Amplifier #1. How to Choose Between Linearity & Power Efficiency for Class A, B, C Amplifiers. скачать в хорошем качестве

Amplifier #1. How to Choose Between Linearity & Power Efficiency for Class A, B, C Amplifiers.

Amplifier (Class A, B and C) playlist. Watch these videos to understand more on Amplifier (Class A, B and C)    • Amplifier #1. How to Choose Between Linear...   For access to this presentation materials, membership is required: I need the Material PPT Sent me an email to Technologies.Discussion@gmail.com If you need the whole playlist material, send me email and we discuss. Give me some time to response. Thanks. Definition of Amplifier An electrical or electronic amplifier is a circuit that uses an external power supply to generate an output signal (a time varying voltage or current) that is a larger replica of its input in term of the magnitude of the amplitude. Example: An audio amplifier is used to increase the volume of a speaker’s voice so they can be heard more easily in a larger area. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current or power to input. An amplifier is defined as a circuit that has a power gain greater than 1. In a circuit diagram, an amplifier is usually represented by a triangle. A typical amplifier system usually consists of several stages of amplifiers cascaded together to achieve the desired gain. The initial stages usually employ small signal amplifiers because the signals being handled are usually smaller. The final stage is normally required to provide certain power level to a targeted load and usually a power amplifier is used. A typical amplifier system usually consists of several stages of amplifiers cascaded together to achieve the desired gain. The initial stages usually employ small signal amplifiers because the signals being handled are usually smaller. The final stage is normally required to provide certain power level to a targeted load and usually a power amplifier is used. Three different classes of amplifiers are compared, their major characteristics and linearity are listed on the next few pages. Linear amplifiers but may not offer very high efficiency. Non-linear amplifiers, the efficiency is normally higher. The efficiency is defined as the ratio of the RF output power to the collector circuit dc input power. Class A Class A is defined as an amplifier that is biased so that the output current flows at all times. The input signal is kept small to prevent driving the transistor into cut off. The conduction angle of the transistor is 360 - meaning that the transistor conducts for the full cycle of the input signal. Most linear Low efficiency, can be less than 50%. Class B Conduction angle for the transistor is about 180. Thus, the transistor conducts only ½ the time, either on the positive or negative half cycle of the input signal. Less linear, and harmonics are generated at the output. Use filter to filter off. Efficiency can be up to 70% Class C Conduction angle is significantly less than 180. The transistor is biased such that under steady state conditions no collector current flows. The transistor idles at cut off. Linearity is poor. Efficiency can be up to 85%. In order to bias a transistor for class C operation, it is necessary to reverse bias the base-emitter junction. External biasing is usually not needed.