Surface acoustic wave (SAW) harmonic oscillator system used for gas sensor

Abstract

The invention relates to a surface acoustic wave (SAW) harmonic oscillator system used for a gas sensor. The SAW harmonic oscillator system used for the gas sensor comprises SAW oscillators and a mixer circuit, wherein the SAW oscillators are divided into two groups, the two groups of SAW oscillators adopt two ends, with single resonant mode and a high Q value, of an aluminum / gold electrode to manufacture SAW resonators on the same piezoelectric substrate. Each SAW oscillator comprises an SAW resonator, an operational amplifier, a matched network and a phase-shift network, wherein the output end of the SAW resonator is directly connected with an input end of the operational amplifier through the matched network, an output end of the operational amplifier is connected with the phase-shift network, an output end of the phase-shift network is connected with an input end of the SAW resonator through the matched network, and therefore output signals of the operational amplifier are fed back to the SAW resonator. Output ends of the two groups of SAW oscillators are connected with the mixer circuit, output of the mixer circuit is interfered by a low pass filter which filters high-frequency signals, and then difference frequency signals of the two groups of SAW oscillators are output after the amplification of a low-frequency amplifier.

Description

technical field [0001] The present invention relates to an oscillator, in particular to a resonant surface acoustic wave (SAW) oscillator system for a gas sensor. Background technique [0002] Usually for high-performance SAW gas sensors, the core component is an oscillator with high frequency stability. In the prior art, two device structures are generally used, one is the delay line type, this device structure can provide enough sensitive film coating area between the transducers, but its Q value is low and the loss is high, which affects the The frequency stability of the oscillator is further improved; the other is a pair of SAW resonators (hereinafter referred to as SAW) composed of two reflectors and two adjacent interdigital transducers (IDTs). Resonator) structure, this device structure has the characteristics of simple design, low loss and high Q value, which is conducive to obtaining ideal frequency stability performance. Therefore, this oscillator is more suitab...

AI Technical Summary

Problems solved by technology

Since the gas sensor needs to provide a larger coating area, the resonator needs to have a wider resonant cavity, which makes the frequency response of the resonator appear multi-mode characteristics, and the loss between each mode is close, which is possible in multiple Each frequency point satisfies the oscillation condition, which affects the frequency stability of the oscillator; in addition, the resonators in the prior art mostly use aluminum electrode structures, which are easy to be corroded in some toxic gas detection environments, thus affecting the oscillator. Stability and service life

In order to improve the corrosion problem in the gas environment to be measured, some literatures proposed a resonator structure using gold electrodes (Avramov I D, Voigt A, Rapp M. Rayleigh SAW resonators using gold electrode structure for gas sensor applications in chemically reactive environments. Electronics Letters ;2005;41(7):450-452.), but this kind of gold electrode increases the manufacturing cost of the device. In addition, the high density of the gold material makes the effect of the film thickness on the device very obvious, which increases the Difficulty in the manufacturing process of the device

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