IMPOTANCE OF TRANSDUCER

A transducer is a device that converts one form of energy to another. Energy types include (but are not limited to): electrical, mechanical, electromagnetic (including light),chemical, acoustic, and thermal energy. Usually a transducer converts a signal in one form of energy to a signal in another^[1] (for example, a loudspeaker driver converts anelectric signal to sound), but any variable attenuation of energy may serve as input; for example, the light reflecting off the landscape, although it is not a signal, conveys information that image sensors, one form of transducer, can convert. A sensor is a transducer whose purpose is to sense (i.e. detect) some characteristic of its environs; it is used to detect a parameter in one form and report it in another form of energy, often an electrical signal. For example, a pressure sensor might detect pressure (a mechanical form of energy) and convert it to electrical signal for display at a remote gauge. Transducers are widely used in measuring instruments.

An actuator is a transducer that accepts energy and produces the kinetic energy of movement (action). The energy supplied to an actuator might be electrical or mechanical (pneumatic, hydraulic, etc.). An electric motor and a hydraulic cylinder are both actuators, converting electrical energy and fluid power into motion for different purposes.

Combination transducers have both functions; they both detect and create action. The most common example is an antenna, a transducer of radio waves that can transmit,receive, or both (transceiver). Another example is the typical ultrasonic transducer, which switches back and forth many times a second between acting as an actuator to produce ultrasonic waves, and acting as a sensor to detect ultrasonic waves. Rotating a DC electric motor's rotor will produce electricity, and voice-coil speakers can also act asmicrophones.

IMPORTANCE OF AMPLIFIERS

Amplifiers are used to strengthen analog signals. Analog signals become weaker after travelling a certain distance,they need to be amplified so that the data is not lost on the way and reaches intact.A device used to make an instrament louder, usually an electric guitar. Sound signals have a certain amplitude behind them (power). If the signal is week, it is difficult to hear and transmit. Therefore, you need an amplifier to add power to a signal in order for it to be heard and transmitted

WHEN YOU’RE CHOOSING AN AMPLIFIER, WE RECOMMEND LOOKING OUT FOR THESE SPECIFICATIONS FIRST AND FOREMOST:

1. Power output:

Power output is roughly equivalent to how loud you can pump out music, the bigger the speakers or larger the room, generally the more power you want although your housemates and neighbours may disagree. You don’t actually need as much power as you expect. Generally 10W is pretty loud for average listening and 100W is enough to blow the roof off most parties.

.2. THD+N:

Total Harmonic Distortion + Noise (THD + N) is a measure of just how much effect the amplifier has on the sound output. More distortion generally means more colouration to the sound. The lower this figure, the closer the output of the amplifier will sound to the original recording. Of course, speakers will have the biggest effect on sound, so choose some that are well matched to your listening preference.

3. SNR:

Signal to Noise Ratio (SNR), if you stand in a quiet room in the country, far from anywhere, all of a sudden, the noises you never noticed previously become apparent like the noise of the radiators, a distant motorway. None of this is apparent when the kids are home and the TV is on, but that background noise is still there. An amplifier is the same, there is always a very small amount of noise from the electrons whizzing around, bumping into things. The goal is to make this background noise imperceptible, this means you hear more of the music and less of the noise. The measure of this is the signal to noise ratio.

4. Crosstalk:

Left is Left, Right is Right and Crosstalk is a measure of how much undesirable left signal is mixed with right output. Amplifiers all being one box are doing their best to be separate boxes one per channel, splitting apart the signals to ensure when it reaches the speakers, you can tell that the singer is standing slightly to the left of the stage and the violins towards the right. The more crosstalk there is, the harder it is to pick out the positions of the instruments as stereo separation is affected.

5. Inputs/Connections:

Can you connect up the things you want to? You’ll want to make sure you have enough in’s to match the number of things you want to connect. Remember the different type of connections, like 3.5mm for iPods, Phono for turntables and USB for laptops and home theatre PC’s. They all have advantages and when there are a few options, choose the one which provides the best sound quality.

IMPORTANCE OF MOSFET

FETs of all types are widely used electronics components today. Of all the types of FET, the MOSFET is possibly the most widely used.

Even though MOSFETs have been in use for many years, these electronics components are still a very important element in today's electronics scene. Not only are MOSFETs found in many circuits as discrete components, but they also form the basis of most of today's integrated circuits.

