Liu Heng, Zhang Chun, Weng Zhaoyang, Guo Yanshu, Wang Zhihua
Tsinghua National Laboratory for Information Science and Technology, Institute of Microelectronics, Tsinghua University, Beijing 100084, China.
Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057, China.
Sensors (Basel). 2017 Sep 15;17(9):2131. doi: 10.3390/s17092131.
A monolithic resonance frequency readout circuit with high resolution and short measurement time is presented for a 900 MHz RF surface acoustic wave (SAW) sensor. The readout circuit is composed of a fractional-N phase-locked loop (PLL) as the stimulus source to the SAW device and a phase-based resonance frequency detecting circuit using successive approximation (SAR). A new resonance frequency searching strategy has been proposed based on the fact that the SAW device phase-frequency response crosses zero monotonically around the resonance frequency. A dedicated instant phase difference detecting circuit is adopted to facilitate the fast SAR operation for resonance frequency searching. The readout circuit has been implemented in 180 nm CMOS technology with a core area of 3.24 mm². In the experiment, it works with a 900 MHz SAW resonator with a quality factor of Q = 130. Experimental results show that the readout circuit consumes 7 mW power from 1.6 V supply. The frequency resolution is 733 Hz, and the relative accuracy is 0.82 ppm, and it takes 0.48 ms to complete one measurement. Compared to the previous results in the literature, this work has achieved the shortest measurement time with a trade-off between measurement accuracy and measurement time.
本文提出了一种用于900 MHz射频表面声波（SAW）传感器的具有高分辨率和短测量时间的单片谐振频率读出电路。该读出电路由一个分数N锁相环（PLL）作为SAW器件的激励源和一个基于逐次逼近（SAR）的基于相位的谐振频率检测电路组成。基于SAW器件的相频响应在谐振频率附近单调过零这一事实，提出了一种新的谐振频率搜索策略。采用了专用的即时相位差检测电路，以促进用于谐振频率搜索的快速SAR操作。该读出电路采用180 nm CMOS技术实现，核心面积为3.24 mm²。在实验中，它与品质因数Q = 130的900 MHz SAW谐振器配合工作。实验结果表明，该读出电路从1.6 V电源获取7 mW的功耗。频率分辨率为733 Hz，相对精度为0.82 ppm，完成一次测量需要0.48 ms。与文献中先前的结果相比，这项工作在测量精度和测量时间之间进行了权衡，实现了最短的测量时间。
