Electronic Circuits: Syllabus
• Instructor: Dr. Tamer ElBatt
• Teaching Assistant: Eng. Ahmed Gad
• Textbook:
- A. Sedra and K. Smith, “Microelectronic Circuits, 5th Ed.,” Oxford University
Press, 2004.
- J. Millman and A. Grabl, “Microelectronics, 2nd Ed.,” Mc-Graw Hill, 1987
• Contents:
- Revision: Circuits (R, L, C) + Diodes
- Introduction to Transistors
- MOSFET Device Structure and Physical Operation
- MOSFET Current-Voltage Characteristics
- MOSFET Circuits at DC
- The MOSFET as an Amplifier and as a Switch
- Biasing in MOS Amplifier Circuits
- Small-Signal Operation and Models
- Single-Stage Amplifiers
Microelectronic Circuits - Fifth Edition
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Diodes: Two-terminal Devices
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3.1 The Ideal Diode
• A diode is a passive 2-terminal device; hence it provides no gain
• Applications: Switch, Clamping circuit, Rectifier
Figure 3.1 The ideal diode: (a) diode circuit symbol; (b) i–v characteristic; (c) equivalent circuit in the reverse direction;
(d) equivalent circuit in the forward direction.
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Forward and Reverse Bias
Forward Bias
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Reverse Bias
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Application: Rectifier
DC = ??
Figure 3.3 (a) Rectifier circuit. (b) Input waveform. (c) Equivalent circuit when vI ≥ 0. (d) Equivalent circuit when vI 0.
(e) Output waveform.
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Exercise 1:
Q1: Sketch the waveform of vD.
Q2: Find the peak value of iD and the DC component of vo when peak vl = 10 V and
R = 1 kΩ
Figure E3.1
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Simple Application: Diode Logic Gates
OR Gate
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A+D Gate
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3.2 The i-v Characteristic of a silicon junction diode
Figure 3.7 The i–v characteristic of a silicon junction diode.
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The i-v Characteristic of a silicon junction diode
cont.
• Forward Bias:
i = Is (ev/nVT -1)
where Is: saturation current
VT = kT/q
(Thermal Voltage)
n = 1 or 2
Figure 3.8 The diode i–v relationship with some scales expanded and others compressed in order to reveal details.
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Temperature Effect
Figure 3.9 Illustrating the temperature dependence of the diode forward characteristic. At a constant current, the voltage
drop decreases by approximately 2 mV for every 1°C increase in temperature.
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3.3 Modeling the Diode Forward Characteristics
• Several models exist
- The Exponential Model
- The Piecewise-Linear Model
- The Constant-Voltage-Drop
Model
• The Exponential Model
- Graphical Analysis
- Iterative Analysis
Figure 3.10 A simple circuit used to illustrate the analysis of circuits in which the diode is forward conducting.
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Graphical Analysis
Figure 3.11 Graphical analysis of the circuit in Fig. 3.10 using the exponential diode model.
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Iterative Analysis
Example:
VDD = 5v
R = 1 KΩ
Diode current = 1mA at voltage = 0.7 v
and its voltage drops by 0.1 for every decade
change in current
Determine ID and VD
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The Piece-wise Linear Model
Figure 3.12 Approximating the diode forward characteristic with two straight lines: the piecewise-linear model.
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The Piece-wise Linear Model cont.
Figure 3.13 Piecewise-linear model of the diode forward characteristic and its equivalent circuit representation.
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The Piece-wise Linear Model cont.
Figure 3.14 The circuit of Fig. 3.10 with the diode replaced with its piecewise-linear model of Fig. 3.13.
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The 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.
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The Constant-Voltage-Drop Model cont.
Figure 3.16 The constant-voltage-drop model of the diode forward characteristics and its equivalent-circuit representation.
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3.3.8 The Small-Signal Model
• It can be shown that for small AC signals,
the diode is modeled as a resistor (rd),
rd = nVT/ID
Figure 3.17 Development of the diode small-signal model. Note that the numerical values shown are for a diode with n = 2.
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3.4 The Breakdown Region — Zener Diode
according to specs
Important Application: voltage regulators
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Zener Diode Model
• rz (incremental resistance): given by
the inverse of the slope of the almostLinear i-v curve at point Q.
• rz ranges from few ohms to few tens of
ohms
• The lower the rz the more ideal the
Zener diode becomes in the design of
voltage regulators
VZ = VZ0 + rz IZ
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