5) Digital Electronics:

[Self-study - Different types of number system, OR ,AND, NOT gates

realization through diode and Transistors, Advantage and disadvantage of digital
electronics]
Minimization of Boolean functions using Karnaugh map and representation using
logic gates, JK and MSJK and D flip-flops, shift registers using D and JK flip flops
and their operations, shift registers as counters, ring counter, design of synchronous
and asynchronous counters, state diagram, cascade counters, basic idea of static and
dynamic RAM, basics of charge coupled devices. R-2R ladder D/A converter,
Introduction to 8 bit microprocessor; internal architecture of Intel 8085, register
organization.
Digital electronics is a field of electronics involving the study
of digital signals and the engineering of devices that use or produce
them. This is in contrast to analog electronics which work primarily
with analog signals. Despite the name, digital electronics designs
includes important analog design considerations.
Digital electronic circuits are usually made from large assemblies
of logic gates, often packaged in integrated circuits. Complex
devices may have simple electronic representations of Boolean logic
functions.[1]
 Properties

An advantage of digital circuits when compared to analog

circuits is that signals represented digitally can be transmitted
without degradation caused by noise.[29] For example, a
continuous audio signal transmitted as a sequence of 1s and 0s,
can be reconstructed without error, provided the noise picked
up in transmission is not enough to prevent identification of the
1s and 0s.
 FLIP- FLOPS
The flip-flops are basically the circuits that maintain a certain
state unless and until directed by the input for changing that state.
We can construct a basic flip-flop using four-NOR and four-NAND
gates.
A flip-flop is a sequential digital electronic circuit having two
stable states that can be used to store one bit of binary data. Flip-
flops are the fundamental building blocks of all memory devices.

Types of Flip-Flops
The flip-flops are of the following types:
1. S-R Flip Flop
2. J-K Flip Flop
3. T Flip Flop
4. D Flip Flop
Flip-Flops

Flip-flops are the fundamental element of sequential circuits

– bistable –
(gates are the fundamental element for combinational circuits) •
Flip-flops are essentially 1-bit storage devices –
outputs can be set to store either 0 or 1 depending on the inputs –
even when the inputs are de-asserted, the outputs retain their prescribed
value •

Flip-flops have (normally) 2 complimentary outputs – and •

Three main types of flip-flop – R-S J-K D-type

Flip-Flops
 S-R Flip Flop
•This is the simplest flip-flop circuit. It
has a set input (S) and a reset input (R).
When in this circuit when S is set as
active, the output Q would be high and
the Q’ will be low. If R is set to active
then the output Q is low and the Q’ is
high. Once the outputs are established,
the results of the circuit are maintained
until S or R get changed, or the power
is turned off.
 J K FLIP FLOP

•Because of the invalid state corresponding to

S=R=1 in the SR flip-flop, there is a need of
another flip-flop. The JK flip-flop operates with
only positive or negative clock transitions. The
operation of the JK flip-flop is similar to the SR
flip-flop. When the input J and K are different
then the output Q takes the value of J at the
next clock edge. When J and K both are low
then NO change occurs at the output. If both J
and K are high, then at the clock edge, the
output will toggle from one state to the other.
 D FLIP FLOP

•In a D (Delay or Data) flip-flop, the output

can only be changed at positive or
negative clock transitions, and when the
inputs changed at other times, the output
will remain unaffected. The D flip-flops are
generally used for shift-registers and
counters. The change in output state of D
flip-flop depends upon the active
transition of clock. The output (Q) is same
as input and changes only at active
transition of clock
Master Slave Flipflop
The master-slave flip flop is constructed by combining two JK flip flops.
These flip flops are connected in a series configuration. In these two flip
flops, the 1st flip flop work as "master", called the master flip flop, and the
2nd work as a "slave", called slave flip flop. The master-slave flip flop is
designed in such a way that the output of the "master" flip flop is passed to
both the inputs of the "slave" flip flop. The output of the "slave" flip flop is
passed to inputs of the master flip flop.
Applications of Flip-Flops
In this article, we have summed up the different types of
flip-flops that we use in digital electronic circuits. You can
find the various applications of the flip-flops below:
•Frequency dividers
•Counters
•Storage registers
•Shift registers
•Data storage
•Bounce elimination switch
•Latch
•Data transfer
•Memory
•Registers
A Register is a device that is used to store such information. It is a group of flip-
flops connected in series used to store multiple bits of data. The information
stored within these registers can be transferred with the help of shift registers.

