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Integrated Circuit
An integrated circuit is electronic circuit or device that has electronic components on
a small semiconductor chip.
These are mainly two types of circuits: Digital or Analog.
Analog ICs handle continuous signals such as audio signals and Digital ICs handle discrete
signals such as binary values.
Types of Integrated Circuits
Digital Integrated Circuits handle discrete signals such as binary values (0 and 1). These
circuits use digital logic gates, multiplexers, flip flops etc. These circuits are easier to design
and economical.
Analog Integrated Circuits handle continuous signals. These are two types: linear integrated
circuits (Linear ICs) and Radio frequency integrated circuits (RF ICs).
Mixed Integrated Circuits are obtained by the combination of analog and digital integrated
circuits. Therefore it have digital to analog (A/D) converter, digital to analog (D/A) converter,
and clock/timing integrated circuits.
General types of integrated circuits are as following: Comparators, Switching IC, Audio
amplifiers, Operational amplifiers, Timers ICs.
Families of Integrated Circuits
• Diode Transistor Logic (DTL)
• Transistor - Transistor Logic (TTL)
• Emitter Coupled Logic (ECL)
• Complementary Metal Oxide Semiconductor Logic (CMOS)
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How does TTL work?
TTL gates are designed using at least two transistors and supporting components,
including resistors and diodes. Each component serves specific purposes:
• Transistors provide switching, turning on or off in response to input signals.
• Resistors limit current and help optimize voltage levels for the transistors.
• Diodes ensure current flows in only one direction, helping to stabilize the circuit.
Transistor Q1 is the input transistor. Inputs, such as A and B, feed the emitter of Q1.
Transistor Q2 serves as a phase splitter, and transistors Q3 and Q4 create a totem pole output
that provides high stability and a high fan-out capability for the output.
When inputs A and B are on -- logic 1 or high -- transistors Q2 and Q3 turn on and act
as amplifiers, while transistor Q4 turns on to create a logic 0 or low logic output. When either
or both inputs A and B are off -- logic 0 or low -- transistors Q2 and Q4 turn off to create a
logic 1 or high logic output.
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Characteristics and considerations of TTL
• Fan-in. This is the number of inputs connected to a gate or the number of inputs a TTL
gate can handle.
• Fan-out. This is the number of outputs a TTL gate can drive or operate without affecting
the gate's performance. This is typically 10 loads from other TTL gates.
• Power dissipation. This is the amount of power the gate or device will use. It's taken as
the product of supply voltage, measured in volts, multiplied by the current drawn,
measured in amperes, and is typically measured in milliwatts (mW). Power dissipation
for a typical TTL gate is about 10 mW.
• Propagation delay. This is the time needed for the gate's output to change in response to
a change in the gate's inputs. This is an expression of latency, and it limits the overall
digital circuit's top speed. Propagation delay is measured in nanoseconds (ns). The delay
for a typical TTL gate is about 10 ns.
• Noise margin. Digital signals aren't perfect; noise margin is the voltage range allowed
for the input signal voltage that won't affect the output logic level. Standard TTL gates
allow a noise margin of about 0.4 volts.
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• Temperature range. This is the range of safe operating temperatures allowed for the
gate. Standard 7400 family TTL gates have a temperature range from 0 to 70 degrees
Celsius; 5400 family gates have an extended range of minus 55 to 125 degrees Celsius.
• Special characteristics. Some TTL gate products were fabricated for high reliability and
radiation resistance for military and aerospace uses.
Types of TTL
• Standard TTL represents the traditional 7400 family of components with standard
characteristics, including a typical power dissipation of 10 mW per gate and a
propagation delay of 10 ns per gate.
• Fast TTL trades faster switching speeds for higher power consumption. For example, a
fast TTL gate might switch in 6 ns but use 22 mW. This is sometimes called high-power
TTL.
• Low-power TTL trades lower power consumption for slower switching speeds. For
example, a low-power TTL gate might use 1 mW but have a delay of up to 33 ns.
• Low-voltage TTL uses a 3.3 volts direct current supply voltage instead of the usual 5
VDC supply voltage, resulting in only about 2 mW of power per gate. The lower supply
voltage will lower power dissipation per gate and can help speed propagation delays
because the difference in logic 0 and logic 1 voltage levels is smaller.
• Schottky TTL includes Schottky diode clamps in the TTL gate, which accelerates gate
switching time to about 3 ns. However, this increases power use to about 19 mW per
gate.
• Low-power Schottky TTL, also called advanced Schottky TTL, combines low-power
TTL and Schottky diodes to offer a fast 9.5 ns propagation delay and 2 mW of power use
per gate.
