Abstract: The present invention relates to novel inventive compound device structures, enabling charged-based logic gates. In particular, a switched p-channel and/or n-channel current field effect transistor, a solid state device based on a complimentary pair of a switched p-channel and n-channel current field effect transistors, and/or a solid state device based on a complimentary pair of a p-channel and n-channel current field effect transistors are used for constructing such logic gates. The switched current field effect transistor comprising a source and a drain, wherein the source and drain defines a channel, a diffusion that divides the channel into a source channel segment between the source and the diffusion and a drain channel segment between the drain and the diffusion, a source channel gate that is coupled to the source channel, and a drain channel gate that coupled to the drain channel. These novel device structures provide various improvements over the conventional devices.

Abstract: This invention relates to low noise sensor amplifiers and trans-impedance amplifiers using a complementary pair of current injection field effect transistor (iFET) devices (CiFET). CiFET includes a N-type current field-effect transistor (NiFET) and a P-type current field-effect transistor (PiFET), each of the NiFET and PiFET has a source, a drain, a gate, and a diffusion (current injection) terminal (iPort). Each iFET also has a source channel with a width and a length between the source and diffusion terminal, and drain channel with a width and a length between the drain and the diffusion terminal. A trans-impedance of the CiFET device is adjusted by a ratio of width/length of source channel over width/length of drain channel of the iFET and supply power voltage. In one configuration, the gate terminals of the NiFET and PiFET are connected together to form a common gate. In another configuration that common gate is configured as a voltage input for a high input impedance mode.

Abstract: In an implantable medical device system such as a pacemaker system, there is provided a system and method for measuring lead impedance so as to obtain reliable data concerning any indication of the need to replace the lead. A relatively short duration low current AC burst is delivered after a standard pacing pulse, at a time to coincide with the heart's refractory period. The pulse is long enough in duration, e.g., 50-125 ms and preferably around 100 ms, to achieve the benefit of substantially steady state measurement, but short enough to substantially avoid the possibility of inducing any cardiac arrhythmia. The current level of the burst is limited to about 30 microamps, providing a further factor of safety against inducing an unwanted arrhythmia. The PPAC technique is adaptable for automatic measurement within an implantable device, or for implementation involving an external programmer which triggers the test.

Abstract: A rate-responsive pacemaker pulse generator and lead system that allows the rate at which the pacemaker delivers electrical stimulation pulses to the heart to be adjusted as needed in order to satisfy the body's physiological needs. The pulse generator and lead system include first and second electrodes coupled to a virtual load and monitoring circuit for monitoring the electrical energy provided through the virtual load in order to detect the magnitude of cardiac depolarization signals. The impedance of the virtual load is intentionally mismatched to the source impedance of the cardiac tissue in order to increase the peak-to-peak variation of the cardiac depolarization signals as a function of modulation of the tissue source by respiratory activity. The peak to peak modulation of the cardiac signals is processed to provide a pacing rate control signal.

Abstract: An apparatus for producing signals indicative of power levels of depolarizations of heart tissue, particularly adapted for use in an implantable antiarrhythmia device or an implantable pacemaker. The device distinguishes between the power level of sensed depolarization signals in order to distinguish between different types of depolarization waveforms. In particular, the measured power level of the sensed depolarizations may be employed to distinguish between normally conducted and ectopic beats, for use in controlling the operation of an implantable antiarrhythmia device such as an implantable pacemaker/cardioverter/defibrillator or for use in controlling the operation of a bradycardia pacemaker.

Abstract: A cardiac pacemaker or other tissue stimulator including first and second stimulation electrodes mounted adjacent to one another and adjacent the tissue to be stimulated, such as a chamber of a heart, a return electrode and a pulse generator which independently generates two or more stimulation pulses. The pulses are applied between the first stimulation electrode and the return electrode and between the second electrode and the return electrode in an overlapping fashion. By controlling the relative timing and polarity of the pulses, the potential gradient between the electrodes and the rate of change of the potential gradient may be varied.

