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Transistors (MOSFETs)

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Presentation on theme: "Transistors (MOSFETs)"— Presentation transcript:

1 Transistors (MOSFETs)
MOS Field-Effect Transistors (MOSFETs) 1

2 sedr42021_0401a.jpg Figure 4.1 Physical structure of the enhancement-type NMOS transistor: (a) perspective view; (b) cross-section. Typically L = 0.1 to 3 mm, W = 0.2 to 100 mm, and the thickness of the oxide layer (tox) is in the range of 2 to 50 nm. Microelectronic Circuits - Fifth Edition Sedra/Smith

3 sedr42021_0402.jpg Figure 4.2 The enhancement-type NMOS transistor with a positive voltage applied to the gate. An n channel is induced at the top of the substrate beneath the gate. Microelectronic Circuits - Fifth Edition Sedra/Smith

4 sedr42021_0403.jpg Figure 4.3 An NMOS transistor with vGS > Vt and with a small vDS applied. The device acts as a resistance whose value is determined by vGS. Specifically, the channel conductance is proportional to vGS – Vt’ and thus iD is proportional to (vGS – Vt) vDS. Note that the depletion region is not shown (for simplicity). Microelectronic Circuits - Fifth Edition Sedra/Smith

5 sedr42021_0404.jpg Figure 4.4 The iD–vDS characteristics of the MOSFET in Fig. 4.3 when the voltage applied between drain and source, vDS, is kept small. The device operates as a linear resistor whose value is controlled by vGS. Microelectronic Circuits - Fifth Edition Sedra/Smith

6 sedr42021_0405.jpg Figure 4.5 Operation of the enhancement NMOS transistor as vDS is increased. The induced channel acquires a tapered shape, and its resistance increases as vDS is increased. Here, vGS is kept constant at a value > Vt. Microelectronic Circuits - Fifth Edition Sedra/Smith

7 sedr42021_0406.jpg Figure 4.6 The drain current iD versus the drain-to-source voltage vDS for an enhancement-type NMOS transistor operated with vGS > Vt. Microelectronic Circuits - Fifth Edition Sedra/Smith

8 sedr42021_0407.jpg Figure 4.7 Increasing vDS causes the channel to acquire a tapered shape. Eventually, as vDS reaches vGS – Vt’ the channel is pinched off at the drain end. Increasing vDS above vGS – Vt has little effect (theoretically, no effect) on the channel’s shape. Microelectronic Circuits - Fifth Edition Sedra/Smith

9 sedr42021_0408.jpg Figure 4.8 Derivation of the iD–vDS characteristic of the NMOS transistor. Microelectronic Circuits - Fifth Edition Sedra/Smith

10 sedr42021_0409.jpg Figure 4.9 Cross-section of a CMOS integrated circuit. Note that the PMOS transistor is formed in a separate n-type region, known as an n well. Another arrangement is also possible in which an n-type body is used and the n device is formed in a p well. Not shown are the connections made to the p-type body and to the n well; the latter functions as the body terminal for the p-channel device. Microelectronic Circuits - Fifth Edition Sedra/Smith

11 sedr42021_0410a.jpg Figure (a) Circuit symbol for the n-channel enhancement-type MOSFET. (b) Modified circuit symbol with an arrowhead on the source terminal to distinguish it from the drain and to indicate device polarity (i.e., n channel). (c) Simplified circuit symbol to be used when the source is connected to the body or when the effect of the body on device operation is unimportant. Microelectronic Circuits - Fifth Edition Sedra/Smith

12 sedr42021_0411a.jpg Figure (a) An n-channel enhancement-type MOSFET with vGS and vDS applied and with the normal directions of current flow indicated. (b) The iD–vDS characteristics for a device with k’n (W/L) = 1.0 mA/V2. Microelectronic Circuits - Fifth Edition Sedra/Smith

13 sedr42021_0412.jpg Figure The iD–vGS characteristic for an enhancement-type NMOS transistor in saturation (Vt = 1 V, k’n W/L = 1.0 mA/V2). Microelectronic Circuits - Fifth Edition Sedra/Smith

14 sedr42021_0413.jpg Figure Large-signal equivalent-circuit model of an n-channel MOSFET operating in the saturation region. Microelectronic Circuits - Fifth Edition Sedra/Smith

15 sedr42021_0414.jpg Figure The relative levels of the terminal voltages of the enhancement NMOS transistor for operation in the triode region and in the saturation region. Microelectronic Circuits - Fifth Edition Sedra/Smith

