Electronic Circuits - Chapter 4 Field-Effect Transistors II...

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Chapter 4 Field-Effect Transistors II EE4313 Electronic Circuits II
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Internal Capacitances in Electronic Devices • Limit high-frequency performance of the electronic device they are associated with. • Limit switching speed of circuits in logic applications • Limit frequency at which useful amplification can be Chap 4-2 obtained in amplifiers. • MOSFET capacitances depend on operation region and are non-linear functions of voltages at device terminals.
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NMOS Transistor Capacitances: Triode Region C ox =Gate-channel capacitance per unit area(F/m 2 ). C GC =Total gate channel capacitance Chap 4-3 capacitance. C GS = Gate-source capacitance. C GD =Gate-drain capacitance. C GSO and C GDO = overlap capacitances (F/m). C GS = C GC 2 + C GSO W = C ox " WL 2 + C GSO W C GD = C GC 2 + C GSO W = C ox " WL 2 + C GSO W
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NMOS Transistor Capacitances: Triode Region (contd.) C SB = Source-bulk capacitance. C DB = Drain-bulk capacitance. A S and A D = Junction bottom area capacitance of the source and drain regions. C SB = C J A S + C JSW P S C DB = C J A D + C JSW P D Chap 4-4 P S and P D = Perimeter of the source and drain junction regions. C J = Junction bottom capacitance per unit area (F/m 2 ). C JSW = Junction sidewall capacitance per unit length (F/m).
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NMOS Transistor Capacitances: Saturation Region Chap 4-5 • Drain no longer connected to channel C GS = 2 3 C GC + C GSO W C GD = C GDO W
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NMOS Transistor Capacitances: Cutoff Region • Conducting channel region completely gone. Chap 4-6 C GB = Gate-bulk capacitance C GBO = gate-bulk capacitance per unit width. C GD = C GDO W C GS = C GSO W C GB = C GBO W
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SPICE Model for NMOS Transistor Typical default values used by SPICE: K n or K p = 20 µ A/V 2 γ = 0 λ = 0 Chap 4-7 V TO = 1 V µ n or p = 600 cm 2 /V.s 2 Φ F = 0.6 V C GDO = C GSO =C GBO =C JSW = 0 T ox = 100 nm
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This note was uploaded on 10/27/2010 for the course EE Electronic taught by Professor Ortiz during the Spring '10 term at The University of Texas at San Antonio- San Antonio.

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Electronic Circuits - Chapter 4 Field-Effect Transistors II...

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