Chapter 1 Analog and digital electronics

 

Analog and Digital Electronics

 

UNIT I 06 Special Diodes: LED, Varactor diode, Photo diode, Schottky diode, Tunnel diode and their characteristics and applications, Transistors as a switch.

 UNIT II 07 Frequency Response: -Amplifier transfer function, low and high frequency response of common emitter and common source amplifiers.

 Feedback: General feedback structure, properties of negative feedback: series-series, series-shunt, shunt-series and shunt-shunt feedback amplifiers.

UNIT III 07 Basic principle of sinusoidal oscillator, R-C Phase Shift and Wein Bridge oscillators, tuned oscillators-Collpits, Hartley and Crystal oscillators.

 

 

1. LED (Light-Emitting Diode)

Definition: A light-emitting diode (LED) is a semiconductor device that emits light when an electric current passes through it.

Characteristics:

• Emits light when forward-biased
• Low power consumption
• Long lifespan
• Available in various colours
• High efficiency

Applications:

• Indicator lights
• Backlighting for displays
• Flashlights
• Traffic signals
• Automotive lighting
• General illumination

2. Varactor Diode

Definition: A varactor diode, also known as a voltage-variable capacitor diode, is a semiconductor device that changes its capacitance in response to an applied voltage.

Characteristics:

• Capacitance varies with applied voltage
• Useful for tuning circuits
• Offers low power consumption

Applications:

• Frequency tuning circuits
• Voltage-controlled oscillators
• Phase-locked loops
• Radio frequency amplifiers

3. Photodiode

Definition: A photodiode is a semiconductor device that converts light into an electrical current.

Characteristics:

• Converts light into current
• High sensitivity to light
• Fast response time
• Wide range of spectral response

Applications:

• Light sensors
• Optical communication systems
• Smoke detectors
• Position sensors
• Automatic lighting controls

4. Schottky Diode

Definition: A Schottky diode is a semiconductor device that has a lower forward voltage drop than a standard p-n junction diode.

Characteristics:

• Low forward voltage drops
• Fast switching speed
• High efficiency
• Low leakage current

Applications:

• High-frequency switching circuits
• Power electronics
• Schottky rectifiers
• Voltage regulators
• Low-noise amplifiers

5. Tunnel Diode

Definition: A tunnel diode is a semiconductor device that exhibits a negative resistance region in its current-voltage characteristic.

Characteristics:

• Negative resistance region
• High-frequency operation
• Low power consumption
• Fast switching speed

Applications:

• High-frequency oscillators
• Voltage-controlled oscillators
• Microwave amplifiers
• Tunnel diode logic circuits

6. Transistors as a Switch

A transistor can be used as a switch by controlling the current flow between its collector and emitter terminals. When the base current is zero, the transistor is turned off and no current flows between collector and emitter. When a small base current is applied, it allows a much larger current to flow between collector and emitter, effectively turning the transistor on. This switching action makes transistors essential components in various electronic circuits, including:

• Logic gates
• Amplifiers
• Power electronics
• Switching regulators
• Microprocessors

Characteristics:

• High input impedance
• Low output impedance
• Current controlled devices
• Can be used to amplify or switch signals

Applications:

• Digital circuits
• Analog circuits
• Power electronics
• Microprocessors
• Audio amplifiers