Working principle of MEMS Huygens clock (IMAGE) Engineering Caption (a) Schematic of original Huygens’s clock. (b) Structure of MEMS Huygens clock system. (c) Operating mode of MEMS resonator. (d) Image of microfabricated MEMS resonator. PLL: phase locked loop; TIA: trans-impedance amplifier; Va: DC driving voltage of the active oscillator; Vb: DC driving voltage of the passive oscillator; Ref: reference. Credit Xueyong Wei et al. Usage Restrictions Credit must be given to the creator. Only noncommercial uses of the work are permitted. No derivatives or adaptations of the work are permitted. License CC BY-NC-ND Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.