2003 IEEE Topical Conference on Wireless Cbmmunication Technology

Modified Silicon Base Station Chips as Biomedical Sensors

Amy D. Droitcour', adroit@stanford.edu'; Olga Boric-Lubecke, olga@ieee.or& Victor Lubecke, lubecke@ieee.org2; Jenshan Lin, jenshan@ieee.org3; Gregoly T. A. Kovacs'

'Center for Integrated Systems, Stanford University, Stanford, California, USA 943'05 Electrical Engineering Dept., University of Hawaii at Manoa, Honolulu, Hawaii, USA 96822

'University of Florida, Gainesville, Florida, 3261 1 2

Abstract - Subcircuits designed for DCS 1800/PCS1900 base stations have been reconfigured into single-chip Doppler radar transceivers. Three of these radar chips have been fully integrated in 0.25 pm silicon CMOS and BiCMOS, and they have been used to remotely monitor heart and respiration activity. These radar chips have detected heartbeat and respiration rate 50cm from the subject, which may be useful in home monitoring, continuous monitoring, and physiological research.

INTRODUCTION The drive of the digital market has led to smaller, faster transistors, suitable for RFICs for wireless applications, including cellular base station circuits. Physiologic movement has been sensed with microwave Doppler radar systems since the early 1970's [l], but with heavy, expensive, and bulky waveguide components. By leveraging technology developed for base stations, it is possible to integrate such a system on a single silicon chip [2,3], which is compact, lightweight,' and could be inexpensively mass-produced. These advances come with a price, however: CMOS oscillators have notoriously high phase noise, and this becomes a limiting factor in a CMOS radar system. Though this makes it more difficult, detection of beart motion with CMOS radar is possible [2,3].

Radar motion sensing systems usually transmit a continuous wave (CW) signal, which is reflected off the target and then demodulated in the receiver. A target with time.-varying position reflects the signal and modulates its phase proportional to the target's time- varying position. Therefore, a CW radar with the chest as the target will receive a signal similar to the transmitted signal, with its phase modulated by the time-varying chest position. Demodulating the phase will then give a signal directly proportional to the chest position, which contains information about movement due to both heartbeat and respiration. Heart and respiration rates can be extracted from this data.

IMPLEMENTATION AND MEASURED Pd3SULTS Doppler radar transceivers with a topology similar to that shown in Fig. 1 were developed by adapting subcircuits designed for DCSI800/PCS1900 CMOS and BiCMOS base station receivers [2,3]. A base station uses a heterodyne receiver, while the radar system uses a homodyne transceiver. Since the double balanced mixer used for the base station chip can operate with a RF signal up to 2.5GHz and with an IF signal from DC to 300MHz, no modifications were necessary to use in the homodyne radar architecture. CMOS and BiCMOS VCOs were used without modification in the 1.6GHz CMOS and BiCMOS chips, and the CMOS VCO was re-tuned for the 2.4GHz CMOS chip. I.6GHz is the LO frequency for the DCS1800 system. The BiCMOS oscillator has 12dB lower phase noise than the CMOS oscillators [2]. Buffers, low noise amplifiers, and balms from base station chips were used for amplification and creation of differential signals.

Output traces with CMOS and BiCMOS I.6GHz chips are shown in Fig. 2(a) and @) respectively. The signal due to respiration is easily measured with this technique, and is

0-7803-81 96-3/03/$20.00 02003 IEEE 21 0

17 breaths per minute in (a) and 13 breaths per minute in @). Detecting the heart signal requires more signal processing to detect, and the heart signal is 93 beats per minute in (a) and 84 beats per minute in @). Since the CMOS oscillator has 12dB higher phase noise, the signal obtained with the CMOS chip is noisier than that of the BiCMOS chip.

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