Abstract: A switched capacitor circuit that uses more than one switch in parallel. The control signals of each switch are turned off in sequence, giving an induced offset voltage in the final case due only to the last turned off switch, but with a capacitor charge or acquisition time due to the parallel combinations of all of the switches. An alternative switch capacitor circuit uses a bootstrapped gatedrive control signal. The gatedrive control signal initially assumes a high value resulting in a low switch resistance and, thus, a fast capacitor charge or acquisition time followed by a reduction in voltage to the normal "digital" level until turn off. The resultant induced offset voltage is the same as that due to a simple minimum sized switch.

Abstract: The subject apparatus integrates a two-channel defibrillator with a programmable stimulator to provide a means for assessing lethal ventricular tachyarrhythmias and determining defibrillation thresholds during implantable defibrillator procedures. The subject apparatus includes a number of features to aid doctors as well as improve patient care at substantially decreased patient risk. These features include an automatic charging circuit, as well as dual channel high voltage capacitor circuits to reduce the time in which a rescue shock can be delivered to a patient after an initial test defibrillation shock. Parameter storage is provided to allow the unit to be preprogrammed prior to the initiation of an electrophysiologic procedure. A microprocessor controlled display system provides the physician with information parameters regarding defibrillation shocks. This displayed information includes the energy delivered and the resistance in the patient.

Abstract: The present invention is directed to various features of an implantable combined defibrillation/pacemaker system. The system's defibrillation delivery circuit provides for delivery of a multi-phase defibrillation waveform. It also includes features for insuring low patient current leakage. Protection circuitry is provided for protecting the pacing circuitry from damage by the high voltage defibrillation output. The dual channel cardiac pacing circuit accommodates bipolar and pseudo-unipolar pacing. The system includes the ability to detect defibrillator lead breaks without delivering a defibrillation pulse to the patient. An additional advantage of the disclosed system is its ability to use the pacing output stage for extremely high rate pacing to induce ventricular fibrillation.

Abstract: The subject invention integrates a two-channel defibrillator with a programmable stimulator to provide a means for assessing lethal ventricular tachyarrhythmias and determining defibrillation thresholds during implantable defibrillator procedures. The subject apparatus includes a number of features to aid doctors as well as improve patient care at substantially decreased patient risk. These features include an automatic charging circuit, as well as dual channel high voltage capacitor circuits to reduce the time in which a rescue shock can be delivered to a patient after an initial test defibrillation shock. Parameter storage is provided to allow the unit to be preprogrammed prior to the initiation of an electrophysiologic procedure. A microprocessor controlled display system provides the physician with information parameters regarding defibrillation shocks. This displayed information includes the energy delivered and the resistance in the patient.

Abstract: A low battery detect circuit shuts down high current circuitry in the system in the event that battery voltage drops to a level such that the regulated output voltage is endangered. The trigger voltage is dependent upon capacitor ratios and a reference voltage. The output of the detection circuitry is a digital signal which can be used to disable high current circuitry in an implantable medical device and, thus, allow the battery voltage to recover. Alternatively, the output of the detection circuitry can be used as a battery status indicator flag.

Abstract: A power supply down-conversion, regulation, and low battery detection system has application in an implantible defirillator but is also directly applicable to any battery powered implantible device. Battery voltage is down-converted by a high efficiency switched capacitor voltage divider to a suitable intermediate voltage. This voltage is then linearly regulated down to the desired output voltage. A second regulator, which takes current directly from the battery, supports the output voltage in the event that the load current cannot be supplied by the voltage downconverter. A low battery detect circuit shuts down high current circuitry in the system in the event that battery voltage drops to a level such that the regulated output voltage is endangered.

Abstract: A voltage measurement circuit is provided which can be used in a single supply situation, which has a measurement range from rail to rail and which uses a reference voltage which can lie anywhere between the rails but not at the rail to which measurements are to be referenced. The unknown voltage is sampled to a first plate of a capacitor. The second plate of the capacitor is connected to ground. The first plate of the capacitor is then connected to the first input of a comparator, the second input being connected to receive the reference voltage. If the unknown voltage is less than the reference voltage, the second plate of the capacitor is disconnected from ground and then connected to receive the reference voltage. Otherwise it remains connected to ground. The first plate of the capacitor is then connected to a constant current source, causing the voltage at the first comparator input to decrease linearly with time.

Abstract: A combination two-channel defibrillator and programmable pacing stimulator for assesses lethal ventricular tachyarrhythmias and determine defibrillation thresholds during implantable defibrillator procedures. A pair of switching transistors are provided to protect the pacing circuit when a defibrillation shock is delivered. These switching transistors provide symmetric voltage protection and prevent the defibrillation energy from being shunted back to the patient through the pacing leads.