Abstract: A protective, biocompatible coating or encapsulation material protects and insulates a component or device intended to be implanted in living tissue. The coating or encapsulation material comprises a thin layer or layers of alumina, zirconia or other ceramic, less than 25 microns thick, e.g., 5-10 microns thick. The alumina layer(s) may be applied at a relatively low temperature. Once applied, the layer provides excellent hermeticity, and prevents electrical leakage. Even though very thin, the alumina layer retains excellent insulating characteristics. In one embodiment, an alumina layer less than about 6 microns thick provides an insulative coating that exhibits less than 10 pA of leakage current over an area 75 mils by 25 mils area while soaking in a saline solution at temperatures up to 80° C. over a three month period.

Abstract: A protective, biocompatible coating or encapsulation material protects and insulates a component or device intended to be implanted in living tissue. The coating or encapsulation material comprises a thin layer or layers of alumina, zerconia, or other ceramic, less than 25 microns thick, e.g., 5-10 microns thick. The alumina layer(s) may be applied at relatively low temperature. Once applied, the layer provides excellent hermeticity, and prevents electrical leakage. Even though very thin, the alumina layer retains excellent insulating characteristics. In one embodiment, an alumina layer less than about 6 microns thick provides an insulative coating that exhibits less than 10 pA of leakage current over an area 75 mils by 25 mils area while soaking in a saline solution at temperatures up to 80° C. over a three month period.

Abstract: An implantable sensor includes electronic circuitry for automatically performing on a periodic basis, e.g., every 1 to 24 hours, specified integrity tests which verify proper operation of the sensor.

Abstract: An implantable substrate sensor has electronic circuitry and electrodes formed on opposite sides of a substrate. A protective coating covers the substrate, effectively hermetically sealing the electronic circuitry under the coating. Exposed areas of the electrodes are selectively left uncovered by the protective coating, thereby allowing such electrodes to be exposed to body tissue and fluids when the sensor is implanted in living tissue. The substrate on which the electronic circuitry and electrodes are formed is the same substrate or “chip” on which an integrated circuit (IC) is formed, which integrated circuit contains the desired electronic circuitry. Such approach eliminates the need for an hermetically sealed lid or cover to cover hybrid electronic circuitry, and allows the sensor to be made much thinner than would otherwise be possible. In one embodiment, two such substrate sensors may be placed back-to-back, with the electrodes facing outward.

Abstract: An implantable enzyme-based monitoring system suitable for long term in vivo use to measure the concentration of prescribed substances such as glucose is provided. In one embodiment, the implantable enzyme-based monitoring system includes at least one sensor assembly, an outer membrane surrounding the sensor assembly and having a window therein, and a polymeric window cover affixed to the outer membrane and covering the window. Preferably, the outer membrane of the monitoring system is silicone and the window cover is a polymer of 2-hydroxyethyl methacrylate (HEMA), N,N,-dimethylaminoethyl methacrylate (DMAEMA) and methacrylic acid (MA). Also provided herein is an implantable enzyme-based monitoring system having at least one sensor assembly, an outer membrane surrounding the sensor assembly and a coating affixed to the exterior surface of the outer membrane, wherein the coating resists blood coagulation and protein binding to the exterior surface of the outer membrane.

Abstract: An electrochemical sensor includes electronic circuitry for automatically performing on a periodic basis, e.g., every 1 to 24 hours, specified integrity tests which verify proper operation of the sensor.

Abstract: Improved implantable monitoring systems suitable for long-term in vivo use to measure the concentration of one or more prescribed substances, such as glucose are described herein. In particular, an implantable enzyme-based glucose monitoring system is described that includes at least one of the following: means for replenishing the enzyme solution as it is consumed by the enzymatic reaction; means for replenishing the electrolyte solution bathing the electrode assembly; and microprocessing means proximal the electrode assembly. In preferred embodiments a microprocessor assembly is hermetically associated with the substrate to which the electrode assembly is affixed. Further, the monitoring systems employ one or more reservoir systems in fluid communication with enzyme and electrolyte chambers wherein the enzyme and electrolyte solutions are used.

Abstract: A protective, biocompatible coating or encapsulation material protects and insulates a component or device intended to be implanted in living tissue. The coating or encapsulation material includes a thin layer or layers of alumina, zirconia, or other ceramic, less than 25 microns thick, e.g., 5-10 microns thick. The alumina layer(s) may be applied at relatively low temperature. Once applied, the layer provides excellent hermeticity, and prevents electrical leakage. Even though very thin, the alumina layer retains excellent insulating characteristics. In one embodiment, an alumina layer less than about 6 microns thick provides an insulative coating that exhibits less than 10 pA of leakage current over an area 75 mils by 25 mils while soaking in a saline solution at temperatures up to 80.degree. C. over a three month period.

