Analog telemetry system for biomedical implant

An implant analog telemetry system, comprising

• a fully implantable biomedical device including a tuned coil circuit with a tuned coil and transistor means in circuit therewith having a linear operating region for altering the impedance of said tuned coil circuit as a function of an applied control signal, and a linear amplifier having an input connected to receive an analog signal to be transmitted and an output connected to said transistor means as the control signal, and
• an external telemetry receiver including means for generating a constant frequency carrier at the tuned frequency of said coil and receiver means for producing an output varying in response to the phase shift between the externally generated carrier and the received signal reflected by said tuned coil circuit,
• said implantable device further including means responsive to a predetermined level of coupling of the carrier signal into the tuned coil circuit for supplying power to said linear amplifier,
• said implantable device further including a self calibration circuit responsive to the supplying of power to said amplifier means for applying for a predetermined calibration period an input signal to said amplifier signal which alternates between two levels by a predetermined known value,
• whereby the recovered output of said receiver means can be calibrated by observing the difference between said two levels and noting that said difference corresponds to the known value.

An implant analog telemetry system, comprising

• a fully implantable biomedical device including a tuned coil circuit with a tuned coil and transistor means in circuit therewith having a linear operating region for altering the impedance of said tuned coil circuit as a function of an applied control signal, and a linear amplifier having an input adapted to be connected to a varying electrical signal and an output connected to said transistor means as the control signal, and
• an external receiver including means for generating a constant frequency carrier at the tuned frequency of said coil circuit and receiver means for producing an output varying as the phase shift between the externally generated carrier and the received signal due to the signal reflected by said tuned coil circuit,
• said implantable device further including means for generating and applying a fixed bias voltage to said transistor means to bias said transistor means toward the middle of its linear operating region, and
• full wave rectifying diode bridge means connected to said tuned coil circuit for supplying rectified variable power due to the coupling level of said carrier frequency to said bias voltage to provide a supplemental variable component to compensate for variations in the level of coupling.

A cardiac pacer/ICEG telemetry system, comprising

• a fully implantable cardiac pacer including conductor means making electrical contact with the heart, means for generating and applying electrical stimulation pulses to the heart via said conductor means, a tuned coil circuit including a tuned coil and transistor means in circuit therewith having a linear operating region for altering the impedance of said tuned coil circuit as a function of an applied input signal, a linear amplifier having an input and an output connected to said transistor means as the control signal, and analog switch means for coupling said amplifier input to said conductor means on command to feed the natural ICEG signal appearing on said conductor means through said amplifier, and
• an external telemetry receiver including means for generating a constant frequency carrier at the tuned frequency of said coil and receiver means for producing an output varying as the phase shift between the externally generated carrier and the received signal due to the signal reflected from said tuned coil circuit,
• said cardiac pacer further including
• automatic means for momentarily grounding said conductor means following the application of a stimulation pulse and means for closing said analog switch means immediately following the grounding of said conducting means, whereby
• residual charge decaying on said conductor means is removed in order to observe the ICEG signal immediately following stimulation to evaluate the capture threshold.