ECE 250 Homework #5
Due 4/22/02
Problem 1:
a) Bias the circuit below to allow a ± 4 volt swing. Design for IC = 1 mA, and use VBE = 0.7 V and ß=150 in your design
calculations.
Vcc
+
-
Vcc
+
R2
Q1
+
R1
+
Rc
b) Verify you bias using PSpice. Use a part called QbreakN and change model parameter BF to 150. See Section 3.E of the
PSpice manual for an example.
c) By hand, calculate IC and VCE for your bias using ß=300. What is the maximum possible symmetric ± voltage swing
allowed by this bias?
d) By hand, calculate IC and VCE for your bias using ß=75. What is the maximum possible symmetric ± voltage swing
allowed by this bias?
e) Create a table with your results from parts a through d. What do you conclude about the stability of this bias due to
variations in ß.
Problem 2:
Vcc
+
-
Vcc
DC = 15
+
R2
24k
+
Rc
+
R3
180
Q1
+
R1
270k
When calculating the maximum swing, assume that VE does not change.
a) By hand, calculate IC and VCE for this bias using ß=300. What is the maximum possible symmetric ± voltage swing
allowed by this bias?
b) By hand, calculate IC and VCE for this bias using ß=75. What is the maximum possible symmetric ± voltage swing allowed
by this bias?
c) Create a table with your results from parts a and b. What do you conclude about the stability of this bias due to variations
in ß.