Abstract: An implantable living tissue stimulator avoids the use of conventional coupling capacitors in its output stage, yet still prevents an average dc current flow from flowing through living tissue in electrical contact with the stimulator. The output stage generates and applies a biphasic stimulating current pulse to selected paired output terminals. The terminals, in turn, are electrically connected to respective electrodes which are positioned so as to contact the living tissue to be stimulated. In one embodiment, special circuitry is employed within the output stage to block dc current flow through the living tissue and to balance the electrical charge that is delivered to the living tissue. In another embodiment, the electrodes themselves are made from a material that allows them to function as a capacitor. In yet an additional embodiment, the coupling capacitors are integrated into the leads that connect the output terminals of the output stage with the electrodes.

Abstract: A low power switched rectifier circuit is realized using P-MOS and N-MOS FET switches that are turned ON/OFF at just the right time by a detector and inverter circuit (which form an integral part of the rectifier circuit) to rectify an incoming ac signal in a highly efficient manner. Parasitic diodes and transistors that form an integral part of the FET circuitry respond to and rectify the incoming signal during start up, i.e., when no supply voltage is yet present, thereby providing sufficient operating voltage for the FET switches to begin to perform their intended rectifying function. In the absence of an incoming ac signal, i.e., during the time between biphasic pulses, the rectifier circuit is biased with an extremely small static bias current; but in the presence of an incoming ac signal, at a time when the positive and negative phases of the incoming signal are to be connected to positive and negative supply lines, a much larger dynamic bias current is automatically triggered.

Abstract: An implantable sensor/stimulator is connectable to a controller using just two conductors, which two conductors carry both operating power and data (data commands and/or measured data) between the sensor/stimulator and control circuit. Each sensor/stimulator may be serially connected to another sensor/stimulator, again using only two conductors, thereby allowing a "daisy chain" of such sensors/stimulators to be formed. Each sensor/stimulator in the daisy chain is individually addressable by the control circuit. Input data is sent to the sensors over the two conductors using a phase-modulated biphasic modulation scheme, which scheme also provides operating power for each sensor/stimulator connected to the two conductors. Output data is sent from the sensors to the controller over the same two conductors using a pulse-position presence/absence modulation scheme. The data transmission schemes provide a very high signal-to-noise ratio.

Abstract: A cochlea stimulation system includes a patient wearable system comprising an externally wearable signal processor (WP) and a headpiece in electronic communication with an implanted cochlear stimulator (ICS). The ICS comprises eight output stages each having two electrically isolated capacitor-coupled electrodes, designated "A" and "B", circuits for monitoring the voltages on these electrodes, and circuits for both transmitting status information to and receiving control information from the WP. Based upon information received from the WP, a processor within the ICS can control both the frequency and the widths of the output stimulation pulses applied to the electrodes and may select which electrodes to monitor. The ICS receives power and data signals telemetrically through the skin from the WP. To save power, the ICS may be "powered down" by the WP based upon the absence of audio information or "powered up" if audio is present.

Abstract: A low power current-to-frequency converter circuit provides an output frequency signal F.sub.OUT having a frequency that varies as a function of a low level analog input current signal. The analog input current signal is typically generated by an implantable sensor element, designed to sense a particular substance or parameter within body tissue or fluids to which the sensor is exposed, with the magnitude of the analog signal providing a measure of the sensed substance or parameter. Conversion of the low level analog current to the output frequency signal facilitates transmission of the data signal over a shared data bus and other digital processing of the data signal.

Abstract: A D to A converter comprising a series of stages each including a current mirror having an input and an output transistor (Q1 and Q3) and a current adjusting transistor (Q2, Q4) connected in parallel with each input and output transistor for adjusting the output current from the current mirror as a function of the operating states of the current adjusting transistors. The operating state of each current adjusting transistor is controlled by a digital signal applied to a switch (Q2S, Q2S') connected to the gate of each current adjusting transistor. Each stage also includes a control circuit (Q1C, Q3C) for maintaining equal the drain voltages of its input and output transistors whereby the current changes introduced in the output current of the converter stage are functions of the relative geometric sizes of the input, output and current adjusting transistors comprising the converter stage.