16 sedr42021_0415.jpg Figure Increasing vDS beyond vDSsat causes the channel pinch-off point to move slightly away from the drain, thus reducing the effective channel length (by DL). Microelectronic Circuits - Fifth Edition Sedra/Smith

17 sedr42021_0416.jpg Figure Effect of vDS on iD in the saturation region. The MOSFET parameter VA depends on the process technology and, for a given process, is proportional to the channel length L. Microelectronic Circuits - Fifth Edition Sedra/Smith

18 sedr42021_0417.jpg Figure Large-signal equivalent circuit model of the n-channel MOSFET in saturation, incorporating the output resistance ro. The output resistance models the linear dependence of iD on vDS and is given by Eq. (4.22). Microelectronic Circuits - Fifth Edition Sedra/Smith

19 sedr42021_0418a.jpg Figure (a) Circuit symbol for the p-channel enhancement-type MOSFET. (b) Modified symbol with an arrowhead on the source lead. (c) Simplified circuit symbol for the case where the source is connected to the body. (d) The MOSFET with voltages applied and the directions of current flow indicated. Note that vGS and vDS are negative and iD flows out of the drain terminal. Microelectronic Circuits - Fifth Edition Sedra/Smith

20 sedr42021_0419.jpg Figure The relative levels of the terminal voltages of the enhancement-type PMOS transistor for operation in the triode region and in the saturation region. Microelectronic Circuits - Fifth Edition Sedra/Smith

21 sedr42021_e0408.jpg Figure E4.8 Microelectronic Circuits - Fifth Edition Sedra/Smith

22 sedr42021_tb0401a.jpg Table 4.1 Microelectronic Circuits - Fifth Edition Sedra/Smith

23 sedr42021_0420.jpg Figure 4.20 Circuit for Example 4.2.
Microelectronic Circuits - Fifth Edition Sedra/Smith

24 sedr42021_0421.jpg Figure 4.21 Circuit for Example 4.3.
Microelectronic Circuits - Fifth Edition Sedra/Smith

25 sedr42021_e0412.jpg Figure E4.12 Microelectronic Circuits - Fifth Edition Sedra/Smith

26 sedr42021_0422.jpg Figure 4.22 Circuit for Example 4.4.
Microelectronic Circuits - Fifth Edition Sedra/Smith

27 sedr42021_0423a.jpg Figure (a) Circuit for Example 4.5. (b) The circuit with some of the analysis details shown. Microelectronic Circuits - Fifth Edition Sedra/Smith

28 sedr42021_0424.jpg Figure 4.24 Circuit for Example 4.6.
Microelectronic Circuits - Fifth Edition Sedra/Smith

29 sedr42021_0425a.jpg Figure 4.25 Circuits for Example 4.7.
Microelectronic Circuits - Fifth Edition Sedra/Smith

30 sedr42021_e0416.jpg Figure E4.16 Microelectronic Circuits - Fifth Edition Sedra/Smith

31 sedr42021_0426a.jpg Figure (a) Basic structure of the common-source amplifier. (b) Graphical construction to determine the transfer characteristic of the amplifier in (a). Microelectronic Circuits - Fifth Edition Sedra/Smith

32 sedr42021_0426c.jpg Figure (Continued) (c) Transfer characteristic showing operation as an amplifier biased at point Q. Microelectronic Circuits - Fifth Edition Sedra/Smith

33 sedr42021_0427.jpg Figure Two load lines and corresponding bias points. Bias point Q1 does not leave sufficient room for positive signal swing at the drain (too close to VDD). Bias point Q2 is too close to the boundary of the triode region and might not allow for sufficient negative signal swing. Microelectronic Circuits - Fifth Edition Sedra/Smith

34 sedr42021_0428a.jpg Figure 4.28 Example 4.8.
Microelectronic Circuits - Fifth Edition Sedra/Smith

35 sedr42021_0428b.jpg Figure 4.28 (Continued)
Microelectronic Circuits - Fifth Edition Sedra/Smith

36 sedr42021_0429.jpg Figure The use of fixed bias (constant VGS) can result in a large variability in the value of ID. Devices 1 and 2 represent extremes among units of the same type. Microelectronic Circuits - Fifth Edition Sedra/Smith

37 sedr42021_0430a.jpg Figure Biasing using a fixed voltage at the gate, VG, and a resistance in the source lead, RS: (a) basic arrangement; (b) reduced variability in ID; (c) practical implementation using a single supply; (d) coupling of a signal source to the gate using a capacitor CC1; (e) practical implementation using two supplies. Microelectronic Circuits - Fifth Edition Sedra/Smith

