Explain why the Common Base amplifier circuit has a much higher band width than

Question

Explain why the Common Base amplifier circuit has a much higher band width than a Common Emitter amplifier. Mention one application where a common collector circuit is used for. 0.5 point Explain the diode application when used as a varactor, and when used in voltage regulation? Explain briefly how can you bias an integrated circuit Common Source amplifier? Draw the circuit. Mention two advantages for the integrated circuit biasing over the discrete biasing. What is the purpose of the source resistance in the common source amplifier circuit? Define the threshold voltage of an enhancement MOSFET and the pinch off voltage of the depletion MOSFET.

Explanation / Answer

a) In common emitter amplifier, the collector-base capacitor will be magnified by gain times, due to Miller effect, this decreases the upper cutoff frequency and hence the bandwidth is low. In common base amplifier , the base terminal is at the ground potential, it does not have Miller effect, hence the bandwidth is large. b) Common collector circuit is used as buffer circuit or impedance matching circuit, to avoid loading effect. c) Diode when used as a vactor diode is used as capacitor in tunning circuits of receivers like radio, TV etc Diode when used as regulator is used as voltage regulator in DC power supplies. e) The source resistance in common source amplifier is used to provide self biasing, that is it helps in Q-point (Operating point ) stability. f) The threshold voltage is the minimum voltage required for the drain current to flow in the MOSFET. Pinch off voltage is the gate-source voltage of the MOSFET where the current reduces to zero. It is the voltahe at which the channel width decreases to the minimum and the flow of charges is blocked making the drain current zero.

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