. The number of bits you can store in a shift register is equal to the number of
flip-flops used.
•Serial In Serial Out
•Serial In Parallel Out
•Parallel In Serial Out
•Parallel In Parallel Out
•Bi-directional Shift Register
•Universal Shift Register
 Serial-In Serial-Out Shift Register (SISO)

The shift register, which allows serial input (one bit after the other through a single data
line) and produces a serial output is known as a Serial-In Serial-Out shift register. Since there
is only one output, the data leaves the shift register one bit at a time in a serial pattern, thus
the name Serial-In Serial-Out Shift Register. The logic circuit given below shows a serial-in
serial-out shift register. The circuit consists of four D flip-flops which are connected in a
serial manner. All these flip-flops are synchronous with each other since the same clock
signal is applied to each flip-flop.
 Serial-In Parallel-Out Shift Register (SIPO)

The shift register, which allows serial input (one bit after the other through a single data line) and produces
a parallel output is known as the Serial-In Parallel-Out shift register. The logic circuit given below shows a
serial-in-parallel-out shift register. The circuit consists of four D flip-flops which are connected. The clear
(CLR) signal is connected in addition to the clock signal to all 4 flip flops in order to RESET them. The output
of the first flip-flop is connected to the input of the next flip flop and so on. All these flip-flops are
synchronous with each other since the same clock signal is applied to each flip-flop.
 Parallel-In Serial-Out Shift Register (PISO)
The shift register, which allows parallel input (data is given separately to each flip flop and in a
simultaneous manner) and produces a serial output is known as a Parallel-In Serial-Out shift register. The
logic circuit given below shows a parallel-in-serial-out shift register. The circuit consists of four D flip-flops
which are connected. The clock input is directly connected to all the flip-flops but the input data is
connected individually to each flip-flop through a multiplexer at the input of every flip-flop. The output of
the previous flip-flop and parallel data input are connected to the input of the MUX and the output of MUX
is connected to the next flip-flop. All these flip-flops are synchronous with each other since the same clock
signal is applied to each flip-flop.
 Parallel-In Parallel-Out Shift Register (PIPO)
The shift register, which allows parallel input (data is given separately to each flip flop and in a
simultaneous manner) and also produces a parallel output is known as Parallel-In parallel-Out shift
register. The logic circuit given below shows a parallel-in-parallel-out shift register. The circuit consists
of four D flip-flops which are connected. The clear (CLR) signal and clock signals are connected to all 4
flip-flops. In this type of register, there are no interconnections between the individual flip-flops since no
serial shifting of the data is required. Data is given as input separately for each flip flop and in the same
way, output is also collected individually from each flip flop.
A Counter is a device which stores (and sometimes displays) the number of times a
particular event or process has occurred, often in relationship to a clock
signal. Counters are used in digital electronics for counting purpose, they can count
specific event happening in the circuit
Counters
A special type of sequential circuit used to count the pulse is known as a counter, or
a collection of flip flops where the clock signal is applied is known as counters.
The counter is one of the widest applications of the flip flop. Based on the clock
pulse, the output of the counter contains a predefined state. The number of the
pulse can be counted using the output of the counter.

Counters are broadly divided into two categories

1.Asynchronous counter
2.Synchronous counter
In synchronous counter we use a universal clock that is common to all flip
flops through out the circuit. In asynchronous counter main clock is only
applied to the first flip flop and then for rest of flip flops the output of
previous flip flop is taken as a clock
Truth Table
1. Asynchronous Counter In asynchronous counter we don’t use universal clock, only first flip flop is driven by
main clock and the clock input of rest of the following flip flop is driven by output of previous flip flops. We can
understand it by following diagram-
Operation

1.Condition 1: When both the flip flops are in reset condition.

