course title: electronic circuits

Electronic Circuits, Dept. of Elec. Eng., The Chinese University of Hong Kong, Prof. K.-L. Wu Lesson 1&2

Course Title: Electronic Circuits

Instructor: Prof. Ke-Li Wu

Students: Year 2009 CE Students

Major Text Book:Microelectronic Circuits, by Sedra/Smith, 5e

Teaching Notes: www.ee.cuhk.edu.hk/~klwu


Assessment Scheme :

Middle Term and Final Term , Close-book style

In-class quiz 10%

Assignment 0% (3 sets of answers will be provided.)

Consultation 20% (attendance, questions and understandings…)

Mid-term Exam 20%Final Term 50%


Contents to be discussed

Review of Basic Circuit Theory

Operational Amplifiers

Diodes & Its Applications (Rectifier Circuits, Limiting and Clamping Circuits,…)Bipolar Junction Transistors (BJTs) & Its Applications

(Amplifiers, Inverters, Simple Logic Circuits,…)

Field-Effect Transistors (MOSFET, CMOS, JFET,…)

Feedback Principle and Circuits

Analog Integrated Circuit Applications: Power Amplifiers, Multi-Stage Amplifiers, Oscillators andAnalog Integrated Circuits


Microelectronics is a cornerstone of:

Computing revolution

Communications revolution

Consumer electronics revolution

3 “C”s


Microelectronics: cornerstone of computing revolution

In last 30 years, computer performance per dollar has improved more than a million fold!


Microelectronics: cornerstone of communications revolution

In last 20 years, communication bandwidth through a single optical fiber has increased by ten thousand fold.

Metcalfe's law states that the value of a telecommunications network is proportional to the square of the number of users of the system (n2). First formulated by Robert Metcalfe in regard to Ethernet, Metcalfe's law explains many of the network effects of communication technologies and networks such as the Internet and World Wide Web.


Transistor size scaling

2 orders of magnitude reduction in transistor size in 30 years.

Transistor size scaling

Moore’s Law: doubling of transistor density every 1.5 years⇒ 4 orders of magnitude improvement in 30 years.


Transistor Cost

4 order of magnitude improvement in 30 years

Clock speed

3 order of magnitude reduction in 30 years


The Objectives of This Course

Understand the basic physics related to microelectronic circuits

Learn how to design a functional circuit using semiconductor components or ICs (Ops)

Master how to design amplifiers using BJT and FET transistors

Master how to analyze typical transistor circuits (small / large signal analysis)

Understand the basic functional blocks in an analog IC



(1) Passive elements

Resistor R (Ohm, volt/amp) : iv R=

Inductor L ( Henry (H), volt-second/amp) : dtdiv L=

+ -v

iR

i-+ v

L

Voltage across a resistor is proportional to the current passing through the resistor. The proportionality constant is called Resistance in Ohm and the voltage-current relation is called Ohm’s Law.

Voltage across an inductor is proportional to the time-variation (derivative) of the current passing through it. The proportionality constant is the inductance L in unit of Henry.

An inductor is a short circuit to DC current (v=0) and a open circuit at very high frequency (di/dt -> infinite). Another useful form of inductor is

∫∞−

=t

vdtL

ti 1)( It says an inductor may store energy from previous history.

1.1



Capacitor C Farad (F), coulomb/volt: dtdvi C=

+ -v

i

C

Current passing through a capacitor is proportional to the time-variation of the voltage across the capacitor. The proportionality constant is the capacitance C in unit of Farad.

ττ diC

tvtv

tCvidtq

t

t

)(1)0()(

is that )(

0∫

∫

+==

==∞−

Integrating in time, we have

A capacitor is an open circuit to DC voltage (I=0). It acts as a short circuit at very high frequency (dv/dt -> infinite)

It says a capacitor may also store energy from previous history.

1.1



(2) Basic Sources

+-

Rs

Vs(t)

0

Is(t) Rs oo

Independent Voltage Source

Independent Current Source

The output voltage of an independent voltage source is independent of the current delivered by the source. Therefore, the source resistance is very small.

