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In this article, the architectural choices and design of a fully integrated integer-N frequency synthesizer operating in the 902-928 MHz Industrial, Scientific and Medical (ISM) band is presented. This frequency synthesizer, optimized for ultra-low power operation, is being integrated in the transceiver of an implantable wireless sensing microsystem (IWSM), which is dedicated to in vivo monitoring of biological parameters such as temperature, pressure, pH, oxygen, and nitric oxide concentrations. This phase-locked loop-based synthesizer includes a 1.830 GHz LC voltage-controlled oscillator (VCO) using a 10 nH on chip inductor. Varactors are implemented using P+ in N-well diodes for their linearity and high quality factor. The transistors of the VCO are operated in moderate inversion, and their bias point was chosen using the g m /I d design methodology. The output of the VCO, operating at twice the ISM frequency band, is divided by 2 to generate differential, quadrature versions of the carrier. Power minimization of the programmable divider was achieved by designing the latches and flip-flops using appropriate circuit techniques such as True Single Phase Clocking (TSPC) and first-type Dynamic Single Transistor Clocking (DSTC1) depending on their operating frequency. The power consumption of the proposed synthesizer is 580 lW under 1 V; almost an order of magnitude lower compared to that of recent synthesizer designs having a similar architecture.

A 902-to 928-MHz industrial, scientific, and medical band transceiver using a wake-up link for wireless body area networks wearable and implantable medical devices is presented. The design reaches exceptionally low-power dissipation and provides an adapted data-rate by gathering the advantages of frequency-shift-keying (FSK) and amplitude-shift-keying (ASK) modulation techniques. Transmitter (Tx) includes a new efficient FSK modulation scheme to generate up to 20 Mb/s of data-rate and consumes around 0.084 nJ/b. The integrated receiver (Rx) is based on a new FSK-to-ASK conversion technique using on-off keying fully passive wake-up circuit (WuRx) with energy harvesting from radio frequency link. The adopted scheme leads to the scalability of energy consumption versus data-rate at constant transceiver sensitivity, insuring high-performances requirements. The transceiver is implemented in IBM 0.13-m CMOS process. The WuRx achieves a sensitivity of −53 dBm while the main receiver shows −78-dBm sensitivity. Thanks to the simplified hardware, the receiver consumes only 640 W while the transmitter uses 1.4 mW from 1.2-V supply voltage. KEYWORDSFSK-to-ASK conversion, injection-locking oscillator, ISM band, RF FSK transceiver, scalable data-rate, wake-up link 2266

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Several papers on induced current electrical impedance tomography (IC-EIT) have dwelt on potential advantages of this technique over conventional EIT which uses applied current (AC-EIT). Experimental evidence that IC-EIT could surpass AC-EIT in similar imaging conditions is lacking. In this paper, we describe a system that can switch rapidly between both AC-EIT and IC-EIT. The system makes it possible to image objects in a saline-filled tank, providing data acquired in identical test conditions for comparing the performance of the two modes. The system uses eight circular coils and 16 electrodes to acquire 120 linearly independent measurements in IC-EIT and 104 in AC-EIT. Difference images were reconstructed from data acquired with both modes using the maximum a posteriori method. Spatial resolution was lower in IC-EIT images than in AC-EIT, especially in the radial direction. IC-EIT also exhibits a bias toward the center for positioning a conductivity perturbation. These results were obtained for a typical coil configuration widely used in the literature and may not be representative of alternate coil configurations. The system described in this paper provides stable experimental conditions for comparing the performance of the two EIT imaging modes and would be a valuable tool for validating new coil configurations.