Enhancement of Vital-Sign Sensor Signal-to-Noise Ratio Using Wireless Frequency-Locked Loop

Conventional continuous wave (CW) vital-sign sensor generally suffer the phase noise of the voltage-controlled oscillator (VCO). This work develops a novel wireless frequency-locked loop (FLL) technique to overcome this problem. The wireless FLL can not only enhance the strength of the detected signal but also reduce the phase noise of VCO. The signal-to-noise ratio (SNR) of the vital-sign sensing of proposed wireless-FLL-based sensor is therefore greatly enhanced. Experimental results demonstrate that the maximum detection range of the developed 2.4 GHz wireless-FLL-based sensor is 4 m. Under the same condition, the maximum detection range of a 2.4 GHz conventional CW sensor is only 1.5 m.