Operation: The outputs of both flip flops, i.e., QA QB, will be 0.
2.Condition 2: When the first negative clock edge passes.
Operation: The first flip flop will toggle, and the output of this flip flop will change from 0 to 1.
The output of this flip flop will be taken by the clock input of the next flip flop. This output will
be taken as a positive edge clock by the second flip flop. This input will not change the second
flip flop's output state because it is the negative edge triggered flip flop.
So, QA = 1 and QB = 0
3.Condition 3: When the second negative clock edge is applied.
Operation: The first flip flop will toggle again, and the output of this flip flop will change from
1 to 0. This output will be taken as a negative edge clock by the second flip flop. This input will
change the second flip flop's output state because it is the negative edge triggered flip flop.
So, QA = 0 and QB = 1.
1.Condition 4: When the third negative clock edge is applied.
Operation: The first flip flop will toggle again, and the output of this flip flop
will change from 0 to 1. This output will be taken as a positive edge clock by
the second flip flop. This input will not change the second flip flop's output
state because it is the negative edge triggered flip flop.
So, QA = 1 and QB = 1
2.Condition 5: When the fourth negative clock edge is applied.
Operation: The first flip flop will toggle again, and the output of this flip flop
will change from 1 to 0. This output will be taken as a negative edge clock by
the second flip flop. This input will change the output state of the second flip
flop.
So, QA = 0 and QB = 0
Synchronous Counter:
In the Asynchronous counter, the present counter's output passes to the input of the
next counter. So, the counters are connected like a chain. The drawback of this system
is that it creates the counting delay, and the propagation delay also occurs during the
counting stage. The synchronous counter is designed to remove this drawback.
In the synchronous counter, the same clock pulse is passed to the clock input of all the
flip flops. The clock signals produced by all the flip flops are the same as each other.
Below is the diagram of a 2-bit synchronous counter in which the inputs of the first flip
flop, i.e., FF-A, are set to 1. So, the first flip flop will work as a toggle flip-flop. The
output of the first flip flop is passed to both the inputs of the next JK flip flop.
Operations

In the Asynchronous counter, the present counter's output passes to the input
of the next counter. So, the counters are connected like a chain. The drawback of
this system is that it creates the counting delay, and the propagation delay also
occurs during the counting stage. The synchronous counter is designed to
remove this drawback.
In the synchronous counter, the same clock pulse is passed to the clock input of
all the flip flops. The clock signals produced by all the flip flops are the same as
each other. Below is the diagram of a 2-bit synchronous counter in which the
inputs of the first flip flop, i.e., FF-A, are set to 1. So, the first flip flop will work as
a toggle flip-flop. The output of the first flip flop is passed to both the inputs of
the next JK flip flop.
1.Condition 2: When the second negative clock edge is passed.
Operation: The first flip flop will be toggled again, and the output of this
flip flop will be changed from 1 to 0. When the second negative clock edge
is passed, the output of the first flip flop will be 1. The clock input of the
first flip flop and both of its inputs will set to 1. In this way, the state of the
second flip flop will change from 0 to 1.
So, QA = 0 and QB = 1
2.Condition 2: When the third negative clock edge passes.
Operation: The first flip flop will toggle from 0 to 1, but at this instance,
both the inputs and the clock input set to 0. Hence, the outputs will
remain the same as before.
So, QA = 1 and QB = 1
3.Condition 2: When the fourth negative clock edge passes.
Operation: The first flip flop will toggle from 1 to 0. At this instance, the
inputs and the clock input of the second flip flop set to 1. Hence, the
outputs will change from 1 to 0.
So, QA = 0 and QB = 0
Ring Counter
A ring counter is a special type of application of the Serial IN Serial OUT Shift register. The
only difference between the shift register and the ring counter is that the last flip flop outcome is
taken as the output in the shift register. But in the ring counter, this outcome is passed to the first
flip flop as an input. All of the remaining things in the ring counter are the same as the shift
register
No. of states in Ring counter = No. of flip-flop used
Below is the block diagram of
the 4-bit ring counter. Here, we
use 4 D flip flops. The same
clock pulse is passed to the clock
input of all the flip flops as a
synchronous counter.
The Overriding input(ORI) is
used to design this circuit.
The output is 1 when the pre-set set to 0. The output is 0 when the clear set to 0. Both PR and
CLR always work in value 0 because they are active low signals.
1.PR = 0, Q = 1
2.CLR = 0, Q = 0
Working
The ORI input is passed to the PR input of the first flip flop, i.e., FF-0, and it is also passed to the
clear input of the remaining three flip flops, i.e., FF-1, FF-2, and FF-3. The pre-set input set to 0 for
the first flip flop. So, the output of the first flip flop is one, and the outputs of the remaining flip flops
are 0. The output of the first flip flop is used to form the ring in the ring counter and referred to
as Pre-set 1.
Cascaded Counters

