Análise comparativa de osciladores senoidais com sensor a onda acústica de superfície na malha de realimentação.

Abstract

Surface acoustic wave sensors can be used in the feedback loop of sinusoidal oscillators to impose the oscillation frequency. The variation in both frequency and amplitude of the oscillation indicates the presence of a liquid or gas sample in contact with the sensor. Additionally, there are different sinusoidal oscillator topologies that can be used with surface acoustic wave sensors. Therefore, a comparative analysis is necessary to determine the oscillator with the best performance to be used with the sensor. To obtain the results, a surface acoustic wave sensor model based on a piezoelectric crystal with a resonance frequency of 117 MHz and three sinusoidal oscillator topologies (Pierce, Colpitts, and Clapp) were chosen. The oscillators were simulated with the sensor model in the feedback loop using the Montecarlo method. The simulation was performed in two steps: individual components were varied by +/­ 20% with 250 iterations, and all components were varied simultaneously by +/­ 20% with 1000 iterations. The analyzed variables in the simulations were the amplitude, the oscillation frequency, and a new parameter indicating the percentage of times there was oscillation, called robustness in this work. The results showed that all three oscillators generated oscillations in the output voltage, allowing their use with the sensor. Additionally, the Clapp oscillator was found to have a robustness of 84.5%, while the Colpitts and Pierce oscillators had a robustness of 56.3% and 49.9%, respectively. However, the frequency variations of the Pierce oscillator with the variation of the sensor model components were 10%, while in the Colpitts and Clapp oscillators, the variation was 0,1%. Therefore, according to the results presented in this work, the Clapp oscillator is the best to be used in conjunction with the surface acoustic wave sensor model for a frequency of 117 MHz if the decision criterion is robustness. However, if sensitivity is the decision criterion, the Pierce oscillator is the most suitable to be used with the sensor model in the feedback loop.