Want this question answered?
A FET (Field Effect Transistor) is mainly used when the input signal needs to be isolated from the output. A FET has a very high input resistance, so very little current is required from the input. Voltage gain is not the main objective when using a FET.
the final stage of a power amp is a current amplifier in a bipolar design and a voltage amp in a FET design.
nnm,n,n,mn
Zin=Vds/Id [Vds=drain to source voltage ; Id = drain current]
fet is a voltage controlled device...cut off voltage in fet refers to that voltage of the gate - source junction at which the current flow through channel is zero
fet is a voltage controlled device...cut off voltage in fet refers to that voltage of the gate - source junction at which the current flow through channel is zero
The small signal model for the common source FET can be used for analysing the basic FET amplifierconfigurations:(i)common source(CS),(ii)commondrain(CD) or source follower,and(iii)common gate(CG). The CS amplifier which provides good voltage amplification is most frequentlyused.The CD amplifier with high input impedance andnear-unity voltage gain is used as a buffer amplifier and the CG amplifier is used as a high frequencyamplifier.The small signal current-sourcemodel for the FET in CS configuration and the voltage source model can be derived by finding the Thevenin'sequivalent for the output part of amplificationfactor,drain resistance andtransconductance/mutual conductance of the FET.
It can be answered in two ways : 1. ratio of output & input voltages [Vout / Vin] i.e Drain voltage(Vds)/Source voltage(Vs). 2. multiplication of trans-conductance & drain resistance .
If it is a variable cap, apply AC signal to the capacitor as per its specifications.This is done because the variation in the voltage gives a corresponding current output due to the charging and discharging of capacitor. Then a Trans-impedance amplifier can be used to convert this input current to voltage. Current amplifier can be used to amplify the current at the input of the trans-impedance amplifier. Similarly a voltage amplifier can be used at the out put of the trans-impedance amplifier to amplify the voltage output.
In audio look at an amplifier. It will be always a voltage amplifier.
FET
A voltage amplifier does not have to supply significant current bur a power amplifier does.