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Phase Locked Loop

A phase locked loop (PLL) is a control system that tries to generate an output signal whose phase is related to the phase of the input "reference" signal. It is an electronic circuit consisting of a variable frequency oscillator and a phase detector that compares the phase of the signal derived from the oscillator to an input signal. The signal from the phase detector is used to control the oscillator in a feedback loop. The circuit compares the phase of the input signal with the phase of a signal derived from its output oscillator and adjusts the frequency of its oscillator to keep the phases matched.

Frequency is the derivative of phase. Keeping the input and output phase in lock step implies keeping the input and output frequencies in lock step. Consequently, a phase-locked loop can track an input frequency, or it can generate a frequency that is a multiple of the input frequency. The former property is used for demodulation , and the latter property is used for indirect frequency synthesis .

Advantages of PLC over micro controller.

1.Rugged and designed to withstand vibrations, temperature, humidity, and noise.
2. Have interfacing for inputs and outputs already inside the controller.
3. Easily programmed and have an easily understood programming language .

Programable Logic Controller

A PLC is a modular device which one can program using Ladder diagrams (relay logic) or Statement List (a bit like assembly). It is optimized to handle several digital inputs and outputs, and is more rugged for use in industrial applications. Basically it scans the inputs, and determines the outputs based on the logical conditions programmed into it by the user. It internally uses a microcontroller to handle all input, output and logic scans. Application area is mostly industrial automation.

Classification of electronics
General Circuits

1 Electric Circuits

2 Electronic Circuits

3 Computer Circuits

General Components and Materials

1 Electric Components and Materials

2 Electronic Components and Materials

3 Computer Components and Materials

General Photonics

1 Lasers

2 Optics

3 Light

4 Vision

General Control and Systems

41 Computer Control

42 Microcontrollers

43 Guidance Systems

44 Robotic Systems

45 Control Devices

General Telecommunications

1 Telephone and Other Line Communications

2 Television Communications

3 Radio Communications

4 Radar Communications

General Telecommunications Equipment and Instrumentation

1 Telephone and Other Line Equipment and Instrumentation

2 Television Equipment and Instrumentation

3 Radio Equipment and Instrumentation

4 Radar Equipment and Instrumentation

Power Systems

1 Electric Machinery, Generators, and Motors

2 Electric Batteries

3 Fuel Cells

4 Solar Cells

Theoretical

1 Electromagnetic Waves

2 Acoustic Waves

3 Electricity

4 Magnetism

Electronics and Communications Milieux

1 The Electronics and Communications Industry

2 History of Electronics and Communications

3 Electronics and Communications Education

4 Management of Electronics and Communications Systems

Electronics -the branch of physics that deals with the emission and effects of electrons and with the use of electronic devices.