• Open-collector TTL leaves the output transistor's collector lead open and effectively
unpowered from the chip's supply voltage, allowing designers to incorporate high-
voltage or grouped outputs to drive non-TTL loads. Examples of open-collector TTL ICs
include the traditional 7401 and 7403.
• Tri-state TTL, sometimes called three-state TTL, includes additional circuitry that lets
the gate be disconnected. It's often used in the design of bus TTL circuitry where
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21CMRE42 – Unit 3
numerous gates might be present on the same wire. The third disconnected state creates a
high-impedance state that isolates or disconnects the gate and prevents it from interfering
with other gates using the common bus connections.
The CMOS Inverter or NOT Gate
A NOT gate reverses the input logic state. Figure 1 shows a NOT gate employing two series-
connected enhancement-type MOSFETS, one n-channel (NMOS) and one p-channel
(PMOS).
The input is connected to the gate terminal of the
two transistors, and the output is connected to both drain
terminals.
Applying +V (logic 1) to the input (Vi), transistor Q2 is
“on,” and transistor Q1 remains “off.” Under this
condition, the output voltage (Vo) is close to 0 V (logic
0).
Connecting the input to ground (Vi = 0 V), transistor Q2 is “off,” and transistor Q1 is “on.”
Now, the output voltage is close to +V (logic 1).
A Y
0 1
1 0
Table 1. The truth table for a NOT circuit.
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The CMOS NAND Gate
NAND denotes NOT-AND.
Table 2 shows the truth table for a NAND circuit.
A B Y
0 0 1
0 1 1
1 0 1
1 1 0
Table 2. The truth table for a two-input NAND circuit.
Figure 2 shows a CMOS two-input NAND gate. P-channel transistors Q1 and Q2 are
connected in parallel between +V and the output terminal. N-channel transistors Q3 and Q4
are connected in series between the output terminal and ground.
Figure 2. A CMOS two-input NAND gate.
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With Q3 and Q4 transistors ”on” and Q1 and Q2 transistors “off,” the output is a logic 0. This
condition happens when both inputs, A and B, are logic 1, confirming the lowest row in the
above truth table.
With logic 0 in inputs A and B, Q3 and Q4 transistors are “off,” and Q1 and Q2 transistors
are “on,” producing a logic 1 output. This is consistent with the first row of the truth table.
When one of the inputs is a logic “1” and the other one is a logic “0”, either Q3 is “off” and
Q2 is “on” or Q4 is “off” and Q1 is “on.” The output in both cases is a logic “1,” validating
the second and the third rows of the truth table.
The NOR Gate
NOR signifies NOT-OR.
Table 3 shows the truth table for a NOR circuit.
A B Y
0 0 1
0 1 0
1 0 0
1 1 0
Table 3. The truth table for a two-input NOR circuit.
The output of a NOR gate is logic 1 with logic 0 in both inputs. The outcomes for other input
combinations are logic 0.
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Figure 3 shows a CMOS two-input NOR gate. P-channel transistors Q1 and Q2 are
connected in series between +V and the output terminal. N-channel transistors Q3 and Q4 are
connected in parallel between the output and ground.
Figure 3. A CMOS two-input NOR gate.
When both inputs, A and B, are logic 0, Q1 and Q2 are “on,” and Q3 and Q4 are “off,” and
the output is logic 1. This confirms the first row of the truth table above.
With both inputs logic 1, Q3 and Q4 are “on,” and Q1 and Q2 are “off,” producing a logic 0
output that confirms the last row of the truth table.
For the two remaining input combinations, either Q1 is “off” and Q3 is “on” or Q2 is “off”
and is Q4 “on”. In these cases, the output is logic 0 which is consistent with the above truth
table.
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The AND Gate
We can say that an AND gate is a NOT-NOT-AND or NOT-NAND. Then, it is just a NAND
gate followed by an inverter.
Table 4 shows the truth table for an AND circuit.
A B Y
0 0 0
0 1 0
1 0 0
1 1 1
Table 4. The truth table for a two-input CMOS AND circuit.
Figure 4 shows a CMOS two-input AND gate.
Figure 4. A CMOS two-input AND gate.
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The OR Gate
An OR gate is a NOT-NOT-OR or NOT-NOR. Then, it is a NOR gate followed by an
inverter.
Table 5 shows the truth table for the OR circuit.
A B Y
0 0 0
0 1 1
1 0 1
1 1 1
Table 5. The truth table for a two-input OR circuit.
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Figure 5. A CMOS two-input OR gate.
