of defects per square inch on the
wafer, which is dependant on the quality of the wafer production, the probability of a
microprocessor containing a defect increases non-linearly with the microprocessor area.
Beyond a certain surface area (beyond a certain complexity) the fabrication yield
decreases considerably. Of course the selling price of the good microprocessors is
increased to offset the cost of having to process and test the defective ones. In other
words the cost of a microprocessor increases much faster than its complexity and
surface area.
Power consumption of a microprocessor
As we discussed earlier, some microprocessors are optimized to have a low power
consumption. Today almost all microprocessors are implemented in CMOS technology.
For this technology, the electric current drawn by the microprocessor is almost entirely
attributable to the electric charges used to charge and discharge the parasitic input
capacitance of its gates during transitions from 0 to 1 and 1 to 0. This charge loss is
proportional to the following factors:
• The voltage swing (normally the supply voltage).
• The input gate capacitance.
• The number of gates in the microprocessor.
• The average number of transitions per second per gate.
The input gate capacitance is fairly constant. As manufacturing processes improve, the
lateral dimensions of transistor gates get smaller, but so does the thickness of the oxide
layers used for the gates. Typical values are on the order of a few pF per gate.
With thinner oxide layers, lower supply voltages can be used to achieve the same
electric field. A lower supply voltage mean that less charge is transferred during each
transition, which leads to a lower current consumption. This is the main factor behind the
push for decreasing supply voltages in digital electronics.
[attachment=36679]
INTRODUCTION
COMPUTERS AND MICROPROCESSORS
Charles Babbage invented the concept of computer in the mid 19th century, but the
concept had to wait for the development of vacuum tube electronics in the 1930s to
achieve its full potential.
John W. Mauchly and J. Presper Eckert at University of Pennsylvania’s Moore School of
Electrical Engineering developed one of the first electronic computers between 1942
and 1946. Called ENIAC (Electronic Numerical Integrator and Computer), it was
originally used to calculate ballistic tables for the military. With 17 468 vacuum tubes
and 100 feet of front panel, this 30 tons mighty machine was capable of doing 5000
additions and 300 multiplications a second. Although it is less than 1/10 000th the
computational speed found in a modern cellular phone, due to its “all electronic” design,
it was the fastest computer in use at the time. Later models were used for nuclear
physics and aerodynamics research, two fields where the super-computer is still a tool
of the trade today.
Although not publicised at the time, the first electronic computer was actually built by
Tommy Flowers, an electronics engineer in the British secret service, during the Second
World War. This computer called Colossus was used by the British secret service to
decipher German military codes. Because of the secrecy that surrounded these
operations it was not recognized as the first electronic computer until recently.
Initially computers were used to carry out numerical computations, but nowadays they
are used in many applications from music players to flight control systems.
A computer performs its task by the sequential execution of elementary binary
operations called “instructions”. These elementary instructions may represent the
addition of two numbers for instance, or a comparison between two numbers, or the
transfer of a binary word from one memory location to another. They are assembled in a
complete “program” that defines the global task carried out by the computer.
The part of the computer that executes the instructions is called the Central Processing
Unit (CPU).
APPLICATION AREAS OF THE MICROPROCESSOR
The most obvious application of the microprocessor is the computer. From the supercomputer
used for scientific computation to the pocket personal computer used for word
processing or Internet browsing, computers have become an essential tool in our
everyday life.
The world of computer systems however accounts only for a small fraction of the total
number of microprocessors deployed in applications around the world. The vast majority
of microprocessors are used in embedded systems. Embedded systems are electronic
devices or sub-systems that use microprocessors for their operation. The low cost of
microprocessors, combined to the flexibility offered by programming makes them
omnipresent in areas ranging from customer electronics to telecommunication systems.
Today, it is actually very difficult to find electronic devices or sub-systems that do not
incorporate at least one microprocessor. Needless to say, the vast majority of the
engineering and design activity related to microprocessor systems is in the area of
embedded systems.
By contrast to computer systems, the program of an embedded system is fixed, usually
unique, and designed during the development of the device. It is often permanently
stored in a Read Only Memory and begins its execution from the moment the device
powered on. Because it is fixed and usually resides in a Read Only Memory, the
software of an embedded system is often called firmware.
EXAMPLES OF EMBEDDED SYSTEMS
At home, the microprocessor is used to control many appliances and electronic devices:
microwave oven, television set, compact-disk player, alarm system are only a few
examples. In the automobile microprocessors are used to control the combustion of the
engine, the door locks, the brake system (ABS brakes) and so on… Microprocessors
are used in most measuring instruments (oscilloscopes, multi-meters, signal
generators…etc). In telecommunication systems microprocessors are used in systems
ranging from telephone sets to telephone switches. In the aerospace industry they are
used in in-flight navigation systems and flight control systems.
Microprocessors are even used in very low-cost applications such as wristwatches,
medical thermometers and musical cards.
Even in computer systems, embedded microprocessors are used in pointing devices,
keyboards, displays, hard disk drives, modems… and even in the battery packs of
laptop computers!
Cost of a microprocessor
Like many other electronic components, microprocessors are fabricated from large disks
of mono-crystalline silicon called “wafers”. Using photolithographic processes hundreds
of individual microprocessor chips are typically fabricated on a single wafer. The cost of
processing a wafer is in general fixed, irrespective of the complexity of the
microprocessors that are etched onto it.
The silicon surface occupied by a microprocessor on the wafer is dependant on several
factors. The most important factors being its complexity (number of gates, or
transistors), and the lithographic scale indicating how small a gate can be.
At first glance, for a given fabrication process and a given lithographic scale, it would
seem that the cost of a microprocessor is roughly proportional to its surface area,
therefore to its complexity.
However things are a little bit more complex. In practice the wafers are not perfect and
have a number of defects that are statistically distributed on their surface. A
microprocessor whose area includes the defect is generally not functional. There are
therefore always some defective microprocessors on the wafer at the end of the
process. The ratio of good microprocessors to the total number fabricated on the wafer
is called the “fabrication yield”. For a fixed number of defects per square inch on the
wafer, which is dependant on the quality of the wafer production, the probability of a
microprocessor containing a defect increases non-linearly with the microprocessor area.
Beyond a certain surface area (beyond a certain complexity) the fabrication yield
decreases considerably. Of course the selling price of the good microprocessors is
increased to offset the cost of having to process and test the defective ones. In other
words the cost of a microprocessor increases much faster than its complexity and
surface area.
Power consumption of a microprocessor
As we discussed earlier, some microprocessors are optimized to have a low power
consumption. Today almost all microprocessors are implemented in CMOS technology.
For this technology, the electric current drawn by the microprocessor is almost entirely
attributable to the electric charges used to charge and discharge the parasitic input
capacitance of its gates during transitions from 0 to 1 and 1 to 0. This charge loss is
proportional to the following factors:
• The voltage swing (normally the supply voltage).
• The input gate capacitance.
• The number of gates in the microprocessor.
• The average number of transitions per second per gate.
The input gate capacitance is fairly constant. As manufacturing processes improve, the
lateral dimensions of transistor gates get smaller, but so does the thickness of the oxide
layers used for the gates. Typical values are on the order of a few pF per gate.
With thinner oxide layers, lower supply voltages can be used to achieve the same
electric field. A lower supply voltage mean that less charge is transferred during each
transition, which leads to a lower current consumption. This is the main factor behind the
push for decreasing supply voltages in digital electronics.