Name ______________________________
ES 330 Electronics II Homework # 3
(Fall 2016 – Due Monday, September 26, 2016)
Problem 1 (25 points)
A common-emitter amplifier uses a BJT with current gain  = 100 when biased at IC =
0.5 mA. It has a collector resistance of RC = 10 k.
(a) Calculate Rin, Ro and AVO.
(b) The amplifier is driven with a signal source vsig has resistance Rsig = 10 k and has
a load resistance RL = 10 k connected to the output terminal. Calculate both AV and
GV .
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(d) Continuing on with part (c) above, what peak-to-peak output voltage appears across
the load resistor RL?
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(c) If the peak-to-peak voltage of a sinusoidal signal across the base-emitter junction is
limited to 5 mV, what signal source voltage vsig is allowed?
Problem 2 (15 points)
A MOSFET connected in a common-source configuration has transconductance gm = 5
mA/V (mS). When a source resistor RS is connected to the source terminal, the
effective transconductance g’m is reduced to 2 mA/V (mS). Estimate the value of this
resistor RS. [Note: Source resistor RS is not bypassed with a capacitor.]
Problem 3 (20 points)
A bipolar common-gate (CG) amplifier is operated with a load resistance of RL = 10 k,
a collector resistance of RC = 10 k and a signal source resistance of Rsig = 50 .
(a) What collector current IC will give an input resistance of Rin = 50 ?
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(b) What is the resulting overall voltage gain assuming   1 (i.e., unity)?
(c) For the common-base amplifier shown schematically below, Find the output voltage
vo if Rsig >> re and   1. [Remember that re is the emitter resistance (See page 404 of
Sedra & Smith).]
Problem 4 (20 points)
An emitter follower (i.e., common-collector) stage is operating at a collector current bias
of 0.5 mA and is used to connect a 10 k source resistance to a 1k load resistance.
Assume the nominal current gain  of the transistor to be 100.
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(a) What output resistance Rout is obtained at the emitter follower’s output and what is
its overall voltage gain Gv?
(b) If  is reduced to 50 (from 100), find the corresponding Rout and Gv values.
Problem 5 (20 points)
Two identical common-emitter gain stages are cascaded together. The collector
terminal resistance is identical for both stages, namely, RC1 = RC2 = 10 k. The first
stage is driven from voltage source vsig having source resistance Rsig = 10 k. A load
resistance of RL = 10 k is connected to the collector of the second stage. Both BJT
transistors (i.e., both stages) are biased at IC = 0.25 mA and both have a current gain
 = 100.
(a) Sketch the small-signal equilvalent circuit for the overall amplifier. Label the
important voltages.
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(b) Calculate the overall voltage gain, v02/vsig.