Implantable-ingestible-electronic-thermometer

  
This oscillator circuit includes a quartz crystal that has a nominal resonant frequency of 262,144 Hz and is cut in the orientation that gives a large linear coefficient of frequency variation with the temperature. In this type of circuit, the oscillation frequency is controlled primarily by the crystal-as long as the gainbandwidth product is at least four times the frequency. In this case, the chosen component values yield a gain-bandwidth product of 1 MHz.
Implantable-ingestible-electronic-thermometer - schematic

Inductor Ll can be made very small: 100 to 200 turns with a diameter of 0.18 in. (4.8 mm) and a length of 0.5 in. (12. 7 mm). Although the figure shows two transistors in parallel, one could be used to reduce power consumption or three could be used to boost the output. The general oscillator circuit can be used to measure temperatures from -10 to + 140°C. A unit made for use in the human body from about 30 to 40°C operates at 262,144 ±50 Hz with a frequency stability of 0.1 Hz and a temperature coefficient of 9 Hz/°C.




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