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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...

Common Source JFET Amplifier Common Source JFET Amplifier uses junction field effect transistors as its main active device offering high input impedance characteristics. Transistor amplifier circuits such as the common emitter amplifier are made using Bipolar Transistors, but small signal amplifiers can also be made using Field Effect Transistors. These devices have the advantage over bipolar transistors of having an extremely high input impedance along with a low noise output making them ideal for use in amplifier circuits that have very small input signals. The design of an amplifier circuit based around a junction field effect transistor or “JFET”, (N-channel FET for this tutorial) or even a metal oxide silicon FET or “MOSFET” is exactly the same principle as that for the bipolar transistor circuit used for a Class A amplifier circuit we looked at in the previous tutorial. Firstly, a suitable quiescent point or “Q-point” needs to be found for the correct biasing of the ...