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전자회로I
셋째주 2강
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일2 pages
3.3) Modeling The Diode Forward CharacteristicThe Exponential Model
Figure 3.10 A simple circuit used to illustrate the analysis of circuits in which the diode is forward conducting.
V / V (3.6)D TnD SI I e
V V (3.7)DD D
DIR
Kirchhoff loop equation, resulting in
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일3 pages
3.3) Modeling The Diode Forward CharacteristicGraphical Analysis Using the Exponential Model
Figure 3.11 Graphical analysis of the circuit in Fig. 3.10 using the exponential diode model.
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일4 pages
3.3) Modeling The Diode Forward CharacteristicThe Piecewise-Linear Model
Figure 3.12 Approximating the diode forward characteristic with two straight lines: the piecewise-linear model.
0
0 0
0, V( V ) / , V (3.8)
D D D
D D D D D D
ii r
VD0 is the intercept of line B on the voltageaxis and rD is the inverse of the slope ofline B.
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일5 pages
3.3) Modeling The Diode Forward CharacteristicThe Piecewise-Linear Model
Figure 3.13 Piecewise-linear model of the diode forward characteristic and its equivalent circuit representation.
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일6 pages
3.3) Modeling The Diode Forward CharacteristicThe Piecewise-Linear Model
Figure 3.10 A simple circuit used to illustrate the analysis
of circuits in which the diode is forward conducting.Figure 3.14 The circuit of Fig. 3.10 with the diode replaced with
its piecewise-linear model of Fig. 3.13.
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일7 pages
3.3) Modeling The Diode Forward CharacteristicThe Constant-Voltage-Drop Model
Figure 3.15 Development of the constant-voltage-drop model of the diode forward characteristics. A vertical straight line (B) is used to approximate the fast-rising exponential. Observe that this simple model predicts VD to within 0.1 V over the current range of 0.1 mA to 10 mA.
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일8 pages
3.3) Modeling The Diode Forward CharacteristicThe Constant-Voltage-Drop Model
Figure 3.16 The constant-voltage-drop model of the diode forward characteristics and its equivalent-circuit representation.
V 0.7
5 0.7 = 4.3 mA1
DDDI
R
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일9 pages
3.3) Modeling The Diode Forward CharacteristicThe Small-Signal Model
Figure 3.17 Development of the diode small-signal model. Note that the numerical values shown are for a diode with n = 2.
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일10 pages
3.3) Modeling The Diode Forward CharacteristicThe Small-Signal Model In the absence of the signal vd(t) the diode voltage is equal to VD, and
correspondingly, the diode will conduct a dc current ID given byV / V (3.9)D Tn
D SI I e
(t) V + (t) (3.10)D D d
/ V( ) (3.11)D TnD Si t I e
(V ) / V( ) D d TnD Si t I e
/ VV / V( ) d TD T nnD Si t I e e
When the signal vd(t) is applied, the total instantaneous diode voltagevd(t) will be given by
Correspondingly, the total instantaneous diode current iD(t) will be
Substituting for vD from Eq. (3.10) gives
which can be rewritten
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일11 pages
3.3) Modeling The Diode Forward CharacteristicThe Small-Signal Model
/ V( ) (3.12)d TnD Di t I e
Using Eq. (3.9) we obtain
if the amplitude of the signal vd(t) is kept sufficiently small such that
(3.13) 1T
d
nVv
then we may expand the exponential of Eq. (3.12) in a series and truncatethe series after the first two terms to obtain the approximate expression
(3.14) 1)(
T
dDD nV
vIti
• This is the small-signal approximation.
Chapter 3
Lecture Homepage : http://signal.korea.ac.kr
Signal Processing Lab., http://signal.korea.ac.krDept. of Elec. and Info. Engr., Korea Univ.
2016년 6월 27일12 pages
3.3) Modeling The Diode Forward CharacteristicThe Small-Signal Model From Eq. (3.14) we have
( ) + (3.15)VD
D D dT
Ii t I
n
+ (3.16)D D di I i
(3.17)VD
d dT
Ii
n
V (3.18)T
dD
nr
I
superimposed on the dc current ID, we have a signal current component directly proportional to the signal voltage vd. That is,
the diode small-signal resistance, or incremental resistance, rd,
1 (3.19)D D
Dd
D i I
ir