Cascaded counters are those counters which are made up of cascading or grouping of
small counters together to the larger ones. Doing this helps in the increasing of both the
modulus of the count sequence and also in the frequency division. The making of these
types of counters includes digital time clocks, frequency dividers, and also
synchronization circuits. In this type of counters, there is the use of rollover signals to
communicate when the upper counters should roll over. The cascaded counter will
increment only when the counter below it is at its terminal count and it is also increasing.
Cascaded Counter can be either synchronous or asynchronous counters. Let us take the
example of the asynchronous counter. The individual toggle stages of the flip-flops of the
asynchronous counters are MOD-2 counters. These are cascaded by routing the output of
the one-stage into the clock input of the next stage. With each of the deluged stages, the
modulus of the counter increases. The final one is equal to that of the modulus of the
individual stages of the counter. These underwent multiplication earlier for cascading. A
4-Bit asynchronous counter has a modulus of 2 x 2 x 2 x 2 = 16.
Semiconductor memory A device for storing digital information that is fabricated by using integrated
circuit technology is known as semiconductor memory. Also known as integrated-circuit memory,
large-scale integrated memory, memory chip, semiconductor storage, transistor memory.

Definition:- Semiconductor memory is the main memory element of a microcomputer-based system

and is used to store program and data. The main memory elements are nothing but semiconductor
devices that stores code and information permanently. The semiconductor memory is directly
accessible by the microprocessor.
Thus semiconductor devices are preferred as primary memory. With the rapid growth in the
requirement for semiconductor memories there have been a number of technologies and types of
memory that have emerged.
Names such as ROM, RAM, EPROM, EEPROM, Flash memory, DRAM, SRAM, SDRAM, and the very new
MRAM can now be seen in the electronics literature.
Each one has its own advantages and area in which it may be use. Types of semiconductor memory
Electronic semiconductor memory technology can be split into two main types or categories,

according to the way in which the memory operates : 1. RAM - Random Access Memory 2. ROM -
Read Only Memory
RAM (Random Access Memory) is Computer Memory that is directly
accessible by the CPU. RAM stores temporary data, that is in case of power
loss, the stored information gets lost. In Simple words, it stores the data which
is currently processing by the CPU. The data which is easily modifiable are
generally stored in the RAM. RAM is of two types:
1.Static Random Access Memory (SRAM)
2.Dynamic Random Access Memory (DRAM)

Static Random Access Memory (SRAM)

Data is stored in transistors and requires a constant power
flow. Because of the continuous power, SRAM doesn’t need
to be refreshed to remember the data being stored. SRAM is
called static as no change or action i.e. refreshing is not
needed to keep the data intact. It is used in cache memories.
Characteristics of Static RAM
•Static RAM is much faster than DRAM.
•Static RAM has greater storage than DRAM.
•Static RAM takes less power to perform.
Advantages of Static RAM
•Static RAM has low power consumption.
•Static RAM has faster access speeds than DRAM.
•Static RAM helps in creating a speed-sensitive cache.
Disadvantages of Static RAM
•Static RAM has less memory capacity.
•Static RAM has high costs of manufacturing than DRAM.
•Static Ram comprises of more complex design.
Dynamic Random Access Memory (DRAM)
Data is stored in capacitors. Capacitors that store data in DRAM gradually discharge
energy, no energy means the data has been lost. So, a periodic refresh of power is
required in order to function. DRAM is called dynamic as constant change or
action(change is continuously happening) i.e. refreshing is needed to keep the data
intact. It is used to implement main memory.
Characteristics of Dynamic RAM
•Dynamic RAM is slower in comparison to SRAM.
•Dynamic RAM is less costly than SRAM.
•Dynamic RAM has high power consumption.
Advantages of Dynamic RAM
•Dynamic RAM has Low costs of manufacturing than SRAM.
•Dynamic RAM has greater memory capacities.
•Dynamic RAM does not need to refresh its memory contents.
Disadvantages of Dynamic RAM
•Dynamic RAM has a slow access speed.
•Dynamic RAM has high power consumption.
•Dynamic RAM data can be lost in case of Power Loss.
 Charged Coupled Devices (CCD): Understanding The Basics

Charged coupled devices (CCD) are an integral part of digital imaging technology.
CCDs are electronic image sensors that convert light into digital signals by
generating charges through photons. The technology has been in use since the early
1980s and has played a significant role in the development of digital cameras and
other image-capturing devices.

The fundamental concept behind CCDs is the use of linked capacitors that transfer
electric charges to neighboring capacitors. The external circuit controls the transfer
of charges, and each pixel generates an electrical charge proportional to the
intensity of light captured by that pixel. CCDs are widely used in digital cameras,
video cameras, and other imaging devices because of their ability to capture high-
quality images with excellent color accuracy and low noise.
•Charged Coupled Devices (CCD) are electronic image sensors that convert
light into digital signals.
•CCDs use linked capacitors to transfer electric charges and generate an
electrical charge proportional to the intensity of light captured by each pixel.

