MOS Basics

MOS Basics - Transistor Basics MOSFETs Bob York Transistors...

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©B ob Y o rk Transistor Basics - MOSFETs
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©B obY o rk Back to TOC Transistors, Conceptually Control Terminal I(V) I ( V, V c ) I ( V, I c ) or V V V c or I c FETs BJTs So far we have considered two-terminal devices that are described by a current-voltage relationship I = f ( V ) Transistors add a third terminal to control the current flow through the device. The two most common types of transistors are: Field-Effect Transistors (FETs): voltage-controlled current flow Bipolar Junction Transistors (BJTs): current-controlled current flow In ECE 2, we will not discuss the physics of device operation in depth. The transistor is simply a black box with certain well-defined terminal properties. Resistors: Capacitors: Inductors: Diodes: / IV R dV dt IC 1 L d t / 1 T VnV s IIe 
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©B obY o rk Back to TOC MOSFETs V gs Gate Source Drain I ds (V gs ,V ds ) V ds I d V gs V ds I g 0 Gate Source Drain G D S NMOS There are many types of FETs but all share some common features and nomenclature. Key points: Every FET has a gate , drain , and source Current flows between the drain and source. The gate is the control terminal. The DC gate “leakage” current is negligible, I g 0 Start with n-channel enhancement MOS (NMOS) (MOS=Metal-Oxide-Semiconductor). If we take the source as the voltage reference (ground), the drain current will depend on the gate voltage and drain voltage as shown : V gs V ds I d Current-Voltage Characteristic for NMOS D r a i n C u e t V o l g G Vo “Common-source” configuration
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©B obY o rk Back to TOC Common-Source NMOS Characteristic Saturation region I D Ohmic or Triode region V ds V gs = V tn + 0.5 V gs = V tn + 1.0 V gs = V tn + 1.5 V gs = V tn + 2.0 Increasing V gs I d vs V ds for specific values of V gs V ds = V gs -V t V gs V tn (cutoff) I d V gs V ds I g = 0 G D S I D V gs V t Important observations: No current flows for V gs < V tn . V tn is called the “Threshold voltage” Once the drain voltage exceeds V gs - V tn , a constant current flows that depends on V gs
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MOS Basics - Transistor Basics MOSFETs Bob York Transistors...

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