# Analog and Digital Electronics

Logic Gates

The logic gates are the basic building blocks of the binary logic circuits which are used in digital system.
A logic simply an electronic circuit that operates an one or more input signal to produce an output signal.

#### Commonly used gates in digital system

AND Gate

The output of AND gate is high only when all the input are heigh.When any one of the input is low the output is low.

OR Gate

The output of OR gate is high when any of the input is high and the output is low only when all the inputs are low.

NOT Gate (inverter)

The output of NOT gate is the complement of the input.

NAND Gate(inverter)

NAND gate is functionally equivalent to an AND gate followed by a NOT gate. Hence the output of the NAND gate is the compliment of the output of AND gate.

NOR Gate

The output of the NOR gate is the compliment of the output of OR gate.

Exclusive OR Gate

The output of the exclusive OR gate is high only if one and only one of the input is high and hence the name exclusive OR.

Note
• NAND and NOR can be used to construct all the three basic gates AND, OR NOT gates or any combination of these gates and hence it is called universal gate.
• Demorgan’s Theorems
##### The first theorem is states

The compliment of the product of two variables is equal to the sum of the compliment of each variable

If A and B are the two inputs

(A.B)’ = A’ + B’
Where ‘complement

##### The second theorem is states.

The compliment of the sum of two variables is equal to the product of the compliment of each variable.

If A and B are the two inputs

(A+B)’ = A’ . B’
Where ‘ complement

Binary number system

In the binary number system there are only two digits ‘0’ and ‘1’.Binary number conversion.

For binary number conversion refer Binary Decimal Octal and Hexadecimal number systems(Analog and Digital Electronics)

Thyristor

Thyristor is used for switching device ,Its construction and operation of the silicon controlled rectifier.Thae main parts of thyristor are anode,cathode and gate.Thyristor turn ON need small trigger pulse of current in to the gate terminal when the thyristor is in its forward direction.

Thyristor are semiconductor device and they are specially designed for the for use in high-power switching applications

Combinational logic circuits

A combinational circuit can be defined from the behavioral point of view as a circuit whose output is dependent only on the inputs at the same time instant.

• Examples of combinational circuits half and full adder,Decoder,Multiplexer,
• Sequential Logic circuits
• The behavioral point of view as a circuit whose output depends not only on the present inputs but also on the past history of inputs.

• Examples:
• Flip-flop, Counters, Registers and accumulator

• A flip-flop can store a single bit, a group of flip-flop can be used to store a word which is called register.
• That is a register is a group of flip-flop, a flip-flop can store are bit information so an n bit register as a group of n flip – flop.
• Operational Amplifier (OPAMP)

Operational amplifier abbreviated as OPAMP ,was originally the name of circuit used for carrying out mathematical operation such as addition , subtraction , multiplication, division, integration, differentiation etc of electrical signal.

An opamp is a high gain direct coupled voltage amplifier to which feed back is added to control the overall response characteristics.

Typically an OPAMP has two input terminal and one output terminal and gain of at least 10^5.In the symbol the input terminal with ‘-‘ mark is the inverting input terminal, with’+’ mark is non inverting input terminal.

Note

CMRR
Is the ratio of the differential mode gain to the common mode gain of OPAMP.

Ideal OPMAP

An ideal OPAMP is one which has the following characteristics

a. Differential voltage gain = infinity
b. Common mode voltage gain =0
c. Band width = infinity
d. Input resistance= infinity
e. Output resistance= 0
f. CMRR =infinity
g. Output voltage =0,when input voltage =0
h. Parameter drift with temperature =0
i. Equivalent input noise= 0
Oscillator

Oscillator is an electronic device that produces an output wave form without any external signal. The only input to an oscillator is the dc power supply.
Oscillator can defined as a converter of dc energy in to ac energy.

Multi vibrator

This device used for producing sine waves such as square wave, saw tooth wave, rectangular wave etc. Multi vibrators are basically two stage amplifier.

Note
• Free running multi vibrator: Astable multi vibrator which does not need any external pulse for its operation.
• Voltage regulator :
• IC (Integrated circuit are available for the regulated power supply.)

• SMPS: Switch mode power supply is used to overcome the short coming of linear voltage.
• UPS: Uninterrupted power Supply(UPS).
• Modulation

The low frequency intelligence is transmitted with the help of a high frequency carrier wave .The process of making this carrier convey the low frequency signal is called modulation.
Three types of modulation
Amplitude modulation, Frequency modulation, Phase modulation.

Amplitude modulation

Frequency modulation
Sound transmission TV, Stereo-sound transmission, satellite communication, mobile services.

Note
• Linear wave shaping circuits: Differentiator, integrator.
• Differentiator: If the input of the differentiator is a triangular wave output will be a square or rectangular wave.
• For sine wave input output will be a cosine wave.

• Integrator: when the square wave is applied at the integrating circuit output will be a triangular wave.
• Non linear wave shaping circuits :
• Clipping and clamping

• Clippers
• The circuit which is used to change the shape of an input signal by removing a portion of it without destroying the remaining part of the wave is called clipper.

Tony

Hi, Myself Tony George. An Electrical Engineer by Education, a Software Developer by Profession and an Education Blogger by Passion. In the past, I had been working as an Engineer in KSEB. The knowledge that I have acquired I would like to share here with you. I will be happy if these articles can give you a way to your career growth. Feel free to contact me.

### 1 Response

1. sameer says:

thanks