Homework#5 for Microelectronics (I)
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Sections：5.5，5.6，5.7
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Deadline：1 月 3 日(四)課堂上繳交。　provided by 陳旻珓助教
5.82
The pnp transistor in the circuit of Fig. 5.82 has β = 50. Find the
value for RC to obtain VC = 4 V. What happens if the transistor
is replaced with another having β = 100?
Fig. 5.82
5.97
A circuit that can provide a very large voltage gain for a
high-resistance load is show in Fig. 5.97. Find the value of I and
RB to bias the BJT at IC = 2 mA and VC = 1.5 V. Let β = 90.
Fig. 5.97
5.98
The circuit in Fig. 5.98 provides a constant current IO as long as the
circuit to which the collector is connected maintains the BJT in the
active mode. Show that
V [R / (R + R2 )] − VBE
I O = α CC 2 1
RE + (R1 R2 ) / (β + 1)
Fig. 5.98
5.105
A pnp BJT is biased to operate at IC = 1.0 mA. What is the associated value of gm? If β = 50,
what is the value of the small-signal resistance seen looking into the emitter (re)? Into the base
(rπ)? If the collector is connected to a 3-kΩ load, with a signal of 2-mV peak applied between
base and emitter, what output signal voltage results?
5.112
The transistor amplifier in Fig. 5.112(a) is biased with a current source I and has a very high
β. Find the dc voltage at the collector, VC. Also, find the value of gm. Replace the transistor
with the simplified hybrid-π model of Fig. 5.112(b) (note that the dc current source I should
be replaced with an open circuit). Hence, find the voltage gain vc/vi.
Fig. 5.112 (a)
Fig. 5.112 (b)
5.115
For the circuit shown in Fig. 5.115, draw a
complete small-signal equivalent circuit
utilizing an appropriate T model for the BJT
(use α = 0.99). Your circuit should show the
values of all components, including the
model parameters. What is the input
resistance Rin? Calculate the overall voltage
gain (vo/vsig).
Fig 5.115
5.116
In the circuit shown in Fig. 5.116, the
transistor has a β of 200. What is the dc
voltage at the collector? Find the input
resistance Rib and Rin and the overall voltage
gain (vo/vsig). For an output signal of ±0.4 V,
what values of vsig and vb are required?
Fig. 5.116
5.122
When a collector of a transistor is connected to its base, the transistor still operates in the
active region because the collector-base junction is still in effect reverse biased. Use the
simplified hybrid-π model to find the incremental resistance of the resulting two-terminal
device.
5.124
The transistor in the circuit shon in Fig. 5.124(a) is biased to operate in the active mode.
Assuming that β is very large, find the collector bias current IC. Replace the transistor with
the small-signal equivalent circuit model of Fig. 5.124(b). Analyze the resulting amplifier
equivalent circuit to chow that
vo1
RE
=
vi RE + re
vo 2 − αRC
=
vi
RE + re
Find the values of these voltage gain (for α = 1). Now if the terminal labeled vo1 is connected
to ground, what does voltage gain vo2/vi become?
Fig. 5.124(a)
Fig. 5.124(b)
5.128
A common-emitter amplifier of the type shown in Fig. 5.128 is biased to operate at IC = 0.2 mA
and has a collector resistance RC = 10 kΩ. The transistor has β = 100 and a large VA. The
signal source is directly coupled to the base, and CC1 and RB are eliminated. Find Rin, the
voltage gain Avo, and Ro. Use these results to determine the overall voltage gain when a 10-kΩ
load resistor is connected to the collector and the source resistance Rsig = 10 kΩ.
Fig. 5.128
5.130
For the common-emitter amplifier shown in
Fig. 5.130, let VCC = 9 V, R1 = 27 kΩ, R2 = 15
kΩ, RE = 1.2 kΩ, and RC = 2 kΩ. The
transistor has β = 100 and VA = 100 V.
Calculate the dc bias current IE. If the
amplifier operates between a source for
which Rsig = 1 kΩ and a load of 3 kΩ, replace
the transistor with its hybrid-π model, and
find the value of Rin, the voltage gain vo/vsig,
and the current gain io/ii.
Fig. 5.130
5.137
The BJT in the circuit of Fig. 5.137 has β = 100.
(a) Find the dc collector current and the dc
voltage at the collector.
(b) Replacing the transistor by its T model,
draw the small-signal equivalent circuit of the
amplifier. Analyze the resulting circuit to
determine the voltage gain vo/vi.
Fig. 5.137
5.139
Consider the CB amplifier of Fig. 5.139
with RL = 2 kΩ, RC = 3 kΩ, VCC = 5 V, and
Rsig = 100 Ω. To what value must I be set in
order that the input resistance at E is equal
to that of the source (i.e., 100 Ω)? What is
the resulting voltage gain from the source to
the load? Assume β is infinite.
Fig. 5.139
5.144
For the emitter follower in Fig. 5.144, the signal
source is directly coupled to the transistor base. If
the dc component of vsig is zero, find the dc emitter
current. Assume β = 100. Neglecting ro, find Rin,
the voltage gain vo/vsig, the current gain io/ii, and
the output resistance Rout.
Fig. 5.144