Electrical computers and digital processing systems: support – Clock – pulse – or timing signal generation or analysis
Reexamination Certificate
1993-04-26
2001-05-22
Banankhah, Majid A. (Department: 2755)
Electrical computers and digital processing systems: support
Clock, pulse, or timing signal generation or analysis
C713S601000
Reexamination Certificate
active
06237105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to implantable medical devices and more specifically relates to a system and method for monitoring master clock oscillator operation in microprocessor and state machine based implantable pulse generators and for modifying the master clock oscillator output signal in response to a low power intelligent feedback signal from the monitoring system.
2. Description of the Prior Art
Early pulse generators such as cardiac pacemakers were asynchronous in operation, providing stimulating pulses to the heart at a fixed rate independent of the physiologic demand of the patient. In recent years, pacemakers which vary the pacing rate in response to numerous patient parameters have become widely available. For example, a rate responsive pacemaker may be responsive to patient physical activity. Such a pacemaker includes a sensor which produces an output that varies between a maximum sensor output level and a minimum sensor output level and provides for a pacing rate which typically varies between a selectable lower pacing rate and an upper pacing rate. Such a pacemaker which utilizes a piezoelectric transducer, is disclosed in U.S. Pat. No. 4,485,813, issued to Anderson et al., and assigned to Medtronic, Inc.
It has become common practice in recent years to provide programmable pacemakers in order to permit the physician to select and adjust the desired parameters to match or optimize the pacing system to the heart patient's physiologic requirements in an effort to minimize patient problems and to prolong or extend the useful life of an implanted pacemaker. Such pacemakers typically are microprocessor based systems or are based on state machines requiring accurate clocking, or timing signals. These timing signals are used to synchronize the various electronic functions within the pacemaker. Generally, a single master clock source, such as a clock oscillator, is employed to provide a periodic clocking signal at a single frequency. This clocking signal can be divided by various numerical values to result in a plurality of separate clock signals, all of which are at a fraction of the master clock signal for coordinating various handshaking operations within the programmable pacemaker.
Accurate clock signals are essential for proper functioning of the programmable pacemaker. If the frequency of the master clock signal deviates from its predetermined clock frequency, the pacemaker will not perform in the manner as intended. For example, the master clock circuit, typically including a piezo-electric crystal, may be susceptible to a noisy environment in certain rare circumstances including EMI and Cautery, and as a result not be able to guarantee the master clock signal that is delivered to the programmable pacemaker system meets the clock duty cycle requirements. In these rare cases, if the master clock signal is too narrow either in the positive or the negative half of the signal, the microprocessor, telemetry port and programmable pacemaker itself may fail to function properly. Thus, a failure at any time will result in operational failure where any programmable pacemaker block is state machine based.
SUMMARY OF THE INVENTION
To avoid operational failures attributable to an out-of-spec implantable pulse generator master clock, a new sub-system block is added. This block receives the output clock signal from the master clock, and from it, generates a modified master clock signal that replaces the original master clock signal to control the handshaking operations within the pulse generator to ensure proper operation. The function of the new sub-system block is to guarantee that the modified master clock signal delivered to the rest of the pulse generator system always has a duty cycle sufficient to ensure correct functionality of the system microprocessor, the programmable pulse generator itself and the telemetry port.
The microprocessor, pulse generator and telemetry port all require master clock signals received to be of certain duration. The pulse generator and system microprocessor generate event completion signals during each master clock period. These event completion signals allow the pulse generator and system microprocessor to perform one asynchronous event after another which are not synchronized with the master clock. The event completion signals are used to trigger the start of the subsequent, but in either case, never the last event. The inventive sub-system block guarantees a sufficient duty cycle by using the event completion signals from the pulse generator and system microprocessor. The sufficiency is achieved by incorporating an appropriate time delay into the modified master clock signal which is slightly longer than the last event in each half of the modified master clock signal. Thus, the combination of the event completion signals from the microprocessor and the pulse generator, combined with the delay provided by the inventive sub-system, provide the missing event completion signal for each half of the master clock cycle. The new half cycle event completion signals are then used to guarantee the duty cycle of the original master clock, thereby ensuring uninterrupted functionality of the implantable pulse generator, even during external disturbances of the battery voltage or other conditions which create disturbances of the master clock period or duty cycle.
Another feature of the inventive sub-block is the elimination of any necessity for a back-up master clock for redundancy. The sub-block design requires only 100-150 nanoamperes of current for full functionality, allowing it to operate simultaneously along with the original master clock within the implantable pulse generator system. The new sub-block does not require that it be left in a standby mode for conservation of energy.
REFERENCES:
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patent: 5227672 (1993-07-01), Sawtell
Korsunsky Roman
Reinke James D.
Walsh Kevin K.
Banankhah Majid A.
Duthler Reed A.
Medtronic Inc.
Patton Harold R.
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