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Name ______________________________
ES 330 Electronics II Homework # 6
(Fall 2016 – Due Monday, October 26, 2016)
Problem 1 (18 points)
You are given a common-emitter BJT and a common-source MOSFET (n-channel).
Fill in the table below. Assume the BJT to be in the forward active mode and the nchannel MOSFET to be in the saturation region of operation. [The purpose of this
exercise is to compare BJT and MOSFET parameters. Remember that A0 is the voltage
gain without a separate load resistance RL.]
NPN BJT Cell
 = 100, VA = 100 V and
VTH = kT/q = 25 millivolt
Bias Current is
IC = 0.1 mA
IC = 1 mA
N-channel MOSFET Cell
nCOX = 200 A/V2, (W/L) = 40
and VA = 10 V
ID = 0.1 mA
ID = 1 mA
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gm (mA/V)
r0 (k)
A0 (V/V)
RIN (k)
Problem 2 (20 points)
You are given the circuit drawn below. It is fabricated in a CMOS process for which
nCOX = 2pCOX = 200 A/V2, V’An = |V’Ap| = 20 V/m, Vtn = -Vtp = 0.5 volt and VDD = 2.5
volts. The two transitor types have L = 0.5 m and are to be operated at |VOV | = 0.3
volt. Find the required gate node voltage VG, and the (W/L) ratios for both the n-channel
and p-channel MOSFETs to meet the required conditions.
VG = _________ volts
(W/L)n = ________
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(W/L)p = ________
Problem 3 (12 points)
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The schematic below shows a “cascoded” n-channel MOSFET pair used to achieve
higher output resistance ROUT. We want to achieve ROUT = 200 k using this cascode
pair operating at drain current ID = 0.5 mA. Assuming identical geometrical device
layouts so that (W/L)1 = (W/L)2 = (W/L), nCOX = 0.1 mA/volt2, and VA = 10 volts; what is
the required gate width-to-length ratio (W/L) for this circuit?
Problem 4 (20 points)
George Wilson (was an IC designer at Tektronix who lead a highly productive bipolar IC
design group that made many contributions to Tektronix oscilloscope products in the
1980’s and 1990’s) proposed an improved current mirror over the basic current mirror
using only two BJT transistors. What is now known as the “Wilson current mirror” adds
transistor Q3 to the basic current mirror as is illustrated in the schematic below.
(a) Derive an expression for the ratio of (IREF/IC).
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(b) Compare the (IREF/IC) ratio for the Wilson current mirror to the (IREF/IC) ratio of the
basic current mirror, that is, a current mirror without transistor Q3. What improvement in
(IREF/IC) does the Wilson current mirror over the basic current mirror?
Problem 5 (15 points)
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Starting with the basic current mirror (with transistor Q1 and Q2 only), we place a small
resistance RE in series with the emitter of transistor Q2 as shown in the schematic
below. For this problem assume you can neglect base currents (that is, assume infinite
), the npn transistor saturation current IS is 1  10-15 A, and both transistors are
identical. If resistor RE = 0, then IREF = IC. But the presence of RE reduces IC. Let IREF =
1 mA. If IC = 0.75 IREF, what is the value of RE?
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Problem 6 (15 points)
Current mirrors are often used for DC biasing in integrated circuits. But they can also
be used as signal-current amplifiers. Consider the circuit schematic below for an
example of a signal-current amplifier. Transistor Q1 acts as the input current source
(driven by voltage VIN). Derive an expression for the small-signal current gain (I0 /ID1)
and the small-signal voltage gain (vout /vin) with (W2 /L) and (W3 /L) being the primary
variable parameters?