Overview of Electronics Register:-
A register is a
very small amount of very fast memory
that is built into the CPU (central processing unit) in order to speed up its
operations by providing quick access to commonly used values.
Memory refers
to semiconductor devices whose contents can be accessed (i.e., read and written
to) at extremely high speeds but which are held there only temporarily (i.e.,
while in use or only as long as the power supply remains on). Most memory
consists of main memory, which is comprised of RAM (random access memory) chips that are
connected to the CPU by a bus .Registers are the top of the memory hierarchy
and are the fastest way for the system to manipulate data. Below them are
several levels of cache memory, at least some of which is also built into the
CPU and some of which might be on other, dedicated chips. Cache memory is
slower than registers but much more abundant. Below the various levels of cache
is the main memory, which is even slower but vastly more abundant (e.g.,
hundreds of megabytes as compared with only 32 registers). But it, in turn, is
still far faster and much less capacious than storage devices and media (e.g., hard disk
drives and CDROMs).
Most registers
are implemented as an array of SRAM (static random access memory) cells. SRAM
is a type of RAM that is much faster and more reliable than the DRAM (dynamic
random access memory), which is used for main memory because of its lower cost
and smaller space consumption. The term static is employed because SRAM does
not need to be electrically refreshed as does DRAM, although it is still
volatile .
Registers are
normally measured by the number of bits they can hold, for example, an 8-bit
register or a 32-bit register. The x86 (i.e., Intel-compatible) instruction set
defines a set of eight 32-bit registers. However, CPUs that implement this
instruction set generally contain many more registers than just these eight,
including various specialized types. An instruction set is the aspects of a
computer architecture visible to a programmer, including the native datatypes,
instructions, registers, addressing modes, memory architecture, interrupt and
exception handling and external input/output.
Registers can
also be classified into general purpose and special purpose types. The former
serve as temporary holding places for data that is being manipulated by the
CPU. That is, they hold the inputs to the arithmetic/logic circuitry and store
the results produced by that circuitry.
Special
purpose registers store internal CPU data, such as the program counter (also
termed instruction pointer), stack pointer and status register.
Capacitor and Inductors:-
A capacitor (originally
known as condenser) is a passive two-terminal electrical
component used to store energy in an electric field. The forms
of practical capacitors vary widely, but all contain at least two electrical
conductors separated by a dielectric(insulator); for
example, one common construction consists of metal foils separated by a thin
layer of insulating film. Capacitors are widely used as parts of electrical circuits in
many common electrical devices.
When there is
a potential
difference (voltage) across the conductors, a static electric field develops
across the dielectric, causing positive charge to collect on one plate and
negative charge on the other plate. Energy is stored in the electrostatic
field. An ideal capacitor is characterized by a single constant value, capacitance, measured
in farads. This is the ratio
of the electric charge on
each conductor to the potential difference between them.
The capacitance
is greatest when there is a narrow separation between large areas of conductor,
hence capacitor conductors are often called plates, referring to an early
means of construction. In practice, the dielectric between the plates passes a
small amount of leakage current and
also has an electric field strength limit, resulting in a breakdown voltage, while
the conductors and leadsintroduce an
undesired inductance and resistance.
Capacitors are
widely used in electronic circuits for blocking direct current while
allowing alternating
current to pass, in filter networks, for smoothing the output
of power supplies,
in the resonant circuits that
tune radios to particular frequencies,
in electric power transmission systems for stabilizing voltage and power flow,
and for many other purposes.
Inductor-
An inductor
(also choke, coil, or reactor) is a passive
two-terminal
electrical
component that stores energy
in its magnetic field.
For comparison, a capacitor
stores energy in an electric field,
and a resistor does not store
energy but rather dissipates energy as heat.
Any conductor
has inductance. An inductor is
typically made of a wire or other conductor wound into a coil, to increase the magnetic field.
When the
current flowing through an inductor changes, a time-varying magnetic field is
created inside the coil, and a voltage is induced, according to Faraday’s law of
electromagnetic induction, which by Lenz's law opposes the
change in current that created it. Inductors are one of the basic components
used in electronics where current and voltage change with time, due to the
ability of inductors to delay and reshape alternating currents.
