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mosfet - ECEN 325 Electronics MOS Field-Eect Transistors Dr...

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ECEN 325 Electronics MOS Field-Effect Transistors Dr. Aydın ˙ Ilker Kar¸ sılayan Texas A&M University Department of Electrical and Computer Engineering
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NMOS Physical Structure NMOS Physical Structure p- Drain (D) L W Body (B) n+ n+ Polysilicon Metal Metal Source (S) Gate (G) ECEN 325 Electronics - Aydın ˙ I. Kar¸ sılayan - MOS Field-Effect Transistors 1
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CMOS Physical Structure CMOS Physical Structure Cross-section PMOS NMOS S G D D G S p- n-well n+ 2 p+ p+ 2 n+ 2 SiO SiO SiO ECEN 325 Electronics - Aydın ˙ I. Kar¸ sılayan - MOS Field-Effect Transistors 2
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Physical Operation Physical Operation NMOS V GS p- G S D n+ n+ V GS > V tn V DS = 0 V GS V DS p- G S D n+ n+ V GS > V tn V DS : very small ECEN 325 Electronics - Aydın ˙ I. Kar¸ sılayan - MOS Field-Effect Transistors 3
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Physical Operation Physical Operation NMOS V GS V DS p- G S D n+ n+ V GS > V tn V DS < V ov V ov = V GS - V tn V GS V DS p- G S D n+ n+ V GS > V tn V DS > V ov V ov = V GS - V tn ECEN 325 Electronics - Aydın ˙ I. Kar¸ sılayan - MOS Field-Effect Transistors 4
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I D -V DS Characteristics I D -V DS Characteristics NMOS Active GS4 V GS3 V GS2 V GS1 V DS I D V GS V DS I D V DS <V ov V DS >V ov Triode V ECEN 325 Electronics - Aydın ˙ I. Kar¸ sılayan - MOS Field-Effect Transistors 5
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I D -V SD Characteristics I D -V SD Characteristics PMOS Active I D V SG V SD V SG4 V SG3 V SG2 V SG1 V SD I D V SD <V ov V SD >V ov Triode ECEN 325 Electronics - Aydın ˙ I. Kar¸ sılayan - MOS Field-Effect Transistors 6
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NMOS DC Operation NMOS DC Operation G GS I D D S V I G =0 V ov = V GS - V tn Cutoff: V GS < V tn , I D = 0 Triode (linear) region: V DS < V ov I D = k n W L V ov V DS - V 2 DS 2 Active (saturation) region: V DS > V ov I D = k n 2 W L V 2 ov ECEN 325 Electronics - Aydın ˙ I. Kar¸ sılayan - MOS Field-Effect Transistors 7
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PMOS DC Operation PMOS DC Operation G D S D I V SG I G =0 V ov = V SG - | V tp | Cutoff: V SG < | V tp | , I D = 0 Triode (linear) region: V SD < V ov I D = k p W L V ov V SD - V 2 SD 2 Active (saturation) region: V SD > V ov I D = k p 2 W L V 2 ov ECEN 325 Electronics - Aydın ˙ I. Kar¸ sılayan - MOS Field-Effect Transistors 8
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MOSFET DC Biasing MOSFET DC Biasing Resistive R G2 -V SS R D -V SS R G2 R S R G1 V DD R S R D R G1 V DD V 2 V 1 V 2 = R G2 (V DD + V SS ) R G1 + R G2 V 2 = V GSn + R S I Dn I Dn = k n 2 W L (V GSn - V tn ) 2 V 1 = R G1 (V DD + V SS ) R G1 + R G2 V 1 = V SGp + R S I Dp I Dp = k p 2 W L (V SGp - V tp ) 2 ECEN 325 Electronics - Aydın ˙ I. Kar¸ sılayan - MOS Field-Effect Transistors 9
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MOSFET DC Biasing MOSFET DC Biasing NMOS Current Mirror I D1 I D2 M 2 M 1 Assuming V GS1 > V tn V GS1 = V DS1 V DS1 > V GS1 - V tn M 1 is ACTIVE I D1 = k n 2 W L 1 (V GS1 - V tn ) 2 Assuming M 2 is ACTIVE I D2 = k n 2 W L 2 (V GS2 - V tn ) 2 Since V GS1 = V GS2 I D1 I D2 = W L 1 W L 2 ECEN 325 Electronics - Aydın ˙ I. Kar¸ sılayan - MOS Field-Effect Transistors 10
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NMOS Current Mirror NMOS Current Mirror Example R I D1 M 1 M 2 M 3 M 4 M 5 M 6 I D2 I D3 I D4 I D5
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