Issue link: https://iconnect007.uberflip.com/i/1174596
OCTOBER 2019 I DESIGN007 MAGAZINE 79 route differential nets using the same automa- tion techniques. Design rules are critical to us- ing this type of automation. In Figures 8 and 9, 12 differential pairs are being routed using sketch autorouting. This process takes the tool about 20 seconds to complete, and there's zero clean-up afterward. If we were to hand-route these pairs, clicking each corner as we go, it would take 15–20 minutes with clean up and deciding how to enter the BGA. This example constitutes a 45X reduction in routing time. 3. Interactive or Autotuning Traces We've routed our critical nets, and now they need to be length-matched for timing require- ments. Every tool al- lows you to manually draw in the serpentine or meander required to meet your length rules. But as with fanout, dif - ferential pair rules, and routing, doing these processes manually takes time and can eas - ily be automated. Tun- ing traces is no differ- ent. Tools with prop- er automation provide two options for tuning: interactive and auto- matic. Tuning options can be defined global- ly (Figure 10), which allows you to control the typical distance be- tween traces with ser- pentining, rounded or chamfered corners, the typical amplitude of the serpentines, saw - tooth tuning, and with- in differential pair saw- tooth matching. Interactive tuning, like interactive rout- ing, requires you to touch each trace but gives you the most control. After selecting a single trace or differ- ential pair, selecting interactive tune starts a Figure 8: Differential pair group sketch path. Figure 9: Completed differential sketch routing. Figure 10: Tuning options.