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ES 330 Electronics II Homework # 4
(Fall 2016 – Due Monday, October 3, 2016)
Problem 1 (25 points)
An NMOS transistor is connected in the bias circuit shown below. It is biased at VG = 5
volts and RS = 3 k connected to ground. The transistor parameters are Vt = 1 volt and
kn = 2 mA/V2.
(a) What is the bias current ID (= IS)?.
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(b) Now suppose we switch transistors where the new transistor has a 50% higher
value for kn. By what percentage does drain current ID change as a result?
Problem 2 (25 points)
Consider the circuit shown below for an NMOS transistor having a Vt = 1 volt and with kn
= 4 mA/V2. Let VDD = 5 volts and VSS = - 5 volts.
Design for a DC bias drain current of 0.5 mA and for the largest possible voltage gain
(that means for the largest value of RD) consistent with a 2-V peak-to-peak swing at the
drain node. Simplifying assumption: Take the AC signal voltage on the source node to
be essentially zero (i.e., meaning it remains at the DC terminal voltage you caluclated
when determining VGS). Thus, the minimum drain node voltage vDrain will be 1 volt in
magnitude in meeting the 2-V peak-to-peak output voltage swing requirement.
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What is VGS? What values do you calculate for RD and RS?
Problem 3 (25 points)
The transistor used in the circuit shown below is to be biased at a collector current IC =
1 mA. Whereas the current gain  of the transistor is “nominally” equal to 100, this type
of BJT actually can range from  = 50 (minimum) to  = 150 (maximum). You are told
that VCC = + 3 volts and RC = 2 k.
(a) Find the required RB value to achieve IC = 1 mA for a “nominal transistor.”
(b) What is the expected range of IC and VCE values from  = 50 to  = 150?
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(c) Comment on the efficacy or viability of this design.
Problem 4 (25 points)
You are given a bipolar transistor amplifier which is drawn schematically below (See
Figure 7.54 in Sedra/Smith):
Using VCC = + 3 volts, design the circuit to have a collector current IC = 0.5 mA. The
“nominal”  of the transistor selected is 100. With  = 100, find the value of resistor RC
giving VCE = VCE(sat) + 1 volt = 0.3 V + 1 V = 1.3 V. (Note: An often assumed value for
VCE(sat) is 0.3 V.)
(a) Using “nominal” parameter values for the transistor, what is the base resistor RB
value?
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(b) If the resistor RB you pull out of the bin is low in value by 5% (remember resistors
have tolerance ranges), how much does the emitter current IE change from what you
calculated in part (a)?