EE 330 Lecture 28. Comparison of MOS and BJT performance Basic amplifier architectures

Transcription

1 EE 330 Lecture 28 Comparison of MOS and BJT performance Basic amplifier architectures

2 Engineering Trends and Study Abroad Options

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9 Some more of the 52 citing documents: over 20% of the articles on this search are now in non-english venues

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14 Engineers educated today will be under increasing pressure to be able to communicate with, supervise, work with, and work for Asian engineers that may or may not have good English communication skills and must understand the culture of engineers around the world to be effective This is not something that may happen in the future but rather is something that is already occurring and WILL become increasingly critical in the next decade

15 Study Abroad Opportunities in Asia Two Opportunities in Taiwan The increasing role Asia is playing in both the engineering field and the world s economy is unlike anything we have seen in many decades All indicators suggest that this role will become even more significant in the future Both opportunities and expectations in the field will invariable show increased alignment with business and engineering in a global economy Understanding the culture and the environment of engineers working in Asia will offer substantial benefits for many/most engineers in the short-term and will likely be expected of many/most engineers within a decade

16 Taipei 101 The tallest building in the world!

17 Landmark Architecture The Grand Hotel in Taipei

18 The two schools in Taipei Taiwan with exchange programs with ISU College of Engineering Tatung University National Taiwan University of Science and Technology (NTUST) Both good schools with strong engineering programs Ongoing interactions between faculty and students Strong ties with industry in Taiwan Interactions expected to expand in years to come

19 Exchange program principles: Both schools will offer selected courses to ISU students in English Courses pre-approved so that progress towards graduation is not delayed Approximately revenue neutral exchange (often costs less than spending the time in Ames) Internship opportunity often provided

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23 Current Status / Academics College Engineering Elec. Eng. & Comp. Sci. Management Design Liberal Arts & Soc. Sci. Honors Mech. Electronic Industrial Architecture Applied Foreign Lang. University Inter-discipline Department Polymer Construction Electrical Computer Science & Information Business Information Industrial & Commercial Design Design Humanities General Education Engineering Chemical Electro- Optical MBA Technological & ocational Education Graduate Institute Automation & Control Materials Science & Technology EMBA Management Finance Technology Management 13 Departments 21 Graduate Institutes

24 Introduction to College of Electrical Engineering and Computer Science (CEECS) College of Electrical Engineering & Computer Science Founded in full-time faculty members: 42 Professors, 35 Associate Professors, 38 Assistant Professors, 5 Instructors. 2,645 students: (1,386 undergraduates, 1,020 Master candidates, 239 Doctoral candidates). Department of Electronic Engineering Department of Electrical Engineering Deptartment of Computer Science & Information Graduate Institute of Opto-Electronic Engineering

25 Introduction to Electronic Engineering Dept. Faculty Associa Assistant Founded in Prof. Members te Prof. Prof. Faculty Members: 54 active members. Teaching and research are categorized into three major groups: Lect urer Tot al Joint Appointment included The Computer Engineering Group features parallel and distributed processing, multimedia processing, embedded system and FPGA design, computer architecture, and LSI design. The Electronic System Group focuses on broadband networks, communication systems, digital signal and image processing, microwave engineering, and power electronics. The Optoelectronics and Semiconductor Group emphasizes on semiconductor materials and devices, optoelectronics, fiber-optic modules and systems, display technology, lighting, solar cells, and biophotonics.

26 Research Achievements of Electronic Engineering Dept. Journal Paper Conference Paper Patent Industry and Academia Cooperation To realize the advanced technologies for industrial applications. The industry and academia cooperation is strongly encouraged. The department seeks to build up strong links with the industry. This elegantly balances the focus between theory and practice. In the past few years, the department has achieved excellence in the fields of embedded systems, IC chip design, wireless and broadband networks, optical communications, image display, nanophotonic materials and devices, bio-medical technologies and solid-state lighting.

