Lect_03 - ECE 442 ECE 442 Electronic Circuits 3. MOS...

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CE 442 ECE 442 Electronic Circuits 3. MOS Transistors Jose E. Schutt-Aine lectrical & Computer Engineering Electrical & Computer Engineering University of Illinois jschutt@emlab.uiuc.edu ECE 442–Jose Schutt Aine 1
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NMOS Transistor Typically L = 0.1 to 3 m, W = 0.2 to 100 m, and the thickness of the oxide layer (t ox ) is in the range of 2 to 50 nm. ECE 442–Jose Schutt Aine 2
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NMOS Transistor NMOS Transistor – N-Channel MOSFET – Built on p-type substrate – MOS devices are smaller than BJTs – MOS devices consume less power than BJTs ECE 442–Jose Schutt Aine 3
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NMOS Transistor - Layout Top View Cross Section ECE 442–Jose Schutt Aine 4
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MOS Regions of Operation S T V Resistive GS VV DS Vs m a l l Triode S T Nonlinear GS < ( ) DS GS T V GS T Saturation Active ECE 442–Jose Schutt Aine DS GS T V  5
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MOS Transistor Operation As V G increases from zero – Holes in the p substrate are repelled from the gate area leaving negative ions behind depletion region is created – A depletion region is created – No current flows since no carriers are available As V increases G – The width of the depletion region and the potential at the oxide-silicon interface also increase – When the interface potential reaches a sufficiently positive value, electrons flow in the “ channel ”. The transistor is turned on As V rises further G – The charge in the depletion region remains relatively constant – The channel current continues to increase ECE 442–Jose Schutt Aine 6
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MOS – Triode Region - 1     D ox GS T DS W IC V V V L C ox : gate oxide capacitance : electron mobility   DS GS T VV V  L : channel length W : channel width V T : threshold voltage 3.9  ox o x C ECE 442–Jose Schutt Aine ox ox ox tt 7
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MOS – Triode Region FET is like a linear resistor with  1 ds no x G S T r W CV V ECE 442–Jose Schutt Aine L 8
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MOS – Triode Region - 2  2 1  D n ox GS T DS DS W IC V V V V GS T VV 2  L    D SG S T V – Charge distribution is nonuniform across channel – Less charge induced in proximity of drain ECE 442–Jose Schutt Aine 9
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MOS – Active Region Saturation occurs at pinch off when    DS GS T DSP VV V V V  2  Dn o x G S T W IC V V DS GS T V  GS T aturation) ECE 442–Jose Schutt Aine 2 L (saturation) 10
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NMOS – Drain Current ECE 442–Jose Schutt Aine 11
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NMOS – Circuit Symbols ECE 442–Jose Schutt Aine 12
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NMOS – IV Characteristics haracteristics for a device with =10mA/V ECE 442–Jose Schutt Aine 13 characteristics for a device with k n ( W / L ) = 1.0 mA/V 2 .
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MOS Threshold Voltage The value of V G for which the channel is “inverted” is alled the threshold voltage r Characteristics of the threshold voltage called the threshold voltage V T (or V t ).
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This note was uploaded on 05/05/2010 for the course ECE 329 taught by Professor Franke during the Spring '08 term at University of Illinois at Urbana–Champaign.

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Lect_03 - ECE 442 ECE 442 Electronic Circuits 3. MOS...

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