38 sedr42021_0431.jpg Figure 4.31 Circuit for Example 4.9.
Microelectronic Circuits - Fifth Edition Sedra/Smith

39 sedr42021_0432.jpg Figure Biasing the MOSFET using a large drain-to-gate feedback resistance, RG. Microelectronic Circuits - Fifth Edition Sedra/Smith

40 sedr42021_0433a.jpg Figure (a) Biasing the MOSFET using a constant-current source I. (b) Implementation of the constant-current source I using a current mirror. Microelectronic Circuits - Fifth Edition Sedra/Smith

41 sedr42021_0434.jpg Figure Conceptual circuit utilized to study the operation of the MOSFET as a small-signal amplifier. Microelectronic Circuits - Fifth Edition Sedra/Smith

42 sedr42021_0435.jpg Figure Small-signal operation of the enhancement MOSFET amplifier. Microelectronic Circuits - Fifth Edition Sedra/Smith

43 sedr42021_0436.jpg Figure Total instantaneous voltages vGS and vD for the circuit in Fig Microelectronic Circuits - Fifth Edition Sedra/Smith

44 sedr42021_0437a.jpg Figure Small-signal models for the MOSFET: (a) neglecting the dependence of iD on vDS in saturation (the channel-length modulation effect); and (b) including the effect of channel-length modulation, modeled by output resistance ro = |VA| /ID. Microelectronic Circuits - Fifth Edition Sedra/Smith

45 sedr42021_0438a.jpg Figure Example 4.10: (a) amplifier circuit; (b) equivalent-circuit model. Microelectronic Circuits - Fifth Edition Sedra/Smith

46 sedr42021_0439.jpg Figure Development of the T equivalent-circuit model for the MOSFET. For simplicity, ro has been omitted but can be added between D and S in the T model of (d). Microelectronic Circuits - Fifth Edition Sedra/Smith

47 sedr42021_0440a.jpg Figure (a) The T model of the MOSFET augmented with the drain-to-source resistance ro. (b) An alternative representation of the T model. Microelectronic Circuits - Fifth Edition Sedra/Smith

48 sedr42021_0441a.jpg Figure Small-signal equivalent-circuit model of a MOSFET in which the source is not connected to the body. Microelectronic Circuits - Fifth Edition Sedra/Smith

49 sedr42021_tb0402a.jpg Table 4.2 Microelectronic Circuits - Fifth Edition Sedra/Smith

50 sedr42021_0442.jpg Figure Basic structure of the circuit used to realize single-stage discrete-circuit MOS amplifier configurations. Microelectronic Circuits - Fifth Edition Sedra/Smith

51 sedr42021_e0430a.jpg Figure E4.30 Microelectronic Circuits - Fifth Edition Sedra/Smith

52 sedr42021_tb0403a.jpg Table 4.3 Microelectronic Circuits - Fifth Edition Sedra/Smith

53 sedr42021_0443a.jpg Figure (a) Common-source amplifier based on the circuit of Fig (b) Equivalent circuit of the amplifier for small-signal analysis. (c) Small-signal analysis performed directly on the amplifier circuit with the MOSFET model implicitly utilized. Microelectronic Circuits - Fifth Edition Sedra/Smith

54 sedr42021_0444a.jpg Figure (a) Common-source amplifier with a resistance RS in the source lead. (b) Small-signal equivalent circuit with ro neglected. Microelectronic Circuits - Fifth Edition Sedra/Smith

55 sedr42021_0445a.jpg Figure (a) A common-gate amplifier based on the circuit of Fig (b) A small-signal equivalent circuit of the amplifier in (a). (c) The common-gate amplifier fed with a current-signal input. Microelectronic Circuits - Fifth Edition Sedra/Smith

56 sedr42021_0446a.jpg Figure (a) A common-drain or source-follower amplifier. (b) Small-signal equivalent-circuit model. (c) Small-signal analysis performed directly on the circuit. (d) Circuit for determining the output resistance Rout of the source follower. Microelectronic Circuits - Fifth Edition Sedra/Smith

57 sedr42021_tb0404a.jpg Table 4.4 Microelectronic Circuits - Fifth Edition Sedra/Smith

58 sedr42021_tb0404c.jpg Table 4.4 (Continued)
Microelectronic Circuits - Fifth Edition Sedra/Smith

