Cadence OrCAD PCB Designer

The first two should be familiar from last year but the third is new. These programs are accessed
via networked Windows PCs in the department, with up to 40 users at any one time. Unfortunately
the licensing arrangements do not permit access from outwith the Rankine Building. A
demonstration version is available; please ask.
We are using PCB Designer for the first time this year because our previous application,
Layout, is being discontinued. OrCAD PCB Designer is the most basic version of Cadence’s
Allegro suite for PCB design and much of the documentation refers to ‘Allegro’ rather than
‘PCB Editor’. Allegro is widely used in industry and is similar to the Cadence software for
laying out integrated circuits (ICs), which you will experience in Digital Circuit Design 3.
That’s the good news: Allegro is far more powerful than we need for laying out our simple
circuits and the vast number of features can seem bewildering. It is also new to your instructors
and this course will be a learning experience for all of us!
Fixup. I have encountered numerous problems with the software, mainly due to incompatibilities
between the libraries supplied for Capture and those for PCB Editor. These are marked
as Fixups. I expect that we will find smoother ways around these difficulties in the future but
you are the guinea-pigs. I’d also be grateful for suggestions for improving these instructions.
There is extensive online help for all these programs although I have to admit that it could be
better organised. Please try this before asking a demonstrator for help – it is part of the learning
process. Most ‘professional’ software is so complicated that even experts make regular use of
the help files.
Three types of information are needed for each component and are stored in libraries.
• Electrical symbols are used to draw the circuit in Capture.
• Electrical models allow you to simulate the circuit in PSpice.
• Footprints show the size and shapes of the pads (where the pins are soldered to the
board) and the outline of the package. They are used to lay out the circuit in PCB Editor.
The first two should again be familiar from last year. Remember that each type of component
is kept in a different library file and you must select the files needed for a particular design. The
third piece of information is new. You might wonder why yet another library is needed. The
reason is that components with the same electrical behaviour come in different packages. For
example, an integrated circuit might come in two versions:
• a traditional, plastic dual-in-line package (PDIP) with pins 0.1 ′′ apart
• a smaller, surface-mount device (SMD) with pins only 0.5 mm apart, if it has pins at all
The opposite is also true: resistors of a particular shape come in a wide range of values. Further
information is needed to describe the characteristics of the printed circuit board on which the
components are mounted.
Each circuit design is regarded as a project and a project manager groups all the files together
in a subdirectory. These files should be stored in your work space on the University’s
central system, accessed via the network as the H drive. Do not store files in any other place on
the network or on a computer – they will be erased.
The Cadence system provides many facilities which are not needed for these introductory
designs. Please do not attempt to use commands which are not described in these instructions;
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