A 20 ppb Resolution Readout Circuit Dedicated to Optomechanical Mass Sensors

Optomechanical resonators are the new basis for the design of ultra-sensitive mass sensors [1]. With a mechanical quality factor Q ∼ 50 in liquid environment and a sensitivity of 1 Hz/10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−18</sup> g, they are well suited to detect chemical or biological particles. To the best of the authors' knowledge, no electronics has yet been proposed to read such a sensor. Therefore, in this paper we present a circuit dedicated to the readout of optomechanical mass sensors. The chosen architecture is an Adjustable Heterodyne Frequency Locked-Loop (AH-FLL). This electronic presents fast convergence, frequency flexibility and robustness to disturbances. Concerning the performance, the readout circuit alone has a frequency stability of 20 ppb. Once coupled with the optomechanical transducer the system resolution reaches 500 ppb. For a 316 MHz resonator with 1 Hz/ag sensitivity, this corresponds to a mass resolution of 158 ag.