IEEE Biomedical Circuits and Systems Conference : healthcare technology : [proceedings]. IEEE Biomedical Circuits and Systems Conference最新文献

Here, we present 2048 low-noise, low-offset, and low-power action-potential recording channels, integrated in a multi-functional high-density microelectrode array. A resistively loaded open-loop topology has been adapted for the first-stage amplifier to achieve 2.4 µVrms noise levels at low power consumption. Two novel pseudo-resistor structures have been used to realize very low HPF corner frequencies with small variations across all channels. The adjustability of pseudo resistors has been exploited to realize a "soft" reset technique that suppresses stimulation artifacts so that the amplifiers can recover from saturation within 200 µs. The chips were fabricated in a 0.18 µm 6M1P CMOS process, and measurement results are presented to show the performance of the proposed circuit structures and techniques.

Implanted pressure sensors suffer from long-term offset drift due to atmospheric changes, package moisture absorption, and patient factors such as posture, implant shift, and tissue overgrowth. Traditionally, wide dynamic range instrumentation is used to satisfy the full-scale and sensitivity requirements for a given application. Transmission of extra bits greatly increases the power draw of an implanted medical device, and simple AC-coupling cannot monitor static pressures. We present a mixed-signal offset cancellation loop to maximize the AC dynamic range of instrumentation circuitry. A digital implementation allows for designer control of the cancellation system time constant and was specifically designed for power-gated pressure sensors. Pressure offset is calculated by digital integration and a bipolar IDAC with coarse/fine tuning injects an offset-cancelling current into a standard piezoresistive MEMS pressure sensor. Test results showed a dynamic range increase of 2.9 bits using dynamic offset cancellation, for an effective sensing range of 11 bits using 8-bit instrumentation. The measured step response of the system showed an overall highpass response of 2.3 - 3.8 mHz. This approach is therefore relevant for bio-sensing of pressures in organs with a very slow physiologic response, e.g. the bladder.

Conditional neuromodulation in which neurostimulation is applied or modified based on feedback is a viable approach for enhanced bladder functional stimulation. Current methods for measuring bladder pressure rely exclusively on external catheters placed in the bladder lumen. This approach has limited utility in ambulatory use as required for chronic neuromodulation therapy. We have developed a wireless bladder pressure monitor to provide real-time, catheter-free measurements of bladder pressure to support conditional neuromodulation. The device is sized for submucosal cystoscopic implantation into the bladder. The implantable microsystem consists of an ultra-low-power application specific integrated circuit (ASIC), micro-electro-mechanical (MEMS) pressure sensor, RF antennas, and a miniature rechargeable battery. A strategic approach to power management miniaturizes the implant by reducing the battery capacity requirement. Here we describe two approaches to reduce the average microsystem current draw: switched-bias power control and adaptive rate transmission. Measurements on human cystometric tracings show that adaptive transmission rate can save an average of 96% power compared to full-rate transmission, while adding 1.6% RMS error. We have chronically implanted the wireless pressure monitor for up to 4 weeks in large animals. To the best of our knowledge these findings represent the first examples of catheter-free, real-time bladder pressure sensing from a pressure monitor chronically implanted within the bladder detrusor.

Current technology has enabled a significant increase in the number of electrodes for electrical stimulation. For large arrays of electrodes, it becomes increasingly difficult to monitor and detect failures at the stimulation site. In this paper, we propose the idea that the residual voltage from a biphasic electrical stimulation pulse can serve to recognize damage at the electrode-tissue interface. We use a simple switch circuit approach to estimate the relaxation time constant of the electrode model, which essentially models the residual voltage in biphasic electrical stimulation, and compare it with standard electrode characterization techniques. Out of 15 electrodes in a polyimide-based SIROF array, our approach highlights 3 damaged electrodes, consistent with measurements made using cyclic voltammetry and electrode impedance spectroscopy.

Safety features embedded in a 256-channel retinal prosthesis integrated circuit are presented. The biology of the retina and the electrochemistry of the electrode-tissue interface demand careful planning and design of the safety features of an implantable retinal stimulation device. We describe the internal limits and communication safety features of our ASIC, but we focus on monitoring and protection circuits for the electrode-tissue interface. Two independent voltage monitoring circuits for each channel measure the electrode polarization voltage at two different times in the biphasic stimulation cycle. The monitors ensure that the charged electrode stays within the electrochemical water window potentials, and that the discharged electrode is within a small window near the counter electrode potential. A switch to connect each electrode to the counter electrode between pulses protects against a wide range of device failures. Additionally, we describe work on an active feedback system to ensure that the electrode voltage is at zero.

This paper describes the development of a smartphone-based electrochemical biosensor module. The module contains a low power potentiostat that interfaces and harvests power from a smartphone through the phone's audio jack. A prototype with two different potentiostat designs was constructed and used to conduct proof of concept cyclic voltammetry experiments with potassium ferro-/ferricyanide (K₄[Fe(CN)₆] / K₃[Fe(CN)₆]) in a side-by-side comparison with a laboratory grade instrument. Results show that the module functions within the available power budget and that the recovered voltammogram data matches well with the data from an expensive bench top tool. Excluding the loses from supply rectification and regulation, the module consumes either 5.7 mW or 4.3 mW peak power, depending on which of the two discussed potentiostat designs is used. At single quantity pricing, the hardware for the prototype device costs less than $30.

A CMOS low-power transceiver for implantable and external health monitoring devices operating in the MICS band is presented. The LNA core has an integrated mixer in a folded configuration to reuse the bias current, allowing high linearity with a low power supply levels. The baseband strip consists of a pseudo differential MOS-C band-pass filter achieving demodulation of 150kHz-offset BFSK signals. An all digital frequency-locked loop is used for LO generation in the RX mode and for driving a class AB power amplifier in the TX mode. The MICS transceiver is designed and fabricated in a 0.18μm 1-poly, 6-metal CMOS process. The sensitivities of -70dBm and -98dBm were achieved with NF of 40dB and 11dB at the data rate of 100kb/s while consuming only 600μW and 1.5mW at 1.2V and 1.8V, respectively. The BERs are less than 10^-3 at the input powers of -70dBm at 1.2V and -98dBm at 1.8V at the data rate of 100kb/s. Finally, the output power of the transmitter is 0dBm for a power consumption of 1.8mW.