Basic Principles of Amplifiers

Definition: An amplifier is an electronic device that increases the power, voltage, or current of a signal.
Key Functions:
- Signal amplification: Increases the magnitude of input signals.
- Input/Output relation: Output signal is typically larger than the input.
Types:
- Voltage amplifiers: Boost voltage levels.
- Current amplifiers: Boost current levels.
- Power amplifiers: Combine both voltage and current amplification.

Overview: Widely used transistor amplifier configuration.
Features:
- Inverts the input signal (180-degree phase shift).
- Provides significant voltage gain.
Connections:
- Emitter connected to ground.
- Collector is the output.
- Base is the input.
Advantages:
- High gain.
- Good frequency response.
Disadvantages:
- Lower input impedance.
- Requires DC biasing.

Input Characteristics:
- Input impedance: Determined by base-emitter junction; typically low.
- Input current increases with base-emitter voltage.
Output Characteristics:
- Output impedance: Determined mainly by the collector-emitter voltage; generally high.
- Output current increases with collector-emitter voltage, showing saturation at high input level.
Load Line Analysis:
- Graphical representation of operating points regarding power supply and load.

Definition: Describes how the amplifier's gain varies with frequency.
Key Points:
- Midband frequency: Region where gain is relatively constant.
- Low-frequency response: Affected by coupling and bypass capacitors.
- High-frequency response: Affected by internal capacitances (Miller effect).
Roll-off:
- Gain decreases at frequencies beyond midband limits.
Bandwidth: The range of frequencies over which the amplifier operates effectively.

Purpose: Ensures the transistor operates in the desired region of its characteristic curve.
Common Techniques:
- Fixed bias: Simple but less stable.
- Emitter bias: Higher stability; includes a resistor in the emitter.
- Voltage divider bias: Provides improved stability against temperature and transistor variations.
Importance of Proper Biasing:
- Prevents distortion in the output signal.
- Maintains desired operating point (Q-point).
Factors Affecting Biasing:
- Temperature variations.
- Transistor beta (current gain) variations.

An amplifier is an electronic device that increases the power, voltage, or current of a signal.
They increase the magnitude of input signals.
Output signal is generally larger than the input.

Input impedance is determined by the base-emitter junction, typically low.
Input current increases with base-emitter voltage.
Output impedance is primarily determined by the collector-emitter voltage, generally high.
Output current increases with collector-emitter voltage, showing saturation at a high input level.
Load line analysis is a graphical representation of the operating points regarding power supply and load.

Describes how the amplifier's gain varies with frequency.
Midband frequency: The region where gain remains relatively constant.
Low-frequency response is affected by coupling and bypass capacitors.
High-frequency response is affected by internal capacitances (Miller effect).
Roll-off: Gain decreases at frequencies beyond midband limits.
Bandwidth: The range of frequencies over which the amplifier operates effectively.

Ensures the transistor operates in the desired region of its characteristic curve.
Fixed bias: Simple but less stable.
Emitter bias: Higher stability, includes a resistor in the emitter.
Voltage divider bias: Provides improved stability against temperature and transistor variations.
Proper biasing prevents distortion in the output signal, maintains the desired operating point (Q-point).
Factors affecting biasing: Temperature variations and transistor beta (current gain) variations.

Describes the force between two stationary point charges.
The force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
The force is attractive if the charges are opposite and repulsive if they are the same.

Represent the electric field around charged objects.
They are drawn so that the direction of the line at any point represents the direction of the force that a positive test charge would experience at that point.
The density of lines represents the strength of the field, where closer lines mean a stronger field.
Electric field lines never cross each other.

Relates the electric flux through a closed surface to the total charge enclosed by the surface.
The electric flux is proportional to the total charge enclosed by the surface.
Gauss's law is useful for calculating electric fields with symmetry, such as spherical, cylindrical, or planar symmetry.

Energy stored due to the position of charges in an electric field.
The potential energy is positive for an unstable configuration and negative for a stable configuration.
The work done on a charge moving in an electric field changes its electric potential energy.

The ability of a system to store an electric charge per unit voltage.
It's measured in Farads (F).
Different types of capacitors exist, such as parallel plate capacitors, which consist of two conductive plates separated by a dielectric material.
The capacitance of a parallel plate capacitor is proportional to the area of the plates and inversely proportional to the distance between them.
Capacitors can store energy in the electric field between their plates.
The energy stored is proportional to the capacitance and the square of the voltage across the capacitor.