Course Roadmap Rectification Bipolar Junction Transistor

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1 Course oadmap ectification Bipolar Junction Transistor Acnowledgements: Neamen, Donald: Microelectronics Circuit Analysis and Design, 3 rd Edition Spring 2017 Lecture 3 1

2 6.101 Spring 2017 Lecture 3 2 Time Domain Analysis ] ) cos( ) [cos( 2 cos )*cos cos ( t t KA t A v t t KA A v m c m c m c c c m m c

3 Fourier Series amp function [ t, sum ] = ramp(number) %generate a ramp based on fixed number of terms % t = 0:.1:pi*4; % display two full cylces with 0.1 spacing sum = 0 for n=1:number sum = sum sin(n*t)*(-1)^(n1)/(n*pi); end plot(t, sum) shg end Spring 2017 Lecture 3 3

4 6.101 Course oadmap Passive components: LC with F Diodes Transistors: BJT, MOSFET Op amps, 555 timer, ECG Switch Mode Power Supplies Fiber optics, PPG Applications Spring 2017 Lecture 3 4

5 CT: center tap ectifier Circuits 120 V 60 Hz 1N VCT MS C F L v OUT V out = - Pri Sec 3a) Half-wave rectifier circuit diagram 1N V 60 Hz 12.6 VCT MS C F L v OUT V out = - Pri Sec 3b) Full-wave rectifier circuit diagram 1N4001 4x 1N V 60 Hz 12.6 VCT MS C F L v OUT V out = - Pri Sec 3c) Bridge rectifier circuit diagram C >> 16.6ms why? Spring 2017 Lecture 3 5

6 Power Supply ipple Voltage Calculation D 2 conduction angle in degrees Spring 2017 Lecture 3 6

7 5 V Adapters 500 ma 1000 ma 300 ma Spring 2017 Lecture 3 7

8 Diode AC esistance Spring 2017 Lecture 3 8

9 Log Amplifier bypass caps 0.1uf caps (2) I D 1N914 I = - I D I V out = - V D v in 1.5k F LF _ F v out qv D kt I I (e D S 1) IS e qv D kt Spring 2017 Lecture 3 9

10 Bipolar Junction Transistors NPN i b base PNP collector emitter i c = βi b i b i c BJT can operate in a linear mode (amplifier) or can operate as a digital switch. Current controlled device Two families: npn and pnp. BJT s are current controlled devices NPN 2N2222 PNP 2N2907 V CE ~30V, 500 mw power Spring 2017 Lecture 3 10

11 Why BJT s? Preferred device for demanding analog application, both integrated and discrete (lower noise) Great for high frequency applications; characteristics well understood. High reliability makes it a key device in automotive applications. Lower output resistance at emitter vs source Larger g m compared to FET Spring 2017 Lecture 3 11

12 6.101 Spring 2017 Lecture 3 12

13 BJT Symbols 2N2222 2N3904 2N P2N2222 pinout reversed Spring 2017 Lecture 3 13

14 Packaging TO-18 TO-220 TO Spring 2017 Lecture 3 14

15 BJT Current elationship NPN base collector emitter i b i c i c = βi b h FE = β = large signal (DC) gain at fixed current i i i i E C E C i ( C i i 1 B E i 1) i B B h FE < h fe Spring 2017 Lecture 3 15

16 max voltage max continuous current max power at 25 o C Spring 2017 Lecture 3 16

17 β h FE = f(i c ) peaks at ~5-10ma h < h Spring 2017 Lecture 3 17

18 hfe & Current & Temperature Characteristics Spring 2017 Lecture 3 18

19 NPN Common Emitter V I elationship β =? Spring 2017 Lecture 3 19

20 A large V A is desirable for high voltage gains ~ 30-50v. V A is determined by transistor design and varies with base width, base and collector doping concentration. Early effect: the rise of Ic due to basewidth modulation. (James) Early Voltage Spring 2017 Lecture 3 20

21 Tek 575 Curve Tracer Vertical axis: current Horizontal axis: voltage Voltage sweep: positive and negative with resistor current limit 0 20v; 0 200v! Input: fixed current steps ( ma); 240 steps Tests: diodes, BJT, MOSFETs Calibrate zero current step Spring 2017 Lecture 3 21

22 Mcube Tests: Diodes (forward drop) BJT (type, beta) MOSFET (type, V TH and more) Auto terminal identification Spring 2017 Lecture 3 22

23 LC BJT MOSFET Testor Spring 2017 Lecture 3 23

24 BJT Configurations Voltage Gain Current Gain Power Gain Common Emitter X X X Common Collector X X Common Base X X Common emitter: hgh input impedance, for general amplification of voltage, current and power from low power, high impedance sources. Common collector: aka "emitter follower" for high input impedance and current gain without voltage gain, as in an amplifier output stage. Common base: low input impedance for low impedance sources, for high frequency response. Grounding the base short circuits the Miller capacitance from collector to base and makes possible much higher frequency response Spring 2017 Lecture 3 24

