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Chapter 1 Semiconductor Materials and Diodes 61
*1.36 The reverse-saturation current of a silicon pn junction diode at T = 300 K
is IS = 10−12 A. Determine the temperature range over which IS varies
from 0.5 × 10−12 A to 50 × 10−12 A.
*1.37 A silicon pn junction diode has an applied forward-bias voltage of 0.6 V.
Determine the ratio of current at 100 C to that at −55 C.
Section 1.3 DC Diode Analysis
1.38 A pn junction diode is in series with a 1 M resistor and a 2.8 V power
supply. The reverse-saturation current of the diode is IS = 5 × 10−11 A.
(a) Determine the diode current and voltage if the diode is forward biased.
(b) Repeat part (a) if the diode is reverse biased.
1.39 Consider the diode circuit shown in Figure P1.39. The diode reverse-
saturation current is IS = 10−12 A. Determine the diode current ID and
diode voltage VD .
*1.40 The diode in the circuit shown in Figure P1.40 has a reverse-saturation cur-
rent of IS = 5 × 10−13 A. Determine the diode voltage and current.
1.41 (a) For the circuit shown in Figure P1.41(a), determine ID1,ID2,VD1,and VD2
for (i) IS1 = IS2 = 10−13 A and (ii) IS1 = 5 × 10−14 A, IS2 = 5 × 10−13 A.
(b) Repeat part (a) for the circuit shown in Figure P1.41(b).
1.42 (a) The reverse-saturation current of each diode in the circuit shown in Fig-
ure P1.42 is IS = 6 × 10−14 A. Determine the input voltage VI required to
produce an output voltage of VO = 0.635 V. (b) Repeat part (a) if the 1 k
resistor is changed to R = 500 .
1.43 (a) Consider the circuit shown in Figure P1.40. The value of R1 is reduced
to R1 = 10 k and the cut-in voltage of the diode is Vγ = 0.7 V. Determine
ID and VD . (b) Repeat part (a) if R1 = 50 k.
1.44 Consider the circuit shown in Figure P1.44. Determine the diode current ID
and diode voltage VD for (a) Vγ = 0.6 V and (b) Vγ = 0.7 V.
1.45 The diode cut-in voltage is Vγ = 0.7 V for the circuits shown in Figure
P1.45. Plot VO and ID versus II over the range 0 ≤ II ≤ 2 mA for the cir-
cuit shown in (a) Figure P1.45(a), (b) Figure P1.45(b), and (c) Figure
P1.45(c).
Figure P1.39
Figure P1.41
+
– ID
VD
+5 V
–5 V
20 kΩ
Figure P1.40
+
–
+
–
VPS =
1.2 V
ID
VD
R1 = 50 kΩ
R2 =
30 kΩ
(a)
+
D1
D1
VD1
+
VD1
ID1
ID1
Ii =
1 mA
Ii =
1 mAID2
+D2 V
D2
+V
D2
(b)
ID2
D2
–
– – –
Figure P1.42
+
–
VI
VO
1 kΩ
Figure P1.44
+–
ID
VD
+5 V
2 kΩ
2 kΩ2 kΩ
3 kΩ
Cut-in = trun-onIn a straight-lineapproximation
Asuma n=1 y VT = 25mV, a menos que se indique lo contrario
62 Part 1 Semiconductor Devices and Basic Applications
–
–
+
+
D1
D1
D2
VO
ID
ID2
II
RF
1 kΩ
–
+
VB = 1 V
VO
ID
IIR1 =
1 kΩ
RF =
1 kΩ
–
+
VO
ID1
II
(a)
(b)
(c)
Figure P1.46
VPS+–
I1
I2 IDR2
R1
Figure P1.47
IVO
+5 V
20 kΩ
IVO
+2 V
5 kΩ
I
VO
+5 V
–5 V
20 kΩ
20 kΩ
–8 V
20 kΩ
IVO
+5 V
–5 V
20 kΩ
(a) (b) (c) (d)
Figure P1.49
+
–
++
–
–
5 V
I
V
VD
R = 4.7 kΩ
*1.46 The cut-in voltage of the diode shown in the circuit in Figure P1.46 is
Vγ = 0.7 V. The diode is to remain biased “on” for a power supply voltage
in the range 5 ≤ VP S ≤ 10 V. The minimum diode current is to be
ID(min) = 2 mA. The maximum power dissipated in the diode is to be no
more than 10 mW. Determine appropriate values of R1 and R2.
1.47 Find I and VO in each circuit shown in Figure P1.47 if (i) Vγ = 0.7 V and
(ii) Vγ = 0.6 V.
*1.48 Repeat Problem 1.47 if the reverse-saturation current for each diode is
IS = 5 × 10−14 A. What is the voltage across each diode?
1.49 (a) In the circuit shown in Figure P1.49, find the diode voltage VD and the
supply voltage V such that the current is ID = 0.4 mA. Assume the diode
cut-in voltage is Vγ = 0.7 V. (b) Using the results of part (a), determine the
power dissipated in the diode.
Figure P1.45
1.50 Assume each diode in the circuit shown in Figure P1.50 has a cut-in voltage
of Vγ = 0.65 V. (a) The input voltage is VI = 5 V. Determine the value of
R1 required such that ID1 is one-half the value of ID2. What are the values
of ID1 and ID2? (b) If VI = 8 V and R1 = 2 k, determine ID1 and ID2.
Chapter 1 Semiconductor Materials and Diodes 63
Figure P1.50
+
–
VI
VO
R2 = 1 kΩ
ID2
ID1
R1
Section 1.4 Small-Signal Diode Analysis
1.51 (a) Consider a pn junction diode biased at IDQ = 1 mA. A sinusoidal volt-
age is superimposed on VDQ such that the peak-to-peak sinusoidal current
is 0.05IDQ . Find the value of the applied peak-to-peak sinusoidal voltage.
(b) Repeat part (a) if IDQ = 0.1 mA.
1.52 Determine the small-signal diffusion resistance rd for a diode biased at
(a) ID = 26 μA, (b) ID = 260 μA, and (c) ID = 2.6 mA.
*1.53 The diode in the circuit shown in Figure P1.53 is biased with a constant cur-
rent source I. A sinusoidal signal vs is coupled through RS and C. Assume
that C is large so that it acts as a short circuit to the signal. (a) Show that the
sinusoidal component of the diode voltage is given by
vo = vs
(
VT
VT + I RS
)
(b) If RS = 260 , find vo/vs , for I = 1 mA, I = 0.1 mA, and
I = 0.01 mA.
Section 1.5 Other Types of Diodes
1.54 The forward-bias currents in a pn junction diode and a Schottky diode are
0.72 mA. The reverse-saturation currents are IS = 5 × 10−13 A and
IS = 5 × 10−8 A, respectively. Determine the forward-bias voltage across
each diode.
1.55 A pn junction diode and a Schottky diode have equal cross-sectional areas
and have forward-bias currents of 0.5 mA. The reverse-saturation current of
the Schottky diode is IS = 5 × 10−7 A. The difference in forward-bias volt-
ages between the two diodes is 0.30 V. Determine the reverse-saturation
current of the pn junction diode.
1.56 The reverse-saturation currents of a Schottky diode and a pn junction
diode are IS = 5 × 10−8 A and 10−12 A, respectively. (a) The diodes are
connected in parallel and the parallel combination is driven by a constant
current of 0.5 mA. (i) Determine the current in each diode. (ii) Determine
the voltage across each diode. (b) Repeat part (a) for the diodes con-
nected in series, with a voltage of 0.90 V connected across the series
combination.
Figure P1.53
+
–
vovs
RS C
I
V+
+–