The output current of an independent current source delivers arbitrary current independent of the voltage across it. Therefore, the source resistance is very large.

1.1


+-


Dependent Voltage Source

Dependent voltage source is a voltage source with its output voltage magnitude proportional to the voltage across another circuit element, or proportional to the current flowing throughanother circuit element.

Dependent Current Source

Dependent current source is a current source with its output current magnitude proportional to the voltage across another circuit element, or proportional to the current flowing throughanother circuit element.

+

-

B

E E

C

g VVr mB

C

E

Example: A voltage controlled current source can be used to present a simple circuit model for an npn bipolar silicon transistor

1.1



βi 1i 1

(b) CCCS

i 1 1Κi

(d) CCVS

1A vv1

+

-

(c) VCVS

g vm 1v 1

+

-

(a) VCCS

F igu r e 1 . 1 0 - C o n t r o l l e d S o u r c e s(a ) Vo l t a ge - c o n t r o l l e d c u r r e n t s o u r c e - (VC C S )(b )C u r r e n t - c o n t r o l l e d c u r r e n t s o u r c e - (C C C S )(c ) Vo l t a ge - c o n t r o l l e d vo l t a ge s o u r c e - (VC VS )

(d ) C u r r e n t - c o n t r o l l e d vo l t a ge s o u r c e - (C C VS ).

Dependent Sources

1.1



ii i

iD C

BA

0=−−+ DCBA iiii

(4) Kirchhoff’s Voltage Law (KVL)

The algebraic sum of the voltages around any closed path in a circuit is zero

0231 =−+ vvv

v2

B

v11-

+ v3 3+

-

+

A C-2

(3) Kirchhoff’s Current Law (KCL)

The algebraic sum of the currents entering any node is zero

1.1



-+

R R

Ri

1 2

nV

-+

R 1 R 2 RnV

i i i i1 2 n

Example: Applying KVL to the circuit on the right we have

0...21 =++++− niRiRiRv

or 0)...( 21 =++++− nRRRiv

Then we have )...( 21 nRRRiv

+++=

It says that the total resistance of series-connected resistors = sum of all resistance values.

Example: Applying KCL to the circuit on the right we have

0...21 =++++− niiiiAccording to Ohm’s law that nniRiRiRv ==== ...2211

)/1.../1/1/1(... 321321 nn RRRRviiiii ++++=++++=

We know the current supplied by the voltage source

iRRRRiRRRRv nn //...////// )/1.../1/1/1/(1 321321 =++++=That is

1.1


+- V R 1 R 2

ii1 i2


If we define conductance is the inverse of resistance, we can conclude that the equivalent conductance of resistors connected in parallel = sum of all conductance values. For special case n=2

PrincipleDivider Voltage 2

1

21

2

21

1

⎪⎪

⎭

⎪⎪

⎬

⎫

⎟⎟⎠

⎞⎜⎜⎝

⎛+

=

⎟⎟⎠

⎞⎜⎜⎝

⎛+

=

vRR

Rv

vRR

Rv

PrincipleDivider Current 2

1

21

1

21

2

⎪⎪

⎭

⎪⎪

⎬

⎫

⎟⎟⎠

⎞⎜⎜⎝

⎛+

=

⎟⎟⎠

⎞⎜⎜⎝

⎛+

=

iRR

Ri

iRR

Ri

V+

-

R 1

R 2

v1+ -

v2+

-

1.1


+

S1

-V

+-

1

+

S2

- +

-V

+-

2

+ -V

+-

+-S3

3

+

S4

-V

+-

4


In any linear network containing several sources, the steady state response of (the voltage across or the current through) any component or source may be calculated by adding algebraically all the individual steady state response (voltages or currents) caused by the separate independent sources acting alone, with all other independent sources disabled (voltage sources replaced by short circuits and all current sources replaced by open circuits.)

Note that dependent sources are in general active in every experiment. Superposition Theorem can also be applied by grouping independent sources collectively. For example, suppose there are three independent sources, we may find the response due to the first and second sources operating with the third inactive, and then add to this the response caused by the third source acting alone.

