Wireless biosensors are playing a pivotal role in health monitoring, disease detection and management. The development of wireless biosensor nodes and networks strongly relies on the design of novel low-power, low-cost and flexible CMOS sensor readouts. This brief presents a CMOS potentiostat that integrates a control amplifier, a dual-slope ADC and a wireless unit on the same chip. It implements a novel time-based readout scheme, whereby the counter of the dual-slope ADC is moved to the receiver and the sensor current is encoded in the timing between two wireless pulses transmitted via pulse-harmonic modulation across an inductive link. Measured results show that the potentiostat chip can resolve a minimum input current of 10pA at a sampling frequency of 125 Hz and a power consumption of 12 μW .

In this paper, the design of a wireless power transfer system (WPT) targeting biomedical implants is considered. The novelty of the approach is to propose a co-design of the transmitter and receiver side based on the design of class-E isolated DC-DC converters. The solution, along with the simple introduction of a shunt regulator at the receiver, allows us to solve the problem of ensuring optimal efficiency in the WPT link. In conventional solutions, in order to cope with coupling factor and load variations, information from the receiver is needed, which is usually relayed back onto the transmitter by means of telemetry. With the proposed approach, a very simple minimum power point tracking (mPPT) algorithm can be used to maximize the WPT efficiency based on the information already available at the transmitter side. This reduces the complexity of the circuitry of the implant and thereby its power overhead and possibly its size, both being crucial constraints of a biomedical implant.

Kilohertz frequency alternating current (KHFAC) stimulation can induce fast-acting, reversible and repeatable nerve conduction block, and is a candidate therapeutic method for diseases caused by undesired neural activities, such as urinary retention. In this paper, we first show that ultra-high frequency (UHF) current pulses can also lead to successful nerve conduction block, based on simulation results using the McIntyre-Richardson-Grill (MRG) model. This model describes a myelinated axon of mammalian animals. Second, we present a prototype of a power efficient neural stimulator using UHF current pulses with active charge balancing (CB). The stimulator is built using off-the-shelf components and can be battery-powered. It uses a DC-DC boost converter without a big filtering capacitor, for generating UHF current pulses. The power efficiency of the complete system is up to 98% when testing with an equivalent circuit model of electrode tissue interface (ETI). Safety measurement results show that the electrode offset voltage can be as high as 1.3 V without charge balancing, in in vitro experiments with titanium electrodes in a phosphate buffered saline (PBS) solution. However, this electrode offset voltage can be successfully lowered to less than 42.5 mV, by means of negative-feedback duty cycle control of the H-bridge clock. The active CB is adopted for KHFAC stimulation for the first time.

Wireless data telemetry for implantable medical devices (IMDs) has, in general, been limited to a few Mbps, and used for applications such as transmitting recordings from an implanted monitoring device, or uploading commands to an implanted stimulator. However, modern neural interfaces need to record high resolution potentials from hundreds of neurons; this requires much higher data rates. While fast wireless communication is possible using existing standards such as WiFi, power consumption demands are far too high for IMDs. Short range inductive link based telemetry, in particular impulse-based systems such as pulse-harmonic modulation (PHM), have demonstrated transfer speeds of up to 20 Mbps with a small power budget. However, these systems require complex and precise circuits, making them potentially susceptible to inter-symbol-interference. This work presents a new method named Short-range Quality-factor Modulation (SQuirM), which retains the low power consumption and high data rate of PHM, while improving the resilience of the system and simplifying the circuit design. Transmitter and receiver circuits were fabricated using 0.35 μm CMOS. The circuits were capable of reliably transceiving data at speeds of up to 50.4 Mbps, with a BER of < 4.5 × 10^-10 , and a transmitter energy consumption of 8.11 pJ/b.

The original paper entitled "Practical Inductive Link Design for Biomedical Wireless Power Transfer: A Tutorial" [1], aimed to provide an accessible review and guide, describing the necessary steps for designing effective biomedical inductive links, without the need for FEM Software. While the majority of the information in this paper is accurate and applicable, some errors in formulas have been brought to the attention of the authors, which could generate erroneous results if used in calculations. The aim of this paper is to highlight and correct these errors. It should be noted that the accompanying software for performing these calculations has also been corrected where necessary, in line with the corrections presented here [2]. The errors largely relate to the equations presented throughout, and are listed below: First, [1, Eq. (2)], defining an approximation for Nagaoka's coefficient, contains erroneous squares and is missing a term in the fraction of the large denominator. The correct form is presented below: Second, [1, Eq. (14)] considers the ac losses of a Litz-wire coil. The original form contains errors of coefficients and signs. The correct formulation is given as follows: (Formula presented). Third, [1, Eq. (17)] is missing a square. The correct form is as follows: Fourth, [1, Eq. (26)], that defines ang, is missing a cos a from the numerator of the top fraction under the square root. The correct form is given below: Finally, the caption of [1, Fig. 17] is in error; it currently refers to coupling coefficient, while it shows Q-factor. It should read as follows: "Changing Q-factor as winding pitch is modified, with respect to frequency.