•CCDs are widely used in digital cameras, video cameras, and other imaging
devices because of their ability to capture high-quality images with excellent
color accuracy and low noise.
Microprocessor
A Microprocessor is an important part of a computer architecture without which you will not be
able to perform anything on your computer. It is a programmable device that takes in input
performs some arithmetic and logical operations over it and produces the desired output. In
simple words, a Microprocessor is a digital device on a chip that can fetch instructions from
memory, decode and execute them and give results.
Basics of Microprocessor –
A Microprocessor takes a bunch of instructions in machine language and executes them, telling
the processor what it has to do. Microprocessor performs three basic things while executing the
instruction:
1.It performs some basic operations like addition, subtraction, multiplication, division, and some
logical operations using its Arithmetic and Logical Unit (ALU). New Microprocessors also perform
operations on floating-point numbers also.

2.Data in microprocessors can move from one location to another.

3.It has a Program Counter (PC) register that stores the address of the next instruction based on
the value of the PC, Microprocessor jumps from one location to another and takes decisions.
 Register Organization

Register organization is the arrangement of the registers in the processor. The

processor designers decide the organization of the registers in a processor.
Different processors may have different register organization. Depending on the
roles played by the registers they can be categorized into two types, user-visible
register and control and status register.
What is Register?
Registers are the smaller and the fastest accessible memory units in the central
processing unit (CPU). According to memory hierarchy, the registers in the
processor, function a level above the main memory and cache memory. The
registers used by the central unit are also called as processor registers.
A register can hold the instruction, address location, or operands. Sometimes, the
instruction has register as a part of itself.
 DIGITAL TO ANALOGUE CONVERTER (R-2R)
R-2R DAC
R-2R Digital-to-Analogue Converter, or DAC, is a data converter which use
two precision resistor to convert a digital binary number into an analogue
output signal proportional to the value of the digital number
The R-2R resistive ladder network uses just two resistive values. One resistor has the
base value “R”, and the second resistor has twice the value of the first resistor, “2R”, no
matter how many bits are used to make up the ladder network.

https://www.electronics-tutorials.ws/combination/r-2r-dac.html
So for example, we could just use a standard 1kΩ resistor for the base resistor
“R”, and therefore a 2kΩ resistor for “2R” (or multiples thereof as the base
value of R is not too critical). Thus the resistive value of 2R will always be
twice the value of the base resistor, R. That is 2R = 2*R. This means that it is
much easier for us to maintain the required accuracy of the resistors along the
ladder network compared to the previous weighted resistor DAC. But what is
a “R-2R resistive ladder network”
R-2R Resistive Ladder Network

As its name implies, the “ladder” description comes from the ladder-like configuration
of the resistors used within the network. A R-2R resistive ladder network provides a
simple means of converting digital voltage signals into an equivalent analogue output.
Input voltages are applied to the ladder network at various points along its length and
the more input points the better the resolution of the R-2R ladder. The output signal as a
result of all these input voltage points is taken from the end of the ladder which is used
to drive the inverting input of an operational amplifier.
Then a R-2R resistive ladder network is nothing more than long strings of parallel and
series connected resistors acting as interconnected voltage dividers along its length, and
whose output voltage depends soley on the interaction of the input voltages with each
other. Consider the basic 4-bit R-2R ladder network (4-bits because it has four input
points) below.
 4-bit R-2R Resistive Ladder Network

This 4-bit resistive ladder circuit may look complicated, but its all about
connecting resistors together in parallel and series combinations and working back
to the input source using simple circuit laws to find the proportional value of the
output. Lets assume all the binary inputs are grounded at 0 volts, that is: VA = VB =
VC = VD = 0V (LOW). The binary code corresponding to these four inputs will
therefore be: 0000.
Starting from the left hand side and using the simplified equation for two parallel resistors
and series resistors, we can find the equivalent resistance of the ladder network as:

Resistors R1 and R2 are in “parallel” with each other but in “series” with resistor
R3. Then we can find the equivalent resistance of these three resistors and call it
RA for simplicity
Then RA is equivalent to “2R”. Now we can see that the equivalent resistance
“RA” is in parallel with R4 with the parallel combination in series with R5.

Again we can find the equivalent

resistance of this combination and
call it RB.