Design Con 2015

Book review: Analog Design and Simulation using OrCAD Capture and PSpice

-January 31, 2013

In the EDA sector, there are a lot of books about research and new techniques, or how to learn and use new languages, but there are not many how-to, practical books that enable you to come up to speed with a tool. We tend to rely on the tool vendor and their user guides or tutorials, but often these are not the most helpful of texts as they are not written by real users who have struggled with learning it from scratch and as such often assume a lot of knowledge that isn’t there or go to the trivial end and almost teach you how to use a graphical interface.

So, I was pleased to be sent a copy of “Analog Design and Simulation using OrCAD Capture and PSpice” by Dennis Fitzpatrick – a book recently published (2012) by Newness (Elsevier). So, who is Dennis Fitzpatrick? Well, first he is a Brit, and when you hear a British accent, you know he should be believed at all times – except you can’t get the accent from the book. Well, Dennis has also worked in the electronics industry for over 15 years with experience of analogue (yup that is a British accent right there) and digital IC design. He gained experience using the Cadence EDA software tools and ultimately ended up working for OrCAD and then Cadence as a Senior Lead Engineer specializing in the IC and board level analog, digital simulation and Signal Integrity tools before becoming an expert in PSpice. Dennis worked at Cadence for eight years providing support and delivering Cadence EDA software training courses. He joined the University of West London in 2007 as a senior lecturer teaching a wide range of electronic engineering subjects and now is a Reader in the University’s Institute for Practice, Interdisciplinary Research and Enterprise (INPSIRE) conducting Biomedical research and heads the Biomedical engineering and DSP research group.

This book is aimed at electronic engineers and students.

Let’s take a quick look at the chapters.

Chapter 1 Getting Started – This chapter talks about things such as setting up projects and some of the basics associated with entering circuits. It finishes, as do all of the chapters with a number of exercises. You can download a free copy of OrCAD PCB Designer Lite here.

Chapter 2 DC Bias Point Analysis – When you apply power to most circuits, they will reach a stable condition known as the DC steady-state condition. Here, all voltages and currents have stabilized, initial conditions set and capacitors fully charged. This is basically the starting point for other kinds of analysis such as transient analysis which is when input stimulus is provided. This chapter takes you through a PSpice analysis and display capabilities. This can be saved and used to start off other simulations.

Chapter 3 DC Analysis – Perhaps you want to know how the circuit DC conditions vary depending on supply voltage or other changes in operating conditions. This chapter tells you all about it and how to set up sweeps so that things such as transistor characteristic curves can be created.

Chapter 4 AC Analysis – Enough of the steady state – it is time to apply signals and AC analysis is used to calculate the frequency and phase response of a circuit. AC analysis assumes that everything is linear and thus analysis can use simpler and faster models, but you had better be sure that you aren’t clipping or any non-linear behaviors in the design. This is useful for finding out how filters behave.

Chapter 5 Parametric Sweep – Similar to chapter 3, this looks at varying parameters of the design for AC analysis and is performed by varying a parameter in the design. This chapter is very heavy on the practical exercises.

Chapter 6 Stimulus Editor – Not all inputs are simple sine waves that cover the linear part of the design. Sometimes you want to apply transient stimulus and this is done using a waveform editor. This chapter takes you through the various kinds of stimulus generators that exist and how to prepare for a transient analysis.

Chapter 7 Transient Analysis – This is where you really start to learn about PSpice simulation and the notion of the timestep. Several exercises help you to understand the basics and how to create files with discrete time and voltage data.

Chapter 8 Convergence Problems and Error Messages. Even with variable time steps, there can be cases when the simulator fails to converge to a solution – often caused by a non-linearity or when faced with a step input. Other simulation errors are also discussed.

Chapter 9 Transformers. As the title implies, this chapter deals with the subject of transformers including linear, non-linear and predefined transformers.

Chapter 10 Monte Carlo Analysis. PSpice simulation, while a very efficient simulator for what it does, can take a long time for complex designs or for those that contain many variables that could be varied as part of the simulation process. Instead of simulating all of them, a statistical process is usually used called Monte Carlo analysis.

Chapter 11 Worst Case Analysis. Designs are sensitive to variations in certain components, but it can help to know which ones are the critical ones. Once known, it becomes easier to find the worst case conditions in a design so that sufficient design tolerances can be used.

Chapter 12 Performance Analysis. Knowing the value of a voltage or current is one thing, but there are many other kinds of measurement that might be useful, such as the bandwidth or center frequency of a waveform.

Chapter 13 Analog Behavioral Models. So far all of the models have been circuit level models, but there are times when a more abstract model may allow analysis that could not be performed at the low level. This chapter looks at abstract voltage-controlled sources.

Chapter 14 Noise Analysis. Where does noise come from and how do you model it? This chapter gets you started on the subject.

Chapter 15 Temperature Analysis. Temperature affects almost all electronic devices and this is one sweep that most people will want to run. This may be especially true if you are working on circuitry for cars or other extreme environments.

Chapter 16 Adding and Creating PSpice Models. So far, the devices have come from a library of models, but what do you do if the device you need isn’t there? This chapter introduces you to the model editor.

Chapter 17 Transmission Lines. Signal integrity is perhaps one of the thorniest problems for all high-speed interconnect and this chapter starts to introduce you to a few of the fundamentals.

Chapter 18 Digital Simulation. While the world is analog, most complex chips contain significant amounts of digital logic. This chapter provides you with some of the basic information.

Chapter 19 Mixed Simulation. At the end of the day, every system is a mixture of analog and digital and it may be important to simulate the two pieces together. Neither simulator can do it all, so it is important to understand how to run them cooperatively.

Chapter 20 Creating Hierarchical Designs. Almost no design is created from scratch and neither is it practical to design it without employing some amount of hierarchy. This can help with things such as project management, verification and dealing with complexity. This is a meaty chapter and necessarily so.

Chapter 21 Magnetic Parts Editor. When designing circuits such as switch mode power supplies, transformers and inductors play an important part. These can be modeled with the Magnetic parts editor.

Chapter 22 Test Benches. It is sometimes necessary to add additional parts to a design in order to perform a simulation, and these can be contained in a testbench rather than having to modify the design.

Overall opinion

The book has divided the problem into many parts and each is tackled at a reasonable pace. A lot of learning is contained in the exercises, so it is important to make sure you have downloaded OrCAD PCB Designer Lite. It can be obtained here.

This is a great introduction to a complex subject and is very reasonably priced at $69.95 or cheaper at places such as Amazon. I highly recommend it for anyone looking at this subject for the first time.

Cadence has also made the full suite of OrCAD tools available to students on a yearly basis.


Brian Bailey – keeping you covered

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