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Problem 1
(20 pts total)
Parts (a) thru (f)
of this problem concern two npn silicon bipolar junction transistors, A
and B. All of the dimensions of these two devices, and the magnitudes of all of the
doping levels in these two devices are identical, except that the base width, w
B
, of
Transistor A is twice that of Transistor B.
(a)
Which transistor, if either, has the larger dc current gain,
b
F
?
Explain your
answer and estimate the ratio of the two
b
F
's.
o
Transistor A
o
Transistor B
o
neither, because
Ratio,
b
F,A
/
b
F,B
=
(b)
Which transistor, if either, has the larger emitter-base junction saturation current,
I
ES
? Explain your answer and estimate the ratio of the two I
ES
's.
o
Transistor A
o
Transistor B
o
neither, because
Ratio, I
ES,A
/I
ES,B
=
(c)
With the base-collector junctions of both transistors reverse biased with the same
values of base-collector junction voltage, V
BC
, which transistor, if either, has the
largest small-signal base-collector junction capacitance, C
µ
?
Explain your answer
and estimate the ratio of the two C
µ
's.
o
Transistor A
o
Transistor B
o
neither, because
Ratio, C
µ,A
/C
µ,B
=
(d)
With both transistors biased at the same quiescent current level, I
C
, which
transistor, if either, has the largest small-signal transconductance, g
m
? Explain your
answer and estimate the ratio of the two g
m
's.
o
Transistor A
o
Transistor B
o
neither, because
Ratio, g
m,A
/g
m,B
=
Problem 1 continues on the next page