MOSFETs provide many advantages. In particular they offer a very high input impedance and they are able to be used in very low current circuits. This is particularly important for integrated circuit technology where power limitations are a major consideration.

There a several MOSFET circuit symbols that are used. Some MOSFET symbols are equivalents of each other, while others indicate more detail about the MOSFET itself.

As there are several varieties of MOSFET, the symbols used to indicate them need to be different.

MOSFET symbols for N-channel and P-channel types (enhancement mode)

MOSFET symbol used above generally indicates that the device has a bulk substrate - this is indicated by the arrow on the central area of the substrate.The MOSFET provides some key features for circuit designers in terms of their overall performance.

KEY MOSFET FEATURES
FEATURE	DETAILS
Gate construction	gate is physically insulated from the channel by an oxide layer. Voltages applied to the gate control the conductivity of the channel as a result of the electric field induced capacitively across the insulating dielectric layer.
N / P channel	Both N-channel and P-channel variants are available
Enhancement / depletion	Both enhancement and depletion types are available. As the name suggests the depletion mode MOSFET acts by depleting or removing the current carriers from the channel, whereas the enhancement type increases the number of carriers according to the gate voltage.

The two main types of MOSFET are N-channel and P-channel. Each has different features:

COMPARISON OF THE KEY FEATURES OF N-CHANNEL AND P-CHANNEL MOSFETS
PARAMETER	N-CHANNEL	P-CHANNEL
Source / drain material	N-Type	P-Type
Channel material	P-Type	N-Type
Threshold voltage Vth	negative	doping dependent
Substrate material	P-Type	P-Type
Inversion layer carriers	Electrons	Holes

There are basically three regions in which MOSFETs can operate:

• Cut-off region:   In this region of the MOSFET is in a non-conducting state, i.e. turned OFF - channel current IDS = 0. The gate voltage VGS is less than the threshold voltage required for conduction.
• Linear region:   In this linear region the channel is conducting and controlled by the gate voltage. For the MOSFET to be in this state the VGS must be greater than the threshold voltage and also the voltage across the channel, VDS must be greater than VGS.
• Saturation region:   In this region the MOSFET is turned hard on. The voltage drop for a MOSFET is typically lower than that of a bipolar transistor and as a result power MOSFETs are widely used for switching large currents. 
  
  

  SWITCHING FOR DIFFERENT TYPES OF MOSFET
  MOSFET TYPE	VGS +VE	VGS 0	VGS -VE
  N-Channel Enhancement	ON	OFF	OFF
  N-Channel Depletion	ON	ON	OFF
  P-Channel Enhancement	OFF	OFF	ON
  P-Channel Depletion	OFF	ON	ON

IMPORTANCE OF FIELD EFFECT TRANSISTOR

The field-effect transistor (FET) is a transistor that uses an electric field to control the shape and hence the electrical conductivity of a channel of one type of charge carrier in a semiconductor material. FETs are also known as unipolar transistors as they involve single-carrier-type operation. The FET has several forms, but all have high input impedance. While the conductivity of a non-FET transistor is regulated by the input current (the emitter to base current) and so has a low input impedance, a FET's conductivity is regulated by a voltage applied to a terminal (the gate) which is insulated from the device. The applied gate voltage imposes an electric field into the device, this in turn attracts or repels charge carriers to or from the region between a source terminal and a drain terminal. The density of charge characters in turn influences the conductivity between the source and drain

The Field Effect Transistor is a device which enables us to use one electrical signal to control another. The name ‘transistor’ is a shortened version of the original term, transfer resistor, which indicates how the device works. Most transistors have three connections. The voltage on (or current into/out of) one wire has the effect of controlling the ease with which current can move between the other two terminals. The effect is to make a ‘resistance’ whose value can be altered by the input signal. We can use this behaviour to ‘transfer’ patterns of signal fluctuation from a small input signal to a larger output signal. 

A wide variety of devices are called transistors. Here will just look at one example, called an N-channel Junction-FET (J-FET). This sort of transistor is made by forming a channel of N-type material in a substrate of P-type material. Three wires are then connected to the device. One at each end of the channel. One connected to the substrate. In a sense, the device is a bit like a PN-junction diode, except that we've connected two wires to the N-type side.
Electrons can move along the channel, so when we apply a voltage between the two end-wires a current will flow along the channel. We can maintain this by continually putting electrons in one end (the source) and removing them at the other (the drain). The effective resistance between the two ends will depend upon the size & shape of the channel and the properties of the N-type material. Note, however, that electrons moving in the channel will — just as with the diode — be repelled by the fixed charges in the P-type substrate. As a result, the current doesn't fill the whole channel. It avoids the depletion zones near the walls.