Semiconductor devices:
Diodes:- In electronics,
a diode is a two-terminal electronic
component with an asymmetric transfer characteristic,
with low (ideally zero) resistanceto
current flow in one direction, and high (ideally infinite) resistance in
the other. A semiconductor diode, the most common type today, is a crystalline piece
of semiconductor material
with a p-n junction connected
to two electrical terminals.[5] A vacuum
tube diode is a vacuum tube with
two electrodes,
a plate (anode)
and heated cathode.
The most common
function of a diode is to allow an electric current to pass in one direction
(called the diode's forward direction), while blocking current in the
opposite direction (the reverse direction). Thus, the diode can be
viewed as an electronic version of a check valve. This unidirectional
behavior is called rectification,
and is used to convert alternating HYPERLINK
"http://en.wikipedia.org/wiki/Alternating_current" HYPERLINK
"http://en.wikipedia.org/wiki/Alternating_current"HYPERLINK
"http://en.wikipedia.org/wiki/Alternating_current" HYPERLINK
"http://en.wikipedia.org/wiki/Alternating_current"HYPERLINK "http://en.wikipedia.org/wiki/Alternating_current"
HYPERLINK "http://en.wikipedia.org/wiki/Alternating_current"HYPERLINK
"http://en.wikipedia.org/wiki/Alternating_current"current to direct current, including
extraction ofmodulation from
radio signals in radio receivers—these diodes are forms of rectifiers.
However, diodes
can have more complicated behavior than this simple on–off action.
Semiconductor diodes begin conducting electricity only if a certain threshold
voltage or cut-in voltage is present in the forward direction (a state in which
the diode is said to be forward-biased).
The voltage drop across a forward-biased diode varies only a little with the
current, and is a function of temperature; this effect can be used as atemperature sensor or voltage reference.
Semiconductor
diodes' nonlinear current–voltage characteristic can be tailored by varying
the semiconductor materials and doping,
introducing impurities into the materials. These are exploited in
special-purpose diodes that perform many different functions. For example,
diodes are used to regulate voltage (Zener diodes), to protect
circuits from high voltage surges (avalanche diodes), to
electronically tune
Transistors (BJT and
FET)- A transistor is a semiconductor
device used to amplify and switch electronic signals
and electrical power. It is composed of semiconductormaterial with
at least three terminals for connection to an external circuit. A voltage or
current applied to one pair of the transistor's terminals changes the current
flowing through another pair of terminals. Because the controlled
(output) power can
be higher than the controlling (input) power, a transistor can amplify a signal. Today, some
transistors are packaged individually, but many more are found embedded
in integrated
circuits.
The transistor
is the fundamental building block of modern electronic devices, and is
ubiquitous in modern electronic systems. Following its development in the early
1950s the transistor revolutionized the field of electronics, and paved the way
for smaller and cheaper radios, calculators, and computers, among other
things.
JFET
and BJT
IMPEDENCE IS HIGH COMPARED THEN BJT. JFET IS VOLTAGE DRIVEN DEVICE WHILE AS BJT CURRENT DRIVEN DEVICE. IN JFET THERE ARE NO JUNCTIONS AS IN ORDINARY TRANSISTOR, CONDUCTION IS THROUGH AN n-TYPE OR p-TYPE SEMICONDUCTOR MATERIAL. FOR THIS REASON NOISE LEVEL IS VERY SMALL.
== Answer == bjt is a bipolar device involving both types of charge carriers ,where as fet is a unipolar device involving only one type of charge carrier.the main difference is that bjt is current controller device and fet is voltage controller device
-------------------and----------------------------------------------
fet has high input impedance compared to bjt
fet has low noise compared to bjt.
fet has low power dissipation compared to bjt
Fet has better temp stability as compared to bjt.
Bjt is more temp sensitive than fet
Bjt has better driving capability (fanout) than fet
and bjt also has has high speed switching compared to fet
IMPEDENCE IS HIGH COMPARED THEN BJT. JFET IS VOLTAGE DRIVEN DEVICE WHILE AS BJT CURRENT DRIVEN DEVICE. IN JFET THERE ARE NO JUNCTIONS AS IN ORDINARY TRANSISTOR, CONDUCTION IS THROUGH AN n-TYPE OR p-TYPE SEMICONDUCTOR MATERIAL. FOR THIS REASON NOISE LEVEL IS VERY SMALL.
