scholarly journals Optically isolated current source

2019 ◽  
Vol 6 (1) ◽  
pp. 18-21
Author(s):  
F. J. Pettersen ◽  
J. O. Høgetveit
Keyword(s):  
Current Source ◽  
Operational Amplifiers ◽  
Output Impedance ◽  
Output Current ◽  
Passive Components ◽  
Medical Settings ◽  
Spice Model ◽  
High Linearity ◽  
Small Load ◽  
Bioimpedance Measurement

Abstract There is a need for isolated current sources for use in selected bioimpedance measurement circuits. The requirement for good isolation is particularly important in medical settings because of safety concerns. A new circuit for producing voltage-controlled current is presented. Measurements have been made on a prototype and simulations have been done on a SPICE model. The presented circuit is an H-bridge where the output devices are the output photodiodes of high-linearity optocouplers. Five operational amplifiers, four high linearity optocouplers, and passive components are used. Output current capability is ±35 μA with an output impedance that is more than 1 M Ω. It is possible to achieve bandwidths above 1 MHz for small load impedances. This circuit is well suited for medical applications thanks to the isolation in the optocouplers.

scholarly journals Design of current sources for load common mode optimization

2018 ◽  
Vol 9 (1) ◽  
pp. 59-71
Author(s):  
Vinicius G Sirtoli ◽  
Kaue F Morcelles ◽  
Volney C Vincence
Keyword(s):  
Voltage Drop ◽  
Current Source ◽  
Output Impedance ◽  
Output Current ◽  
Common Mode ◽  
Measurement Systems ◽  
Fully Differential ◽  
Common Mode Voltage ◽  
The Common ◽  
Bioimpedance Measurement

Abstract Bioimpedance measurement systems often use the Howland current sources to excite the biological material under study. Usually, difference or instrumentation amplifiers are used to measure the resulting voltage drop on this material. In these circuits, common mode voltage appears as artifacts in the measurement. Most researches on current sources are focused on improving the output impedance, letting other characteristics aside. In this paper, it is made a brief review on the load common mode voltage and output swing of various topologies of Howland current sources. Three circuits are proposed to reduce load common mode voltage and enhance load capability by using a fully differential amplifier as active component. These circuits are equated, simulated and implemented. The three proposed circuits were able to deliver an output current with cut-off frequency (-3dB) higher than 1 MHz for loads as big as 4.7 kΩ. The worst measured load common mode voltage was smaller than 24 mV for one of the circuits and smaller than 8 mV for the other two. Consequently, it could be obtained increases in the Common Mode Rejection Ratio (CMRR) up to 60 dB when compared to the Enhanced Howland Current Source (EHCS).

scholarly journals Analysis, Simulation, and Development of a Low-Cost Fully Active-Electrode Bioimpedance Measurement Module

Technologies ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 59
Author(s):  
Christos Dimas ◽  
Vassilis Alimisis ◽  
Ioannis Georgakopoulos ◽  
Nikolaos Voudoukis ◽  
Nikolaos Uzunoglu ◽  
...  
Keyword(s):  
Low Cost ◽  
Current Source ◽  
Operational Amplifiers ◽  
Instrumentation Amplifier ◽  
Active Electrode ◽  
Fully Differential ◽  
Transient Simulations ◽  
Load Resistor ◽  
Complete Circuit ◽  
Bioimpedance Measurement

A low-cost 1 kHz–400 kHz operating frequency fully-active electrode bioimpedance measurement module, based on Howland current source, is presented in this paper. It includes a buffered positive feedback Howland current source, implemented with operational amplifiers, as well as an AD8421 instrumentation amplifier, for the differential voltage measurements. Each active electrode module can be connected to others, assembling a wearable active electrode module array. From this array, 2 electrodes can be selected to be driven from a THS413 fully differential amplifier, activating a mirrored Howland current source. This work performs a complete circuit analysis, verified with MATLAB and SPICE simulations of the current source’s transconductance and output impedance over the frequency range between 1 kHz and 1 MHz. Resistors’ tolerances, possible mismatches, and the operational amplifiers’ non-idealities are considered in both the analysis and simulations. A comparison study between four selected operational amplifiers (ADA4622, OPA2210, AD8034, and AD8672) is additionally performed. The module is also hardware-implemented and tested in the lab for all four operational amplifiers and the transconductance is measured for load resistors of 150 Ω, 660 Ω, and 1200 Ω. Measurements showed that, using the AD8034 operational amplifier, the current source’s transconductance remains constant for frequencies up to 400 KHz for a 150 Ω load and 250 kHz for a 1200 Ω load, while lower performance is achieved with the other 3 operational amplifiers. Finally, transient simulations and measurements are performed at the AD8421 output for bipolar measurements on the 3 aforementioned load resistor values.

