Engineering Tripos Part IA

Paper 3 - Linear Circuits and Devices

Resource Material

Welcome to the resource page for Part IA Paper 3, Linear Circuits and Devices, last updated: 27 March 2008

This page is under continuous development and will be updated regularly during the course.
Suggestions for further inclusions are welcome. 
If you have found some interesting and relevant material on the web, please let me know.


Some of the pre-lecture movie excerpts being shown during the term are from Local Heroes series  (Radar, Television).  Others are from the series: Secret Life of the Radio, Secret Life of the Television (and others), by Tim Hunkin, a graduate of CUED and Caius College.  You can find out more about Tim at:


Lecture Notes

Printed copies of lecture notes are distributed at the start of the relevant lectures.  All surplus copies are held in the pigeon holes in the Inglis Building, close to the vending machines.  

Electronic copies of the notes are available here.  Note that they are freely accessible from browsers in the domain.  From anywhere outside this domain you need your CUED PIN

These links point to files in portable document format (PDF).  Most browsers have the facility for displaying these, but if yours does not you can click the 'Get Acrobat Reader' link below to obtain the necessary utility.

Links for Acrobat versions & status

Status of paper copies

Reason for any update
Lectures 1 to 4  for 2007-8   Issued on Thu 4th October  
Lectures 5 to 8  for 2007-8    Issued on Thu 18th October    
Lectures 9 to 12  for 2007-8    Issued on Thu 1st November  
Lectures 13 to 16  for 2007-8   Issued on Thu 15th November
Lectures 17 to 18  for 2007-8   Issued on January 18th 2008  

The versions published here are generally the same as those being issued as paper handouts.  However, those flagged as animupdate.gif (1754 bytes) have had minor corrections or other  amendments implemented.

For historians, copies of earlier notes are available as follows:

Lecture notes issued in 2001-2 (PDF): 1 to 4  |  5 to 8  |  9 to 12  |  13 to 16  |  17 to 18  |
Lecture notes issued in 2002-3 (PDF): 1 to 4  |  5 to 8  |  9 to 12  |  13 to 16  |  17 to 18  |
Lecture notes issued in 2003-4 (PDF): 1 to 4  |  5 to 8  |  9 to 12  |  13 to 16  |  17 to 18  |
Lecture notes issued in 2004-5 (PDF): 1 to 4  |  5 to 8  |  9 to 12  |  13 to 16  |  17 to 18  |
Lecture notes issued in 2005-6 (PDF): 1 to 4  |  5 to 8  |  9 to 12  |  13 to 16  |  17 to 18  |
Lecture notes issued in 2006-7 (PDF): 1 to 4  |  5 to 8  |  9 to 12  |  13 to 16  |  17 to 18  |

More detailed comments on lecture notes:

Lecture notes issued in 2007-8 (PDF): 2 to 8 9 to 16  |  17 to 18  |

Examples Sheets - corrections/additions/hints

Paper copies of Examples Sheets are issued on a self-service basis, as per the schedule published by the Teaching Office.  You can pick them up from boxes adjacent to the pigeon holes in the Inglis Building, near the vending machines.

Resistors, Capacitors, Inductors and Batteries

Occasionally I am asked where to find more information about the some of the basic concepts and components introduced in the early lectures of the IA Linear Circuits and Devices course.  Books like Circuits, Devices and Systems by Smith and Dorf, a recommended book for this course, contain some material, and a number of  A-Level text books may also assist.  

The following web resources provided by the University of Florida are worth consulting if you have access to a computer with direct connection to the Internet.  

It's worth pointing out that some of the basic definitions of capacitance and inductance in the pages linked to below are over-simplistic, and not adequate for the course at Cambridge.  You will meet more rigorous definitions in the Electromagnetics lectures in the Easter term, but for now consider the definitions below which we will find helpful as we investigate linear circuits further.  

Capacitance - a measure of the ability to store electrical potential energy in the form of an electric field

Inductance - a measure of the ability to store electrical kinetic energy in the form of a magnetic field

Some of the pages linked below contain images and interactive applets in Java or Javascript - these may help you visualise some of the important relationships, but may involve moderately large downloads.  

The following page at University of Texas introduces some topics in Circuit Theory under the wing of (!) Professor Owlbert.  The site is still under development but the material on 

could be a useful supplement to the lectures.  Thanks to Warren Rieutort-Louis (T) for alerting me.  Here's the link:

Please note, certain links are to external sites over which we have no control.  

