What is digital electronics?

Digital electronics are those electronics systems that use a digital signal instead of an analog signal. Digital electronics are the most common representation of Boolean algebra and are the basis of all digital circuits.In digital electronics all values are expressed in terms of 0's and 1's combination.

working of amplifier

Single Stage RC Coupled CE Amplifier

The figure shows a single stage CE amplifier. C₁ and C₃ are coupling capacitors, they are used for blocking the dc component and passing only ac part they also ensure that the dc basing conditions of the BJT remains unchanged even after input is applied. C₂ is the bypass capacitor which increases the voltage gain and bypasses the R₄ resistor for ac signals.

The BJT is biased in the active region using the necessary biasing components. The Q point is made stable in the active region of the transistor. When input is applied as shown below the base current starts to vary up and down, hence collector current also varies as I_C = β × I_B. Therefore voltage across R₃ varies as the collector current is passing through it. Voltage across R₃ is the amplified one and is 180° apart from the input signal. Thus voltage across R₃ is coupled to the load and amplification has taken place. If the Q point is maintained to be at the centre of the load very less or no waveform distortion will take place. The voltage as well as current gain of the CE amplifier is high (gain is the factor by which the voltage of current increases from input to output). It is commonly used in radios and as low frequency voltage amplifier.

To further increase the gain multistage amplifiers are used. They are connected via capacitor, electrical transformer, R-L or directly coupled depending on the application. The overall gain is the product of gains of individual stages. Figure below shows a two stage CE amplifier. various parameters of CE amplifier are

	Definition	Expression (with emitter degeneration)	Expression (without emitter degeneration, i.e., RE = 0)
Current gain
Voltage gain
Input impedance
Output impedance

types of transistor amplifier

1. common Emitter amplifier
2. common Base amplifier
3. common Collector amplifier

COMMON-COLLECTOR CONFIGURATION 

 Since there is no phase reversal between the input and output circuits of a common-collector configuration, the feedback network does not need to provide a phase shift. However, since the voltage gain is less than unity and the power gain is low, the common-collector configuration is very seldom used in oscillator circuits.

COMMON-BASE CONFIGURATION

The power gain and voltage gain of the common-base configuration are high enough to give satisfactory operation in an oscillator circuit. The wide range between the input resistance and the output resistance make impedance matching slightly harder to achieve in the common-base circuit than in the common-emitter circuit. An advantage of the common-base configuration is that it exhibits better high-frequency response than does the common-emitter configuration.

COMMON-EMITTER CONFIGURATION 

The common-emitter configuration has high power gain and is used in low-frequency applications.For the energy which is fed back from the output to be in phase with the energy at the input, the feedback network of a common-emitter oscillator must provide a phase shift of approximately 180 degrees.

Advantages and Disadvantages of transistor amplifier

Advantages of CE amplifier:

1. A common emitter amplifier is inverting and has low input impedance
2. high output impedance 
3. high voltage gain
4. high current gain.

Disadvantages of CE amplifier: 

1. 1. It has a high output resistance. 
2. 2. It responds poorly to high frequencies. 
3. 3. It has high thermal instabilities. 
4. 4. It's voltage gain is very unstable.

Advantages of CB amplifier:

1.  decent voltage amplifier, and current in is about equal to current out (actually current in is slightly greater than current out).
2. The common base circuit works best as a current buffer. It can take an input current at a low input impedance, and deliver nearly that same current to a higher impedance output.

Disadvantages of CB amplifier:

1. It requires two DC power sources to run this type of circuit.
2. Measure another voltage between emitter (input) and Collector(output). 
3. Compare voltage between Emitter and Base to see it is within the limit of transistor. 
4. Common Base circuit mostly use on OSC circuit or matching circuit. It has less gain than CE type.
5. amplification factor of common base amplifier is less less than common emitter amplifier.

Advantages of CC amplifier:

1. It has current gain but maintain voltage gain unchanged
2. It has the lowest output impedance compare to other type amplifier
3. It can be used for impedance matching between an amplifier stage with a high output impedance and an amplifier stage with a low input impedance.
4.  When used like this it is sometimes called a buffer amp or isolation amp. 
5. When placed between the the two stages it prevents the stage with the low input impedance from overloading the stage with the high output impedance.
6. The Voltage gain of a common collector amp is at best slightly less than 1

COMPARISON AMONG DIFFERENT TYPES OF AMPLIFIER:

	Common Emitter	Common Collector	Common Base
Voltage Gain	Medium	Low	High
Current Gain	Medium	High	Low
Input Impedance	Medium	High	Low
Output Impedance	Medium	Low	High

Resistor colour coding

Application of network theorem

• Both the methods are used to solve the complex network.
• Norton's Theorem & Thevenin's Theorem are "Duals". 
•  substitution theorem can be used in both linear and nonlinear circuits. For those nonlinear circuits that have a unique solution, we can use the substitution theorem in the equivalent transformation.
• they can be applied to both ac and dc source.
• For easy detemination of circuit parameter

Conversion between thevienin circuit to norton circuit

A Norton equivalent circuit is related to the Thevenin equivalent by the following: