A Micropower Pulsewidth-Modulation-Pulse-Position-Modulation Two-Channel Telemetry System for Biomedical Applications

A novel micropower, two-channel telemetry system, which has been used to transmit the occurrence of the QRS complex of the heart waveform and temperature information, is described. The system employs pulsewidth-modulation (PWM) and pulse-position-modulation (PPM) methods plus a few unique circuits and system-design techniques so that it has the following desirable features. 1) The transmitting unit consumes extremely low power due to low duty cycle and yet delivers high peak power for better receiving. In addition, the unit is compensated (not regulated) for battery voltage variation. 2) By means of adaptive threshold, pulse-width-discrimination and pulse-rate-discrimination networks, the receiving unit is relatively noise free in signal identification. Information in analog and digital form are available at the output for convenience. A prototype system was designed and fabricated. Test results are presented. Due to the availability of the integrated circuits on the market, medical doctors and biologists will be able to duplicate the system if the system-size problem is not severe. Although the design was not trivial, the implementation is quite straightforward. Hence it is believed that device or integrated-circuit manufacturers would be able to implement it in a much more compact form.