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Transistor Fundamentals

9. Transistor Fundamentals. r. o. +. +. r. v. i. _. in. o. in. v. i. r. r. in. in. i. i. _. (a) Current-controlled current source. (b) Voltage-controlled voltage source. r. o. +. +. v. i. r. _. in. in. o. v. r. i. r. i. in. i. in. _.

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Transistor Fundamentals

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  1. 9 Transistor Fundamentals

  2. r o + + r v i _ in o in v i r r in in i i _ (a) Current-controlled current source (b) Voltage-controlled voltage source r o + + v i r _ in in o v r i r i in i in _ (c) Voltage-controlled current source (d) Current-controlled voltage source Figure 9.1 Controlled-source models of linear amplifier transistor operation

  3. i 0 i 0 in in i i r r in i in i Current-controlled switch + + v 0 v 0 in in v r r v in i i in _ _ Voltage-controlled switch Figure 9.2 Models of ideal transistor switches

  4. Collector Collector C C C C p n Base n B B Base p B B + + p n E E E E Emitter Circuit symbols Emitter Circuit symbols pnp transistor npn transistor Figure 9.4 Bipolar junction transistors

  5. R C 1 k C R B B 40 k V 3 V CC V E BB V 12 V 1 R 4 V E V 2 500 Figure 9.10 Determination of the operation region of a BJT

  6. By appropriate choice of I , R BB C and V , the desired Q point may CC be selected. I C C + R I C B B V CE + _ V I V BE CC BB _ E Figure 9.12 A simplified bias circuit for a BJT amplifier

  7. 50 m 45 m 40 m I = 250 A B 35 m I = 200 A Collector current, A 30 m B Q 25 m I = 150 A B 20 m I = 100 A 15 m B 10 m I = 50 A 5 m B 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Collector-emitter voltage, V Figure 9.13 Load-line analysis of a simplified BJT amplifier

  8. I + I C C C R + C I + I B B V + V CE CE + B R B – + V + V ~ _ BE BE V V B CC – E V BB Figure 9.15 Circuit illustrating the amplification effect in a BJT

  9. I (mA) C 50 I 230 A = B 190 A 28.6 150 A Q 22 t 110 A 15.3 75 A 0 0 5 10 15 V (V) CE t Figure 9.16 Amplification of sinusoidal oscillations in a BJT

  10. I C R R 1 C I + B V V CC + CE – V I BE E – R 2 R E Figure 9.20 Practical BJT self-bias DC circuit

  11. I I C C + + I I R R R B B C C 1 V V CE + + CE R _ _ B V V BE _ BE _ V R V V V 2 CC I I CC R R CC BB E E E E (a) (b) Figure 9.21 DC self-bias circuit represented in equivalent-circuit form

  12. C C I I I CEO C Cutoff state conditions: Active state conditions: B I = 0 B V = V V V BE BE B B I = 0 I 0 B B + – I = I I = I V C CEO C B V 0 V V CE CE E E C I C + I Saturated state conditions: V B sat – V = V BE B I 0 B + – I I V C B V = V CE sat E Figure 9.22 npn BJT large-signal model

  13. Gate i D D Source Drain + n + n + p + V V _ DS DD + _ V G _ DD Bulk (substrate) S Figure 9.30(a) An n-channel MOSFET is normally off in the absence of an external electric field

  14. i D D + + V V _ DS DD _ G + V _ + GS V S GG _ Figure 9.30(d) If the drain and gate supply voltages are both varied a family of curves (shown in Figure 9.31(b)) can be generated, illustrating the MOSFET cutoff, ohmic, saturation, and breakdown regions

  15. (mA) i D = 2.8 V v 100 GS 80 2.6 V Q 60 2.4 V i D D 2.2 V 40 R + D G 2.0 V v DS + 20 – 1.8 V v V GS V GG – S ON 1.6 V 1.4 V 0 (V) 0 2 4 6 8 10 v DS Figure 9.32 n-channel enhancement MOSFET circuit and drain characteristic for Example 9.8

  16. Gate Source Drain p Channel n p Figure 9.40(a) When the gate-source voltage is lower than -Vp, no current flows. This is the cutoff region

  17. Gate Source Drain p n Channel p depletion regions Figure 9.40(b) For small values of drain-source voltage, depletion regions form around the gate sections. As the gate voltage is increased, the depletion regions widen, and the channel width (i.e., the resistance) is controlled by the gate-source voltage. This is the ohmic region of the JFET

  18. Gate Source Drain p n Channel p Pinched-off channel Figure 9.40(c) As the drain-source voltage is increased, the depletion regions further widen near the drain end, eventually pinching off the channel. This corresponds to the saturation region

  19. 4 m 0 V 3 m – 0.5 V Drain Current, A 2 m – 1.0 V 2 m – 1.5 V 800 u – 2.0 V – 2.5 V V = – 3 V 0 GS 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Drain-source voltage, V Figure 9.41 JFET characteristic curves

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