Issue link: https://resources.pcb.cadence.com/i/1533020
Analog vs. Digital Know Your Workarounds Life in the analog design world became much easier when we could assign properties to nets that allowed a repeatable ground pour that gave extra space where needed and tightened up to the nominal value wherever that applied. Whatever tool we were using, it seemed like the high-speed digital domain got the useful commands and we designers on the analog boards had to be crafty with the shapes to complete our boards. Figure 2. Small form factors give rise to assembly sub-panels that allow several printed circuit boards to be processed in one go. Image Credit: Author This was way back before the rise of the internet so, obviously, the internet of things didn't exist. That meant that the majority of designers lived in the digital realm where support for length and width were stronger than support for things like tuning stubs or antennas that connect to the RF lines but also to the ground plane without a break in the metal. So, we had a short to ground at DC frequencies but also an antenna at 2.4 GHz. Doing unusual analog things like that meant that we were compelled to use some kind of undocumented workaround to arrive at the artwork we needed. The Net Short Property for Joining Two Connections The good news is that wireless technology has become more mainstream and the PCB Design tools have stepped up with better ways to document the eccentricities of the analog world. For instance, Cadence lets me assign two nets to a shape, via or other element so that it can be used as a short between two nets. This comes in handy when a small AGND area is tied to the primary GND plane(s) at a single point; probably the most frequent use-case of joining different nets together without having to live with a design rule check (DRC) violation. If at all possible, I'd rather not be in a position where I have to waive a DRC so I look for rules and properties that allow us to tape out a clean design. The net short property is one such avenue. This is one of many little hooks that can be applied to a Printed Circuit Board design. Every iteration of the software adds more ways to define and control the outcome of our design efforts. The experienced designer knows that the first trace routed will very likely go through several revisions by the time the last trace is drawn. Even then, when all of the work is done, the board goes to the archive until the day that a new iteration has to be fleshed out. 3 www.cadence.com Introduction to PCB Constraints