== Answer == bjt is a bipolar device involving both types of charge carriers ,where as fet is a unipolar device involving only one type of charge carrier.the main difference is that bjt is current controller device and fet is voltage controller device
-------------------and----------------------------------------------
fet has high input impedance compared to bjt
fet has low noise compared to bjt.
fet has low power dissipation compared to bjt
Fet has better temp stability as compared to bjt.
Bjt is more temp sensitive than fet
Bjt has better driving capability (fanout) than fet
and bjt also has has high speed switching compared to fet
Analog vs Digital electronics- In
a very simplistic way, the field of electronics can be divided into two
branches: analog electronics and digital electronics.
Analog electronics is that branch of electronics
that people usually think of when they think of electronics. It is the branch
that deals with such things as resistors and capacitors. In analog
electronics, voltages and currents can take on practically any value (to within
the physical limitations of the equipment or electrical components of the
circuit being used). Thus, in an analog circuit, information tends to be
conveyed by the magnitude of the voltage or current signal. For example,
the intensity of light being measured by a light sensor may be proportional to
the current being produced in the sensor circuit which exploits the
photoelectric effect. (This is of course the branch of electronics that we
studied earlier in this course.)
Digital electronics is that branch of electronics
that deals with such beasts as logic gates, counters, flip-flops, or, more
generically, the digital integrated circuit chip (often simply called circuit
chips).In digital electronics, voltages can take on only one of two possible
values (to within limited ranges). This means that information in a
digital circuit cannot be conveyed by the magnitude of the voltage signal, but
rather must be conveyed using the concepts of binary logic.
For our purposes, logical 1 and 0 will be
represented by voltage signals. A logical 1 will be represented by a voltage in
the range 3 to 5 V, and a logical 0 will be represented by a voltage in the
range 0 to 1.7 V. These voltage signals may be used as inputs or measured
as outputs in digital circuits.
We were originally introduced to the logic
functions AND, OR and NOT from the viewpoint of symbolic logic. In
digital electronics these operations are performed by what are called
electrical logic gates. All logical operators can be reduced to
operations involving the AND, OR and NOT gates.
In the following sections we will be introduced to
the circuit symbols used to represent the three fundamental logic gates. We
will then see how to build a truth table from a given circuit diagram
containing logic gates.
Transistor as a switch- When used as an AC
signal amplifier, the transistors Base biasing voltage is applied in such a way
that it always operates within its "active" region, that is the
linear part of the output characteristics curves are used. However, both the
NPN & PNP type bipolar transistors can be made to operate as
"ON/OFF" type solid state switches by biasing the transistors base
differently to that of a signal amplifier.
Solid state switches are one of the main
applications for the use of transistors, and transistor switches can be used
for controlling high power devices such as motors, solenoids or lamps, but they
can also used in digital electronics and logic gate circuits.
If the circuit uses the Bipolar Transistor as a
Switch, then the biasing of the transistor, either NPN or PNP is arranged to
operate the transistor at both sides of the " I-V "
characteristics curves we have seen previously.
The areas of operation for a transistor switch are
known as the Saturation Region and the Cut-off Region. This means then that we
can ignore the operating Q-point biasing and voltage divider circuitry required
for amplification, and use the transistor as a switch by driving it back and
forth between its "fully-OFF" (cut-off) and "fully-ON"
(saturation) regions as shown below.
Integrated circuits- An integrated
circuit or monolithic integrated circuit (also referred to as
an IC, a chip, or a microchip) is a set of electronic circuitson one
small plate ("chip") of semiconductor
material, normally silicon. This can be made
much smaller than a discrete circuit made
from independent components.
Integrated circuits are used in virtually all
electronic equipment today and have revolutionized the world of electronics. Computers, mobile phones, and other
digital home appliances are
now inextricable parts of the structure of modern societies, made possible by
the low cost of producing integrated circuits.
