Abstract: An analog data transmission circuit for a biomedical implant employs a linear amplifier to modulate the impedance of a resonant circuit tuned to an externally generated constant carrier frequency. The resonant circuit comprises a tuned coil in circuit with a linear modulating switch and a digital modulating switch. The digital switch is gated by the digital data output from digital control circuitry within the implant. The linear amplifier output drives the linear modulation switch. The switches are preferably matched pairs of MOSFET's of opposite polarity having complementary parasitic diodes which form a phantom diode bridge. The bridge acts as a full wave rectifier and boosts the bias voltage on the sources of the FET pair forming the linear modulation switch such that the radiated amplitude is independent of the distance of the programming head. A timed power-up circuit supplies power to the amplifier and starts a square wave calibration period in response to the approach of the programming head.

Abstract: An implantable, microprocessor-based cardiac pacer provides physiologically adaptive pacing in four fundamental modes: ventricular-inhibited; atrial-synchronized ventricular with or without ventricular sensing; and atrial-ventricular (AV) sequential. In the AV sequential mode, the pacer automatically shifts to atrial synchronous ventricular pacing when the atrial rate exceeds the programmed minimum rate. Temporary pacing modes are available for treatment of arrhythmia and either atrial or ventricular overdrive pacing via chest wall stimulation. The pacer continuously monitors tachyarrhythmia and automatically enters and exits a special arrhythmia response mode. Eight parameters can be altered one at a time or reprogrammed to a standard set in a single programming step using pre-existing magnetic programmers. A weak battery is signified by substituting a lower frequency voltage-sensitive backup oscillator and by dropping the atrial beat in the magnet rate.