1. Field effect Transistors: Operation, Circuit, Models, and Applications
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1

2. Context 11.1 Classification of Field-Effect Transistor
11.2 Overview of Enhancement-mode Mosfet
11.3 Biasing Mosfet Circuit
11.4 Mosfet Large-Signal Amplifiers
11.5 Mosfet Switches 2 2

3. Classification of Field-Effect Transistors
This figure depicts the classification of field- effect transistors, as well as the more commonly used symbols for these devices.
Classification of field-effect transistors 3 3

4. Overview of Enhancement-Mode Mosfets
This figure depicts the circuit symbol and the approximate construction of a typical n-channel enhancement-mode MOSFET.
The n-channel enhancement MOSFET construction and circuit symbol 4 4

5. Channel formation in NMOS transistor: (a) With no external gate voltage, the source-substrate and substrate-drain junctions are both reverse-biased, and no conduction occurs; (b) when a gate voltage is applied, charge- carrying electrons are drawn between the source and drain regions to form a conducting channel. 5 5

6. Operation of the n-channel Enhancement-Mode Mosfet
Saturation region
Regions of operation of NMOS transistor 6 6

7. Drain characteristic curves for a typical NMOS transistor with VT = 2 V and K = 1.5 mA/V27 7

8. EXAMPLE 11.1 Determining the Operating State of a Mosfet Problem
Determine the operating state of the MOSFET shown in the circuit of figure for the given value of VDD and VGG if the ammeter and voltmeter shown read the following value: 8

9. a. VGG = 1V; VDD = 10V ;νDS = 10V; ίD = 0mA; RD = 100Ώ b
a. VGG = 1V; VDD = 10V ;νDS = 10V; ίD = 0mA; RD = 100Ώ b. VGG = 4V; VDD = 10V ;νDS = 2.8V; ίD = 72mA; RD = 100Ώ c. VGG = 3V; VDD = 10V ;νDS = 1.5V; ίD = 13.5mA; RD = 630Ώ 9

10. CHECK YOUR UNDERSTANDING
What is the operating state of the MOSFET of the example 11.1 for the following conditions?
VGG = 10/3V; VDD = 10V ;νDS = 3.6V;ίD = 32mA; RD = 200Ώ 10

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12. EXAMPLE 11.2 Mosfet Q-Point Graphical Determination Problem
Determine the Q point for the MOSFET in the circuit of figure 11.7.
The n-channel enhancement MOSFET circuit and drain characteristic for Example 11.2 12 12

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14. CHECK YOUR UNDERSTANDING
Determine the operating region of the MOSFET of example 11.2 when νGS = 3.5V. 14

15. EXAMPLE 11.3 Mosfet Q-Point Calculation Problem
Determine the Q point for the MOSFET in the circuit of figure 11.7. 15

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17. CHECK YOUR UNDERSTANDING
Find the lowest value of RD for the MOSFET of the example 11.3 that will place the MOSFET in the ohmic region. 17

18. EXAMPLE 11.4 Mosfet Self-Bias Circuit Problem
Figure 11.8(a) depicts a self-bias circuit for a MOSFET. Determine the Q point for the MOSFET by choosing Rs such that νDSQ =8V. 18

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20. CHECK YOUR UNDERSTANDING
Determine the appropriate value of RS if we wish to move the operating point of the MOSFET of example 11.4 to νDSQ =12V. Also find the value of νGSQ and ίDQ. Are these values unique? 20

21. EXAMPLE 11.5 Analysis of Mosfet Amplifier Problem
Determine the gate and drain-source voltage and the drain current for the MOSFET amplifier of figure11.9. 21

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23. Operation of the P-channel Enhacement-Mode Mosfet
The p-channel enhancement-mode field-effect transistor (PMOS) 23 23

24. The Resulting equations for the three modes of operation of the PMOS24

25. Mosfet Large-Signal Amplifiers
Common-source MOSFET amplifier 25 25

26. Thus, the load voltage, across the load resistance, is given by the expression.26 26

27. Where △υ= VG-VT. We can then solve for the load current from the quadratic equation27

28. (a) Source-follower MOSFET amplifier
(a) Source-follower MOSFET amplifier. (b) Drain current response for a 100-Ω load when K = and VT = 1.2 V 28 28

29. EXAMPLE 11.6 Using a Mosfet as a Current Source for Battery Charging
Analyze the two battery charging circuit shown in figure use the transistor parameters to determine the range of require gate voltages, VG ,to provide a variable charging current up to a maximum of 0.1A. Assume that the terminal voltage of a fully dischanged battery is 9V, and of a fully charged battery 10.5V. 29

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32. CHECK YOUR UNDERSTANDING
What is the maximum power dissipation of the MOSFET for each of the circuit in example 11.6? 32

33. EXAMPLE 11.7 Mosfet DC Motor Drive Circuit Problem33

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35. CHECK YOUR UNDERSTANDING
What is the range of duty cycle needed to cover the current range of the Lego motor? 35

36. Digital Switches and Gates
CMOS inverter approximate by ideal switches: (a) When Vin is “high,” Vout is tied to ground; (b) when Vin is “low,” Vout is tied to VDD.
CMOS inverter 36 36

37. EXAMPLE 11.8 Mosfet Switch Problem
Determine the operating points of the MOSFET switch of figure when the signal source output is equal to 0and 2.5V, respectively. 37

38. CHECK YOUR UNDERSTANDING
What value of RD would ensure a drain-to- source voltage νDS of 5V in the circuit of example 11.8? 38

39. EXAMPLE 11.9 COMS Gate Problem
Determine the logic function implemented by the CMOS gate of figure use the table below to summarize the behavior of the circuit. 39

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41. CHECK YOUR UNDERSTANDING
Analyze the CMOS gate of figure and find the output voltage for the following conditions: (a) ν1 = 0v, ν2 =0V (b) ν1 = 5V, ν2 =0V (c) ν1 = 0V, ν2 =5V (d) ν1 = 5V, ν2 =5V.identify the logic function accomplished by the circuit. 41

42. Analog Switches 42 42

43. Symbol for bilateral FET analog gate
MOSFET analog switch 43 43

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45. Homework Problem 45