Abstract: Biomedical information is directly digitally telemetered from the patient through a frequency modulated transmitter to a remote receiver and computer station. A phase-lock-loop circuit in the digital transmitter compensates for DC data bias by averaging and generating a scaled measure of the DC content of the digital data fed into the phase-lock-loop circuit. The average signal is then provided as a control signal to a first voltage controlled crystal oscillator, the output of which is then used as a reference frequency for the phase-lock-loop circuit. Frequency modulation of the digital data is provided by coupling the digital data directly into the voltage control input of the voltage controlled oscillator which generates the output frequency. Further control of the phase-lock-loop circuit in the transmitter is achieved by prepositioning the operating frequency of the voltage controlled oscillator by means of a microcontroller.

Abstract: Biomedical information is directly digitally telemetered from the patient through a frequency modulated transmitter to a remote receiver and computer station. DC offset on the biopotential leads and signals from the patient is compensated by converting the output of the amplifier, such as an electrocardiographic amplifier, into digital format, determining the average or DC component of the digital signal, and generating a digital correction word which is then converted into analog form and fed back into the input of the electrocardiographic amplifier to cancel out the DC offset. The same circuitry is used to insert a standard test signal instead of a correction signal and the output of the amplifier is then checked not to determine its DC component, but to determine whether or not the gain of the electrocardiographic amplifier is performing at a predetermined calibration point. If not, a digital correction word is generated and provided as a correction signal to the programmable gain amplifier.