Abstract: A physiological monitoring system for monitoring the condition of a patient's body tissue. The device includes electrodes for contacting the tissue to be monitored, circuitry for generating electrical signals at at least two frequencies for application to the tissue and circuitry for monitoring the impedance of the tissue, at the frequencies applied. The device includes in addition apparatus for detecting changes in the relationship of the measured impedances at the frequencies applied, and for processing the detected changes in impedance relationship to provide an indication of the condition of the tissue. The monitoring apparatus may be practiced in the context of an implantable stimulator, such as a cardiac pacemaker, in which the pulse frequency is varied as a function of the detected condition of the tissue.

Abstract: A pacemaker sense amplifier which includes active circuitry which establishes and attempts to maintain a constant field density between two electrodes, effectively clamping them together at substantially fixed relative electrical potentials. The amount of current or power provided to the electrodes monitored and forms the basis of detection of the passing cardiac depolarization wavefront. A timer is sued to define a detection window after the generation of a pacing pulse. The occurrence of a detected depolarization within the detection window is indicates that the pacing pulse has captured the heart.

Abstract: A pacemaker having two bipolar leads, one atrial, one ventricular, each with TIP and RING electrodes, configured as for conventional bipolar pacing/sensing in both chambers. Switching circuitry in the pacemaker is operable to select from among various possible sensing configurations, including one configuration in which sensing is performed between the ring electrodes of the respective pacing/sensing leads. Pacing is preferably performed in a conventional unipolar configuration in each chamber, from the respective tip electrodes. The "ring-to-ring" EGM signal is applied to filtering and EGM amplifier circuitry, and then provided to a telemetry system for transmission to an external receiver. The ring-to-ring EGM signal possesses the high resolution properties of conventional intracardiac signals, and is relatively unaffected by the after-potentials and tissue polarization effects that arise when the same lead is used for pacing and sensing.

Abstract: A system for detecting changes in the myocardial conduction velocity and deriving control signals therefrom for controlling the delivery of electrical or other therapy to the heart or for monitoring or diagnostic purposes. The system comprises two spaced electrodes coupled to amplifiers which detect the relative arrival times of the depolarization wavefront at the electrodes, measurement circuitry for measuring the difference in arrival times to determine conduction velocity circuitry for deriving control signals for controlling operation of an implantable medical device as a function of measured conduction velocity. The particular embodiment disclosed is a cardiac pacer in which the measured conduction velocity is used to control pacing rate.

Abstract: A medical electrical stimulator employing an operational amplifier output circuit for producing an electrical stimulating pulse for application to body tissue and for sensing electrical activity in the body tissue. A first input to the operational amplifier is coupled through a virtual load to a probe electrode in close proximity to the body tissue. The second input is coupled to a second electrode which may be remote from the tissue to be stimulated. A defined voltage signal may be provided to the second input to the amplifier, and the amplifier correspondingly delivers current through the virtual load to the probe electrode as the amplifier maintains equal voltage levels at its two inputs. The current delivered to the probe electrode functions to stimulate the body tissue. By varying the defined voltage signals provided to the second input of the amplifier, arbitrary stimulation pulse waveforms may be generated.

Abstract: A pacemaker sense amplifier which includes active circuitry which establishes and maintains a constant field density between two electrode poles, effectively clamping them together at a substantially fixed potential difference. The amount of current or power required to maintain this condition in the steady state is monitored and forms the basis of detection of the passing depolarization wavefront.

Abstract: An electrical pacer device which responds to cardiac demand so as to alter the cardiac output in a fashion to satisfy that demand. Changes in the fundamental period of the atrial electrical cycle are detected and averaged over a predetermined time interval and the resulting control signal is used to raise and lower the ventricular heart rate to increase and decrease the aforesaid cardiac output. At the same time, means are provided for continuously driving the ventricular rate toward a predetermined lower rate (the at rest rate) on a time cycle which is significantly longer than the above-mentioned predetermined time interval.