SNOA952 May   2016 FDC2112 , FDC2112-Q1 , FDC2114 , FDC2114-Q1 , FDC2212 , FDC2212-Q1 , FDC2214 , FDC2214-Q1

 

  1.   Ground Shifting in Capacitive Sensing Applications
    1.     Trademarks
    2. 1 Introduction
    3. 2 Mathematical Modeling
      1. 2.1 Different Grounding Configurations
        1. 2.1.1 Earth Ground Referenced
        2. 2.1.2 Floating Ground Referenced
          1. 2.1.2.1 Large Local Ground Plane
    4. 3 Qualitative Test Setup
      1. 3.1 Earth Ground Referenced Laptop
      2. 3.2 Floating Laptop
      3. 3.3 Floating Laptop With Large Local Ground Plane
    5. 4 Conclusion

2.1.1 Earth Ground Referenced

When the laptop is referenced to earth ground and powering the EVM through the laptop’s USB port, it is also referenced to earth ground. In this scenario, the ground shift phenomenon should not be observed since the laptop will not be able to act as a sensor under these conditions.

Figure 1 shows the system configuration when the laptop is referenced to earth ground. As demonstrated earlier in Equation 1 to Equation 3, when Cg is large, the β-factor becomes close to 1 which prevents a shift in frequency minimizing the ground shift phenomenon.