BIASING IN TRANSISTORS

Transistor Biasing is the process of setting a transistors DC operating voltage or current conditions to the correct level so that any AC input signal can be amplified correctly by the transistor. A transistors steady state of operation depends a great deal on its base current, collector voltage, and collector current and therefore, if a transistor is to operate as a linear amplifier, it must be properly biased to have a suitable operating point.

Establishing the correct operating point requires the proper selection of bias resistors and load resistors to provide the appropriate input current and collector voltage conditions. The correct biasing point for a Bipolar Transistor, either NPN or PNP, generally lies somewhere between the two extremes of operation with respect to it being either “fully-ON” or “fully-OFF” along its load line. This central operating point is called the “Quiescent Operating Point”, or Q-point for short.

When a bipolar transistor is biased so that the Q-point is near the middle of its operating range, that is approximately halfway between cut-off and saturation, it is said to be operating as a Class-A amplifier. This mode of operation allows the output current to increase and decrease around the amplifiers Q-point without distortion as the input signal swings through a complete cycle. In other words, the output current flows for the full 360o of the input cycle.

BIASING IN DIODES

When voltage is applied across a diode in such a way that the diodeallows current, the diode is said to be forward-biased. When voltage is applied across a diode in such a way that the diode

.Biasing in electronics is the method of establishing predetermined voltages and/or currents at various points of a circuit to set an appropriate operating point.The operating point of a device, also known as bias point or quiescent point (or simply Q-point), is the DC voltage and/or current which, when applied to a device, causes it to operate in a certain desired fashion. The term is normally used in connection with devices such as transistors and diodes which are used in amplification or rectification. 
To forward bias a diode, the anode must be more positive than the cathode or LESS NEGATIVE.To reverse bias a diode, the anode must be less positive than the cathode or MORE NEGATIVE.A conducting diode has about 0.6 volts across if silicon, 0.3 volts if germanium. ohibits current, the diode is said to be reverse-biased

FORWARD BIASING IN PN JUNCTION DIODE




Forward biasing a pn junction diode is very simple. You just need to take a battery whose values can be varied from (o to V volts), connect its positive terminal to the p-side of pn junction diode and then connect the negative terminal of battery to the n-side of the pn junction diode. If you have done upto this, the forward bias circuit of pn junction diode is complete. Now all we need to do is understand how the pn junction diode behaves when we increase the voltage levels from 0 to say 10 volts or 100 volts. We have learned that if we apply an external voltage higher than the barrier potential of pn junction diode, it will start conducting, which means it will start passing current through it. So how we are going to study the behavior of pn junction diode under forward biased condition? Lets get a voltmeter and ammeter and connect it to the forward biased circuit of pn junction diode.A simple circuit diagram is shown below, which has a pn junction diode, a battery (in picture it is not shown as variable. keep in mind we are talking about a variable power source), an ammeter (in milli ampere range) and a voltmeter.

REVERSE BIASING IN PN JUNCTION DIODE

Why should we reverse bias a pn diode ? The reason is, we want to learn its characteristics under different circumstances. By reverse biasing, we mean, applying an external voltage which is opposite in direction to forward bias. So here we connect positive terminal of battery to n-side of the diode and negative terminal of the battery to p-side of the diode. This completes the reverse bias circuit for pn junction diode. Now to study its characteristics (change in current with applied voltage), we need to repeat all those steps again. Connect voltmeter, ammeter, vary the battery voltage, note the readings etc etc. Finally we will get a graph as shown.Here the interesting thing to note is that, diode does not conduct with change in applied voltage. The current remains constant at a negligibly small value (in the range of micro amps) for a long range of change in applied voltage. When the voltage is raised above a particular point, say 80 volts, the current suddenly shoots (increases suddenly). This is called as “reverse current” and this particular value of applied voltage, where reverse current through diode increases suddenly is known as “break down voltage“.

BIASING

Biasing in electronics is the method of establishing predetermined voltages or currents at various points of an electronic circuit for the purpose of establishing proper operating conditions in electronic components. Many electronic devices such as transistors and vacuum tubes, whose function is processing time-varying (AC) signals also require a steady (DC) current or voltage to operate correctly; this is called bias. The AC signal applied to them is superposed on this DC bias current or voltage. The operating point of a device, also known as bias point, quiescent point, or Q-point, is the steady-state voltage or current at a specified terminal of an active device (a transistor or vacuum tube) with no input signal applied.



