Getting the Most from Design Reuse Print E-mail
Written by Yan Killy   
Saturday, 31 August 2013 00:44

Replicating circuits saves time at layout and test.

Most popular PCB design software tools have a feature that enables the reuse of common circuit layouts. Are designers getting the most out of this feature? Let’s take a look at how physical design reuse works and how to use it to full advantage.

Design reuse is like a component library part on steroids. Instead of grabbing a single package design from the PCB design library, you can select an entire circuit, already laid out and tested. This can be very valuable when designing multi-channel interfaces, incorporating common circuits into multiple products, or to save time when designing to meet EMI or regulatory compliance. The process for most software packages is similar, depending on the tool’s capabilities, of course. There are basically two ways to employ design reuse:

Design the circuit to be replicated. When designing a product that has a multi-channel interface, one option is to design one output channel and then
replicate it. We refer to this as “internal reuse” because it is internal to the design being worked on. Figure 1 shows an example of this process for a 32-channel audio mixer product. The audio output stage is designed and laid out for one circuit. It is tested and verified; then the same circuit layout is designated, copied and replicated 31 more times. The tool can automatically find connections and update reference designators each time the circuit is pasted in place. The replicated circuit will maintain all circuitry, including RF geometries (Figure 2) and even test points.

Create a circuit for reuse on multiple products. Another approach is to design a specific layout to be used on multiple products, now and in the future. This is very handy for impedance-matched circuits, RF shapes, charging circuits, and the like. Figure 3 shows a battery charging circuit that was designed once and can be replicated over and over, ensuring a reliable charger, as well as perfect dimensioning for connectors, always with the same PCB footprint.

Shorter development time. The obvious advantage to design reuse is shortening PCB design time. Using the actual customer data for the board shown in Figure 1, the initial layout of a single audio stage was about two days, whether or not reuse was employed. When replicating manually, the remaining 31 circuits could be completed in three to five days. By leveraging reuse, the remaining 31 channels could be dropped onto the PCB in as few as 30 min. Not every product has multiple, identical circuits that can result in such a dramatic difference in layout time, but even a few replications of buffers, I/O ports, etc., can significantly shorten product development time.

A second area overall product development time is shortened is in test and regulatory compliance. Once the charging circuit (Figure 3) has been developed and determined EMI (or UL/CSA) compliant, reusing that circuit means that a great deal of testing time can be saved. This also can reduce headaches and finger-crossing when submitting products for standards and EMI testing for the first time.

Yan Killy is technical marketing engineer, PADS at Mentor Graphics; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

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TAGS: design reuse, Mentor Graphics, design cycle time, printed circuit board, CAD

Last Updated on Tuesday, 17 September 2013 01:21




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