25 General Configuration Common Emitter Common Collector Common Base Spring 2017 Lecture 3 25

26 Transistor Configurations TANSISTO AMPLIFIE CONFIGUATIONS 15V 15V 15V L L V in - 1 E V OUT - V in - 1 E V OUT - V in - 1 E V OUT - [a] Common Emitter Amplifier [b] Common Collector [Emitter Follower] Amplifier [c] Common Base Amplifier Spring 2017 Lecture 3 26

27 Common Emitter Operation Quiescent Point Spring 2017 Lecture 3 27

28 Load Line Operating Point 20 V I CQ Find V out open circuit voltage: 20V 2N3904 v out Find I CQ max = 20/(910 91) = ~20ma Draw load line BFC - For E = 0, just choose Q at ½ V CC for maximum swing. For E > 0, set Q at ½ [V CC V E ]. For I CQ = 10 ma, V L = 9.1V, V E = 0.91V, V CE = 10V. For I CQ = 10.5mA, V L = 9.6V, V E = 0.96V, V CE = 9.5V Spring 2017 Lecture 3 28

29 Transistor Bias Instability B I B I E F 15V I C = 4 ma 2N3904 E = 2200 I E = 4 ma 100, F 1I B, I E IC I C I F B 8.8V I 07. V I V I 07. V I V I V 07. V I I B B C E CC B B F B E CC B B F E CC B C V CC 07. V B F E F VCC 07. V B F E 1 2 F VCC 07. V I V 0. 7V B mA B 220k k358k B F E B B 138k C Spring 2017 Lecture 3 29

30 Variation of Collector Current with β One esistor B 15V I C = 4 ma I C V 0.7V F CC 2 B F E 2N3904 Variation of Collector Current with Beta I B E = 2200 I E = 4 ma I C F 2.9 ma ma ma ma 300 I C =2.5 ma Spring 2017 Lecture 3 30

31 Two esistor Biasing 15V 15V 2 I C = 4 ma I C = 4 ma I B 2N3904 2N3904 TH = B B 1 E = 2200 I C = 4 ma V TH = V B E = 2200 V B [a] [b] [c] V B 1 V cc 3 B 1 // Spring 2017 Lecture 3 31

32 Two esistor Biasing 2 15V I C = 4 ma 15V I C = 4 ma V I 07. V I 0 B B B C E V I 07. V I B B B F B E V 07. V I I I B B B F B E B B F E 1 E = N3904 I C = 4 ma TH = B V TH = V B B I B V B 2N3904 E = 2200 I B V B 07. V B F E 5 [a] [b] [c] I C F VB 07. V B F E 6 Assume B = 22kΩ, β E = 220kΩ and ignore B 4mA V 22k 220k 100V 0.7V 4mA 242k 100V V B 10.4V B B 70 B Spring 2017 Lecture 3 32

33 Two esistor Biasing Given V B = 10.4 V and B = 22kW, we can now solve equations (3) and (4) for 1 and 2. V B V V V CC 15V V CC B B 22k 22k 22k k k use 68k k319. k use 33k Spring 2017 Lecture 3 33

34 Variation of Collector Current with β Two esistor Biasing I C F VB 0.7V B F E 6 Variation of Collector Current with Beta Two esistor One esistor I C F V 22k 2200 F I C I C F 3.7 ma 2.9 ma ma 4.0 ma ma 5.0 ma ma 5.4 ma 300 I C =0.6 ma I C =2.5 ma Spring 2017 Lecture 3 34

35 Base Current esistor Divider 68K i b I C F 3.7 ma ma ma ma 300 I C =0.6 ma 33K i b Make small compared to the current through 2 See handout: Transistor bias stability Spring 2017 Lecture 3 35

36 BJT Switching Models 15v 15v input signal input signal off state on state Forced beta reduces V ce sat Stored charges in base emitter junction slows turn off IAP Lecture 3 36

37 Common Collector Emitter Follower Biasing 2 A 15V 7.5 ma 2N3904 Β = 100, i B = 7.5ma/100 = 75µa Using Thevenin equivalent, B = 1 2, V B = B 1.0 k 7.5 ma 15V V B = I B B 0.6V 7.5V V B = [75 µa x 10k] 0.6V 7.5V V B = 750 mv 0.6V 7.5V V B = 8.9V I B B V B 7.5 ma 2N V [15 1 ] [ 1 2 ] = 8.9V 15 1 = 8.9 x [ 1 2 ] [15 8.9] 1 = = [ 1 x 2 ] [ 1 2 ] = 10 kω [ x 2 ] [ ] = 10kΩ 2 = 16.9 kω (use 16 kω) 1 = = 24.4 kω (use 24 kω) Spring 2017 Lecture 3 37

