Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-12-14
2002-09-24
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S031000, C607S032000
Reexamination Certificate
active
06456887
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of implantable medical devices, and more particularly to low energy uplink and downlink telemetry control for an implantable medical device (IMD) telemetry transceiver.
BACKGROUND OF THE INVENTION
At present, a wide variety of IMDs are commercially released or proposed for clinical implantation that are programmable in a variety of operating modes and are interrogatable using RF telemetry transmissions. Such medical devices include implantable cardiac pacemakers, cardioverter/defibrillators, cardiomyostimulators, pacemaker/cardioverter/defibrillators, drug delivery systems, cardiac and other physiologic monitors, electrical stimulators including nerve and muscle stimulators, deep brain stimulators, and cochlear implants, and heart assist devices or pumps, etc.
Typically, certain therapy delivery and monitoring operational modes and parameters of the IMD are altered temporarily or chronically in a non-invasive (i.e. non-surgical) manner using downlink telemetry transmission from an external programmer of programming and interrogation commands (herein referred to as “downlink telemetry data”). Moreover, a wide variety of real time and stored physiologic and non-physiologic data (referred to collectively herein as “patient data”) is uplink telemetered by the IMD to the programmer in response to a downlink telemetered interrogation command.
The telemetry transmission system that has evolved into common use currently relies upon the generation of low amplitude magnetic fields by current oscillating in an LC circuit of an RF telemetry antenna in a transmitting mode and the sensing of currents induced a closely spaced RF telemetry antenna in a receiving mode. Short duration bursts of the carrier frequency using a variety of telemetry transmission and encoding formats are transmitted through the patient's skin between the antennae and transceiver circuits in a programming head overlying the skin and the IMD under the skin. In the current MEDTRONIC® product line, the RF carrier frequency is set at 175 kHz and the RF telemetry antenna of the IMD is typically coiled wire wound about a ferrite core that is located within the hermetically sealed enclosure. The hermetically sealed enclosure also typically contains a battery power source and circuitry for controlling the operation of the IMD and a reed switch or MAGFET that is responsive to an externally applied magnetic field within the external programming head to enable decoding of downlink telemetry transmissions by and transmission of uplink telemetry from the IMD.
In an uplink telemetry transmission from an IMD, it is desirable to limit the current drain from the IMD battery as much as possible simply to prolong IMD longevity. As the technology advances, IMDs become ever more complex in possible programmable operating modes, menus of available operating parameters, and capabilities of monitoring increasing varieties of physiologic conditions and electrical signals. These complexities place ever increasing demands on the programming and interrogation system and the medical care providers using them. Thus, as device operating and monitoring capabilities multiply, it is desirable to be able to transmit out ever increasing volumes of data in real time or in as short a transmission time as possible with high reliability and immunity to spurious noise. Moreover, it is desirable to eliminate the need for the magnetic field coupling between the programming head and the IMD and to allow secure programming and interrogation to take place at greater distances between the IMD and programmer antennae.
As a result of these considerations, many RF telemetry transmission data encoding schemes have been proposed or currently are used that increase security and the data transmission rate as well as the safe operating distance between the IMD and programmer antennae. One way to increase data transmission capacity is to increase the RF carrier frequency and the bandwidth allocated to an active transmission channel into the MHz range as set forth in commonly assigned U.S. Pat. No. 5,861,019 and in pending U.S. patent application Ser. No. 09/302,932 for a “Telemetry System for Implantable Medical Devices”, filed Apr. 30, 1999, by Villesca et al.
The above-referenced 175 kHz RF carrier frequency is generated employing a relatively simple low current consuming L-C tank circuit and switching circuitry. But, a high frequency RF generator is necessary to generate the high frequency RF carrier signal in the MHz range, and it is necessary to carefully control the generator to prevent frequency drift without unduly increasing current consumption from the IMD battery.
Similar problems exist in other non-IMD communication systems operating with a particular RF carrier frequency or within particular allocated frequency bands in FM transmission and reception modes as set forth in U.S. Pat. Nos. 4,521,918, 4,955,075, 5,335,365, 5,748,103, 5,767,791 and 5,944,659, for example. Typically, a battery powered remote device, e.g., an external patient monitor or a mobile cellular phone, is powered by a battery and communicates with remote, line powered equipment either periodically, in the case of a monitor, or, in the case of a cellular phone, when a user answers an incoming call or initiates an outgoing call. The battery powered monitor or cellular phone employs a frequency synthesizer to generate the RF carrier signal during transmission of data or voice, and the frequency synthesizer typically comprises a voltage controlled oscillator (VCO) and a phase lock loop (PLL) circuit that regulates the frequency of the generated RF signal. The PLL circuit operates in a feedback path employing a reference frequency to develop a PLL control voltage maintained on a capacitive loop filter that is applied to a control input of the VCO which responds by oscillating at the RF carrier frequency established by the control voltage. In the transmission mode, the RF carrier frequency is modulated in frequency by the superimposition of a data or voice voltage on the control voltage, thereby increasing or decreasing the VCO generated carrier frequency.
The PLL circuit consumes battery energy, and so, it is often only operated to stabilize the VCO and is then turned off during data or voice transmission or during a standby mode, as suggested in the above-referenced '365 patent. In addition, it is proposed in the above-referenced '075 patent to employ automatic frequency control (AFC) during reception of the RF carrier frequency of a received signal to stabilize the VCO frequency. In the receive mode, the VCO frequency is initially stabilized by the PLL circuit, and then the AFC is substituted for the PLL, which is disconnected from the VCO and/or powered off.
It is also proposed to remove power from the PLL circuit or disconnect it from the VCO during the transmission mode after the VCO voltage has stabilized to within acceptable frequency tolerances and provides the control voltage on the capacitive loop filter. However, the control voltage stored by the loop filter tends to is decline due to current leakage over time, and so it is necessary to periodically power up and/or reconnect the PLL circuit to the loop filter and VCO to restore the control voltage as described in the above-referenced '918 patent. Or, the control voltage that is developed in a transmit or receive mode is stored and is used during the standby mode to maintain the control voltage via a feedback loop under the control of a microcomputer as described in the above-referenced '365 patent. The feedback loop employs A/D and D/A converters and is not used during the transmit or receive modes because it would inherently introduce noise on the transmitted or received signal. The circuitry of such a feedback loop also consumes space on the RF module that must be fitted into the limited space within the IMD housing.
Accordingly, it is an objective of the present invention to save IMD battery energy during telemetry sessions while sti
Dudding Charles H.
Haubrich Gregory J.
Medtronic Inc.
Schaetzle Kennedy
Wolde-Michael Girma
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