Feedback Amplifiers

Feedback Pair Connection – Operation and its Equivalent Circuit: The feedback pair connection (Fig. 19.58) is a two-transistor circuit that operates like the Darlington amplifier. It makes use of a PNP transistor driving an NPN transistor, the two devices acting much like one PNP transistor. Like Darlington amplifier the feedback pair connection also provides a …

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Bootstrapped Darlington Circuit Operation and its Equivalent Circuit: The maximum input resistance of a Darlington circuit is limited to 1/hob ≡ 2 MΩ, as 1/hob is the resistance between base and collector. However, the input resistance can be largely increased by bootstrapped darlington circuit through the addition of capacitor C’ between the first collector terminal …

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Darlington Pair Transistor – Circuit Diagram and its Workings: A very popular connection of two BJTs for operation as one “superbeta” transistor is the Darlington connection. In practice, the two transistors are put inside a single package and three terminals E, B and C are brought out, as de­picted in Fig. 19.52. The main fea­ture …

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Darlington Amplifier – Circuit Diagram, Characteristics, Merits and Applications: Darlington amplifier with voltage divider bias is shown in Fig. 19.50. In this circuit the output of one amplifier is coupled into the input of the next one by directly joining emitter of one transistor to the base of the other one, as shown in the …

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Emitter Follower at High Frequencies: Emitter Follower at High Frequencies circuit is given in Fig. 19.48(a). A capacitance CL is included across the load because the emitter follower is often used to drive capacitive loads. This is because of its small output impedance. Applying Kirchhoff’s current law to nodes B′ and E respectively [Fig. 19.48(b)], …

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Emitter Follower Circuit – Operation, Advantages and Applications: Emitter Follower Circuit is also a negative current feedback circuit. This circuits exhibits a large input impedance, a small output impedance, and a voltage gain of approximately unity. Further the output voltage tends to be in phase with the input voltage—hence the term “follower”. At first glance, …

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Current Shunt Feedback Amplifier Circuit: Current Shunt Feedback Amplifier Circuit is also known as series-derived shunt fed feedback or current shunt inverse feedback. In this circuit, the feedback network picks up a part of the output current and produces a feedback voltage in parallel with the input signal voltage, as shown in Fig. 19.10(d). Since …

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Current Series Feedback Amplifier Circuit: Current Series Feedback Amplifier Circuit is also known as series-derived series fed feedback. In such a feedback circuit, a part of the output current is made to develop a voltage proportional to the output current and supplied back in series with the input, as shown in Fig. 19.10 (c). Since …

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Voltage Shunt Feedback Amplifier Circuit: Voltage Shunt Feedback Amplifier Circuit is also known as shunt-derived shunt fed feedback or voltage shunt inverse feedback. Here, a small portion of the output voltage is coupled back to the input voltage, as shown in Fig. 19.10 (b). Since the feedback network shunt both the input and output of …

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Voltage Series Feedback Amplifier or Shunt Derived Series Fed Feedback Amplifier: Voltage Series Feedback Amplifier Circuit is also called the shunt-derived series-fed feedback. Here the amplifier and feedback network are connected in series-parallel. A fraction of the output voltage is applied in series opposition to the input voltage through feedback network, as shown in Fig. …

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