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70 DESIGN007 MAGAZINE I APRIL 2019 trace and the differential pair is 1x the signal trace width. Meanwhile, the spacing between each ground and signal trace is set as 2x, 4x, 6x, and 8x for model 2B, 2C, 2D, and 2E, respectively. The TDR plots depicted in Figure 5a indicate that microstrip experiences an impedance mis- match of 1 ohms when its distance from the adjacent ground at each side is set as 1x the trace width (model 2A). The impedance mis- match is getting smaller or closer to the nomi- nal 100 ohms when the ground at each side is further away from the differential pair (i.e., beyond 2x the trace width). However, with reference to insertion loss plots depicted in Figure 5b, model 2A with adjacent ground-signal spacing of 1x the trace width encounters 0.75-dB channel loss at 10 GHz. When adjacent ground-signal spacing is increased to 2x the trace width, the chan- nel loss is reduced by 0.3 dB. Beyond adjacent ground-signal spacing of 4x the trace width, extra loss reduction of 0.1 dB is achieved. Summary For PCBs with signal routing beyond 1-GHz transmission, the copper ground pour must be set at least 4x the signal trace width away from the signal routing to minimize the impedance mismatch and channel loss. DESIGN007 References 1. Olney, B. "Ground Pours—To Pour or Not to Pour." 2. King Sun PCB Technology, "Some Pros and Cons About PCB Copper Pour," December 27, 2017. Chang Fei Yee is a hardware engineer with Keysight Technologies. His responsibilities include embedded system hardware development, and signal and power integrity analysis. Figure 5a: TDR plots for models listed in Table 2. Figure 5b: Insertion loss plots for models listed in Table 2. Researchers from the University of Minnesota College of Science and Engineering have developed a unique new device using graphene that provides the first step toward ultrasensitive biosensors. "To detect and treat many diseases, we need to detect protein molecules at very small amounts and understand their structure," said Sang-Hyun Oh, University of Minne- sota electrical and computer engineering professor and lead researcher on the study. University of Minnesota researchers combined gra- phene with nanosized metal ribbons of gold and utilized a homegrown high-tech nanofabrication technique called "template stripping" to create an ultra-flat base layer sur- face for the graphene. (Source: University of Minnesota) New Graphene-based Device Paves the Way for Ultrasensitive Biosensors