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Problems and Considerations in PCB Design when using Piezotronic Devices

Piezotronic devices demonstrate the effect of material polarization due to mechanical stress or deformation of the material and vice-versa. This phenomenon can be exploited to get sensor data of temperature, mechanical pressure, vibration etc. – or using the opposite mechanism to control actuators. Since piezotronics technology is mainly related to analog signals and high quality performance, negative effects generated by or acting into analog signals should be taken carefully into consideration when designing the PCB board and selecting its assembly components. This article will describe in short, some of those issues and solutions commonly used to avoid or minimize the negative effect. First of all, it is a common practice that connections which carry analog signals to be as separated as much as possible from the regions in PCB board where digital signal connections take place, since digital signals are source of electromagnetic radiation while on the other hand analog signals are sensitive to this kind of radiation resulting in interference between signals, which can make the whole circuit dysfunctional in the worst case. Besides that, two wires carrying digital signals can result in loss of performance as well. This effect is caused because of the capacitance generated between two wires carrying current as illustrated in the left figure.

 

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C is the capacitance created in the dielectric region between the two signals. After analog signals taken from the inputs of piezotronic sensors are converted into digital using ADC’s, current continually and rapidly changes in the wire thus generating inductance. This causes noisy currents in the other wire. One of the solutions commonly used is utilizing a CMOS Buffer Integrated Circuit by letting all signals pass through the buffer as illustrated in the right figure. Other common practices to reduce coupling (transfer the energy from one wire to another through the changing electromagnetic field) are shortening the routes of signals as in the PCB board. Using a whole layer in PCB as ground helps reduce route lengths targeting ground at minimal level.