Resistor Colour Code and Preferred Values

Resistors and capacitors are sold in bulk in certain preferred values.  The values chosen are not 1, 2, 5 etc, as might be expected, but they are related in a logical way.  The values manufactured are called 'preferred values'.  They are in a geometrical progression, and various ranges have been adopted over the years.  The most common these days is the so-called E12 range in which there are 12 'preferred' resistor values between 1 and 10 ohms.  All other values are simply multiples of 10, 100 etc times these figures.  For more precise work, the E24 range contains 24 different values per decade; these are often a little more expensive.

The E12 range 1.0 1.2 1.5 1.8 2.2 2.7 3.3 4.7 5.6 6.8 8.2

Resistors normally use a colour-coded set of bands to identify them.  You can find an illustrated guide to the resistor colour code here.
Capacitors often have the value printed on them; occasionally colour codes are used.

Interactive Diode, JFET and MOSFET

These links point to applications in a suite developed originally by Edward Hill (PEM) and revised by Mike Khaw (T), as part of their CUED 4th year M. Eng projects, which have concerned the development of Multimedia Teaching Tools.  They are hosted on the web pages of the CUED Multimedia Group (MMG).  To run them, you need to be using a browser that has, or can have, Macromedia's 'Shockwave Flash' feature.  The page will prompt you to download and install this if it is not present.  Please note these are 'works in progress' - they are likely to be updated from time to time. While these models give valuable insight into the behaviour of these devices, in general their features are pictorial impressions only, and are not intended as full quantitative representations. 

diode.jpg (40944 bytes)
See full-size screen image

This is an 'interactive diode' and illustrates the behaviour of the p-n diode discussed in lecture 5 of the Linear Circuits course.  

jfet.jpg (44507 bytes)
See full-size screen image

This is an 'interactive JFET' and illustrates the behaviour of the JFET discussed in lectures 6-7 of the Linear Circuits course.  

mosfet.jpg (48029 bytes)
See full-size screen image

This is an 'interactive MOSFET' and illustrates the behaviour of the MOSFET discussed in lecture 8 of the Linear Circuits course.  

Useful web resources, including educational 'applets'

Note: most of the following require a Java-enabled browser.  Most are links are to external sites over which we have no control.  

Warren Rieutort-Lewis' Web Site

Warren has gathered together a growing collection of very useful resources for IA and IB Engineering.  This is the link for the Linear Circuits & Devices information he has collected.

Fourier Synthesis

This animation shows how arbitrary periodic wave shapes can be synthesised by superposing sine or cosine waves of different frequencies and amplitudes.  This is based on the theory of Fourier Series, which will be covered in the IA Maths course in the Lent Term.  This animation does not require any significant mathematical knowledge.

Another animation shows how adding progressively more sinusoidal waves at higher frequencies can give a more accurate rendition of the arbitrary wave shape 

Semiconductors, diodes, JFET and MOSFET

Animation showing how p-n junction diodes work in forward and reverse bias.   Includes characteristic I-V curves

Shows absolute maximum ratings (operating limits), device specifications and typical characteristic I-V and other curves.  Acrobat file. 

Animation showing how a simple JFET works.  Note that this model has the gate electrode on one side only, not both as in the IA course.  Also, the relative sizes of some of the regions are rather different, but its operation is otherwise identical.  Includes characteristic I-V curves

These are a couple of examples of applets held in an archive at Dept of EE, SUNY, Buffalo USA.  They are rather advanced for Part IA use, but are still good fun!   There is a longer list of other applets relating to materials, microelectronics, etc

AC circuits and resonance

Applet demonstrates the relationships between current and voltage in a series-connected circuit containing resistance, capacitance and inductance.

Visit here for some abbreviated notes showing how to illustrate some key points using the Caltech LRC Laboratory.

This one is ideal for exploring the relationships between current and voltage in capacitors, inductors and resistors, and any combination.  You can set any component to zero to exclude it from the circuit, or vary its value; the frequency and amplitude of the generator are controllable, and the display includes waveforms and animated phasor diagrams.  You can readily see how inductive and capacitive reactance cancel to give the phenomenon of resonance.

An interactive animation showing the frequency-selective properties of the parallel-resonant RLC circuit. 

Teaching Software

Electronic Design Education Consortium

edecbig.gif (10043 bytes)

MOS Transistor operation for 2003

This is a member of a suite of several applications produced by the Electronic Design Education Consortium to illustrate various devices, circuits, methods and design techniques in electronics.  The module illustrating MOS transistor operation has previously been used as a demonstration in the IA course. Licensing restrictions currently prevent us from making this available as a downloadable archive, or placing it on the web, but there is a local alternative!  Click on the EDEC button above to explore the EDEC site, but note that it appears to be undergoing changes at the moment.

