Analog telemetry system for biomedical implant

• US 4,543,953 A
• Filed: 07/18/1983
• Issued: 10/01/1985
• Est. Priority Date: 07/18/1983
• Status: Expired due to Term

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Cordis Corporation (Cardinal Health, Inc.)
• Inventors: Slocum, Chester D., Cutolo, Vincent T.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): Shein, Mitchell J.
• Application Number:
  US06/514,514
• Time in Patent Office: 806 Days
• Field of Search: 128/419 P, 128/419 PS, 128/419 PT, 128/419 PG, 128/631, 128/903, 340/870.1, 340/870.31
• US Class Current: 607/32
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: Y10S 128/903 Radio telemetry

Abstract

An analog data transmission circuit for a biomedical implant employs a linear amplifier to modulate the impedance of a resonant circuit tuned to an externally generated constant carrier frequency. The resonant circuit comprises a tuned coil in circuit with a linear modulating switch and a digital modulating switch. The digital switch is gated by the digital data output from digital control circuitry within the implant. The linear amplifier output drives the linear modulation switch. The switches are preferably matched pairs of MOSFET'"'"'s of opposite polarity having complementary parasitic diodes which form a phantom diode bridge. The bridge acts as a full wave rectifier and boosts the bias voltage on the sources of the FET pair forming the linear modulation switch such that the radiated amplitude is independent of the distance of the programming head. A timed power-up circuit supplies power to the amplifier and starts a square wave calibration period in response to the approach of the programming head. For ICEG transmission, a charge dump circuit depolarizes the lead before it is coupled to the amplifier.

Claims

1. 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 circuit as a function of an applied control input, 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 due to the reflected signal from said tuned coil circuit,

said implanted device further including a linear amplifier having an input connected to said transistor means as the control signal, and

means for supplying a variable bias voltage to said transistor means as a function of the level of energy coupled into said tuned coiled circuit from said external telemetry receiver,

said variable bias means including means for supplying a nominally fixed bias to said transistor means corresponding to the middle of said linear operating region and means for rectifying the signal coupled into the tuned coil circuit due to said carrier frequency and combining the rectified signal with said fixed bias to provide a supplemental variable bias component which creates an inverse relationship with the coupling level,

whereby variations in the proximity or strength of the coupled carrier signal have a reduced effect on the amplitude of the recovered waveform at the output of said receiver means.

2. 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 power supplying means including means for rectifying and accumulating the signal induced by said carrier in said tuned coil circuit, and said power supplying means further including means responsive to the attaining of a predetermined level by said accumulated signal for supplying power to said amplifier following a predetermined additional delay.

3. 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.

4. 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.

5. 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.