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3- Common Source JFET Amplifier

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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 ...
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16- Common Collector Amplifier

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Common Collector Amplifier Common Collector Amplifiers produce an output voltage across its emitter load which is in-phase with the input signal The  Common Collector Amplifier  is another type of bipolar junction transistor, (BJT) configuration where the input signal is applied to the base terminal and the output signal taken from the emitter terminal. Thus the collector terminal is common to both the input and output circuits. This type of configuration is called Common Collector, (CC) because the collector terminal is effectively “grounded” or “earthed” through the power supply. In many ways the common collector configuration (CC) is the reverse of the common emitter (CE) configuration as the connected load resistor is changed from the collector terminal for R C  to the emitter terminal for R E . The common collector or grounded collector configuration is commonly used where a high impedance input source needs to be connected to a low impedance output l...
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9- Emitter Resistance

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Emitter Resistance Emitter Resistance connected to the emitter terminal of a transistor amplifier can be used to increases the amplifiers bias stabilisation The aim of an AC signal amplifier circuit is to stabilise the DC biased input voltage to the amplifier and thus only amplify the required AC signal. This stabilisation is achieved by the use of an  Emitter Resistance  which provides the required amount of automatic biasing needed for a common emitter amplifier. To explain this a little further, consider the following basic amplifier circuit below. Basic Common Emitter Amplifier Circuit The common emitter amplifier circuit shown uses a voltage divider network to bias the transistors base and the common emitter configuration is a very popular way of designing bipolar transistor amplifier circuits. An important feature of this circuit is that an appreciable amount of current flows into the base of the transistor. The voltage at the junction of the two bias...
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