Antti Ruha

A micropower analog-digital heart rate detector chip

A micropower detector chip integrated with CMOS technology has been developed for a hand-held heart rate monitoring instrument mainly used by professional athletes and others who exercise seriously to increase their endurance and overall performance. The chip uses linear bandpass filtering and threshold detection and is implemented with analog switched-capacitor (SC) and digital techniques. The bandpass filter transfer function is derived from the spectral contents of noisy ECG signals. The layout was designed in full custom style in order to minimize the silicon area. The chip achieves a detection rate of 90% with a simulated ECG signal corrupted with Gaussian noise (signal-to-noise ratio = 5) in the heart rate range 60-200 1/min with a total current consumption of less than 30µA from a 3-V supply. The detection rate is 96.9% for a noisy signal obtained from the MIT-BIH arrhythmia database.

Micropower analog structures for a CMOS heart rate indicator

A micropower heart-rate indicator integrated with CMOS technology and using several micropower blocks is currently under development. So far the complete DC-compensated preamplifier and the switched capacitor (SC) filter have been designed and tested. The designs of these structures and measurement results are presented. The SC filter consists of several sections, including an input decimator, lowpass filter, decimation/SH section, and highpass filter. Filter performance was measured by varying the temperature, supply voltage, and bias current. The temperature effects were minor, but any reduction in the GBW of the operational amplifiers with reduced bias current caused marked variations in the results. In addition, any reduction in the supply voltage below +or-1 V caused an abrupt attenuation of the amplitude response of the filter as the on-resistance of the CMOS switches increased due to inadequate clock amplitude.<<ETX>>

A transmitter chip for an ECG heart rate monitor

A transmitter chip for a heart rate indicator is being developed. In addition to bandpass filtering, nonlinear circuitry is being used to improve detection reliability under noisy conditions. The decision level for detection adapts to varying signal levels. A complete test chip has been designed and tested. It is integrated using a microwave analog technique and uses continuous-time, switched-capacitor, and digital circuitry. The detection principle, blocks used in implementation, and test results are presented.<<ETX>>

Skin temperature profiles on the human chest and in the wrist area

Skin temperatures on the chest and in the wrist area are interesting for continuous monitoring because they can be easily instrumented using an elastic belt or wristband which do not hamper movement in sports, for example. An infrared thermograph camera and NTC thermistors were used to take temperature profiles at these sensing points with a resolution of 0.1 degrees Celsius, and colored thermograms were used to analyze and compare the results. The effect of environmental changes on the skin temperature in the wrist area was studied by cooling and heating the fingers in water at 10 degrees Celsius and 40 degrees Celsius, and the effects of a loading situation on the chest area and wrist area were tested by means of a 30 min bicycle ergometer exercise. NTC thermistors were also used to measure wrist and chest temperatures in two environmental tests at minus 10 degrees Celsius and plus 60 degrees Celsius. Cooling of the fingers naturally reduces the skin temperature in the wrist area and heating increases it due to the venous circulation. The area of the radial artery in the wrist seems to be the most stable temperature point, altering by only about 2 degrees Celsius, whereas the temperature change at other points is up to 4 degrees Celsius. The bicycle ergometer exercise caused a decrease in skin temperature on the chest because of sweating. At the same time the skin temperature on the wrist decreased by about 1.5 degrees Celsius after the first 20 minutes and then returned to its previous level. The area of the radial artery in the wrist seems to be an attractive point for continuous temperature monitoring, especially under normal conditions, and also seems to reflect body temperature quite well upon loading and under different environmental conditions.

A design exercise of a micropower analog digital ASIC chip

A micropower heart rate detector chip integrated with CMOS technology has been developed. The chip uses analog SC and digital techniques. A mathematics program was used for system level optimization and analysis, whereas in circuit level verification a mixed mode and transistor level simulators were used. The layout was done in full custom style in order to minimize silicon area. This paper gives a general description of the application together with discussion about the actual design and some practical experiences encountered during the design project.<<ETX>>