Electronics definitions

Analogue Signals

Can take any value between the maximum and minimum values of the power supply

Digital signals

These only have two values at the extremes of the power supply

Floating Input

In digital systems, an unconnected input

Source

When the output gives out current

Sink

When an outputs takes in current

Loading

Connecting circuit B to circuit A affects the operation of circuit A

Interfaces

Needed when joining subsystems together. Interface subsystems allow both circuits to act as expected without affecting/loading each other

Virtual Earth

The section of the circuit maintained at 0V by the negative feedback

Slew rate

How quickly the output voltage of an op amp can change

Nyquist limit

Signals must be sampled at a rate at least 2 x maximum frequency in the signal

Reactance

Equivalent to the resistance of a capacity or inductor

Impedance

Equivalent to the resistance of an RLC circuit

Transmission medium

The means by which wave energy is transferred. A substance which can propagate energy waves, or the electromagnetic field.

Non-wired media examples

Free space (EM WAVES), optical fibre

Wired media examples

Co-axial cable, twisted pair

Carrier signal

A high frequency sinusoidal waveform that is used to transfer a lower frequency signal from one place to another.

Encoding

Converting into digital.

More processing needed, slows down data transfer

Decoding

Converting back into analogue - DAC.

Retrieving a hidden message from encrypted signal

Modulation

The process of mixing an audio signal with a carrier signal before transmission.

The carrier wave has constant amplitude and frequency prior to being modulated

Demodulation

The process of retrieving an audio signal after transmission

Gain

The process of increasing the ratio of output of output voltage to input voltage

Attenuation

A measure if signal degradation through any part of a transmission system

Base bandwidth

Minimum range of frequencies needed to contain the information signal

Broadcast bandwidth

Minimum range of frequencies needed to transmit an information signal through a transmission medium

Available bandwidth

Maximum range of frequencies that can be carried by the transmission medium

Channel bandwidth

Range of frequencies in the transmitted information signal

Noise

Random interference introduced to a signal as it passes through the transmission medium

Difficult/impossible from analogue easy from digital

Distortion

Unwanted additions to the frequency spectrum caused by components of the transmission system itself

Error detection

The ability to detect that an error has occurred during a digital transmission

Error correction

The ability to detect and correct that an error has occurred during a digital transmission

Bandwidth (filter)

Width of the resonance peak at 70% maximum

Propagation delay

In digital systems, the time between a change in input and the subsequent change in output

Switch bounce

Trigger a clock pulse causes many pulses at the clock input.

Mechanical switches con be debounced with bistable later or RC subsystem

BCD

Binary coded decimal. A counting system in which each denary digit (0-9) in a number is represented by a 4 bit binary value. This allows decoding to be carried out for displaying values on 7 segment displays

Stuck State

Occur on power up. An output state in a sequence generator that does not eventually lead to the main sequence

Unused State

An output state in a sequence generator that does not appear in the main sequence

Main sequence

The required output states of a sequence generator. In the correct order

ISR

Interrupt Service Routine- the code that executes when the INT flag is set

Stack

Once the processor has completed the ISR, it uses the stack to return to the point in the main program where it left off when the interrupt was called

FDM

Frequency division multiplexing. users share the transmission medium, each user has a specific frequency range allocated to them (their bandwidth). All signals are on the medium at the same time. The carrier is modulated to convey the information. FM or AM is used.

TDM

Time division multiplexing. Users take it in turns to use the transmission medium. The same medium is shared.

Serial/parallel data transfer

Shift registers are used. Look in PCM notes for details

Laser diode

Laser is monochromatic, intense, can be rapidly switched.

PIN photodiode

Fast responding light detector

Total internal reflection

How light travels along an optic fibre. Light reflects from the interface between the core and cladding as long as the angle of incidence is larger then the critical angle.

Absorption

Impurities in the core absorb energy from the pulse of light causing the pulse to be attentuated

Scattering

Impurities in the core cause energy from the pulse of light to change path direction

Radiation

Light incident on the core / cladding interface at an angle less than the critical angle refracts out of the core

Dispersion

A pulse of light arrives over a longer time period than it was sent. Caused by; different lengths of path, speed of light in the core is dependant upon wavelength

Monochromatic

A single wavelength

Monomode

Only a single path is possible. More expensive to achieve. Requires very narrow core.

Regenerator

Uses Schmitt triggers to convert a weakened digital signal into a perfect copy of the original digital value. Removes noise and amplifies

Repeater

Amplifies a signal. Can be used with analogue or digital systems. Noise is also amplified.

Load regulation

Measures the ability of the output voltage to remain constant when the output current changes due to a change in the load

Line regulation

Measures the ability of the power supply to maintain a steady output voltage when the input line voltage changes

Holding Current- Zener

Minimum reverse bias current required through a zener if Vz is to be maintained

Holding current- Thyristor

Minimum current required to maintain a forward current through a thyristor

Passive Filter

Resistor and capacitor, can only cut

Active Filter

Op amp, gain is frequency. Can cut or boost.

Clipping distortion