By Lindsay Farlow | Sep 23, 2013
Creating a great schematic is more than just producing a technically correct netlist. Ideally, your schematic should be organized in a way that’s easy for others to review and understand. Even someone unfamiliar with the design should be able to pick up a schematic and get a good feel for the design objectives.
Tips for Creating Effective Schematics
1) STArt with a block diagram
At Nuvation Engineering, the second page of a schematic (after the cover page) is usually a block diagram, extracted from the hardware design document. It takes only seconds to add, gives the reader a good overview of the design architecture, and is a handy reference to flip back to. Add the schematic page numbers for each section right on the block diagram, to make schematic navigation even easier
2) Name your nets
Give every net on the board a name which reflects its purpose. This makes simulation and debug much, much easier. You may be tempted to skip naming the smaller nets, thinking it’s such a tedious step, and nobody will notice, and you’ll probably never simulate them anyway. Ignore those feelings. Name your nets.
3) Think design flow
New schematic designers are often tempted to make schematics as compact as possible, as though the fewer the pages and the shorter the nets are, the simpler the schematic will be. This is almost never the case. Take as many pages as you need, and organize your pages where it makes sense from a design standpoint – don’t play Tetrus with your schematic blocks to try to squeeze everything in. Make inputs to outputs flow from left to right on your pages, and order the pages in the way that you would normally review them – referring back to your block diagram can help you figure out what that order is.
4) Make connectors look like the connectors
Number and order the pins in the way they are physically located on the connector, and make the shape of the symbol look like the connector shape. This makes them much easier to find on the schematic (if you know what it looks like from the PCB), and vice versa. It’s also easier to identify pin numbering mistakes, and should you need to probe the connector on the PCB you can just refer to the schematic to figure out which pin you’re looking for.
5) Notes, Notes, Notes
You’ve obviously put a lot of time and thought into your design, so make those thoughts available to anyone who may be reading the schematic and wondering the same thing. If it’s a long analysis, make a note referring to a separate design document. Helpful notes include:
- Why you did/didn’t choose a certain component
- Logic tables or resistor pull-up/pull-down settings for different IC modes of operation (like the configuration mode for an FPGA)
- Power supply considerations, such as the drop-out voltage of an LDO, or the ripple you expect on a regulator output
Basically, if you spent a long time thinking about something, or if there’s a piece of information you will need to refer to often, chances are everyone else will be wondering the same thing, so write it down!
Nuvation provides a full range of services for circuit board design, including schematic capture and PCB layout. Contact Nuvation Engineering to hear about our impressive track record for first-time-right designs.
