Circuits, Devices, Networks, and Microelectronics BJT Single-transistor exercise
Defaults: Resistances in kΩ, β F = 100, VA = 100V unless otherwise indicated.
Version 2.8
9-1. For the circuits shown determine I1 and I2 if
(a) βF = 400, (b) β F = 100, (c) β F = 40.
9-4. Determine VBB, RBB, and VB for the fourresistance biasing network shown.
9-2: For each of the following circuits determine the
labeled voltages and currents and the value of β F for
the transistor.
9-5. For the 4-resistance biasing network shown
determine IE and VB if (a) RE = 2 , (b) RE = 5, (c) RE
= 20.
Answers:
(a){I1=0.594mA,I2=5.7μA,V1=5.406V, β F=103} (b)
{V1=4.7V, I1=1.325mA, V2=1.32V, β F=131}
9-6. For the 4-resistance biasing network shown
determine the value of RE needed for (a) IE =
0.1mA, (b) IE = 0.25mA, (c) IE = 1.2mA.
9-3. For an npn transistor the I-V characteristics are
as shown when IB = 5μA. From these output
characteristics determine the Early voltage VA
,output resistance ro , and forward gain factor β F.
Answers: { ro = 120kΩ, VA = 72V, β F = 120}
1 Circuits, Devices, Networks, and Microelectronics 9-7. Find operating point {IB, IC, VCE} and VB.
9-10. Find operating point {IB, IC, VCE} and VE.
Answers: {.0093, 0.926, 1.99 }, VB = 4.44
9-11. Find operating point {IB, IC, VCE} and VB.
9-8. Find operating point {IB, IC, VCE} and VB.
Answers: { -.0147, -0.735, -4.52 }, VB = 11.18
9-12. Assume β F = large (e.g. infinity) and find
values for VB1, VE1, VB2, VC2 .
9-9. Find operating point {IB, IC, VCE} and VE.
Answers: {.005, 0.495, 4.35}, VE = 4.7
2 Circuits, Devices, Networks, and Microelectronics 9-15. It is desired to have current IE to be 0.25mA in
the circuit shown, in order to have transfer gain vL/vI
= -20V/V.
9-13. Find IE1, VB1, and VB2 .
Answers: {.0492mA, 4.61V, 3.91V }
9-14. Determine the small-signal parameters gm, rπ
and ro of the transistor and the small-signal circuit
characteristics vL/vI and Rin for the circuit shown.
Note that you will need to find the operating point
before you can determine the small-signal
parameters. (Hint: see problem 9-7). Assume all
capacitances = large.
(a) What value R5 is needed if R1 = 300kΩ?
(b) What is the value of VCE (= swing space)
(c) What is the value of Rin?
(d) What value R1 is needed if R5 = 9.5kΩ?
(e) What is Rin for this value of R1?
Answers: (a) 19.5kΩ (b) 5.0V, (c) 40kΩ
638kΩ (e) 43kΩ
9-16. It is desired to have current IE to be 0.10mA in
the circuit shown, in order to have transfer gain vL/vI
= -40V/V.
(a) What value R5 is needed if R1 = 300kΩ?
(b) What is the value of VCE (= output swing space)
(c) What is the value of Rin?
(d) What value R1 is needed if R5 = 19.5kΩ?
(e) What is Rin for this value of R1?
3 Circuits, Devices, Networks, and Microelectronics 9-20. Determine Rin, Rout, vL/vI, and vL/vS for the
circuit shown. Assume all capacitances = large.
9-17. Determine the small-signal parameters gm, rπ
and ro and vL/vI, Rin , rout, and Rout for the circuit
shown. Assume all capacitances = large.
9-21. Determine Rin, rout, Rout, vL/vI, and vL/vS for the
circuit shown. Assume all capacitances = large.
Answers: (4.0mA/V, 12.5kΩ, 1.0MΩ, -20V/V,
23kΩ, 2.88MΩ, 19.86kΩ)
9-18. Determine Rin, Rout, vL/vI, and vL/vS for the
circuit shown. Assume all capacitances = large.
9-19. Determine Rin, Rout, vL/vI, and vL/vS for the
circuit shown. Assume all capacitances = large.
4 Circuits, Devices, Networks, and Microelectronics 9-23. Copy the page and fill in the blanks by inspection (or rough calculation) within 10%. Note that you should
need to first find gm, each case. Default βF = 100, VA = 50V.
5 Circuits, Devices, Networks, and Microelectronics 9-24. Copy the page and fill in the blanks by inspection (or rough calculation) within 10%. Note that you should
need to first find gm, each case. Default βF = 100, VA = 50V.
9-25. For each of the transistors in problem 9-24,
assume that the constraint on active operation of the
circuit is that the base-collector junction never be
allowed to go into forward bias. Also assume that
the base current is negligible for the transistors.
Using these constraints determine the maximum
allowed value of R3 for parts (A), (D), and (E).
6 Circuits, Devices, Networks, and Microelectronics 9-26. For the circuit shown determine (a) Ra necessary for I = 0.25mA (b) parameters gm and ro and
(c) amplifier characteristics Rin and vL/vI (d) pL/pI
(in dB). Assume VA = 50V.
9-29. For the circuit shown determine:
(a) Ra necessary for gm = 20mA/V and
(b) Rin, Rout, vL/vI and pL/pI (in dB)
9-30. Assume VA = 50V and determine
(a) gm , rO,
(b) Rin, Rout, vL/vI, and pL/pI
Answers: (a) 57.2 kΩ (b) 10mA/V, 200kΩ, (c) 30kΩ, -25V/V
9-27. Determine
(a) resistance Ra needed for I = 0.5mA
(b) Rin, Rout, vL/vI, and vL/vS .
9-28. For the circuit shown determine
(a) Ra such that gm = 10mA/V
(b) Rin, vL/vI and pL/pI (in dB)
9-31 For the circuit shown determine
(a) Ra such that gm = 10mA/V
(b) Rin, vL/vI (c) VE
Answers: (a) 61.2 kΩ (b) 30kΩ, -25V/V
7