Abstract: A telemetry system which will transmit data at a relatively high rate while retaining a high degree of accuracy is disclosed which utilizes a servo feedback loop in conjunction with a conventional reflected impedance receiving front end parallel LC circuit, an AM demodulator, and an oscillator to drive the LC circuit at a desired frequency. The feedback loop operates to keep the voltage across the LC circuit constant over time, and does not affect short term variations in the voltage across the LC circuit which are caused by the variations in the reflected impedance. While frequency response of the system without the loop declines from a maximum value at zero frequency, the frequency response of the system of the present invention with the loop is shifted which permits data transmission at a substantially higher rate.

Abstract: An adjustable output level transmitter includes a direct current energy source, an L-C tank circuit and a switching means for sequentially coupling the capacitors of the tank circuit to the direct current energy source and ground. The output signal frequency is equal to the resonant frequency of the L-C tank circuit and the output signal level is a function of which capacitors of the L-C tank circuit are sequentially coupled to the energy source. The circuit functions in a Class D mode with the inherent advantages of minimal power loss and very high efficiency. Due to the manner of switching utilized, the output signal frequency is very stable and unaffected by the mode of capacitor switching.

Abstract: An improved telemetry system for telemetering digital data from an implantable tissue stimulator such as a heart pacemaker. A carrier signal is pulse modulated in accordance with either or both of stored digital data and a digitized electrocardiogram signal, for coupling onto an electrical lead connected directly to the heart. This arrangement facilitates the transmission of substantially higher data rates than previously could be achieved.

Abstract: A pacemaker and a method of operation thereof are provided for configuring or operating a conventional pacemaker having a plurality of lead electrodes. Each lead can be independently configured for any combination of unipolar or bipolar, pacing and sensing. During a pacing mode of operation, a selected return electrode is switchably connected to the most positive battery potential, V.sub.DD. The return electrode of the packemaker, can selectively be either the pacemaker case or one or more ring electrodes. During a fast discharge time period, which occurs immediately subsequent to the delivery of a pacing pulse, the return electrode is disconnected from V.sub.DD and connected to the proximal side of a coupling capacitor through which the pacing pulse has passed. Also during this fast discharge time period, the proximal side of the coupling capacitor is switchable connected to the most negative battery potential, V.sub.SS.

Abstract: A self-oscillating burst mode transmitter transmits an integral number of cycles of a carrier signal in each transmission burst. Each burst commences at a peak value of the carrier signal and terminates at a peak value. The transmitter includes an L-C tank circuit comprising a transmitting coil (L1) connected to a capacitor (C4). The L-C tank circuit is selectively energized through a switching network (Q1, Q2, U1, U2) connected to a power source, causing the tank circuit to resonate at a prescribed frequency (f.sub.0). Selective energization of the tank circuit is achieved by the switching network as controlled by a peak voltage detection circuit (32, 34). The peak detection circuit senses when a peak voltage is present in the oscillatory waveform appearing across the coil of the resonating tank circuit. Power is switched off to the tank circuit at the conclusion of each transmission burst only when the oscillatory voltage waveform, as sensed by the peak detection circuit, is at a peak.

Abstract: A communication system includes self-test means for automatically testing its performance. The communication system is adapted for use between an implantable device, such as a pacemaker, and an external device, such as the pacemaker's programmer. The communication system includes in the external device a transmitter circuit for transmitting an output signal through an antenna, and a receiver circuit for receiving an input signal through an antenna. A driver circuit controls the operation of the transmitter circuit. A microprocessor, connected to the driver circuit, controls the information content and timing of the transmitted output signal. A bandpass filter and AM demodulator process the input signal received through the receiver circuit. A multiplexer selectively allows one of a plurality of status signals from throughout the communication system within the external device, including the demodulated signal obtained from the AM demodulator, to be connected to the microprocessor.

Abstract: A device for use as a self-oscillating Class D transmitter is disclosed which uses feedback to maintain the oscillation at the resonant frequency of the device, thereby optimizing the efficiency of operation and overcoming the frequency mismatching inherent in previously known transmitters. The device uses a series LC combination which is driven by a comparator and a tri-state logic driver, with a feedback loop using a differentiator used to switch the polarity of the square wave generator. The system thus self-oscillates at the resonant frequency of the capacitor and inductor, even when the inductance of the inductor is varied by the inductor coming into close proximity to another inductor.

Abstract: A digital phase-locked looped generates a clock signal synchronized with a carrier signal modulated by amplitude shift keying (ASK). During periods when no carrier signal is present, the generated clock signal coasts at the frequency of the carrier signal most recently present, rather than trying to phase-lock on noise. A binary controlled digital oscillator generates the clock signal. A phase detector determines the difference between the phase of the carrier signal, when present, and the local clock signal. When the average amplitude of the carrier signal exceeds a prescribed threshold level, the phase detector output is sampled and passed to an integrator circuit, where the phase difference is integrated. The output of the integrator circuit is applied to a pulse generator, causing the pulse generator's duty cycle to change proportionally.

Abstract: A high speed digital telemetry system (10) includes a transmitter (12) and a receiver (14), at least one of which is adapted for use in an implantable device. The transmitter includes a data encoder (14), modulator (16), transmitting coil (20), and transmitting coil drive circuit (18). The data encoder examines prescribed incoming data bits and prior encoded data bits, generating an encoded data stream (36) that includes a data transition only when a prescribed correlation is noted amongst the examined bits. The modulator modulates a carrier signal (34) with the encoded data stream, causing a phase reversal of the carrier at each data transition of the encoded data stream. The transmitting coil drive circuit applies the modulated carrier (38) to the transmitting coil. The receiver includes a receiving coil (22) and associated amplifier (24) and bandpass filter (26) for detecting the transmitted modulated carrier.

Abstract: A telemetry system for use with implantable medical devices is disclosed which utilizes both in-phase and quadrature data components, and frequency modulates both data components into a single transmitted sinusoidal signal which varies in frequency between two selected frequencies. The signal is received and decoded, preferably by a coherent decoder, into in-phase and quadrature components, which are then integrated and sampled to produce the two transmitted in-phase and quadrature data components, which may then be recombined to produce the transmitted data. The system requires only low power, and is capable of operating at a relatively high data rate while retaining a high degree of accuracy due to the splitting of the signal into the in-phase and quadrature data components.

Abstract: Isolation circuitry for use with diagnostic ECG devices provides high common mode rejection and low leakage current using optoisolators in conjunction with an isolating operational amplifier. A predetermined pattern of binary input signals selectively energizes, via the optoisolators, a plurality of switches interposed between electrodes positioned on a patient's skin and the isolating operational amplifier. This selection couples a predetermined combination of electrodes to the isolating operational amplifier to provide the desired ECG output. The output from the isolating operational amplifier may be coupled directly to a recording device or coupled to a circuit which processes the ECG signal before the signal is recorded.

Abstract: In an implantable device, transmission and reception of digital information is accomplished as well as the transmission and reception of analog information. The analog signal is FM modulated for transmission and the digital signal is phase modulated for transmission. The FM modulated signal is used as a clock in the phase encoding of the digital signal and thus provides a signal simultaneously carrying analog and digital information. Means for reception of the analog and digital information is taught. The use of PSK (phase shift keying) as the phase modulation scheme for transmission and reception is also taught.