59 sedr42021_0447a.jpg Figure (a) High-frequency equivalent circuit model for the MOSFET. (b) The equivalent circuit for the case in which the source is connected to the substrate (body). (c) The equivalent circuit model of (b) with Cdb neglected (to simplify analysis). Microelectronic Circuits - Fifth Edition Sedra/Smith

60 sedr42021_0448.jpg Figure Determining the short-circuit current gain Io /Ii. Microelectronic Circuits - Fifth Edition Sedra/Smith

61 sedr42021_tb0405.jpg Table 4.5 Microelectronic Circuits - Fifth Edition Sedra/Smith

62 sedr42021_0449a.jpg Figure (a) Capacitively coupled common-source amplifier. (b) A sketch of the frequency response of the amplifier in (a) delineating the three frequency bands of interest. Microelectronic Circuits - Fifth Edition Sedra/Smith

63 sedr42021_0450a.jpg Figure Determining the high-frequency response of the CS amplifier: (a) equivalent circuit; (b) the circuit of (a) simplified at the input and the output; Microelectronic Circuits - Fifth Edition Sedra/Smith

64 sedr42021_0450c.jpg Figure (Continued) (c) the equivalent circuit with Cgd replaced at the input side with the equivalent capacitance Ceq; (d) the frequency response plot, which is that of a low-pass single-time-constant circuit. Microelectronic Circuits - Fifth Edition Sedra/Smith

65 sedr42021_0451.jpg Figure Analysis of the CS amplifier to determine its low-frequency transfer function. For simplicity, ro is neglected. Microelectronic Circuits - Fifth Edition Sedra/Smith

66 sedr42021_0452.jpg Figure Sketch of the low-frequency magnitude response of a CS amplifier for which the three break frequencies are sufficiently separated for their effects to appear distinct. Microelectronic Circuits - Fifth Edition Sedra/Smith

67 sedr42021_0453.jpg Figure 4.53 The CMOS inverter.
Microelectronic Circuits - Fifth Edition Sedra/Smith

68 sedr42021_0454a.jpg Figure Operation of the CMOS inverter when vI is high: (a) circuit with vI = VDD (logic-1 level, or VOH); (b) graphical construction to determine the operating point; (c) equivalent circuit. Microelectronic Circuits - Fifth Edition Sedra/Smith

69 sedr42021_0455a.jpg Figure Operation of the CMOS inverter when vI is low: (a) circuit with vI = 0 V (logic-0 level, or VOL); (b) graphical construction to determine the operating point; (c) equivalent circuit. Microelectronic Circuits - Fifth Edition Sedra/Smith

70 sedr42021_0456.jpg Figure The voltage transfer characteristic of the CMOS inverter. Microelectronic Circuits - Fifth Edition Sedra/Smith

71 sedr42021_0457a.jpg Figure Dynamic operation of a capacitively loaded CMOS inverter: (a) circuit; (b) input and output waveforms; (c) trajectory of the operating point as the input goes high and C discharges through QN; (d) equivalent circuit during the capacitor discharge. Microelectronic Circuits - Fifth Edition Sedra/Smith

72 sedr42021_0458.jpg Figure The current in the CMOS inverter versus the input voltage. Microelectronic Circuits - Fifth Edition Sedra/Smith

73 sedr42021_0459a.jpg Figure (a) Circuit symbol for the n-channel depletion-type MOSFET. (b) Simplified circuit symbol applicable for the case the substrate (B) is connected to the source (S). Microelectronic Circuits - Fifth Edition Sedra/Smith

74 sedr42021_0460a.jpg Figure The current-voltage characteristics of a depletion-type n-channel MOSFET for which Vt = –4 V and k¢n(W/L) = 2 mA/V2: (a) transistor with current and voltage polarities indicated; (b) the iD–vDS characteristics; (c) the iD–vGS characteristic in saturation. Microelectronic Circuits - Fifth Edition Sedra/Smith

75 sedr42021_0461.jpg Figure The relative levels of terminal voltages of a depletion-type NMOS transistor for operation in the triode and the saturation regions. The case shown is for operation in the enhancement mode (vGS is positive). Microelectronic Circuits - Fifth Edition Sedra/Smith

76 sedr42021_0462.jpg Figure Sketches of the iD–vGS characteristics for MOSFETs of enhancement and depletion types, of both polarities (operating in saturation). Note that the characteristic curves intersect the vGS axis at Vt. Also note that for generality somewhat different values of |Vt| are shown for n-channel and p-channel devices. Microelectronic Circuits - Fifth Edition Sedra/Smith