The MOS transistor module is installed on the PC server in the EIET Laboratory, Inglis Building), and it should be possible to access it from any of the coupled PC workstations.  Note that the lab is heavily used on occasions and the workstations may not be available for this work at all times.  If in doubt please check with Mr Furber.  Unfortunately, the colour mapping arrangements on these workstations do not fully match the requirements of the software, so certain colour keys are washed out.  This problem is being investigated.

The PC workstations do not currently have a web browser, and this procedure may involve rebooting the PC.  You cannot therefore keep this page visible on-screen, and we recommend you have a printed copy of the instructions - or at least notes on what to do - before starting.  Mr Furber should have a few printed copies of this section.

Useful Articles

Porthcurno Museum of Submarine Telegraphy

BT's Connected Earth site

Under review

Spice Simulator

The Spice simulator is one of the industry standards, and uses numerical models to predict the performance of a vast range of electronic circuits.  Spice was originally conceived to help chip designers with the design of complex integrated circuits, but its range of applications now extends much further, and virtually every professional circuit designer will use it at some point.  It will re-appear later in the Electrical and Information options of the Engineering course.  ASIC

Several of the numerical problems (both DC and AC) in the Examples Sheets can be solved with considerable ease using Spice - although I do not advocate this approach at this stage, because entering the data and setting up the simulation take almost as long as it would take you to solve the equations on paper!  Click here to see the solution to Questions 5 & 9 on Examples Sheet 1 performed by Spice.

This year I hope to include  demonstrations of how Spice can be used to predict the performance of JFET- and op-amp circuits.  Spice will run on most PCs and workstations.  You may find it is available on your College network.  You can download a student version for your own PC (with some limits on functionality) from the web.

Notes on PC versions of SPICE

The files given below are sufficient to run the Spice simulator but they do not contain any graphical data; that is, the circuit schematic presentation used in the lectures is not available here.  With older versions of pSpice versions 5, 6 and 7 running under DOS (or in a Command window) it is possible to run the Spice Simulator alone without the graphical input; with pSpice 7.1 the simulation engine is called PSPICE.EXE.  This allows you to select an input file, run the simulation and call up the PROBE plotter to plot graphs.  No schematic entry required.

Note: Certain programs in the MicroSim/Cadence pSpice family have seemed to have difficulty with long file names or paths like: 'C:\Program Files\msimev71\file.dat'.   To avoid problems like this install pSpice in a directory like: C:\winapps\msimev71.

Screen shots shown in lectures

A set of pages showing example circuits and simulation results using  pSpice displays to illustrate the lectured material on JFET amplifiers has been compiled:-

Spice files for circuits studied in the course

To use these files in pSpice, select the text (displayed in Courier typeface) starting at the first visible line (begins with '**'), down to the D in .END, and save it in a file e.g. DTRAN.CIR.  Remember that Spice regards the first line as a comment.  Run your installed version of pSpice on the saved file, and start PROBE to look at the results.


** DC and transient responses of pn junction diodes **

.DC LIN V_V2 0 5 0.1
.TRAN 2ns 100ns
D_D1 1 0 D1N4148
V_V1 2 0 PULSE 5 -5 10n 1n 1n 50n 100n
R_R2 1 2 1k

.MODEL D1N4148 D(Is=2.682n N=1.836 Rs=.5664 Ikf=44.17m Xti=3 Eg=1.11 Cjo=4p
+ M=.3333 Vj=.5 Fc=.5 Isr=1.565n Nr=2 Bv=100 Ibv=100u Tt=11.54n)


JFET Amplifier

DC characteristics

** Jfet DC analysis to produce output characteristic **
V1 1 0 DC 0
V2 2 0 DC 0

J1 2 1 0 J2N3819

.model J2N3819 NJF(Beta=1.304m Rd=1 Rs=1 Lambda=2.25m Vto=-3
+ Is=33.57f Cgd=1.6p Pb=1 Fc=.5 Cgs=2.414p Kf=9.882E-18 Af=1)

.DC V2 0 20 .1 V1 -2.6 0 0.2

Audio Amplifier response

** Click for pSpice input file to model JFET Amplifier Response **

Design Example 18.1

This topic was covered in Lecture 18.  A SPICE simulation was shown, demonstrating the power of this tool for electronic design. 

In the lecture notes it is shown that the gain does not quite reach 20 dB in the mid-band region.

Why should this be?  Is it the use of preferred R and C values for convenience, rather than the exact calculated ones?  Or is it because the op-amp is not ideal (for example, its gain A, though high, is not truly infinite)?  The output drives a 15 K load - perhaps this, combined with the output resistance of the circuit is causing the reduction?  Or is there some other reason?  The simulator allows us to explore all these possibilities and more besides, in order to establish the reason.  Click below to find out more!

Op-amp circuit using capacitors to determine the frequency response

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Updated 27 March, 2008

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