(5) Superposition Theorem

-+

- + - +

+ -

S1

S2 S3

S4

V=V1+V2+V3+V4

1.1



(6) Thevenin’s Theorem

An arbitrarily complicated linear circuit can be replaced by an independent voltage source Voc in series with the dead (inactive) load, where Voc is the open-circuit voltage produced by the circuit at the port being looked into and the dead load is the load seen at the port with all the internal sources disabled (voltage sources being shorted and current sources being opened).

All the dependent sources in the linear circuit have their control variables in the circuit. The linear circuit can contain resistors, inductors and capacitors.

Example: The source transformations and resistance combinations involved in simplifying network A are shown in order. The result, given in part d, is the Thevenin equivalent.

1.1



(7) Norton’s TheoremAn arbitrarily complicated linear circuit can be replaced by an independent current source Isc in parallel with the dead (inactive) load, where Isc is the short-circuit current produced by the circuit at the port being looked into and the dead load is the load seen at the port with all the internal sources disabled (voltage sources being shorted and current sources being opened).

Example: Find the Thevenin and Norton equivalent circuits for the network faced by the 1-kW.

We use superposition (activate one source at a time) to obtain Isc:

mAIscIscIscmAV

6.18.08.032

2)2(32

424

=+=+

++

=+=

The “dead load “ can be easily found as

R= 2k+3k = 5 kW

The resultant Norton equivalent circuits is shown in (c).

How about Thevenin equivalent circuit?

1.1



The Norton equivalent of an active resistive network is the Norton current source Iscin parallel with the Thevenin resistance Rth. There is an important relationship between the Thevenin and Norton equivalents of an active resistive network:

Example: Determine the Thevenin Equivalent of the circuit

To find Voc we note that Vx=Voc and that the dependent source current must pass through the 2-k resistor, since there is an open circuit to the right. Summing voltages around the outer loop:

ocxxx vvvv

===+⎟⎠⎞

⎜⎝⎛ −×+− 8 and 0

40001024 3

The original circuit can be replaced by (b), but it is not very simple and helpful. We therefore seek isc. Upon short-circuiting the output terminals in (a), it is apparent that Vx=0 and the dependent current source is zero.

Hence, isc=4/(5X1000)=0.8mA . Thus, Rth =Voc/ isc=8/(0.8X10-3)=10k ohms, and the acceptable Thevenin equivalent of (c) is obtained.

Relation Between Thevenin’s Theorem & Norton’s Theorem

Voc = Rth Isc

1.1

Electronic Circuits, Dept. of Elec. Eng., The Chinese University of Hong Kong, Prof. K.-L. Wu Lesson 1&2+

-VV

+

-R L


Single-time-constant circuits are those circuits that are composed of, or can be reduced to, one reactive component (inductance or capacitance) and one resistive component. An STC circuit formed of an inductance L and a resistance R has a time constant τ=L/R. The time constant τ of an STC circuit composed of a capacitance C and a R is given by τ =CR.

(8) Single-Time-Constant (STC) Circuits

The time constant t measures the rate of signal decay. It is the time required for the response curve to drop to zero if it decays at a constant rate which is equal to its initial rate of decay. In fact, in one time constant the response has dropped to 36.8 percent of its initial value.

1.1



Example:

In many instances it will be important to be able to evaluate rapidly the time constant τ of a given STC circuit:

(1) reducing the excitation to zero and assemble all the reactive component into one reactive component;

(2) “grab hold” of the two terminals of the reactive component (L or C) and find the equivalent resistance Req seen by the component; and

(3) calculate the time constant either by L/Reqor CRreq.

1.1



STC circuits can be classified into two categories, low-pass (LP) and high-pass (HP) types, with each of the two categories displaying distinctly different signal responses. The simplest way to judge is to test the circuit response at ω=0 and ω =∞ . At ω =0 capacitors should be replaced by open circuit and inductors should be replaced by short circuit. Alternatively, at ω=∞ we replace capacitors by short circuits and inductors by open circuits.

Classification of STC circuits

STC circuits of the low-pass type. STC circuits of the high-pass type.

1.1

course title: electronic circuits

Documents