38 Common Collector Emitter Follower Biasing 2 I Divider 15V 7.5 ma With 1 = 24kΩ, 2 = 16 kω, the current through the voltage divider is 15 [40 kω] = 375 µa. The 75 µa base current is 20% of 375 µa. 8.1 V 1 A B 1.0 k 2N ma With 1 = 2 kω, will need a divider current that is ~ 4.1 ma. (75 µa is only ~2% of 4.1 ma, which is negligible) The voltage drop across 2 will be [15 V 8.1 V] = 6.9 V; 2 = 1.7 kω But input impedance will be low = ~890Ω Use bootstrapping configuration = 24.4 kω (use 24 kω) Spring 2017 Lecture 3 38

39 Bootstrapping Higher Input Impedance The base is connected to the emitter through with 3 and C 2. At signal frequency, C 2 is a short so both ends of 3 are at the same voltage so no current flows. Therefore 1 and 2 cannot load the input. So 3 appears to be very high. In real life, there is a small AC voltage across 3. The AC current through 3 is kΩ = 1.1 µa. Horowitz and Hill Figure 2.65 esult: stiff biasing with high input resistance at signal frequency Spring 2017 Lecture 3 39

40 Our treatment of bipolar transistors is going to be quite different from that of many other books. It is a common practice to use the h-parameter (hybrid pi) model and equivalent circuit. In our opinion that is unnecessarily complicated and unintuitive... you also have the tendency to lose sight of which parameters of transistors behavior you can count on and more important, which ones can vary over large ranges. The Art of Electronics, Horowitz & Hill 3 rd edition page Spring 2017 Lecture 3 40

41 Commom Emitter Hybrid π TANSISTO AMPLIFIE CONFIGUATIONS WITH HYBID- EQUIVALENT CICUITS COMMON EMITTE AMPLIFE 15V 0 g m r C B L 2N3904 I C g m I CQ V TH Early Voltage s v in _ I B v out _ r 0 V A I CQ v 1 in 1 v out oibl b c Av 1 v in ibr r i b s v ol out B L then Av o v in e gm g o r m L L Spring 2017 Lecture 3 41

42 Common Emitter with Emitter Degeneration A v v v 1 out 1 in i b i o b r 1 r 1 o L E o o L E ; if r o 1E ; then Av L / E v 1 in v 1 out Input resistance (β1) E Voltage gain reduced by (1g m E ) Voltage gain less dependent on β (linearity) Spring 2017 Lecture 3 42

43 Common Collector (Emitter Follower) Spring 2017 Lecture ; 1 ; 1 ' 1 1 ' v E o E o s E o E o s b E b o in out v A then r if r r i i v v A Buffer with unity gain High input resistance driving low output resistance (current gain). mv V V I g r g TH TH CQ m m 26 0 v 1 out v 1 in

44 Low Frequency Hybrid Equation Chart High gain applications Moderate input resistance High output resistance Unity gain, low output resistance High input resist. High gain, better high frequency response Low input resistance Spring 2017 Lecture 3 44

45 g m q I C kt 0 h fe (datasheet) C C ob Hybrid π Parameters (datasheet) g m 2(C C ) f T (transit frequency datasheet) C g m 2 f T r C r x (low frequency):datasheet or estimate (high frequency):estimate Spring 2017 Lecture 3 45

46 Miller Effect* Common Emitter C M C [ 1 gm( C L )] * Agarwal & Lang Foundations of Analog & Digital Electronics Circuits p Spring 2017 Lecture 3 46

47 h fe and High Frequency Limits Small signal current gain versus frequency, h fe, of a BJT biased in a common emitter configuration: i b v r be v be jc h fe gmv i b be gmr 1 jr C 1 jr C For h fe = 1 = f T, (transit frequency ) h T g m 2 f t C where C (c c ) For 2N3904*, I C =1ma, V CE =10V, c π =25pF, c μ =2pF f T 0.04mho 2 27 pf for a gain of 240MHz g m L 100 f h 2 r 1 g m L c K(100)2 pf 320kHz Miller effect reduces high frequency limit! *Lundberg, Kent: Become One with the Transistor p Spring 2017 Lecture 3 47

BJT Circuits (MCQs of Moderate Complexity)

BJT Circuits (MCQs of Moderate Complexity) 1. The current ib through base of a silicon npn transistor is 1+0.1 cos (1000πt) ma. At 300K, the rπ in the small signal model of the transistor is i b B C r