77 sedr42021_e0451.jpg Figure E4.51 Microelectronic Circuits - Fifth Edition Sedra/Smith

78 sedr42021_e0452.jpg Figure E4.52 Microelectronic Circuits - Fifth Edition Sedra/Smith

79 sedr42021_0463.jpg Figure Capture schematic of the CS amplifier in Example 4.14. Microelectronic Circuits - Fifth Edition Sedra/Smith

80 sedr42021_0464.jpg Figure Frequency response of the CS amplifier in Example 4.14 with CS = 10 mF and CS = 0 (i.e., CS removed). Microelectronic Circuits - Fifth Edition Sedra/Smith

81 sedr42021_p04018a.jpg Figure P4.18 Microelectronic Circuits - Fifth Edition Sedra/Smith

82 sedr42021_p04033a.jpg Figure P4.33 Microelectronic Circuits - Fifth Edition Sedra/Smith

83 sedr42021_p04036.jpg Figure P4.36 Microelectronic Circuits - Fifth Edition Sedra/Smith

84 sedr42021_p04037.jpg Figure P4.37 Microelectronic Circuits - Fifth Edition Sedra/Smith

85 sedr42021_p04038.jpg Figure P4.38 Microelectronic Circuits - Fifth Edition Sedra/Smith

86 sedr42021_p04041.jpg Figure P4.41 Microelectronic Circuits - Fifth Edition Sedra/Smith

87 sedr42021_p04042a.jpg Figure P4.42 Microelectronic Circuits - Fifth Edition Sedra/Smith

88 sedr42021_p04043a.jpg Figure P4.43 Microelectronic Circuits - Fifth Edition Sedra/Smith

89 sedr42021_p04044a.jpg Figure P4.44 Microelectronic Circuits - Fifth Edition Sedra/Smith

90 sedr42021_p04045.jpg Figure P4.45 Microelectronic Circuits - Fifth Edition Sedra/Smith

91 sedr42021_p04046a.jpg Figure P4.46 Microelectronic Circuits - Fifth Edition Sedra/Smith

92 sedr42021_p04047.jpg Figure P4.47 Microelectronic Circuits - Fifth Edition Sedra/Smith

93 sedr42021_p04048.jpg Figure P4.48 Microelectronic Circuits - Fifth Edition Sedra/Smith

94 sedr42021_p04054.jpg Figure P4.54 Microelectronic Circuits - Fifth Edition Sedra/Smith

95 sedr42021_p04061.jpg Figure P4.61 Microelectronic Circuits - Fifth Edition Sedra/Smith

96 sedr42021_p04066.jpg Figure P4.66 Microelectronic Circuits - Fifth Edition Sedra/Smith

97 sedr42021_p04074.jpg Figure P4.74 Microelectronic Circuits - Fifth Edition Sedra/Smith

98 sedr42021_p04075.jpg Figure P4.75 Microelectronic Circuits - Fifth Edition Sedra/Smith

99 sedr42021_p04077.jpg Figure P4.77 Microelectronic Circuits - Fifth Edition Sedra/Smith

100 sedr42021_p04086.jpg Figure P4.86 Microelectronic Circuits - Fifth Edition Sedra/Smith

101 sedr42021_p04087.jpg Figure P4.87 Microelectronic Circuits - Fifth Edition Sedra/Smith

102 sedr42021_p04088a.jpg Figure P4.88 Microelectronic Circuits - Fifth Edition Sedra/Smith

103 sedr42021_p04097.jpg Figure P4.97 Microelectronic Circuits - Fifth Edition Sedra/Smith

104 sedr42021_p04099.jpg Figure P4.99 Microelectronic Circuits - Fifth Edition Sedra/Smith

105 sedr42021_p04101.jpg Figure P4.101 Microelectronic Circuits - Fifth Edition Sedra/Smith

106 sedr42021_p04104.jpg Figure P4.104 Microelectronic Circuits - Fifth Edition Sedra/Smith

107 sedr42021_p04117.jpg Figure P4.117 Microelectronic Circuits - Fifth Edition Sedra/Smith

108 sedr42021_p04120.jpg Figure P4.120 Microelectronic Circuits - Fifth Edition Sedra/Smith

109 sedr42021_p04121a.jpg Figure P4.121 Microelectronic Circuits - Fifth Edition Sedra/Smith

110 sedr42021_p04123.jpg Figure P4.123 Microelectronic Circuits - Fifth Edition Sedra/Smith


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