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The field of electronics is the study and use of electronic devices that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The pure study of such devices is considered as a branch of physics, while the design and construction of electronic circuits to solve practical problems is part of the fields of electrical, electronic and computer engineering.

The main uses of electronic circuits are the controlling, processing and distribution of information, and the conversion and distribution of electric power. Both of these uses involve the creation or detection of electromagnetic fields and electric currents. While electricity had been used for some time to transmit data over telegraphs and telephones, the development of electronics truly began in earnest with the advent of radio. Today, electronic devices perform a wide variety of tasks.

Electronic systems

One way of looking at an electronic system is to divide it into the following parts:

1. Inputs - Electrical or mechanical sensors (or transducers), which take signals (in the form of temperature, pressure, etc.) from the physical world and convert them into current/voltage signals.

2. Signal processing circuits - These consist of electronic components connected together to manipulate, interpret and transform the signals.

3. Outputs - Actuators or other devices (also transducers) that transform current/voltage signals back into useful physical form.

Take as an example a television. Its input is a broadcast signal received by an antenna or fed in through a cable. Signal processing circuits inside the television extract the brightness, colour and sound information from this signal. The output devices are a cathode ray tube that converts electronic signals into a visible image on a screen and magnet driven audio speakers.

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Electronic test equipment

• Ammeter, e.g. Galvanometer (Measure current)
  Ohmmeter, e.g. Wheatstone bridge (Measure resistance)
  Voltmeter (Measures voltage)
  Multimeter (Measures all of the above)
  Oscilloscope (Measures all of the above as they change over time)
  Logic analyzer (Tests digital circuits)
  Spectrum analyzer (SA) (Measures spectral energy of signals)
  Vector signal analyzer (VSA) (Like the SA but it can also perform many more useful digital demodulation functions)
  Electrometer (Measures charge)
  Frequency counter (Measures frequency)
  Time-domain reflectometer for testing integrity of long cables

Analog circuits

Most analog electronic appliances, such as radio receivers, are constructed from arrays of a few types of circuits.

• Analog computer
  Analog multipliers
  electronic amplifiers
  electronic filters
  electronic oscillators
  Phase-locked loops
  electronic mixers
  electronic power supply
  impedance matchers
  operational amplifiers
  comparators

Digital circuits

Computers, electronic clocks, and programmable logic controllers (used to control industrial processes) are constructed of digital circuits. Digital Signal Processors are another example.

Building-blocks:

• logic gates
  flip-flops
  counters
  registers
  multiplexers
  Schmitt triggers

Complex devices:

• microprocessors
  microcontrollers
  DSP
  Field Programmable Gate Array

Mixed-signal circuits

Mixed-signal circuits, also known as hybrid circuits, are becoming increasingly common. Mixed circuits contain both analog and digital components. analog to digital converters and digital to analog converters are the primary examples. Other examples are transmission gates and buffers.

Heat dissipation

Heat generated by electronic circuitry must be dissipated to improve reliability. Techniques for heat dissipation can include heatsinks and fans for air cooling, and other forms of computer cooling such as liquid cooling for computers .

Noise

Associated with all electronic circuits is noise. Types of noise include

• Shot noise in resistors.
  Johnson-Nyquist noise (Thermal noise) in resistors.
  White noise
  1/f noise (pink noise, or flicker noise)

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