Effect of VCO Non-Linearity on Non-Contact Vital Signs Detection in CW and FMCW Radars

Frequency modulated continuous wave (FMCW) radars are being widely used for vital signs detection due to their capability of range determination. Compared to continuous wave (CW) radars, this additional feature of FMCW radars helps in distinguishing between multiple people and targets. In this paper, the impact of voltage controlled oscillator (VCO) non-linearity on vital signs detection is evaluated with detailed mathematical analysis and MATLAB simulations using a transistor-level nonlinearity model. We demonstrate that vital signs detection is indeed possible with a non-linear VCO, when it is used in CW and FMCW radars. This also leads to the conclusion that expensive linear waveform generation techniques are not needed in indoor vital signs monitoring applications. This can substantially reduce the cost of radars-on-chip.