Transistor TJB. Modelo pequenos sinais Modelo alta frequência

Transcrição

1 Transistor TJB Modelo pequenos sinais Modelo alta frequência

2 Modelagem do Transistor TBJ Resposta ac do TBJ para pequenos sinais; Modelos utilizados de representação do TBJ. Amplitude do sinal de entrada: técnica e modelo de pequenos sinais ou grandes sinais Modelos utilizados: modelo r e modelo híbrido equivalente 2

3 Ideia básica - modelo 3

4 The Transistor as an Amplifier (a) Conceptual circuit to illustrate the operation of the transistor of an amplifier. (b) The circuit of (a) with the signal source v be eliminated for dc (bias) analysis. 4

5 5 The Small-Signal Model Parameters of the BJT The Collector Current and the Transconductance The Base Current and the Input Resistence at the Base The Emitter Current and the Input Resistance at the Emitter be c T C I i BE C m v i V I v i g C C m B T b be b g I V i v r r m m E T e be e g g I V i v r 1

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7 Modelagem TBJ Um modelo é a combinação de elementos de circuito, apropriadamente escolhidos, que aproximam melhor o funcionamento real de um dispositivo semicondutor sob condições de operação específicas. Uma vez determinado o circuito equivalente, o símbolo gráfico do dispositivo pode ser substituído, no desenho esquemático, por este circuito (modelo), e os métodos básicos de análise de circuitos. 7

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9 Two slightly different versions of what is known as the T model of the BJT. The circuit in (a) is a voltage-controlled current source representation and that in (b) is a current-controlled current source representation. These models explicitly show the emitter resistance r e rather than the base resistance r featured in the hybrid- model. 9

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15 Idem Coletor-Comum 15

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18 Ganho de corrente divisor de corrente 18

19 Ganho de corrente forma simplificada: 19

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26 Quadro resumo 26

27 Example to Show Wave Forms (=100) 27

28 Signal waveforms in the circuit of former Example 28

29 (a) circuit; (b) dc analysis; (c) small-signal model; (d) small-signal analysis performed directly on the circuit. 29

30 Distortion due to Cutoff or Nonlinearity 30

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32 Augmenting the T-Model to Account for the Early effect for the small-signal operation of the BJT. 32

33 33 Relationships Between the Small- Signal Model Parameters of the BJT Model Parameters in Terms of DC Bias Currents: In terms of g m In terms of r e Relationships between and : T C m V I g C T E T e I V I V r C T b I V r r C A o I V r m e g r m b g r r e m r g e r 1 r e m r r g

34 Graphical construction for the determination of the dc base current in the shown circuit. 34

35 Graphical construction for determining the dc collector current I C and the collector-to-emmiter voltage V CE in the shown circuit. 35

36 Graphical determination of the signal components v be, i b, i c, and v ce when a signal component v i is superimposed on the dc voltage V BB 36

37 Effect of bias-point location on allowable signal swing: Load-line A results in bias point Q A with a corresponding V CE which is too close to V CC and thus limits the positive swing of v CE. At the other extreme, load-line B results in an operating point too close to the saturation region, thus limiting the negative swing of v CE. 37

38 400uA I B = 5 ua V = +12 V CC 22k R C 300uA 314 ua I B = 4 ua R 2 36 k = 75 Q 1 I C I B = 3 ua 200uA Q-point I = 2.7 ua B I = 2 ua B R 1 18 k 16 k R E 100uA I B = 1 ua Note: Early effect has been neglacted ( VA ) Load Line 12V 0A 0V 5V 10V 15V V CC Load line for the four resistor bias circuit Exercice: What s the Q-point if a) = 500 b) c) = 75 and R C = 56 k 38

39 4.0mA t C o l l e c t o r C u r r e n t 3.0mA 2.0mA 1.0mA Q-point V ce (t) 0A 0V 2V 4V 6V 8V 10V 12V Collecter-emitter Voltage v be (t) Load line Q-point and signals for the BJT amplifier Load Line Q-Point and signals for the BJT amplifier V BE = V I = 30 ua B V = V BE I = 20 ua B t V = V BE I = 15 ua B V = V BE I = 10 ua B Load Line v 1.65 V ce AV 206 vbe 8 mv 180 phase shift between input and output signals 39

40 I REF I V CC V R EE V BE 40

41 DC Analysis Analysis Circuits Step-by-Step A B A B 1. ; 2. Find the Q-point using large-signal model AC Analysis C A B A B L A B A B 3. A B ; A B A E B ; A B A B A B 4. BJT small-signal model 5. Analyze the circuit 6. Combine DC AC results 41

42 The common-emitter amplifier. (a) Circuit. (b) Equivalent circuit with the BJT replaced with its model. 42

43 The common-emitter amplifier with a resistance R e in the emitter. (a) Circuit. (b) Equivalent circuit with the BJT replaced with its T model (c) The circuit in (b) with r o eliminated. 43

44 The common-base amplifier. (a) Circuit. (b) Equivalent circuit obtained by replacing the BJT with its T model. 44

45 The common-collector or emitter-follower amplifier. (a) Circuit. (b) Equivalent circuit obtained by replacing the BJT with its T model. (c) The circuit in (b) redrawn to show that r o is in parallel with R L. (d) Circuit for determining R o. 45

46 Acoplamento RC Acoplamento direto 46

47 Acoplamento por transformador 47

48 Resposta em baixas frequências Efeito C s Efeito C C f Ls 1 2 ( R R ) C s i s 48

49 Resposta em baixas frequências Efeito C E 49

50 Exemplo: 50

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52 Simulação BC 337 XFG1 VCC R2 40kΩ 20.0V R6 1kΩ C3 IN XBP1 OUT XSC1 R3 1kΩ C1 10µF 1µF BC337AP Q1 R4 1kΩ + A _ + B _ Ext Trig + _ R1 10kΩ R5 1kΩ C2 20µF 52

53 Figure 5.73 Analysis of the low-frequency response of the CE amplifier: (a) amplifier circuit with dc sources removed; (b) the effect of C C1 is determined with C E and C C2 assumed to be acting as perfect short circuits; 53

54 Figure 5.73 (Continued) (c) the effect of C E is determined with C C1 and C C2 assumed to be acting as perfect short circuits; (d) the effect of C C2 is determined with C C1 and C E assumed to be acting as perfect short circuits; 54

55 Capacitores que influenciam o comportamento em alta frequência 55

56 Efeito da capacitância Miller 56

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58 Modelo de Giacoletto ou π-híbrido 58

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61 Modelo π-híbrido altas frequências 61

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63 60 db The unity-gain frequency ( f T ) : the frequency at which drops to one + + v be - C m i m 0 i c log o - 3 db i b r v be - C g v m be r o 20 f - 20 db/decade Common-emitter current gain versus frequency for the BJT f T 0 f Frequency (Hz - Log Scale) Figure Common-emitter current gain versus frequency for the BJT Finding the short-circuit current gain of the BJT β βo 1 s β β 1 r (C C ) π π μ β T o β T C π gm C μ 63

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66 Figure 5.72 Determining the high-frequency response of the CE amplifier: (a) equivalent circuit; (b) the circuit of (a) simplified at both the input side and the output side; (c) equivalent circuit with C m replaced at the input side with the equivalent capacitance C eq ; (d) sketch of the frequencyresponse plot, which is that of a low-pass STC circuit. 66

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