Biasing means seeting up a fixed level of current, so that there is a constant voltage drop across the transistor, so that the signal is proper amplified.
Generally emitter, base current are the currents and collector base voltage are the voltage..

IMPORTANCE OF BJT (Bipolar Junction Transistor)

A bipolar junction transistor (BJT or bipolar transistor) is a type of transistor that relies on the contact of two types of semiconductor for its operation. BJTs can be used as amplifiers, switches, or in oscillators. BJTs can be found either as individual discrete components, or in large numbers as parts ofintegrated circuits.

Bipolar transistors are so named because their operation involves both electrons and holes. These two kinds of charge carriers are characteristic of the two kinds of doped semiconductor material; electrons are majority charge carriers in n-type semiconductors, whereas holes are majority charge carriers in p-type semiconductors. In contrast, unipolar transistors such as the field-effect transistors have only one kind of charge carrier.

 

Charge flow in a BJT is due to diffusion of charge carriers across a junction between two regions of different charge concentrations. The regions of a BJT are called emitter, collector, and base.^{[note 1]} A discrete transistor has three leads for connection to these regions. Typically, the emitter region is heavily doped compared to the other two layers, whereas the majority charge carrier concentrations in base and collector layers are about the same. By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where there are minority carriersthat diffuse toward the collector, and so BJTs are classified as minority-carrier devices.

A Bipolar Junction Transistor (BJT) has three terminals connected to three doped semiconductor regions. In an NPN transistor, a thin and lightly doped P-type base is sandwiched between a heavily doped N-type emitter and another N-type collector; while in a PNP transistor, a thin and lightly doped N-type base is sandwiched between a heavily diode P-type emitter and another P-type collector. In the following we will only consider NPN BJTs.

Depending on which of the three terminals is used as common terminal, there can be three possible configurations for the two-port network formed by a transistor:

• Common emitter (CE),
• Common base (CB),
• Common collector (CC).
• 

IMPORTANCE OF DIODE

A diode is a two-terminal electronic component with asymmetric conductance, it has low (ideally zero) resistance to current flow in one direction, and high (ideally infinite) resistance in the other.A diode is a one way valve for electricity. It will allow current to flow in one direction but not in the opposite direction.

Diode is a Two terminal device which allows flow of curent in forward direction that means it converts DC to AC.A diode is a semiconductor meaning it will conduct from anode to cathode if the anode is held positive. Reversing the polarity Will in effect block current flow.A diode is an electronic component with two terminals that conduct asymmetrically. Although there are different types of diodes with different invention histories, the thermionic diodes were first described by Frederick Guthrie in 1873.

Forward biasing means to give the p-region of a p-n junction higher potential w.r.t the n-region. Thus the potential barrier for an electron is reduced. so they can easily diffuse across the junction.Similarly holes move through the n-region into the negative terminal of the source.this constitutes a current (diffusion current).when positive terminal of the battery connected to positive terminal of diode it is aid to be in forward bias.

The diode will have two polarities anode and cathode .take multimeter and set it in buzer mode or resistance mode and connect the positive terminal of multimeter to anode of diode and negative to the cathode the multimeter shows the resistance say 500-700ohms 

if it working and doesn't show any impedance i.e, very high impedance in reverse bias i.e, by connecting the positive terminal of multimeter to cathode of diode and negative terminal to anode,and in no working condition it shows same characteristics as in reverse bias connected. 
the simple way of checking diode is connect the 2v led in series with the diode to the battery of 3v the led will glow if the diode is connected in forward bias in circuit and it doesn't glow if the diode is connected in reverse bias in circuit /diode is damaged .
A: a diode will conduct from cathode [negative ] to anode [positive] A stripe at one end is the cathode or a stripe on the arrow is the cathode. By applying the proper voltage it will conduct and show low resistance and a voltage from .6v to .7v. Reversing the lead it will show relatively hi resistance.

Forward biasing means to give the p-region of a p-n junction higher potential w.r.t the n-region. Thus the potential barrier for an electron is reduced. so they can easily diffuse across the junction.Similarly holes move through the n-region into the negative terminal of the source.this constitutes a current (diffusion current).when positive terminal of the battery connected to positive terminal of diode it is aid to be in forward bias.