A Sinusoidal Current Driver With an Extended Frequency Range and Multifrequency Operation for Bioimpedance Applications

This paper describes an alternative sinusoidal current driver suitable for bioimpedance applications where high frequency operation is required. The circuit is based on a transconductor and provides current outputs with low phase error for frequencies around its pole frequency. This extends the upper frequency operational limit of the current driver. Multifrequency currents can be generated where each individual frequency is phase corrected. Analysis of the circuit is presented together with simulation and experimental results which demonstrate the proof of concept for both single and dual frequency current drivers. Measurements on a discrete test version of the circuit demonstrate a phase reduction from 25 ^{\circ} to 4 ^{\circ} at 3 MHz for 2 mAp-p output current. The output impedance of the current driver is essentially constant at about 1.1 M \Omega over a frequency range of 100 kHz to 5 MHz due to the introduction of the phase compensation. The compensation provides a bandwidth increase of a factor of about six for a residual phase delay of 4 ^{\circ

An Improved Wideband CMOS Current Driver for Bioimpedance Applications

A wideband, CMOS current driver for bioimpedance measurement applications has been designed employing nonlinear feedback. With the introduction of phase compensation, the circuit is able to operate at frequencies higher than the pole frequency of the output transconductor with minimum phase delay. Moreover, it isolates the poles required for stability from the high frequency characteristics of the output transconductor. The circuit has been simulated in a 0.35-μm CMOS technology and operates from ±2.5 V power supplies. Simulations show that for a 1 mAp-p output current, the phase delay is less than 1° for frequencies up to 3 MHz, rising to 1.5° at 5 MHz. Dual frequency currents to the load are demonstrated

Towards a system for tracking drug delivery using frequency excited gold nanoparticles

Nanoparticle-based drugs are rapidly evolving to treat different conditions and have considerable potential. A new system based on the combination of electrical impedance tomography (EIT) imaging and a power amplifier with a RF coil has been developed to study the effect of gold nanoparticles (AuNPs) when excited in the MHz frequency range. We show that samples including AuNPs have a temperature increase of 1−1.5 °C due to the presence of RF excitation at 13.56 MHz which provides a higher rate of change for solutions without AuNPs. They also show more than a 50% increase in conductivity in difference imaging as the result of this excitation. The change for samples without AuNPs is 40%

A power efficient time-to-current stimulator for vagal-cardiac connection after heart transplantation

This paper presents a stimulator for a cardiac neuroprosthesis aiming to restore the parasympathetic control after heart transplantation. The stimulator is based on time-to-current conversion, instead of the conventional current mode digital-to-analog converter (DAC) that drives the output current mirrors. It uses a DAC based on capacitor charging to drive a power efficient voltage-to-current converter for output. The stimulator uses 1.8 V for system operation and 10 V for stimulation. The total power consumption is Istim × 10 V +18. u μW during the biphasic current output, with a maximum Istim of 512 μA. The stimulator was designed in CMOS 0.18 μm technology and post-layout simulations are presented

Towards a System for Tracking Drug Delivery Using Frequency Excited Gold Nanoparticles

Nanoparticle-based drugs are rapidly evolving to treat different conditions and have considerable potential. A new system based on the combination of electrical impedance tomography (EIT) imaging and a power amplifier with a RF coil has been developed to study the effect of gold nanoparticles (AuNPs) when excited in the MHz frequency range. We show that samples including AuNPs have a temperature increase of 1–1.5 ◦C due to the presence of RF excitation at 13.56 MHz which provides a higher rate of change for solutions without AuNPs. They also show more than a 50% increase in conductivity in difference imaging as the result of this excitation. The change for samples without AuNPs is 40%

Towards a Universal Methodology for Performance Evaluation of Electrical Impedance Tomography Systems using Full Reference SNR

This paper describes a simple and reproducible methodology towards a universal figure-of-merit (FoM) for evaluating the performance of electrical impedance tomography (EIT) systems using reconstructed images. Based on objective full-referencing and signal-to-noise ratio, the method provides a visually distinguishable hot-map and two new FoM factors, to address the issues where common electrical parameters are not directly related to the quality of EIT images. The paper describes the method with simulation results and develops a 16 electrode EIT system using an ASIC front-end for evaluation using the proposed method. The measured results show both visually and in terms of the proposed FoM factors, the impact on recorded EIT images with different current injection amplitudes

A low-power recursive I/Q signal generator and current driver for bioimpedance applications

This brief presents a power-efficient quadrature signal generator and current driver application-specific integrated circuit (ASIC) for bioimpedance measurements in an electrical impedance tomography system for monitoring lung function. The signal generator is realized by a digital recursive signal oscillator with the ability of generating quadrature signals over a wide frequency range. The generated in-phase signal is applied to a current driver. It uses a balanced current-mode feedback architecture that monitors the output current through a feedback loop to minimize common-mode voltage build-up at the injection site. The quadrature signals can be used for I/Q demodulation of the measured bioimpedance. The ASIC was designed in TSMC 65 nm technology occupying an area of 0.21 mm2. The current driver can generate up to 0.7 mA current up to 200 kHz and consumes 2.7 mW power using ±0.8 V supplies

Live Demonstration: Performance Evaluation of Electrical Impedance Tomography Systems using a Color-Coded Full Reference SNR Method

A color-coded full reference signal-to-noise (FR-SNR) method is proposed as a simple and reproducible performance evaluation method for EIT systems. It will be demonstrated with a 16-electrode high-speed EIT system and a resistive phantom. The performance of the EIT system can be altered by artificially introducing non-ideal operating conditions such as low drive current, low ADC resolution, dc offset in the readout front-end and large electrode impedance. The performance under these conditions will be measured and displayed using the FR-SNR method

1.2V Energy-Efficient Wireless CMOS Potentiostat for Amperometric Measurements

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 paper 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

A Goertzel Filter Based System for Fast Simultaneous Multi-Frequency EIS

Bioimpedance measurement is a non-invasive, radiation-free, and inexpensive method for measuring the electrical properties of biological tissues. In applications where transients occur, the commonly used swept sinewave is replaced with broadband signals such as multisine. This makes the signal generation and the extraction of the real and imaginary parts of the impedance challenging. In this brief, an alternative to traditional fast Fourier transform (FFT) or coherent demodulation is presented. Based on the Goertzel filter, this alternative is simpler and requires very few digital resources. Its robustness to the harmonic fold back phenomenon, enables simple ternary current pulses to be used for excitation. The developed digital architecture is capable of simultaneous demodulation of 16 frequencies with an accuracy of 97% and 96% on the magnitude and phase measurement respectively. Employing a ternary sequence allows the use of a low power H-bridge current driver. The analog front-end and demodulation algorithm were implemented in an ASIC using a 180-nm CMOS technology. The system was tested on an isolated pig heart distinguishing edema from non-edema tissue by impedance changes