ICs can be made very compact, having up to several
billion transistors and
other electronic components in
an area the size of a fingernail. The width of each conducting line in a
circuit (the line width)
can be made smaller and smaller as the technology advances, in 2008 it dropped
below 100 nanometers and
in 2013 it is expected to be in the teens of nanometers.
SSI, MSI, LSI, and VLSI circuits-
The
first integrated circuits contained only a few transistors. Called
"small-scale integration" (SSI), digital circuits containing
transistors numbering in the tens provided a few logic gates for example, while
early linear ICs such as the Plessey
SL201 or the Philips
TAA320 had as few as two transistors. The term Large Scale Integration was
first used by IBM
scientist Rolf Landauer
when describing the theoretical concept[citation needed],
from there came the terms for SSI, MSI, VLSI, and ULSI.
SSI circuits were crucial to early aerospace
projects, and aerospace projects helped inspire development of the technology.
Both the Minuteman missile
and Apollo program
needed lightweight digital computers for their inertial guidance systems; the Apollo guidance
computer led and motivated the integrated-circuit technology,[15] while the Minuteman
missile forced it into mass-production. The Minuteman missile program and
various other Navy programs accounted for the total $4 million integrated
circuit market in 1962, and by 1968, U.S. Government space and defense spending
still accounted for 37% of the $312 million total production. The demand by the
U.S. Government supported the nascent integrated circuit market until costs
fell enough to allow firms to penetrate the industrial and eventually the
consumer markets. The average price per integrated circuit dropped from $50.00
in 1962 to $2.33 in 1968.[16] Integrated circuits
began to appear in consumer products by the turn of the decade, a typical
application being FM
inter-carrier sound processing in television receivers.
The next step in the development of integrated
circuits, taken in the late 1960s, introduced devices which contained hundreds
of transistors on each chip, called "medium-scale integration" (MSI).
They were attractive economically because while
they cost little more to produce than SSI devices, they allowed more complex
systems to be produced using smaller circuit boards, less assembly work
(because of fewer separate components), and a number of other advantages.
Further development, driven by the same economic
factors, led to "large-scale integration" (LSI) in the mid 1970s,
with tens of thousands of transistors per chip.
Integrated circuits such as 1K-bit RAMs, calculator
chips, and the first microprocessors, that began to be manufactured in moderate
quantities in the early 1970s, had under 4000 transistors. True LSI circuits,
approaching 10,000 transistors, began to be produced around 1974, for computer
main memories and second-generation microprocessors.
VLSI
Main article: Very-large-scale
integration
The final step in the development process, starting
in the 1980s and continuing through the present, was "very large-scale
integration" (VLSI).
The development started with hundreds of thousands of transistors in the early
1980s, and continues beyond several billion transistors as of 2009.
Multiple developments were required to achieve this
increased density. Manufacturers moved to smaller design rules and cleaner
fabrication facilities, so that they could make chips with more transistors and
maintain adequate yield. The path of process improvements was summarized by the
International
Technology Roadmap for Semiconductors (ITRS). Design tools
improved enough to make it practical to finish these designs in a reasonable
time. The more energy efficient CMOS
replaced NMOS
and PMOS, avoiding a
prohibitive increase in power consumption.
In 1986 the first one megabit RAM
chips were introduced, which contained more than one million transistors.
Microprocessor chips passed the million transistor mark in 1989 and the billion
transistor mark in 2005. The trend
continues largely unabated, with chips introduced in 2007 containing tens of
billions of memory transistors.
Multivibrators – astable, bistable,
monostable- A
multivibrator is an electronic circuit
used to implement a variety of simple two-state systems such as oscillators, timers and flip-flops.
It is characterized by two amplifying devices
(transistors, electron tubes or other
devices) cross-coupled by resistors
or capacitors. The name
"multivibrator" was initially applied to the free-running oscillator
version of the circuit because its output waveform was rich in harmonics.[1] There are three types
of multivibrator circuits depending on the circuit operation:
•
astable,
in which the circuit is not stable in either state
—it continually switches from one state to the other. It functions as a relaxation
oscillator.
•
monostable,
in which one of the states is stable, but the other state is unstable
(transient). A trigger pulse causes the circuit to enter the unstable state.
