Analyzing the Effect of the Front-end Circuit for the FBAR Sensor

Abstract The FBAR sensor can be affected severely by its front-end circuit, especially the phase noise; however, it has rarely been discussed up to now. Herein, we analyze the influence of phase noise in the front-end circuit on an FBAR humidity sensor. A frequency shift detecting system was designed combined with the theoretical calculation and Advanced Design System (ADS) simulation. The available range of frequency shift is seriously influenced by phase noise particularly for its lower limit, improved from 380 kHz to 200 kHz during the reduction of phase noise from -107.92 dBc/Hz@1 MHz to -135.97 dBc/Hz@1 MHz. Simultaneously, the display range for the FBAR humidity sensor system increases by 23% thanks to the reduction of it by -28 dBc/Hz@1 MHz. Summarily, the phase noise optimization in the front-end circuit can effectively improve the display range of sensor systems, which is not limited to the application of FBAR humidity sensors.