scholarly journals A Low-Power Stable Wideband Current Source for Acupuncture Point Skin Impedance Measurements

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Changpei Qiu ◽  
Tianxia Zhao ◽  
Qiuping Li ◽  
Xin’an Wang ◽  
Kanglin Xiao ◽  
...  
Keyword(s):  
Low Power ◽  
Current Source ◽  
Harmonic Distortion ◽  
Acupuncture Point ◽  
Cmos Technology ◽  
Skin Impedance ◽  
Output Impedance ◽  
Output Current ◽  
Impedance Measurements ◽  
The Stability

A low-power stable wideband current source for acupuncture point skin impedance measurements has been designed employing a differential architecture and negative feedback. The circuits extend bandwidth to 1 MHz, reducing harmonic distortion to 0.24% at 1 MHz. The output impedance is 37 MΩ at 100 kHz and 11 MΩ at 1 MHz. The stability of the output current of the current source when connected to different loads is below 0.1% at frequencies up to 500 kHz and increases to 0.74% at 1 MHz. The circuit was manufactured in a 0.13-μm CMOS technology and measured results are presented. The area of the current source is 0.09 mm2 and its consumption is 1.2 mW. It is intended for low-power acupuncture point skin impedance measurements.

scholarly journals Design of an Ultra-Low Voltage Bias Current Generator Highly Immune to Electromagnetic Interference

2021 ◽  
Vol 11 (1) ◽  
pp. 6
Author(s):  
Orazio Aiello
Keyword(s):  
Integrated Circuits ◽  
Electromagnetic Interference ◽  
Low Voltage ◽  
Current Source ◽  
Building Blocks ◽  
Cmos Technology ◽  
Threshold Region ◽  
Output Current ◽  
Current Generator ◽  
Technology Process

The paper deals with the immunity to Electromagnetic Interference (EMI) of the current source for Ultra-Low-Voltage Integrated Circuits (ICs). Based on the properties of IC building blocks, such as the current-splitter and current correlator, a novel current generator is conceived. The proposed solution is suitable to provide currents to ICs operating in the sub-threshold region even in the presence of an electromagnetic polluted environment. The immunity to EMI of the proposed solution is compared with that of a conventional current mirror and evaluated by analytic means and with reference to the 180 nm CMOS technology process. The analysis highlights how the proposed solution generates currents down to nano-ampere intrinsically robust to the Radio Frequency (RF) interference affecting the input of the current generator, differently to what happens to the output current of a conventional mirror under the same conditions.

High-voltage synthetic inductor for vibration damping in resonant piezoelectric shunt

2020 ◽  
pp. 107754632095261
Author(s):  
Kevin Dekemele ◽  
Patrick Van Torre ◽  
Mia Loccufier
Keyword(s):  
Piezoelectric Material ◽  
High Voltage ◽  
State Of The Art ◽  
Vibration Damping ◽  
Operational Amplifiers ◽  
Frequency Range ◽  
Resonant Condition ◽  
Passive Components ◽  
Resonance Frequencies ◽  
Resonant Shunt

