Amplifier Fundamentals I:Signal Amplification,Voltage,Current and Power Gain

IF YOU WANT TO MAKE YOUR BASICS  STRONG IN AMPLIFIERS THEN YOU’RE AT THE RIGHT PLACE WHERE YOU’LL GET ANSWERS OF EXCITING QUESTIONS,JUST GO THROUGH IT AND YOU’LL FIND IT  MORE  INTERESTING AND AT THE END OF THIS BLOG YOU’LL BE ABLE TO UNDERSTAND ALL  COMPLICATED CIRCUITS YOU’LL STUDY IN BJTs,MOSFET AND SO ON..

AMPLIFIER-

An amplifier is a device for increasing the power of a signal by use of an external energy source.
 In this section i'm gonna write about fundamental signal processing.How signals are amplified in any amplifier and what are the need of amplification and many more interesting things.

Here you will find the answers of some intresting questions which may or may not striked your brain while reading about it like:WHAT IS THE DIFFERENCE BETWEEN AN AMPLIFIER AND A STEP UP TRANSFORMER WHEN BOTH GIVES INCREASIN OUTPUT?? 
IN AMPLIFIERS,THE POWER DELIVERED TO THE LOAD IS GREATER THAN THE POWER DRAWN FROM THE SIGNAL SOURCE,NOW THE QUESTION ARISES WHAT IS THE SOURCE OF THIS ADDITIONAL POWER??FROM WHERE IT GETS EXTRA POWER??
WHAT NEGATIVE DECIBEL(dB) REPRESENTS??? and many more interesting things about it.

Signal Amplification:-

From a conceptual point of view the simplest signal-processing task is that of signal amplification.The need for amplification arises because transducers provide signals that are said to be "weak," that is, in the microvolt (SV) or millivolt (mV) range and possessing little
energy. Such signals are too small for reliable processing, and processing is much easier if
the signal magnitude is made larger. The functional block that accomplishes this task is the
signal amplifier.
It is appropriate at this point to discuss the need for linearity in amplifiers. When amplifying
a signal, care must be exercised so that the information contained in the signal is not,
changed and no new information is introduced to an amplifier, we want the output signal of the amplifier to be an exact replica of that at the input, except of course for having larger magnitude. In other words, the "wiggles" in the output waveform must be identical to those in the input waveform. Any change in waveform is considered to be distortion and is obviously undesirable.

An amplifier that preserves the details of the signal waveform is characterized by the
relationship

                                                           Vo = A Vi
where Vo is the output signal of the amplifier and Vi is input signal to the amplifier,
A is a constant representing the magnitude of amplification, known as amplifier gain.

The above equation is a linear relationship;hence the amplifier it describes is a linear amplifier. It should be easy to see that if the relationship between Vo and Vi contains higher powers of Vi, then the waveform of Vo will no longer be identical to that of Vi. The amplifier is then said to exhibit nonlinear distortion.

The amplifiers discussed so far are primarily intended to operate on very small input
signals. Their purpose is to make the signal magnitude larger and therefore are thought of as voltage amplifiers. The preamplifier in the home stereo system is an example of a voltage
amplifier. However, it usually does more than just amplify the signal.

Before talking about voltage,current and power gain,the question arises is WHAT IS GAIN??

Gain:-

 Gain is the magnitude of amplification by which the input signal provided to the amplifier is amplified.

or

mathematically,it can be defined as the ratio of output quantity to the input quantity.

                                               A=output/input

where A is the gain of any amplifier.

now here i'm gonna tell you 

1.voltage gain

2.current gain and power gain

1.Voltage gain:-

It's the ratio of the output voltage to the input voltage.A linear amplifier accepts an input signal Vi(t) and provides at the output, across a load resistance R an output signal Vo that is a magnified replica of Vi.

A voltage amplifier fed with a signal Vi(t) and connected to a load resistance R

                                        Voltage gain (Av) =Vo(t)/Vi(t) 

 2.Current gain and Power gain:-

So here comes the answer of the question:

 WHAT IS THE DIFFERENCE BETWEEN AN AMPLIFIER AND A STEP UP TRANSFORMER WHEN BOTH GIVES INCREASING OUTPUT??

In the case of a transformer, although the voltage delivered to the load
could be greater than the voltage feeding the input side (the primary), the power delivered to
the load (from the secondary side of the transformer) is less than or at most equal to the power supplied by the signal source. On the other hand, an amplifier provides the load with power greater than that obtained from the signal source and it increases the signal power.

The power gain of the amplifier can be defined as

                               Power gain (Ap)=load power/input power

                                                         

current gain of the amplifier can be defined as

                                      Current gain (Ai)=Io/Ii

             where Io=output current

                        Ii=input current

As gain is a unitless quantity but it can be represented in decibels(dB) as:-
           

                          Voltage gain in decibels = 20 log | Av | dB
                            Current gain in decibels = 20 log|Ai| dB
                             Power gain in decibels = 10 log |Ap| dB

now the main thing i wanna tell you here is difference in A= -20 and A= -20dB

the difference  a negative gain A= -20 simply means that there is a 180° phase
difference between input and output signals; it does not imply that the amplifier is attenuating the signal. On the other hand, an amplifier whose voltage gain is Av= - 20 dB is in fact attenuating the input signal.

symbol used for amplifier throughout this blog

AMPLIFIER POWER SUPPLIES :-

here comes the answer of questions asked in the starting of this blog IN AMPLIFIERS,THE POWER DELIVERED TO THE LOAD IS GREATER THAN THE POWER DRAWN FROM THE SIGNAL SOURCE,NOW THE QUESTION ARISES WHAT IS THE SOURCE OF THIS ADDITIONAL POWER??

The answer is found by observing that amplifiers need dc power supplies for their operation. These dc sources supply the extra power delivered to the load as well as any power that might be dissipated in the internal circuit of the amplifier (such power is converted to heat). 

if you're interested in knowing that how this happen then  you can go through this small derivation:

An amplifier that requires two dc supplies (shown as batteries) for operation

above figure shows an amplifier that requires two dc sources: one positive of value V1
and one negative of value V2. The amplifier has two terminals, labeled V+ and V-, for connection to the dc supplies. For the amplifier to operate, the terminal labeled V+ has to be connected to the positive side of a dc source whose voltage is V1 and whose negative side is connected to the circuit ground. Also, the terminal labeled V has to be connected to the
negative side of a dc source whose voltage is V2 and whose positive side is connected to the circuit ground. Now, if the current drawn from the positive supply is denoted l1 and that
from the negative supply is I2 (see Fig), then the dc power delivered to the amplifier is
                                                                        Pdc = V1I1+V2I2
If the power dissipated in the amplifier circuit is denoted P dissipated,the power-balance equation for the amplifier can be written as

                                                               Pdc+Pi=PL+Pdissipated
where Pi is the power drawn from the signal source and PL is the power delivered to the
load.