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10- Amplifier Classes

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Amplifier Classes Amplifiers are classified into classes according to their construction and operating characteristics Not all amplifiers are the same and there is a clear distinction made between the way their output stages are configured and operate. The main operating characteristics of an ideal amplifier are linearity, signal gain, efficiency and power output but in real world amplifiers there is always a trade off between these different characteristics. Generally, large signal or power amplifiers are used in the output stages of audio amplifier systems to drive a loudspeaker load. A typical loudspeaker has an impedance of between 4Ω and 8Ω, thus a power amplifier must be able to supply the high peak currents required to drive the low impedance speaker. One method used to distinguish the electrical characteristics of different types of amplifiers is by “class”, and as such amplifiers are classified according to their circuit configuration and method of operation. T...
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4- Amplifier Distortion

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Amplifier Distortion Amplifier Distortion can take on many forms such as Amplitude, Frequency and Phase Distortion due to Clipping. For a signal amplifier to operate correctly without any distortion to the output signal, it requires some form of DC Bias on its Base or Gate terminal. A DC bias is required so that the amplifier can amplify the input signal over its entire cycle with the bias “Q-point” set as near to the middle of the load line as possible. The bias Q-point setting will give us a “Class-A” type amplification configuration with the most common arrangement being the “Common Emitter” for Bipolar transistors or the “Common Source” configuration for unipolar FET transistors. The Power, Voltage or Current Gain, (amplification) provided by the amplifier is the ratio of the peak output value to its peak input value (Output ÷ Input). However, if we incorrectly design our amplifier circuit and set the biasing Q-point at the wrong position on the load line or apply too...
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14- MOSFET Amplifier

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MOSFET Amplifier MOSFET Amplifier uses a metal-oxide silicon transistor connected in the common source configuration In our previous tutorial about FET amplifiers, we saw that simple single stage amplifiers can be made using junction field effect transistors, or JFET’s. But there are other types of field effect transistors available which can be used to construct and amplifier, and in this tutorial we will look at the MOSFET Amplifier. Metal Oxide Semiconductor Field Effect Transistor, or MOSFET for short, is an excellent choice for small signal linear amplifiers as their input impedance is extremely high making them easy to bias. But for a mosfet to produce linear amplification, it has to operate in its saturation region, unlike the Bipolar Junction Transistor. But just like the BJT, it too needs to be biased around a centrally fixed Q-point. A Typical MOSFET Transistor MOSFETS conduct through a conductive region or path called “the channel”. We can make this c...
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