Implantable telemetry transmission system for analog and digital data

Abstract

An improved telemetry transmission system for transmitting electrocardiographic information, indications of the occurrence of the pacing pulse and for transmitting digitially encoded information from an implanted pacemaker, an implanted drug dispensing device, or other implanted device, to a remote receiver. Digital data transmitted by the implanted system may include all programmed parameters as well as power source status and self test indications, or other programmed digital data such as the device serial number and lot number.

Having described the invention by way of the above examples and general description, the subject matter in which exclusive rights are claimed is defined as follows: 
     
       1. In a telemetry system for transmitting data from at least one location within a living body to an external receiver, a transmitter comprising: input means for receiving a signal from said location and providing an electrical signal representative of said data;   modulator means for receiving said electrical signal and generating an alternating signal having a frequency which differs from a predetermined nominal frequency by an amount determined by some characteristic of said electrical signal;   antenna means;   current source means;   capacitance means; and   switching means controlled by the alternating signal from said modulator means to connect said capacitance means to said current source means during half of the period of said alternating signal from said modulator means, and to connect said capacitance means to said antenna means during the other half of said alternating signal.   
     
     
       2. The invention of claim 1 wherein said antenna means is tuned to radiate damped sinusoidal signals having a frequency of approximately 10 kHz when said switching means connects to said capacitance means to said antenna means. 
     
     
       3. The invention of claim 1 wherein said antenna means has a resonant frequency of 175 kHz, the resonant frequency of said antenna means being reduced by the connection of said capacitance means to 10 kHz. 
     
     
       4. The invention of claim 1 wherein the predetermined nominal frequency of the output of said modulator means is approximately 1500 Hz. 
     
     
       5. The invention of claim 1 wherein said modulator means comprises a voltage controlled oscillator having a minimum current at which it may be operated and further comprising current limiting means for limiting the current delivered to power said voltage controlled oscillator to an amount slightly exceeding the minimum current at which said voltage controlled oscillator may be operated. 
     
     
       6. In the telemetry system of claim 1, a receiver comprising: receiving antenna means;   band pass filter means connected to said receiving antenna means to receive a signal from said receiving antenna means and said filter delivering an output signal representative of received signals within the pass band; and   a phase lock loop circuit connected to said band pass filter to receive the output therefrom and said circuit producing a demodulated analog output signal representative of said data.   
     
     
       7. A telemetry system for transmitting data from at least one location within a living body to an external receiver, a transmitter comprising: input means for receiving a signal from said location and providing an electrical signal representative of said data;   modulator means for receiving said electrical signal and generating an alternating signal having a frequency which differs from a predetermined nominal frequency by an amount determined by some characteristic of said electrical signal;   transmitting antenna means;   current source means;   capacitance means; and   switching means controlled by the alternating signal from said modulator means to connect said capacitance means to said current source means during half of the period of said alternating signal from said modulator means, and to connect said capacitance means to said transmitting antenna means during the other half of said alternating signal, said transmitting antenna means radiating a signal during said other half of said alternating signal;   a receiver comprising:   receiving antenna means adapted to receive a signal radiated by said transmitting antenna means;   band pass filter means connected to said receiving antenna means to receive a signal from said receiving antenna and said filter delivering an output signal representative of received signals within the pass band; and   a phase lock loop circuit connected to said band pass filter to receive the output therefrom and said circuit producing a demodulated analog output signal representative of said data. .Iadd.   
     
     
       8.  A transmitter for transmitting signals from an implantable medical device which are representative of either analog or digital values comprising a signal controlled variable frequency oscillator means having a control terminal, signal application means for selectively presenting information signals representative of said digital and analog values to said control terminal to vary the frequency of said oscillator means in response thereto relative to a nominal output frequency of said oscillator means that exists when said information signals are not being supplied, tank circuit and antenna means having a predetermined ringing frequency of oscillation when pulsed with energy, and drive circuit means coupled to said oscillator means and to said tank circuit and antenna means for supplying pulses of energy to said tank circuit and antenna means at a rate that is proportional to the output frequency of said oscillator means whereupon said pulses are radiated from said tank circuit and antenna means as damped ringing signals wherein said drive circuit means comprises a storage capacitor and discharge means for discharging said capacitor into said tank circuit and antenna means at a rate proportional to the frequency of said oscillator means so as to cause bursts of energy to be expended in said tank circuit and antenna means and transmitted thereby. .Iaddend. .Iadd.9. A transmitter as claimed in claim 8 wherein said discharge means comprises switching means for controlling the charging and discharging rate of said storage capacitor under the control of the output of said oscillator means. .Iaddend. .Iadd.10. A transmitter as claimed in claim 9 wherein the frequency of said tank circuit and antenna means is higher than said nominal frequency of oscillation of said signal-controlled oscillator means. .Iaddend. .Iadd.11. A transmitter as claimed in claim 10 wherein said tank circuit and antenna means comprises inductance means and capacitance means connected in parallel and said inductance means comprises a radiation coil. .Iaddend. .Iadd.12. A transmitter as claimed in claim 8 wherein said discharge means comprises switching means for controlling the supply of energy pulses to said tank circuit and antenna means under the control of the output of said signal-controlled oscillator means. .Iaddend. .Iadd.13. A transmitter as claimed in claim 12 wherein said tank circuit and antenna means comprises inductance means and capacitance means connected in parallel and said inductance means comprises a radiation coil. .Iaddend. .Iadd.14. A transmitter as claimed in claim 12 wherein the frequency of said tank circuit and antenna means is higher than said nominal frequency of oscillation of said signal-controlled oscillator means. .Iaddend.