Advantages of CMOS
A CMOS gate also draws much less current from a driving gate output than a TTL gate
because MOSFETs are voltage-controlled, not current-controlled, devices. This means that
one gate can drive many more CMOS inputs than TTL inputs. The measure of how many
gate inputs a single gate output can drive is called fanout.
Another advantage that CMOS gate designs enjoy over TTL is a much wider allowable range
of power supply voltages. Whereas TTL gates are restricted to power supply (Vcc) voltages
between 4.75 and 5.25 volts, CMOS gates are typically able to operate on any voltage
between 3 and 15 volts!
TTL gate circuit resistances are precisely calculated for proper bias currents assuming a 5
volt regulated power supply. Any significant variations in that power supply voltage will
result in the transistor bias currents being incorrect, which then results in unreliable
(unpredictable) operation.
The only effect that variations in power supply voltage have on a CMOS gate is the voltage
definition of a “high” (1) state. For a CMOS gate operating at 15 volts of power supply
voltage (Vdd), an input signal must be close to 15 volts in order to be considered “high” (1).
The voltage threshold for a “low” (0) signal remains the same: near 0 volts.
Disadvantages of CMOS
One decided disadvantage of CMOS is slow speed, as compared to TTL. The input
capacitances of a CMOS gate are much, much greater than that of a comparable TTL gate—
owing to the use of MOSFETs rather than BJTs—and so a CMOS gate will be slower to
respond to a signal transition (low-to-high or vice versa) than a TTL gate, all other factors
being equal.
The RC time constant formed by circuit resistances and the input capacitance of the gate tend
to impede the fast rise- and fall-times of a digital logic level, thereby degrading high-
frequency performance.
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Semiconductor Memory
ROM
Read-only memory, or ROM, is a type of computer storage containing non-volatile,
permanent data that, normally, can only be read, not written to. ROM contains the
programming that allows a computer to start up or regenerate each time it is turned on. Once
data is written on a ROM chip, it cannot be removed.
How does ROM work?
• ROM is sustained by a small, long-life battery in the computer.
• It contains two basic components: the decoder and the OR logic gates.
• In ROM, the decoder receives input in binary form; the output will be the decimal
equivalent. The OR gates in ROM use the decoder's decimal output as their input.
• ROM performs like a disk array. It contains a grid of rows and columns that are used to
turn the system on and off. Every element of the array correlates with a specific memory
element on the ROM chip. A diode is used to connect the corresponding elements.
• When a request is received, the address input is used to find the specific memory location.
The value that is read from the ROM chip should match the contents of the chosen array
element.
Advantages of ROM
• Its static nature means it does not require refreshing.
• It is easy to test.
• ROM is more reliable than RAM since it is non-volatile in nature and cannot be altered
or accidentally changed.
• The contents of the ROM can always be known and verified.
• Less expensive than RAM.
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Types of ROM
• ROM may sometimes be called maskROM (MROM). MROM is a form of read-only
memory that is static and programmed into an included circuit by the manufacturer.
• New types of ROM have emerged that are still non-volatile, but can be reprogrammed;
these types are categorized as programmable read-only memory (PROM). PROM can be
used to update firmware, such as BIOS, through the utilization of installation software.
PROM
• PROM full form is programmable read-only memory. It is a type of non-volatile
computer memory. This means that once data has been written to PROM, it cannot be
erased.
• PROM is used to store programs or firmware for microcontrollers and other digital
devices.
Types of PROM
There are many types of PROM, but the most common are:
EPROM (erasable PROM) – EPROM is a type of PROM that can be erased and
reprogrammed using ultraviolet light.
EEPROM (electrically erasable PROM) – EEPROM is a type of PROM that can be
erased and reprogrammed using an electrical signal.
Flash EEPROM (flash electrically erasable PROM) – Flash EEPROM is a type of
EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. This
makes flash EEPROMs faster to erase and program than regular EEPROMs.
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APROM (addressable PROM) – APROM is a type of PROM that can be
programmed without the need for a special device like a PROM programmer. The data is
stored in an array of cells that can be individually addressed.
PROM Applications
Microcontrollers: PROMs are used to store the programs or firmware for these
microcontrollers.
Automotive electronics – PROMs are often used in automotive electronic control units
(ECUs) to store programs that control the engine, transmission, and other systems in a
vehicle.
Industrial electronics – PROMs are used in industrial electronic devices such as
programmable logic controllers (PLCs) and human-machine interfaces (HMIs).
Consumer electronics – PROMs are used in many consumer electronics devices such as
digital cameras, DVD players, and personal computers.