Resonant piezoelectric shunts are a well-established way to reduce vibrations of mechanical systems suffering from resonant condition. The vibration energy is transferred to the electrical domain through the bonded piezoelectric material where it is dissipated in the shunt. Typically, electrical and mechanical resonance frequencies are several orders apart. As such, finding a suitable high inductance component for the resonant shunt is not feasible. Therefore, these high inductance values are mimicked through synthetic impedances, consisting of operational amplifiers and passive components. A downside of these synthetic impedances is that standard operational amplifiers can only handle up to 30 V peak to peak and the state-of-the-art amplifiers up to 100 Vpp. However, as mechanical structures tend to become lighter and more flexible, the order induced voltages over the piezoelectric material electrode voltages increase above these limitations. In this research, a high-voltage synthetic inductor is proposed and built by combining the bridge amplifier configuration and the output voltage boost configuration around a single operational amplifier gyrator circuit, effectively quadrupling the range of the synthetic inductor to 400 Vpp. The impedance of the circuit over a frequency range is numerically and experimentally investigated. The synthetic inductor is then connected to a piezoelectric material bonded to a cantilever beam. Numerical and experimental investigation confirms the high-voltage operation of the implemented circuit and its suitability as a vibration damping circuit.

scholarly journals Bandwidth and Common Mode Optimization for Current and Voltage Sources in Bioimpedance Spectroscopy

2021 ◽  
Vol 12 (1) ◽  
pp. 135-146
Author(s):  
Tobias Menden ◽  
Jascha Matuszczyk ◽  
Steffen Leonhardt ◽  
Marian Walter
Keyword(s):  
Patient Safety ◽  
Current Source ◽  
The Body ◽  
Voltage Source ◽  
Bioimpedance Spectroscopy ◽  
Laboratory Measurements ◽  
Output Impedance ◽  
Frequency Range ◽  
Common Mode ◽  
High Bandwidth

Abstract Bioimpedance measurements use current or voltage sources to inject an excitation signal into the body. These sources require a high bandwidth, typically from 1 kHz to 1 MHz. Besides a low common mode, current limitation is necessary for patient safety. In this paper, we compare a symmetric enhanced Howland current source (EHCS) and a symmetric voltage source (VS) based on a non-inverting amplifier between 1 kHz and 1 MHz. A common mode reduction circuit has been implemented in both sources. The bandwidth of each source was optimized in simulations and achieved a stable output impedance over the whole frequency range. In laboratory measurements, the output impedance of the EHCS had its -3 dB point at 400 kHz. In contrast, the VS reached the +3 dB point at 600 kHz. On average over the observed frequency range, the active common mode compensation achieved a common mode rejection of -57.7 dB and -71.8 dB for the EHCS and VS, respectively. Our modifications to classical EHCS and VS circuits achieved a low common mode signal between 1 kHz and 1 MHz without the addition of complex circuitry, like general impedance converters. As a conclusion we found VSs to be superior to EHCSs for bioimpedance spectroscopy due to the higher bandwidth performance. However, this only applies if the injected current of the VS can be measured.

scholarly journals Stability Analysis and Optimal Design for Virtual Impedance of 48 V Server Power System for Data Center Applications

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5253
Author(s):  
Chien-Chun Huang ◽  
Sheng-Li Yao ◽  
Huang-Jen Chiu
Keyword(s):  
Open Loop ◽  
Buck Converter ◽  
Output Impedance ◽  
Signal Model ◽  
Passive Components ◽  
The Past ◽  
Feedback Compensation ◽  
Series Systems ◽  
The Relationship ◽  
Virtual Impedance

In the past literature on virtual impedance to series systems, most of the discussion focused on stability without in-depth research on the system design of the series converter and the overall output impedance. Accordingly, this study takes an open-loop resonant LLC converter series-connected closed-loop Buck converter as an example. First, the conditions required for the direct connection of the small-signal model in the series, the effect of feedback compensation on the input impedance of the load stage, the operating frequency, and passive components of the two-stage converter are discussed in detail―the relationship between the matching and the output impedance. Afterwards, a mathematical model is used to discuss the effect of adding parallel virtual impedance on the output impedance of the overall series converter and then derive an optimized virtual impedance design. Finally, an experimental platform of 48 V to 12 V and maximum wattage of 96 W are implemented. The output impedance of the series converter is measured with an impedance analyzer to verify the theoretical analysis proposed in this paper.

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