27 Research Areas of Electrical Engineering Dept. Power and Energy Power Electronics System Engineering Integrated Circuits and Systems Computer and Network Communication and Electromagnetic Engineering Communication and Electromagnetic Technology Center Power Electronics Technology Center Building Energy Efficiency and Renewable Energy Center

28 Introduction to Computer Science and Information Engineering Dept. (CSIE) Founded in full-time faculty members: Faculty Members Research in fields such as : (1) Multi-media Systems (2) Information security (3) Artificial intelligence (4) Communication network Research areas in Multi-media Systems include: Image processing, video and data compression Machine vision Augmented reality oice synthesis, song synthesis, and related machine audio processing Prof. Associ ate Prof. Assistan t Prof. Lec ture r Total

29 Research Areas of CSIE Dept. Research areas in Communication network include: Mobile computing Wireless network Wireless sensor network Multi-media network oice over Internet Protocol (oip) High-speed network Network performance analysis Queuing theory Network communication protocol

30 Study Abroad Opportunities in Asia Both are good schools and both should provide a good study abroad opportunity If interested in either program contact: Tatung University Prof. Morris Chang (ISU coordinator) or Prof. Randy Geiger National Taiwan University of Science and Technology Prof. Randy Geiger (ISU coordinator)

31 Review from Last Lecture Graphical Analysis and Interpretation 2 OX Device Model (family of curves) I - 1 DQ GS T DS I D μ C W 2L GS6 DD R 1 OUT M 1 GS5 IN (t) GS4 GS3 GSQ =- SS SS GS2 GS1 DS Saturation region Q-Point Load Line Linear signal swing region smaller than saturation region Modest nonlinear distortion provided saturation region operation maintained Symmetric swing about Q-point Signal swing can be maximized by judicious location of Q-point

32 Review from Last Lecture Further Model Extensions Existing model does not depend upon the bulk voltage! Observe that changing the bulk voltage will change the electric field in the channel region! DS GS ID BS I B I G E ( BS small) Changing the bulk voltage will change the thickness of the inversion layer Changing the bulk voltage will change the threshold voltage of the device T T0 BS

33 Review from Last Lecture Typical Effects of Bulk on Threshold oltage for n-channel Device T T0 BS T T0 ~ -5 BS Bulk-Diffusion Generally Reverse Biased ( BS < 0 or at least less than 0.3) for n- channel Shift in threshold voltage with bulk voltage can be substantial Often BS =0

34 Review from Last Lecture Model Extension Summary I I G B GS T W L 2 W 2 μc 1 2L DS I μc D OX GS T DS GS T DS GS T OX GS T DS GS T DS GS T T T0 BS Model Parameters : {μ,c OX, T0,φ,γ,λ} Design Parameters : {W,L} but only one degree of freedom W/L

35 Review from Last Lecture Large and Small Signal Model Summary Large Signal Model Small Signal Model 0 GS T W L 2 W 2 μc 1 2L DS I μc D OX GS T DS GS T DS GS T OX GS T DS GS T DS GS T T T0 BS saturation i i i g b d g m 0 0 g where g mb m v gs g mb v μc W OX L g m 2 go λi DQ g < g mb m saturation BSQ bs EBQ g o v ds g <<g,g 0 m mb

36 Review from Last Time Example: Obtain the small signal model of the following circuit. Assume MOSFET is operating in the saturation region

37 Review from Last Time Example Obtain the small signal model of the following circuit. Assume MOSFET is operating in the saturation region Solution: G D I g m v gs v gs g 0 m 0 g g I R EQ 1 1 g g g m 0 m

38 Review from Last Time Relative Magnitude of Small Signal Parameters g m I CQ t g I CQ β t g o I CQ AF g g m π I Q t IQ β t β g g π o IQ β I Q t AF β AF t m 77 g m g π g o Often the go term can be neglected in the small signal model because it is so small

39 Small Signal Model Simplifications for the MOSFET and BJT MOSFET BJT Often simplifications of the small signal model are adequate for a given application These simplifications will be discussed next

