Download in PDF Format

For a PDF-Viewer click here ...

Microwave Doppler radar can be used for non-contact, through-clothing measurement of chest wall motion, from which heart and respiration signatures and rates can be derived in real-time. A heart and respiration rate monitor has been developed based on this principle and the radio electronics have been integrated on a single CMOS chip, making inexpensive mass-production and miniaturization of the system possible. Although there are many potential applications for non-contact monitoring of heart and respiration rates, the fully integrated version focuses on the large and growing home monitoring market. This dissertation thoroughly explores the design requirements and trade-offs for this system, analyzing the transceiver architecture, circuit specifications, and the effects of phase noise on the system. Non-quadrature 1.6-GHz direct-conversion continuous-wave transceivers have been developed in 0.25-mm CMOS and BiCMOS, and two different 2.4-GHz quadrature direct-conversion continuous-wave radar transceivers with 1-mW transmit power have been fabricated in 0.25-mm CMOS. In a direct-conversion receiver, the phase relationship between the received signal and the local oscillator has a significant effect on the demodulation sensitivity, and the null points can be avoided with a quadrature receiver. The range-correlation effect on residual phase noise is a critical factor when detecting small phase fluctuations with a high-phase-noise on-chip oscillator. Phase noise reduction due to range correlation has been experimentally evaluated, and the measured phase noise was within 5 dB of predicted values on average. Data is presented from the method comparison study in which heart and respiration rates measured with the 0.25-mm CMOS quadrature Doppler radar system were compared with those measured with standard techniques on 22 human subjects. Accurate measurement of heart rate at 1 m and accurate respiration measurement at 1.5 m are shown. The data from the method comparison study is used to confirm theoretical estimates of the SNR, to evaluate techniques for combining the quadrature output signals and to evaluate techniques for determining the heart rate from the heart signature. Principal components combining is used to combine the quadrature signals and autocorrelation of the heart and respiration signatures is used to determine the heart and respiration rates. The current version of the single-chip Doppler radar cardio-respiratory rate detection system can successfully measure heart rate up to one meter and respiration rates up to two meters in most subjects that have been instructed to sit still, and it could be used to monitor sleeping or unconscious persons from a relatively close range, avoiding the need to apply electrodes or other sensors in the correct position and to wire the subject to the monitor. Doppler radar cardiopulmonary monitoring offers a promising possibility of non-contact, through-clothing measurement of heart and respiration rates. A CMOS single-chip version of this technology offers a potentially inexpensive implementation that could extend applications to consumer home-monitoring products, and could enable the use of multiple transceivers to solve some system-level problems. Further advances in the circuit design, system design and signal processing can increase the range and quality of the rate-finding, broadening the potential application areas of this technology.

 

Droicour, A. D., ìNon-contact measurement of heart and respiration rates with a single-chip microwave doppler radar,î Ph.D. Thesis, Stanford University, CA, 2006.