Chen 19 current gain unity gain frequency the mosfet

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J. Chen 19 Current gain Unity-gain frequency The MOSFET unity-gain freque ncy ) ( gd gs m i o C C s g I I + = ) ( 2 gd gs m T C C g f + = π
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3/2/12 SJTU J. Chen 20 The depletion-type MOSFET Physical structure The structure of depletion-type MOSFET is simila r to that of enhancement-type MOSFET with one important difference: the depletion-type MOSFET has a physically implanted channel Ø There is no need to induce a channel Ø The depletion MOSFET can be operated at both enhancement mode and depletion mode
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3/2/12 SJTU J. Chen 21 Simplified circuit symbol applicable for the case the substrate (B) is connected to the source (S). Circuit symbol for the n -channel depletion-MOS Circuit symbol for the n - channel depletion-type MOSFET
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3/2/12 SJTU J. Chen 22 Characteristic curves Ø Expression of characteristic equation Ø Drain current with the iD vGS characteristic in saturation 2 2 1 ) ' t GS n D V v L W k i - = 0 = GS v 2 2 1 ' t n DSS V L W k I =
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3/2/12 SJTU J. Chen 23 Ø Sketches of the iD vGS characteristics for MOSFETs of enhancement and depletion types Ø The characteristic curves intersect the vGS axis at Vt . The iD v GS characteristic in saturati on
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3/2/12 SJTU J. Chen 24 The output characteristic curves
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3/2/12 SJTU J. Chen 25 N - c h a n n e l Depletion layer G D S G D S n -type Semiconductor The junction FET P+ P +
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3/2/12 SJTU J. Chen 26 U GS = 0 U GS < 0 U GS = U GS(off) D S P+ Physical operation under vDS =0 G P+ D S P+ G P+ D S G P + P+
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3/2/12 SJTU J. Chen 27 The effect of U DS on I D for U GS(off) < U GS < 0 ? ?
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S J T U J. C h e n 28 3/2/12 Summary of semiconductor device s
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3/2/12 SJTU J. Chen 29 Diode, BJT and FET are nonlinear devices made of semiconductor, mostly silicon Diode A diode allows current to flow in forward direct ion and hence can perform functions such as r ectification, demodulation/detection, switch et c.
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  • Fall '10
  • ChengJianping
  • Transistor, Bipolar junction transistor, Buffer amplifier, Field-effect transistor, J. Chen

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