Medtronic, Inc.

Gary E Nelson

David L Thompson

John D Wahlstrand

Eric G Persson

Joseph A Ballis

An implantable medical device uses a solid-state sensor for detecting the application of an external magnetic field. The sensor includes first and second split-drain field-effect transistors (MAGFETs) which are cross-coupled such that an external magnetic field perpendicular to the channel regions of the MAGFETs causes an increase in current through one split-drain half of each MAGFET, and a decrease in current through the other split-drain half of each MAGFET. The sensor also includes a high-gain differential amplifier coupled between the MAGFETs for detecting changes in the current conducted through the respective split-drain halves, and produces an output voltage which changes upon application of an external magnetic field to the implantable medical device. The magnetic sensor operates at low power supply voltages and bias currents available in implantable medical devices such as a cardiac pacemaker, so that current drain and power consumption are minimized.

Magnetic field sensor

A low cost, limited-function implantable medical device. The device's synchronous circuits are driven by an ultra-slow master clock signal produced without utilization of a crystal oscillator. The device is non-invasively programmable by means of an externally applied programming magnet, which is detected by a solid state magnetic sensor (MAGFET) circuit in the implanted device. The MAGFET circuit is capable of discriminating between two polarity orientations of the programming magnet, so that one polarity is associated with increasing programmable parameters and the opposite polarity is associated with decreasing programmable parameters. Upon initial placement and detection of the programming magnet, the disclosed device performs a threshold margin test comprising three asynchronous stimulating pulses at the current pulse width and pulse amplitude settings.

Low cost implantable medical device

A low cost, limited-function implantable medical device. The device's synchronous circuits are driven by an ultra-slow master clock signal produced without utilization of a crystal oscillator. The device is non-invasively programmable by means of an externally applied programming magnet, which is detected by a solid state magnetic sensor (MAGFET) circuit in the implanted device. The MAGFET circuit is capable of discriminating between two polarity orientations of the programming magnet, so that one polarity is associated with increasing programmable parameters and the opposite polarity is associated with decreasing programmable parameters. Upon initial placement and detection of the programming magnet, the disclosed device performs a threshold margin test comprising three asynchronous stimulating pulses at the current pulse width and pulse amplitude settings. After the threshold margin test is performed, each subsequent removal-and-replacement cycle of the programming magnet cause the disclosed device to enter a different programming mode, in which mode a particular operational parameter of the device may be adjusted up or down. Programmable values are retained in the implanted device in the form of analog voltages stored in non-volatile analog memory cells. During operation, the stored analog voltages are applied to voltage-to-current converting circuits to produce signals whose currents control the time-out interval of various multivibrator-type timing circuits.

A battery powered cardioverter or defibrillator employing output capacitors for delivery of cardioversion or defibrillation pulses. The capacitors are charged by means of a step-up transformer, coupled and uncoupled from the battery by means of a voltage controlled oscillator which varies its off and on times as a function of the voltage on the battery and the voltage stored on the output capacitor to allow for rapid charging of the capacitor even under conditions of battery depletion. The voltage controlled oscillator is constructed to provide a highly accurate timing signal with a low current drain.

VCO driven flyback converter for implantable cardoverter/defibrillator

A pacemaker sense amplifier circuit exhibiting a very high common mode rejection ratio for detecting intracardiac electrogram signals is disclosed. The circuit includes a sampling capacitor which is differentially charged by the intracardiac signal. The voltage stored on the sampling capacitor is periodically applied to a high input impedance differential voltage amplifier which is referenced to the battery ground. The signal is smoothed and reconstructed by a bandpass filter, and is applied to a comparator to generate a logic level pulse indicative of the occurrence of a cardiac depolarization.

Growing community of inventors

Schaumburg, IL, United States of America

Gary E Nelson