After entering the unstable state, the circuit will return to the stable state
after a set time. Such a circuit is useful for creating a timing period of
fixed duration in response to some external event. This circuit is also known
as a one shot.
•
bistable,
in which the circuit is stable in either state. It can be flipped from one
state to the other by an external trigger pulse. This circuit is also known as
a flip flop.
It can be used to store a bit of
information.
Multivibrators find applications in a variety of
systems where square waves or timed intervals are required. For example, before
the advent of low-cost integrated circuits, chains of multivibrators found use
as frequency dividers.
A free-running multivibrator with a frequency of one-half to one-tenth of the
reference frequency would accurately lock to the reference frequency. This
technique was used in early electronic organs, to keep notes of different octaves accurately in tune. Other
applications included early television
systems, where the various line and frame frequencies were kept synchronized by
pulses included in the video signal.
Counters Ripple And Decade-
Electronic counters
In electronics, counters can
be implemented quite easily using register-type circuits such as the flip-flop,
and a wide variety of classifications exist:
·
Asynchronous
(ripple) counter – changing state bits are used as clocks to subsequent state
flip-flops
·
Synchronous
counter – all state bits change under control of a single clock
·
Decade
counter – counts through ten states per stage
·
Up/down
counter – counts both up and down, under command of a control input
·
Ring
counter – formed by a shift register with feedback connection in a ring
·
Johnson
counter – a twisted ring counter
·
Cascaded
counter
·
modulas
counter.
Each is useful for different applications. Usually,
counter circuits are digital
in nature, and count in natural binary.
Many types of counter circuits are available as digital building blocks, for
example a number of chips in the 4000 series implement
different counters.
Occasionally there are advantages to using a
counting sequence other than the natural binary sequence—such as the binary coded
decimal counter, a linear feedback
shift register counter, or a Gray-code counter.
Counters are useful for digital clocks and timers,
and in oven timers, VCR clocks, etc.
Asynchronous (ripple) counter
Asynchronous counter created from two JK flip-flops
An asynchronous (ripple) counter is a single JK-type flip-flop,
with its J (data) input fed from its own inverted output. This circuit can
store one bit, and hence can count from zero to one before it overflows (starts
over from 0). This counter will increment once for every clock cycle and takes
two clock cycles to overflow, so every cycle it will alternate between a
transition from 0 to 1 and a transition from 1 to 0. Notice that this creates a
new clock with a 50% duty cycle
at exactly half the frequency of the input clock. If this output is then used
as the clock signal for a similarly arranged D flip-flop (remembering to invert
the output to the input), one will get another 1 bit counter that counts half
as fast. Putting them together yields a two-bit counter:
Cycle
|
Q1
|
Q0
|
(Q1:Q0)dec
|
0
|
0
|
0
|
0
|
1
|
0
|
1
|
1
|
2
|
1
|
0
|
2
|
3
|
1
|
1
|
3
|
4
|
0
|
0
|
0
|
You can continue to add additional flip-flops,
always inverting the output to its own input, and using the output from the
previous flip-flop as the clock signal. The result is called a ripple counter,
which can count to 2n − 1 where n is the number of bits (flip-flop
stages) in the counter. Ripple counters suffer from unstable outputs as the
overflows "Ripple" from stage to stage, but they do find frequent
application as dividers for clock signals, where the instantaneous count is
unimportant, but the division ratio
overall is (to clarify this, a 1-bit counter is exactly equivalent to a divide
by two circuit; the output frequency is exactly half that of the input when fed
with a regular train of clock pulses).
The use of flip-flop outputs as clocks leads to
timing skew between the count data bits, making this ripple technique
incompatible with normal synchronous circuit
design styles.
Decade counter
A circuit diagram of decade counter using JK
FlipFlops (74LS112D)
The decade counter is also known as a mod-counter
when it counts to ten (0, 1, 2, 3, 4, 5, 6, 7, 8, 9). A Mod Counter that counts
to 64 stops at 63 because 0 counts as a valid digit.
edge and level triggering-
Edge-triggered
An edge-triggered interrupt is an interrupt
signalled by a level transition
on the interrupt line, either a falling edge (high to low) or a rising edge
(low to high). A device wishing to signal an interrupt drives a pulse onto the
line and then releases the line to its inactive state. If the pulse is too
short to be detected by polled I/O
then special hardware may be required to detect the edge.