40 Small Signal MOSFET Model Summary An equivalent Circuit: G S gs B bs Alternate equivalent representations for g m g m 2μC L g OX m g W g mb bs g m gs g o i d μc L mb I DQ OX W go λi DQ g m 2 GSQ BSQ g m T from 2IDQ GSQ I D μc T OX 2I g <<g,g 0 m mb g < g mb m W 2L DQ EBQ D ds 2 GS T

41 Small Signal Model Simplifications G gs B bs g mb bs g m gs g o i d D ds S Simplification that is often adequate G i d D gs g m gs g o ds S

42 Small Signal Model Simplifications G gs B bs g mb bs g m gs g o i d D ds S Even further simplification that is often adequate G gs S i d g m gs D ds

43 Small Signal BJT Model Summary An equivalent circuit B i b i c C be g π g m be g o ce E g m I CQ t g I CQ β t g o I CQ AF g m g π g o This contains absolutely no more information than the set of small-signal model equations

44 Small Signal BJT Model Simplifications B i b i c C be g π g m be g o ce E Simplification that is often adequate B i b i c C be g π g m be ce E

45 Gains for MOSFET and BJT Circuits BJT MOSFET DD CC R OUT R 1 OUT IN (t) Q 1 IN (t) M 1 EE SS A B I R CQ 1 t OUT A M 2I R DQ SS T OUT IN Q 1 R For both circuits A R g m IN M 1 R Gains vary linearly with small signal parameter g m Power is often a key resource in the design of an integrated circuit In both circuits, power is proportional to I CQ, I DQ

46 How does g m vary with I DQ? g m 2μC L OX W I DQ aries with the square root of I DQ g m 2I GSQ DQ T 2I DQ EBQ aries linearly with I DQ g m μc L OX W GSQ T Doesn t vary with I DQ

47 How does g m vary with I DQ? All of the above are true but with qualification g m is a function of more than one variable (I DQ ) and how it varies depends upon how the remaining variables are constrained

48 Comparison of BJT and MOSFET How do the small signal models of the MOSFET and BJT compare?

49 Comparison of MOSFET and BJT BJT MOSFET g m I CQ t g g m m μc L OX 2μC L W OX W EB I DQ g m 2I DQ EBQ g g mbjt mmos I 2I CQ t DQ EB 2 EB t EB 50m EB 50m 100m 2 50m m if if EB EB 100m 2 The transconductance of the BJT is typically much larger than that of the MOSFET (and larger is better!) This is due to the exponential rather than quadratic output/input relationship

50 Comparison of MOSFET and BJT BJT g o I DQ MOSFET g o I CQ AF g g objt omos I I CQ AF DQ 1 AF The output conductances are comparable but that of the BJT is usually modestly smaller (and smaller is better!)

51 Comparison of MOSFET and BJT BJT MOSFET g I CQ β t g 0 g π is the reciprocal of the input impedance g π of a MOSFET is much smaller than that of a BJT (and smaller is better!)

52 Review of Small-Signal Analysis Approach In the next few slides we will summarize the results obtained for doing smallsignal analysis and explicitly review the simplified models used for Q-point analysis

53 Standard Approach to small-signal analysis of nonlinear networks Nonlinear Network dc Equivalent Network Q-point alues for small-signal parameters Small-signal equivalent network Small-signal output Total output (good approximation)

54 Systematic Approach to Small-Signal Circuit Analysis Obtain dc equivalent circuit by replacing all elements with large-signal (dc) equivalent circuits Obtain dc operating points (Q-point) Obtain ac equivalent circuit by replacing all elements with small-signal equivalent circuits Analyze linear small-signal equivalent circuit

55 Recall Dc and small-signal equivalent elements Element ss equivalent dc equivalnet MOS Transistors Simplified Simplified Bipolar Transistors Simplified Simplified

56 The simplified large signal models for the MOSFET and the BJT Simplified Simplified Simplified large-signal models (sometimes termed dc equivalent models) are usually adequate for determining operating point in practical MOS and Bipolar circuits Can create circuits where the simplified models are not adequate but these are often not practical circuits Will discuss only for npn and n-channel but similar models for pnp and p- channel devices

