Electronic Circuit for Differential Measurement using Resonant Sensors: Designing Approach

In this paper we present the design of an electronic circuit which implements a differential measurement technique for detecting the presence of an explosive substance by using resonant sensors. Two TF-BAR sensors, with resonance frequencies of about 2 GHz, are employed for this purpose: an active one, which is exposed to the target substance and whose mass changes due to the molecules of that substance attaching to it, and a reference one, which is not exposed to the target substance and whose mass does not change. Due to the mass modification, the resonance frequency of the active sensor slightly changes. The purpose of the presented circuit is to measure this tiny frequency deviation by comparing the resonance frequencies of the two sensors. If both sensors are operated at the same temperature and humidity conditions, the measured frequency deviation is proportional with the amount of mass attached to the active sensor. In the proposed design, we use a frequency-to-voltage converter to translate this frequency deviation into a useful output signal. We present hereinafter the development of the electrical schematics and the simulations results of the functional blocks for the proposed measuring circuit.