Medical devices – medical devices such as pacemakers and defibrillators often use PROMs to
store their operating instructions.
Security systems – security systems such as alarm systems and door locks often use PROMs
to store their programming. It may also be used to store data such as fingerprint templates or
access codes.
Computers – PROMs are often used to store BIOS data on computer motherboards. The
BIOS is a set of instructions that tells the computer how to start up and what basic functions it
should perform.
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What is RAM and its working principle?
RAM provides the shorter-term memory the CPU needs to open files and move data
around as it responds to the tasks given to it by your apps. Both RAM and the CPU work
synchronously and complementarily to ensure that your computer's performance fits your
needs and you have a good experience when using your device.
The following are some common types of RAM:
SRAM: Static random access memory uses multiple transistors, typically four to six, for each
memory cell but doesn't have a capacitor in each cell. It is used primarily for cache.
DRAM: Dynamic random access memory has memory cells with a paired transistor and
capacitor requiring constant refreshing.
FPM DRAM: Fast page mode dynamic random access memory was the original form of
DRAM.
EDO DRAM: Extended data-out dynamic random access memory does not wait for all of the
processing of the first bit before continuing to the next one.
SDRAM: Synchronous dynamic random access memory takes advantage of the burst mode
concept to greatly improve performance.
DDR SDRAM: This is the next generation of SDRAM. Double data rate synchronous
dynamic RAM is just like SDRAM except that is has higher bandwidth, meaning greater
speed.
RDRAM: Rambus dynamic random access memory is a radical departure from the previous
DRAM architecture. Designed by Rambus, RDRAM uses a Rambus in-line memory module
(RIMM), which is similar in size and pin configuration to a standard DIMM. What makes
RDRAM so different is its use of a special high-speed data bus called the Rambus channel.
RDRAM memory chips work in parallel to achieve a data rate of 800 MHz, or 1,600 Mbps or
higher. Since they operate at such high speeds, they generate much more heat than other
types of chips. To help dissipate the excess heat Rambus chips are fitted with a heat spreader,
which looks like a long thin wafer. Just like there are smaller versions of DIMMs, there are
also SO-RIMMs, designed for notebook computers.
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Credit Card Memory: Credit card memory is a proprietary self-contained DRAM memory
module that plugs into a special slot for use in notebook computers.
PCMCIA Memory Card: Another self-contained DRAM module for notebooks, cards of this
type are not proprietary and should work with any notebook computer whose system bus
matches the memory card's configuration. They are rarely used nowadays.
CMOS RAM: CMOS RAM is a term for the small amount of memory used by your
computer and some other devices to remember things like hard disk settings. This memory
uses a small battery to provide it with the power it needs to maintain the memory contents.
VRAM: VideoRAM, also known as multiport dynamic random access memory (MPDRAM),
is a type of RAM used specifically for video adapters or 3-D accelerators.
True multiport VRAM tends to be expensive, so many graphics cards use SGRAM
(synchronous graphics RAM) instead. Performance is nearly the same, but SGRAM is
cheaper.
Photoelectric Devices and Their
Applications
PIN Photodiodes
A PIN photodiode is a diode with a large intrinsic region sandwiched
between P-type and N-type regions. PIN stands for P-type material, insulator,
and N-type material.
The operation of a PIN photodiode is based on the principle that light radiation, when
exposed to a PN junction, momentarily disturbs the structure of the PN junction. The
disturbance is due to a hole created when a high-energy photon strikes the PN junction and
causes an electron to be ejected from the junction. Thus, light creates electron-hole pairs that
act as current carriers. PIN photodiodes are used in gas detectors, spectrometers, and gas
analyzers.
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Figure 2. A PIN photodiode is a diode with a large intrinsic region sandwiched between P-
type and N-type regions.
Phototransistors
A phototransistor is a device that combines the effect of a photodiode and the
switching capability of a transistor.
In a two-lead phototransistor, the base lead is replaced by a clear covering that allows
light to fall on the base region. Light falling on the base region causes current to flow
between the emitter and collector. The collector-base junction is enlarged and works as a
reverse-biased photodiode controlling the phototransistor.
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The phototransistor conducts more or less current, depending on the light intensity.
If the light intensity increases, resistance decreases, and more emitter-to-base current is
created. Although the base current is relatively small, its amplifying capability is used to
control the large emitter-to-collector current.
The collector current depends on the light intensity and the DC current gain of the
phototransistor. In the darkness, the phototransistor is switched off with the remaining
leakage current (collector dark current).
