On the Need for Low Phase Noise Oscillators for Wireless Passive Sensor Probing

Two oscillators are needed for passive wireless sensor readers: a radiofrequency local oscillator generating the carrier within the bandpass of the sensor, and a clock triggering analog to digital conversion of the signals returned by the sensor. We assess the influence on measurement resolution of these two oscillators, hinting at some design rules of the sensor based on the characteristics of the oscillators as driven by cost, size, or power consumption. We demonstrate that local oscillator phase noise is a significant parameter in assessing the resolution of passive acoustic sensor probed through a wireless link, although with different characteristic conditions whether the sensor is in a delay line configuration (short term --far from carrier -- response) or a resonator (long term -- close to carrier -- response).