Short-range, low-power, high data-rate telemetry is an increasingly desirable feature for implantable medical devices (IMDs), and is commonly implemented using an inductive link. Pulse Harmonic Modulation (PHM) provides the desired high data rates and low power consumption, but requires precise pulse timing. This paper presents a modification of PHM, Single-Pulse Harmonic Modulation (SPHM), which offers reduced power consumption and lower implementation complexity. In order to test the SPHM concept, transmitter and receiver circuits were designed in 0.35μm CMOS and simulated. The simulated results suggest that the circuits can transceive data at 50Mb/s, consuming 1.49pJ/b and 2.59pJ/b at the transmitter and receiver respectively, from a 1.2V supply.

Point-of-care systems for the detection of infectious diseases are in great demand especially in developing countries. Lateral flow immunoassays are considered ideal biosensors for point-of-care diagnostics due to their numerous advantages. However, to quantify their results a low power, robust electronic reader is needed. A low power CMOS image sensor is presented that can be used in quantitative lateral flow immunoassay readers. It uses a single low power processing capacitive transimpedance amplifier architecture which includes noise cancellation. A chip containing 4 &#x00D7; 64 pixels was fabricated in CMOS 0.35-&#x03BC;m technology. With uniform illumination at 525 nm and 67 frames per second the chip has 1.9 mVrms total output referred noise and a total power consumption of 21 &#x03BC;W. In tests with lateral flow immunoassays the chip detected concentrations of influenza A nucleoprotein from 0.5 ng/mL to 200 ng/mL.

Wireless power transfer systems, particularly those based on inductive coupling, provide an increasingly attractive method to safely deliver power to biomedical implants. Although there exists a large body of literature describing the design of inductive links, it generally focuses on single aspects of the design process. There is a variety of approaches, some analytic, some numerical, each with benefits and drawbacks. As a result, undertaking a link design can be a difficult task, particularly for a newcomer to the subject. This tutorial paper reviews and collects the methods and equations that are required to design an inductive link for biomedical wireless power transfer, with a focus on practicality. It introduces and explains the published methods and principles relevant to all aspects of inductive link design, such that no specific prior knowledge of inductive link design is required. These methods are also combined into a software package (the Coupled Coil Configurator), to further simplify the design process. This software is demonstrated with a design example, to serve as a practical illustration.

Wireless sensing systems are becoming popular in a range of applications, particularly in the case of biomedical circuits and food monitoring systems. A typical wireless sensing system, however, may require considerable complexity to perform the necessary analog to digital conversion and subsequent wireless transmission. Alternatively, in the case of inductive link based systems, large, manually operated impedance analyzers are required. Based on a detailed analysis of the link impedance, this paper proposes a simple method for wireless capacitive sensing through an inductive link that uses a self-oscillator and a frequency counter. The method enables changes in capacitance to be sensed and wirelessly transmitted simultaneously. In order to test the effectiveness of the method, a self-oscillating circuit was designed and fabricated in 0.18 &#x03BC;m CMOS, and combined with an on-chip humidity sensing capacitor. The system was tested in a humidity chamber across a range of 20-90&#x0025;rh. Measured results from the system demonstrate that capacitive changes as small as 28 fF, translating to &lt;2&#x0025;rh, can be resolved, with a power consumption of 1.44 mW.

This paper discusses the design of an application-specific integrated circuit (ASIC) suitable for mounting on a multi-electrode array for epidural spinal cord stimulation in rats. The ASIC acts as a demultiplexer, driving 12 electrodes on the array in any configuration. It is capable of routing biphasic constant current pulses of up to 1 mA to high impedance loads (with a maximum output voltage swing of approximately 25 V) and is small enough to be implanted into a rat's spinal column. Communication with its driver is achieved via 3 wires to minimize the number of interconnections. The circuit was implemented in a 0.18-μm high-voltage CMOS technology occupying a core area of 0.36 mm ². Power dissipation is about 110 μW. Post-layout simulations are presented which show the correct operation of the system.