Figure 3. A phototransistor is a device that combines the effect of a photodiode and the
switching capability of a transistor.
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Light-Activated SCRs
A light‐activated SCR (LASCR) is an SCR that is activated by light. The symbol of a
LASCR is identical to the symbol of a regular SCR with one difference. The only difference
is that arrows are added in the LASCR symbol to indicate a light-sensitive device.
Similar to a photodiode, a very low level of current is in a LASCR. Even the largest
LASCRs are limited to a maximum of a few amps. When larger current requirements are
necessary, a LASCR can be used as a trigger circuit for a standard high-power switching
SCR.
The primary advantage of a LASCR over an SCR is its ability to provide isolation.
Because the LASCR is triggered by light, it provides complete isolation between the input
signal and the output load current.
Figure 4. A light-activated SCR (LASCR) is an SCR that is activated by light.
Phototriacs
A phototriac is a triac that is activated by light.
The gate of a phototriac is light sensitive. It triggers the triac at a specified light
intensity. In the darkness, the triac is not triggered. The remaining leakage current is referred
to as peak blocking current. A phototriac is bilateral and designed to switch AC signals.
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Figure 5. A phototriac is a triac that is activated by light.
Optocouplers
An optocoupler is an electrically isolated device that consists of an IRED as the input
stage and an NPN phototransistor as the output stage. An optocoupler is normally
constructed as a dual inline package.
An optocoupler uses a
glass dielectric sandwich to
separate input from the output.
The coupling medium between
the LED and sensor are the
transmitting glass. This
provides one-way transfer of
electrical signals from the LED to the photodetector (phototransistor) without an electrical
connection between the circuitry containing the devices.
Input and output devices are always spectrally matched by their wavelengths for
maximum transfer characteristics. The signal cannot go back in the opposite direction
because the emitters and detectors cannot reverse their operating functions.
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POWER SUPPLY & RACK
The rack is the component that holds everything together. Depending on the needs of the
control system it can be ordered in different sizes to hold more modules. Like a human spine,
the rack has a backplane at the rear which allows the cards to communicate with the CPU.
The power supply plugs into the rack as well and supplies a regulated DC power to other
modules that plug into the rack. The most popular power supplies work with 120 VAC or 24
VDC source.
CPU (Central Processing Unit)
The brain of the whole PLC is the CPU module. The CPU consists of a
microprocessor, memory chip and other integrated circuits to control logic,
monitoring and communications. The CPU has different operating modes. In
programming mode it accepts the downloaded logic from a PC. The CPU is then
placed in run mode so that it can execute the program and operate the process.
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CPU MODES
• RUN: The processor scans/executes the ladder program, monitors input devices, energizes
output devices.
• PROG: This position places the processor in the Program mode. The processor does not
scan/execute the ladder program, and the controller outputs are de- energized. You can perform
online/offline(SD card) program editing.
I/O (Input/Output Section)
• The I/O system provides the physical connection between the equipment and the PLC.
There are many different kinds of I/O cards which serve to condition the type of input
or output so the CPU can use it for its logic. Its simply a matter of determining what
inputs and outputs are needed, filling the rack with the appropriate cards, and then
addressing them correctly in the CPUs program.
I/O cards are sometime referred to as IO Module/Card & similarly input/ouput terminals
are referred to as channels. These modules are categorized as, DI (Digital Input)
module: Most commonly used DI inputs are Push Buttons, Selector Switch, Limit
Switches, Pressure Switches, Temperature Switches, etc are connected to DI cards. DI
card internal circuit consists of Photocoupler inputs. Typical digital input voltages are 12-
24V DC or 120V AC.
• REM: This position sets the processor in remote test mode. You can perform online editing by
Network or Serial data cable.
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DO (Digital Output) module: Output of DO card is connected to Relays, Indication Lights,
Motor Starter, etc. DO card internal circuit may consist of a relay contact output or TRIAC
output or Transistor output. Typical digital input voltages are 12-24V DC or 120V AC.
AI (Analog Input) module: Typical analog signals come from temperature, pressure,
position, and motor speed. Analog input modules convert analog signals to digital
words (Basically internal circuits are made up of comparator or wheatstone bridge).
Analog input signals are current or voltage. Typical analog inputs are -10 to +10V
DC, 0-5V DC, 4-20mA.
AO (Analog Output) module: Typical analog signals are required by
Proportional Valves, VFD, Servo Motors, Meters. Analog Output modules convert Digital
bits to analog signal. Analog Output signals are current or voltage. Typical analog outputs
are -10 to +10V DC, 0-5V DC, 4-20mA.
