Munir Farasat, Wathen Adam, Hunt William D
School of Electrical and Computer Engineering, Georgia Institute of Technology, 791 Atlantic Dr., Atlanta, Georgia 30332, USA.
Rev Sci Instrum. 2011 Mar;82(3):035119. doi: 10.1063/1.3567005.
A new approach to the electronic instrumentation for extracting data from resonator-based sensing devices (e.g., microelectromechanical, piezoelectric, electrochemical, and acoustic) is suggested and demonstrated here. Traditionally, oscillator-based circuitry is employed to monitor shift in the resonance frequency of the resonator. These circuits give a single point measurement at the frequency where the oscillation criterion is met. However, the resonator response itself is broadband and contains much more information than a single point measurement. Here, we present a method for the broadband characterization of a resonator using white noise as an excitation signal. The resonator is used in a two-port filter configuration, and the resonator output is subjected to frequency spectrum analysis. The result is a wideband spectral map analogous to the magnitude of the S21 parameters of a conventional filter. Compared to other sources for broadband excitation (e.g., frequency chirp, multisine, or narrow time domain pulse), the white noise source requires no design of the input signal and is readily available for very wide bandwidths (1 MHz-3 GHz). Moreover, it offers simplicity in circuit design as it does not require precise impedance matching; whereas such requirements are very strict for oscillator-based circuit systems, and can be difficult to fulfill. This results in a measurement system that does not require calibration, which is a significant advantage over oscillator circuits. Simulation results are first presented for verification of the proposed system, followed by measurement results with a prototype implementation. A 434 MHz surface acoustic wave (SAW) resonator and a 5 MHz quartz crystal microbalance (QCM) are measured using the proposed method, and the results are compared to measurements taken by a conventional bench-top network analyzer. Maximum relative differences in the measured resonance frequencies of the SAW and QCM resonators are 0.0004% and 0.002%, respectively. The ability to track a changing sensor response is demonstrated by inducing temperature variations and measuring resonance frequency simultaneously using the proposed technique in parallel with a network analyzer. The relative difference between the two measurements is about 5.53 ppm, highlighting the impressive accuracy of the proposed system. Using commercially available digital signal processors (DSPs), we believe that this technique can be implemented as a system-on-a-chip solution resulting in a very low cost, easy to use, portable, and customizable sensing system. In addition, given the simplicity of the signal and circuit design, and its immunity to other common interface concerns (injection locking, oscillator interference, and drift, etc.), this method is better suited to accommodating array-based systems.
本文提出并展示了一种用于从基于谐振器的传感设备（如微机电、压电、电化学和声学设备）中提取数据的新型电子仪器方法。传统上，基于振荡器的电路用于监测谐振器谐振频率的变化。这些电路在满足振荡条件的频率处进行单点测量。然而，谐振器响应本身是宽带的，包含的信息比单点测量多得多。在此，我们提出一种使用白噪声作为激励信号对谐振器进行宽带表征的方法。谐振器用于两端口滤波器配置中，对谐振器输出进行频谱分析。结果是一个类似于传统滤波器S21参数幅度的宽带频谱图。与其他宽带激励源（如频率啁啾、多正弦或窄时域脉冲）相比，白噪声源无需设计输入信号，并且在很宽的带宽（1 MHz - 3 GHz）内都很容易获得。此外，它在电路设计上具有简单性，因为它不需要精确的阻抗匹配；而对于基于振荡器的电路系统，此类要求非常严格且可能难以满足。这导致测量系统无需校准，这是相对于振荡器电路的一个显著优势。首先给出仿真结果以验证所提出的系统，随后是原型实现的测量结果。使用所提出的方法对一个434 MHz的表面声波（SAW）谐振器和一个5 MHz的石英晶体微天平（QCM）进行测量，并将结果与传统台式网络分析仪的测量结果进行比较。SAW谐振器和QCM谐振器测量谐振频率的最大相对差异分别为0.0004%和0.002%。通过引入温度变化并使用所提出的技术与网络分析仪并行同时测量谐振频率，展示了跟踪变化的传感器响应的能力。两次测量之间的相对差异约为5.53 ppm，突出了所提出系统令人印象深刻的精度。使用商用数字信号处理器（DSP），我们相信这种技术可以实现为片上系统解决方案，从而得到成本非常低、易于使用、便携式且可定制的传感系统。此外，鉴于信号和电路设计的简单性以及它对其他常见接口问题（注入锁定、振荡器干扰和漂移等）的免疫力，这种方法更适合于适应基于阵列的系统。