57 Square-Law Model I I G B GS T W L 2 W 2 μc 1 2L DS I μc D OX GS T DS GS T DS GS T OX GS T DS GS T DS GS T T T0 BS

58 Simplified MOS Model for Q-point Analysis I G 0 IB 0 W I μc 2L 2 D OX GS T Simplified Simplified dc equivalent circuit G OX GS 2 S D μc W GS - 2L T

59 dc BJT model I C βi B JSA IB β 1 E e CE BE t AF BE >0.4 BC <0 Forward Active t kt q BE =0.7 CE =0.2 I C <βi B Saturation I C =I B =0 BE <0 BC <0 Cutoff A small portion of the operating region is missed with this model but seldom operate in the missing region

60 Simplified dc BJT model for Q- point Analysis I C βi JSA IB β E B e BE t I C βi B 0.6 BE Simplified Simplified dc equivalent circuit B I B C 0.6 βi B E

61 Examples CC R 1 out in B C E Q 1 EE Not convenient to have multiple dc power supplies OUTQ very sensitive to EE

62 Examples CC CC =12 R 1 R B =500K R 1 =2K out out in B C E Q 1 in C 1 =1uF B C Q 1 E EE Not convenient to have multiple dc power supplies OUTQ very sensitive to EE Compare the small-signal equivalent circuits of these two structures

63 Examples CC CC =12 R 1 R B =500K R 1 =2K out out in B C E Q 1 in C 1 =1uF B C Q 1 E EE Compare the small-signal equivalent circuits of these two structures OUT OUT R 1 R 1 IN IN R B Since Thevenin equivalent circuit in red circle is IN, both circuits have same voltage gain

64 Examples Determine OUTQ, A, R IN CC =12 R B =500K R 1 =2K out in C 1 =1uF B C Q 1 E

65 Examples Determine OUT and OUT (t) if IN =.002sin(400t) CC =12 R B =500K R 1 =2K out in C 1 =1uF B C Q 1 E

66 Examples Biasing Circuit R B =500K CC =12 R 1 =2K IN (t) C=1uF Q 1 OUT (biasing components: C, R B, CC in this case, all disappear in small-signal gain circuit) Several different biasing circuits can be used

67 Examples Biasing Circuit R B =500K CC =12 R 1 =2K IN (t) C=1uF Q 1 OUT Determine OUTQ and the SS voltage gain, assume β=100

68 Examples CC =12 R R 1 =2K B =500K C=1uF IN (t) Q 1 OUT β=100 Determine OUTQ CC =12 R R 2 =2K B1 =500K I B βi B 0.6 OUTQ R B1 =500K CC =12 R 2 =2K OUT dc equivalent circuit I CQ = βi BQ = mA 500K = 12-I R =12-2.3mA 2K 7.4 OUTQ CQ 1 I B Q 1 simplified dc equivalent circuit

69 Examples Determine the SS voltage gain CC =12 i B OUT R B =500K R 1 =2K IN R B g m BE BE g π R 1 IN (t) C=1uF Q 1 OUT β=100 ss equivalent circuit g R OUT m BE 1 IN R B ss equivalent circuit R 1 OUT A IN BE R g 1 m ICQR1 A - t 2.3mA 2K A m This basic amplifier structure is widely used and repeated analysis serves no useful purpose Have seen this circuit before but will repeat for review purposes

70 Examples Determine the R IN CC =12 R B =500K R 1 =2K i IN i B OUT IN (t) C=1uF Q 1 OUT β=100 IN R B g m BE BE g π R 1 R IN OUT IN Rin i IN IN R B ss equivalent circuit R 1 Rin RB // r Usually R B >>r π Rin R in R // r r B ICQ r β t

71 Examples Determine OUT and OUT (t) if IN =.002sin(400t) R B =500K CC =12 R 1 =2K out OUT OUTQ+A IN sin(400 t) OUT in C 1 =1uF B C Q 1 E sin(400 t) OUT

72 End of Lecture 28