Field - Effect Transistor (FET)bandi. nsk/ele1/fet.pdf · PDF file- 1 - Field - Effect...

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Transcript of Field - Effect Transistor (FET)bandi. nsk/ele1/fet.pdf · PDF file- 1 - Field - Effect...

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    Field - Effect Transistor (FET)

    A, MOSFET Operation

    B, Electrical Characteristic

    C, DC 특성

    D, 증폭특성 및 소신호 등가회로

    E, Single - Stage FET Amplifier Configurations

    1, Basing FET

    2, CS (Common Source)

    3, CG (Common Gate)

    4, CD (Common Drain)

    F, FET Switch

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    A, MOSFET Operration

    Gate에 +전압을 가하면 SiO2밑에 - 전하, 즉 전자가 축적하여

    Channel형성

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    •Vt(Threshold Voltage) : Channel을 형성하는데 필요한 최소 전압

    Vg( 강반전이 생기는 최소 전압)

    •Enhancement-mode Tr : 0 Vg 전압에서 채널을 형성치 않음.

    (normally off). 전도성 채널을 유기시키는데

    + Vg인가

    •Depletion-mode Tr : Gate 전압이 가하지 않았는데도 채널이

    형성되어 있음.

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    B, Electrical Characteristics

    Mos Current

    dV = IDdR , dR = ρdy

    Xc(y)W (R = ρ L

    A )

    ρ = 1 qμnN

    , Thus dV = IDdy qμnXc(y)W

    The inversion charge Qn(y) = qXc(y)n

    Hence dV = IDdy Qn(y)μW

    , IDdy = Qn(y)μWdV

    Qn(y) = [Vg -Vt -V(y)]C0

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    integrating from Source to Drain

    ID⌠⌡

    L

    0 dy=⌠⌡

    L

    0 C0μW[Vg-VtV( y) ]dV

    ※ ID= C 0μ W L [ (Vg-Vt) V D-

    1 2 VD 2 ]

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    In Saturation region, pinch- off condition

    VG = VDSat + VT

    VDSat = VG - VT

    ※ I D= 1 2

    C 0μW

    L ( V G- V T)

    2

    Triode Region

    I D=β[ ( V G- V T ) V D- 1 2 V D

    2 ]

    β= C 0μW

    L

    채널전도도 g= ∂ I D ∂ V D

    ≒ β(VG-VT) VG>VT

    Saturation Region

    ID = 1 2

    β(VG-VT) 2

    Transconductance gm = ∂ I D ∂ V G

    = β(VG-VT)

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