Download Tutorial I - Bipolar Junction Transistor Amplifiers

DMT 231 / 3 Electronics II
DMT 231 / 3 ELECTRONICS II
BIPOLAR JUNCTION TRANSISTOR AMPLIFIER
A. Current Relationships
1. Explain, with the help of an example, the meaning of the term ‘biasing’.
2. What are the bias voltages need to be applied to an npn bipolar transistor such that
the transistor is biased in the forward-active, cut-off and saturation modes of
operations?
3. With the aid of a diagram, state the relationships between collector, emitter and
base currents in a bipolar transistor biased in the forward-active mode.
4. In a bipolar transistor biased in the forward-active mode, the base current is
iB  6.0A and the collector current is iC  510A . Determine  ,  and i E .
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B. BJT Common-Emitter Amplifiers (DC Analysis)
1. The transistor parameters for the circuit in Figure 1 are   120
and VBE ( on)  0.7V .
The circuit elements are VCC  5V , VBB  2V RB  200k and RC  4k .
Figure 1
Determine:
(a) base current, IB
(b) collector current, IC
(c) collector-emitter voltage, VCE
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DMT 231 / 3 Electronics II
2. The transistor parameters
and VEB( on)  0.7V .
for
the
circuit
in
Figure
2
are
  80
The circuit elements are V   5V , VBB  2.8V and RB  325k .
Figure 2
Given that VEC  2V , determine:
(a) base current, IB
(b) collector current, IC
(c) emitter current, IE
(d) collector resistor, RC
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3. For the circuit shown in Figure 3, the transistor parameters are   50 ,
VBE ( on)  0.7V and VCE ( sat)  0.2V
Given that VI  3.6V , determine:
Figure 3
(a) output voltage, VO
(b) base current, IB
(c) collector current, IC
(d) power dissipated in the transistor, PT
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4. The circuit elements in Figure 4 are VCC  12V , VBB  8V ,
RC  0.4k , RE  1.2k and RB  30k .
Figure 4
Let   75 and VBE ( on)  0.7V .
(i)
Determine:
(a) base current, IB
(b) collector current, IC
(c) emitter current, IE
(d) collector-emitter voltage, VCE
(ii)
Sketch the DC load line
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5. Assuming   100 , design the circuit in Figure 5 such that IC = 1.5 mA and VC =
+ 4 V.
Figure 5
6. Given that   120 , VCC = 5 V and VBE(ON) = 0.7 V for the circuit shown in
Figure 6, design the circuit such that IC Q = 0.25 mA and VCEQ = 2.5 V.
Figure 6
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C. BJT Common-Emitter Amplifiers (AC Analysis)
1.
Figure 1
Referring to Figure 1, given that RE = 0.6 kΩ, RC = 5.6 kΩ, β = 120, VBE(on) = 0.7 V, R1 =
250 kΩ, R2 = 75kΩ.
(a) For VA=∞, determine small-signal voltage gain, Av
(b) Determine the input resistance looking into the base of the transistor.
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2.
Figure 2
Let β = 100, VBE(on) = 0.7 V and VA = 100V.
Determine:
(a) Small-signal voltage gain
(b) Input resistance seen by the signal source, Rin
(c) Output resistance looking back into the output terminal, Ro
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3.
Figure 3
Assume that β = 100, VA = ∞, R1 = 10 kΩ and R2 = 50 kΩ for the circuit in Figure 3.
(a) Plot the Q-point on dc load line
(b) Determine the small-signal voltage gain
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4.
Figure 4
Given β = 180, VA = ∞.
(a) Find ICQ and VCEQ
(b) Plot dc and ac load lines
(c) Calculate small-signal voltage gain
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D. BJT Common-Base Amplifiers (DC & AC Analysis)
1. The transistor parameters for circuit in Figure 1 are   75 and VEB(ON )  0.7V .
Design the common-base circuit such that IEQ = 0.25 mA and VECQ = 2 V.
Figure 1
2. For the circuit shown in Figure 2, the measured value of VC is +6.34 V.
Figure 2
Determine:
(a) base current, IB
(b) collector current, IC
(c) emitter current, IE
(d) collector-emitter voltage, VCE
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(e) common-emitter current gain, 
(f) common-base current gain, 
3. Assuming   50 for the circuit shown in Figure 3, determine:
(a) base current, IB
(b) collector current, IC
(c) emitter current, IE
(d) emitter-collector voltage, VEC
Figure 3
4. For the circuit shown in Figure 4, the transistor parameters are   100 ,
VBE (ON )  0.7V , V A   .
The circuit elements are VCC  VEE  10V , RB  100k , RE  10k , RC  10k ,
RL  1k and RS  1k .
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Figure 4
(a) Determine the small-signal transistor parameters:
(i) g m
(ii) r .
(iii) ro
(b) Determine the small-signal current gain, Ai 
io
.
ii
(c) Determine the small-signal voltage gain, Av 
vo
vs
(d) What is the input resistance, Ri ?
(e) Find the output resistance, Ro .
5. For the circuit shown in Figure 4, let   100 , VBE (ON )  0.7V , V A   ,
VCC  VEE  5V , RC  RL  2k , CB  0F and RS  0 .
Design RE and RB for a dc quiescent collector current of 1mA and a small-signal
voltage gain of 20.
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E. BJT Common-Collector Amplifiers (DC & AC Analysis)
1. For the circuit in Figure 1, the transistors parameters are   100 ,
VBE (ON )  0.7V and VA  125V . Assume RS  0 and RL  1k .
Figure 1
(a) Design a bias-stable circuit i.e. determine the values of RE , R1
and R2 such that I CQ  125mA and VCEQ  4V .
io
.
ii
(c) What is the output resistance looking back into the output
terminals, Ro ?
(b) Determine the small-signal current gain, Ai 
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2.
For the circuit shown in Figure 2, VCC  5V ,   120 ,
VBE (ON )  0.7V , VA  100V , RE  1k , R1  25k and R2  50k .
Figure 2
(a) Determine the small-signal voltage gain, Av 
vo
.
vs
(b) Determine the input resistance looking into the base of the
transistor, Rib
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