Bioimpedance analysis is a non-invasive and inexpensive technology to investigate the electrical properties of biological tissues. The analysis requires demodulation to extract the real and imaginary parts of the impedance. Conventional systems use complex architectures such as I-Q demodulation. In this paper, a very simple alternative time-to-digital demodulation method or 'time stamp' is proposed. It employs only three comparators to identify or stamp in the time domain, the crossing points of the excitation signal and the measured signal. In a CMOS proof of concept design, the accuracy of impedance magnitude and phase is 97.06% and 98.81% respectively over a bandwidth of 10 kHz to 500 kHz. The effect of fractional-N synthesis is analysed for the counter-based zero crossing phase detector obtaining a finer phase resolution (0.51˚ at 500 kHz) using a counter clock frequency (= 12.5 MHz). Because of its circuit simplicity and ease of transmitting the time stamps, the method is very suited to implantable devices requiring low area and power consumption.

This paper presents the design of an integrated power management circuit for use in an implantable optoelectro stimulator. It features an active rectifier with pulse width modulation (PWM) regulation to generate a 3.3 V regulated output, and a 3-stage high voltage charge pump that generates a 12 V output from a 3.3 V input with a 20 MHz, two-phase nonoverlapping clock generator. The circuits were designed in a 0.18-m CMOS technology requiring a chip area of 0.048 mm 2 . Simulation results show that the regulating rectifier has a voltage conversion efficiency of 94.3% and 92.8% with an input of 3.5 V and 3.6 V, respectively. The peak power transfer efficiency for a regulated output voltage of 3.3 V is 70.7% with an output power range of 30.3 mW. The charge pump overall capacitance is 60 pF. Keywords-Active rectifier, charge pump, integrated circuits, optogenetics, power management.' ) depending on the output of the PWM controller. The comparators ( 1 and 2 ) drive the cross-coupled nMOS ( 1 and 2) via the inverters. A dynamic body

This paper presents a fully implantable closed-loop device for use in freely moving rodents to investigate new treatments for motor neuron disease. The 0.18 µm CMOS integrated circuit comprises 4 stimulators, each featuring 16 channels for optical and electrical stimulation using arbitrary current waveforms at frequencies from 1.5 Hz to 50 kHz, and a bandwidth programmable front-end for neural recording. The implant uses a Qi wireless inductive link which can deliver >100 mW power at a maximum distance of 2 cm for a freely moving rodent. A backup rechargeable battery can support 10 mA continuous stimulation currents for 2.5 hours in the absence of an inductive power link. The implant is controlled by a graphic user interface with broad programmable parameters via a Bluetooth low energy bidirectional data telemetry link. The encapsulated implant is 40 mm × 20 mm × 10 mm. Measured results are presented showing the electrical performance of the electronics and the packaging method.

This paper presents a prototype integrated bidirectional stimulator ASIC capable of mixed opto-electro stimulation and electrophysiological signal recording. The development is part of the research into a fully implantable device for treating motor neurone disease using optogenetics and stem cell technology. The ASIC consists of 4 stimulator units, each featuring 16-channel optical and electrical stimulation using arbitrary current waveforms with an amplitude up to 16 mA and a frequency from 1.5 Hz to 50 kHz, and a recording front-end with a programmable bandwidth of 1 Hz to 4 kHz, and a programmable amplifier gain up to 74 dB. The ASIC was implemented in a 0.18-µm CMOS technology. Simulated performance in stimulation and recording is presented.

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This paper presents the design of a power management circuit consisting of a dual output regulating rectifier configuration featuring pulse width modulation (PWM) and pulse frequency modulation (PFM) to control the regulated output of 1.8 V, and 3.3 V from a single input ac voltage. The PFM control feedback consists of feedback-driven regulation to adjust the driving frequency of the power transistors through the buffers in the active rectifier. The PWM mode control provides a feedback loop to accurately adjust the conduction duration. The design also includes an adiabatic charge pump (CP) to power stimulators in an implantable neural interface. The adiabatic CP consists of latch up and power saving topologies to enhance its energy efficiency. Simulation results show that the dual regulating rectifier has a voltage conversion efficiency 94.3% with an ac input magnitude of 3.5 Vp. The power transfer efficiency of the regulated 3.3 V output voltage is 82.3%. The dual output regulating rectifier topology is suitable for multi-functional implantable devices. The adiabatic CP has an overall efficiency of 92.9% with an overall on-chip capacitance of 60 pF. The circuit was designed in a 180-nm CMOS technology.

Deep tissue energy harvesters are of increasing interest in the development of battery-less implantable devices. This paper presents a fully integrated ultra-low quiescent power management interface. It has power optimization and impedance matching between a piezoelectric energy harvester and the functional load that could be potentially powered by the heart's mechanical motions. The circuit has been designed in 0.18-µm CMOS technology. It dissipates 189.8 nW providing two voltage outputs of 1.4 V and 4.2 V. The simulation results show an output power 8.2x times of an ideal full-bridge rectifier without an external power supply. The design has the potential for use in self-powered heart implantable devices as it is capable providing stable output voltages from a cold startup.