Multiple devices may share an edge-triggered
interrupt line if they are designed to. The interrupt line must have a
pull-down or pull-up resistor so that when not actively driven it settles to
one particular state. Devices signal an interrupt by briefly driving the line
to its non-default state, and let the line float (do not actively drive it)
when not signalling an interrupt. This type of connection is also referred to
as open collector.
The line then carries all the pulses generated by all the devices. (This is
analogous to the pull cord
on some buses and trolleys that any passenger can pull to signal the driver
that they are requesting a stop.) However, interrupt pulses from different
devices may merge if they occur close in time. To avoid losing interrupts the
CPU must trigger on the trailing edge of the pulse (e.g. the rising edge if the
line is pulled up and driven low). After detecting an interrupt the CPU must
check all the devices for service requirements.
Edge-triggered interrupts do not suffer the
problems that level-triggered interrupts have with sharing. Service of a
low-priority device can be postponed arbitrarily, and interrupts will continue
to be received from the high-priority devices that are being serviced. If there
is a device that the CPU does not know how to service, it may cause a spurious
interrupt, or even periodic spurious interrupts, but it does not interfere with
the interrupt signalling of the other devices. However, it is fairly easy for
an edge triggered interrupt to be missed - for example if interrupts have to be
masked for a period - and unless there is some type of hardware latch that
records the event it is impossible to recover. Such problems caused many
"lockups" in early computer hardware because the processor did not
know it was expected to do something. More modern hardware often has one or
more interrupt status registers that latch the interrupt requests; well written
edge-driven interrupt software often checks such registers to ensure events are
not missed.
The elderly Industry Standard
Architecture (ISA) bus uses edge-triggered interrupts, but does not
mandate that devices be able to share them. The parallel port also uses
edge-triggered interrupts. Many older devices assume that they have exclusive
use of their interrupt line, making it
Level-triggered
A level-triggered interrupt is an interrupt for
which an unserviced interrupt is indicated by a particular state, high level or
low level, of the interrupt request
line. A device wishing to signal an interrupt drives the line to its active
level, and then holds it at that level until serviced. It ceases asserting the
line when the CPU commands it to or otherwise handles the condition that caused
it to signal the interrupt.
Typically, the processor samples the interrupt
input at predefined times during each bus cycle such as state T2 for the Z80 microprocessor. If the interrupt isn't
active when the processor samples it, the CPU doesn't see it. One possible use
for this type of interrupt is to minimize spurious signals from a noisy
interrupt line: a spurious pulse will often be so short that it is not noticed.
Multiple devices may share a level-triggered
interrupt line if they are designed to. The interrupt line must have a
pull-down or pull-up resistor
so that when not actively driven it settles to its inactive state. Devices
actively assert the line to indicate an outstanding interrupt, but let the line
float (do not actively drive it) when not signalling an interrupt. The line is
then in its asserted state when any (one or more than one) of the sharing
devices is signalling an outstanding interrupt.
This class of interrupts is favored by some because
of a convenient behavior when the line is shared. Upon detecting assertion of
the interrupt line, the CPU must search through the devices sharing it until
one requiring service is detected. After servicing this device, the CPU may
recheck the interrupt line status to determine whether any other devices also
need service. If the line is now de-asserted, the CPU avoids checking the
remaining devices on the line. Since some devices interrupt more frequently
than others, and other device interrupts are particularly expensive, a careful
ordering of device checks is employed to increase efficiency.
There are also serious problems with sharing
level-triggered interrupts. As long as any device on the line has an
outstanding request for service the line remains asserted, so it is not
possible to detect a change in the status of any other device. Deferring
servicing a low-priority device is not an option, because this would prevent
detection of service requests from higher-priority devices. If there is a
device on the line that the CPU does not know how to service, then any interrupt
from that device permanently blocks all interrupts from the other devices.
The original PCI
standard mandated shareable level-triggered interrupts. The rationale for this
was the efficiency gain discussed above. (Newer versions of PCI allow, and PCI Express requires the
use of message-signaled
interrupts.)
