Analysis and modeling of electrostatic discharge in a tactile glass featured watch

Electrostatic discharge (ESD) in quartz watches is becoming more and more important due to the use of plastic materials and tactile sensors. The discharge can lead to different type of dysfunction such as a simple reset, a latch-up or the destruction of the electronics. In this paper, only the reversible dysfunction is considered. Electrostatic finite element (FEM) simulation completed with analytical calculation is carried out. Spatial distribution of the voltages will be shown. Values of the discrete elements are determined either by the electrostatic FEM (capacitors) or by analytical methods. Validation of the theory is done by DC (resistors) and AC (impedance) measurements. The watch is then modeled with these discrete impedances forming a global equivalent circuit in order to simulate its dynamic behavior. Results will show the discharge propagation on key components like the micro-controller IC.