Chapter 11 Field effect Transistors: Operation, Circuit, Models, and Applications Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

3 Classification of field-effect transistors 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.

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

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.

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

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

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 11.6 for the given value of V DD and V GG if the ammeter and voltmeter shown read the following value:

9 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

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

11

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

13

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

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

16

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

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 R s such that ν DSQ =8V.

19

20 CHECK YOUR UNDERSTANDING Determine the appropriate value of R S if we wish to move the operating point of the MOSFET of example 11.4 to ν DSQ =12V. Also find the value of ν GSQ and ί DQ. Are these values unique?

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.

22

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

24 The Resulting equations for the three modes of operation of the PMOS

25 Mosfet Large-Signal Amplifiers Common-source MOSFET amplifier

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

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

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

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, V G,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.

30

31

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

33 EXAMPLE 11.7 Mosfet DC Motor Drive Circuit Problem DC motor drive circuit

34

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

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

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.

38 CHECK YOUR UNDERSTANDING What value of R D would ensure a drain-to- source voltage ν DS of 5V in the circuit of example 11.8?

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.

40

41 CHECK YOUR UNDERSTANDING Analyze the CMOS gate of figure and find the output voltage for the following conditions: (a) ν 1 = 0 v, ν 2 =0V (b) ν 1 = 5V, ν 2 =0V (c) ν 1 = 0V, ν 2 =5V (d) ν 1 = 5V, ν 2 =5V.identify the logic function accomplished by the circuit.

42 Analog Switches

43 MOSFET analog switch Symbol for bilateral FET analog gate

44

45 Homework Problem