An analogue signal uses some attribute of the medium to convey the signal's information. For example, an aneroid barometer uses the angular position of a needle as the signal to convey the information of changes in atmospheric pressure. Electrical signals may represent information by changing their voltage, current, frequency, or total charge. Information is converted from some other physical form (such as sound, light, temperature, pressure, position) to an electrical signal by a transducer which converts one type of energy into another (e.g. a microphone).
The signals take any value from a given range, and each unique signal value represents different information. Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents. For example, suppose the signal is being used to represent temperature, with one volt representing one degree Celsius. In such a system 10 volts would represent 10 degrees, and 10.1 volts would represent 10.1 degrees.
Another method of conveying an analogue signal is to use modulation. In this, some base carrier signal has one of its properties altered: amplitude modulation (AM) involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation (FM) changes the frequency. Other techniques, such as phase modulation or changing the phase of the carrier signal, are also used.
In an analogue sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it or voltage across it. An increase in the volume of the sound causes the fluctuation of the current or voltage to increase proportionally while keeping the same waveform or shape.
Mechanical, pneumatic, hydraulic and other systems may also use analogue signals.
A analog device is a device which is designed to operate over a continuous range of voltage/current.
All natural quantities are analog by default; all measurements are digital!
Characteristics are defined in term of voltage-current relation (temporal response) or frequency response.
Ex: radio, fan, etc.
A semiconductor is a material which is neither a conductor nor an insulator.
Somewhat similar to resistors.
P type: contains electron deficient ‘impurities’; acts as (+)ve charge.
N type: contains electron rich ‘impurities’; acts as (-)ve charge.
Isolated P or N type material has no appreciable characteristics.
A diode is the simplest semiconductor devices, formed by joining one N type and one P type material.
IS = reverse saturation or scaling current
VT = thermal voltage (=25.7mV at 300K)
VD,ID = voltage & current across the diode
Forward bias: when N side (e- rich) is at connected to negative terminal of battery.
Reverse bias: when N side (e- rich) is at connected to positive terminal of battery.
Bipolar Junction Transistor
A BJT is a 3 terminal device (Emitter, Base & Collector), which contains two junction. Hence on the basis of structure, there are two types of BJTs:
There are three types of general configurations:
- Common Emitter (most popular)
- Common Base
- Common Collector
The classification is based on the terminal used as ‘common’ between input and output.