Amplifier classes
- 1. Assignment no ;01 Topic; Amplifier Classes Submitted by; Abdulrehman Submitted to; DR Ahmad Raza
- 2. Amplifier An amplifier is an electronic device or circuit which is used to increase the magnitude of the signal applied to its input.
- 3. What are classes of amplifier? AMPLIFIER CLASS DESCRIPTION CONDUCTION ANGLE Θ Class A Conduction over the full 360° of the cycle θ = 2π Class B Conduction occurs over half the cycle, i.e. for 180° θ = π Class AB Conduction occurs for slightly more than half the cycle, i.e. slightly more than 360° θ < θ < 2π Class C Conduction occurs for less than 180° of the cycle, but this creates distortion θ < π Classes D to T These amplifier classes utilise non-linear switching techniques to improve efficiency. N/A
- 4. Class a Amplifier; The most popular sort of power amplifier is the Class A amplifier. Using a single transistor to produce a single inverted output in the standard typical circuit configuration, the class A amplifier is the simplest type of power amplifier. This is the simplest kind of power amplifier circuit in Class A. It uses a single-ended transistor for its output stage, with a resistive load directly connected to the collector terminal. The output current sinks through the collector as the transistor turns on, resulting in an eventual drop in voltage through the emitter resistance, thus limiting the negative output capability
- 5. The efficiency of this type of circuit is very poor (less than 30 percent) and produces small outputs on the DC power supply for a large drain. Even when no input signal is applied, the amplifier stage Class A passes the same load current so that large heat sinks are needed for the output transistors. Applications of Class A Amplifier: For outdoor music systems, the Class A amplifier is better suitable, as the resistor reproduces the entire audio waveform without being broken off. The sound is also more stable and more linear, i.e. it has much lower distortion levels.
- 6. Group A Amplifier Advantages: 1.It has high accuracy thanks to the exact output copy of the input signal. 2.High-frequency response has increased when the activated system is on full time, i.e. no time is taken to turn the device on. 3. There is no crossover distortion since the active unit works for the entire input signal duration. 4. The single-ended structure can be quickly and technically realized in class A amp. Class A amplifier disadvantage: 1.Class A amplifier is expensive and cumbersome due to the large power source and heat sink. 2.They've got low performance. 3.The frequency response of the transformer coupling is not as strong
- 7. Class B Amplifier: Class B is a type of power amplifier in which the active device (transistor) for only half a cycle conducts the input signal. The conductivity angle on a Class B amplifier is 180 °. For two or more transistors, Class-B amps are used in such a way that only half of the input waveform loop can be carried out by each transistor. In its output level, also called a push pull enhancer configuration, the power amplifiers can be equipped with two transistors, producing what is usually called a Class B amp, to increase the maximum power efficiency of the previous Class A amplifier by decreasing waste heat power.
- 9. Applications: Products working in Class B are used in linear amplifiers, so-called because the output of the radio frequency is equal to the input voltage square. This function avoids the distortion of amplitude-modulated or frequency- modulated signals going through the amplifier. Advantages of Class B amplifier: • High efficiency when compared to the Class A configurations. • Push-pull mechanism avoids even harmonics. • No DC components in the output (in ideal case).
- 10. Disadvantages of Class B amplifier: • The major disadvantage is the cross- over distortion • Coupling transformers increases the cost and size. • It is difficult to find ideal transformers.
- 11. Class AB amplifiers: In order to make the amplifier more efficient than Class A but with less distortion than Class B, Class AB amplifiers combine Class A and Class B. This is done by bias in both transistors in such a way that they work when the signal is close to zero (the point where class B amplifiers introduce non-linearities).
- 12. As the current passes through the resistor, as defined by Ohm's law, a voltage drop is generated across the resistor. So, we can create a voltage divider network by placing two or more resistors in series around the supply voltage, which generates a range of fixed voltages at our preferred values. The simple circuit is similar to the above voltage bias circuit in that the input waveform is performed by the transistors, TR1 and TR2 during the opposite half of the loop. That is, TR1 is positive when VIN is positive, and TR2 is positive when VIN is negative. Advantages: • The class AB has a linear behavior • The design of this amplifier is very simple • The distortion of this amplifier is less than 0.1% • The sound quality of this sound is very high
- 13. Disadvantages: • The power dissipation of this amplifier generates the heat and requires large amount of heat sink • This amplifier has low power efficiency and the average efficiency is less than the 50%
- 14. Class C Amplifier: As the collector current flows from the input signal in less than half a loop, the power amplifier is known as the class C power amplifier. The efficiency of the class C amplifier is high, while the linearity is low. For class C, the driving angle is less than 180 degrees. As seen in the circuit diagram. Resistor Rb binds to the base of transistor Q1. In a DC load line, a biasing resistor joining the base of Q1 attempts to move the base of the transistor further down to set the working point dc bias below the cut-off point (ICO, which is supposed to be zero) in the cut-off of the collector current. ICO is the DC load line. In the active region where BJT resides, the load line for dc is the locus of IC and VCE.
- 16. Inductor L1 an capacitor C1 forms a tuned circuit which is also called a tank circuit. LC circuits are used either for generating signals at a particular frequency, or picking out a signal at a particular frequency from a more complex signal which extract the required signal from the pulsed output of the transistor. Applications of Class C Amplifier: Class C Amplifier is used in: – RF oscillators. RF amplifier. FM transmitters. Booster amplifiers. High frequency repeaters. Tuned amplifiers.
- 17. Advantages of Class C Amplifier: The advantages of Class C Amplifier are as follows: – • Higher efficiency. • Best result in RF applications. • Physical size is suitable for given power.
- 18. Disadvantages of Class C Amplifier: The disadvantages of Class C Amplifier are as follows: – • Poor linearity. • Not suitable for audio applications. • Lot of noise and RF interference. • To obtain ideal inductors and coupling transformers it is very difficult. • Not good dynamic range.
- 19. Class D Amplifier: A Class D amplifier is an electronic amplifier in which the amplifier components are used as electronic switches (transistors, usually MOSFETs, not as linear gain devices, as with other extensions.
- 20. Applications of Class D amplifier: In programs such as hand-held audio systems, mobile home theaters, mobile phones, etc. Where all of their outputs must be good (in terms of energy and loyalty) and size must be as small as possible, Class-D amplifiers have been popular. The Class D amplifier is a switching amplifier and it will drive current but will almost have zero voltage on the switches while the "On" state is in place. In "OFF" mode, the voltage will go over the MOSFETs, but because of no current flow, the switch does not need any power. Only when the leakage currents are not taken into account during the on/off transitions does the amplifier require power. The following Class D amplifier measurements:
- 22. Advantages Class D amplifier: A high performance of about 90 per cent is the main advantage of the class D amplifier. The Class AB amplifier with an efficiency of 50 to 70 percent is much greater than its nearest analog competitor. High performance helps the physical component to be minimized and heatsinks and refreshments can theoretically be eliminated. • Low heat dissipation. • Reduced size and weight. • High power conversion efficiency. Almost all power drawn is supplied to the load.
- 23. Disadvantages of Class D amplifiers: When the power transistor of the Class D power amplifier is initially connected and shut off, the potential near to the ground can fluctuate to increase the noise level. For any cause, Class D power amplifier speakers can be skewed. • Requires a very clean and stable power supply. • The high frequency response is dependent on the loudspeaker impedance.
- 24. Thank-you