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39 202 R. Puers and P. Wouters Fig. 10. Photograph of the fully assembled and operational telemetry device. Overall diameter is 33mm. in figure 11. Apart from the telemetry transmitter and receiver stages, two building blocks in the form of integrated circuits are part of the internal circuitry of this device. A first IC is the Philips PCD3343A microcontroller. It supervises the telemetry functions, and the in- and outgoing communication between the Sensor Interface Chip (SIC) and the outside world.

In the case of a stand-alone, remote monitoring device, this is a bad idea, since a lot of the power will be waisted during monitoring and even more during transmission. For battery operated systems that equals a limited time of operation, which is in most cases unwanted by the users. What is then the frequency at which a specific parameter should be looked at? Of course, the frequency contents of the monitored signal primarily defines the 'sampling' or 'monitoring' frequency. g. often sufficient to measure body temperature only once every 15 minutes, whereas it is pointless to do the same for movement.

O~/ f4 RUN l' : ' : "iL. . •... . 9O'll 215 ~. :, ••• - ••. ':, •••• . .. input signal. ___" . diff~~~~t ii'~~~~ity' ................ calibrations different offset calibrations L 1~37:24 Wed Nov 6. 1996 Time (lms/div) Fig. 9. Oscilloscope graph showing the triangular input signal and the output signal for several different calibration factors programmed in the calibration chip. input-output transfer of the chip can be programmed, according to the presented calibration principle. Because the analog signal goes through a cascade of local-feedback amplifiers (IV- and VI-converters) with relatively large bandwidth, the bandwidth of the complete circuit can be kept large as well.