High Accurate Howland Current Source: Output Constraints Analysis

Bertemes-Filho, Pedro; Felipe, Alexandre; Vincence, V. C.

doi:10.4236/cs.2013.47059

Cited by 50 publications

(35 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Acceptable results by Macias et al [12] were found in the AFE-1 topology when assessing the circuit performance up to 1 MHz. The AFE-2 topology has a good stability for the frequency range used in this work, but depends strongly on the symmetry between the current sources [13].…”

Section: Discussionmentioning

confidence: 99%

“…The VCCS provides a constant output current (=1 mApp) that is given by the ratio between V out (=1 Vpp) and the resistor r (=1 kΩ). All resistors have a low precision tolerance (±1%) in order to obtain a good current source performance [13]. In order to reduce power consumption, the resistor r of the Howland circuit (see Figure 3) should be much smaller than the value of R (=47 kΩ).…”

Section: Mirrored Modified Howland Current Source -Afe-2mentioning

confidence: 99%

See 1 more Smart Citation

Analog Front-End for the Integrated Circuit AD5933 Used in Electrical Bioimpedance Measurements

2016

View full text Add to dashboard Cite

-In the recent decades the bioimpedance has been used in many areas of medicine. The technological advance of electronics has enabled the increase of bioimpedance applications. Measuring biological tissues is a hard work, which leads to the need of continuous research based on better methods and equipments for diagnosis. Many electronics manufacturers have helped the biomedical area through the development of new electronic components and equipment. The objective of this work is to adapt the impedance meter AD5933 for bioimpedance measurements. Two Analog Front-End (AFE) circuits were built with different Voltage Controlled Current Source (VCCS) topologies, which are a load-in-the-loop and a mirrored modified Howland current sources. Circuits were implemented and both two and four electrode measurements in the frequency range of 5 to 100 kHz were performed. Results showed that both front-end circuits are suitable to be used with the AD5933 at lower frequencies. Also, it might be a lowcost alternative for electrical bioimpedance applications.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Mirrored Modified Howland Current Source -Afe-2mentioning

confidence: 99%

Analog Front-End for the Integrated Circuit AD5933 Used in Electrical Bioimpedance Measurements

2016

View full text Add to dashboard Cite

show abstract

“…The design of an appropriate VCCS is one of the most challenging parts in an EIT system design, since the specifications must satisfy high output impedance z out , Common Mode Rejection Ratio (CMRR) and sufficient current amplitude (low enough for the patients' safety and high enough to avoid notable noise rates) for as high frequency range as possible. In this study the topologies simulated are based on the modified Howland current source, described in [14,20,21]. Specifically, two main approaches have been tested: (a) the grounded load and (b) the mirrored modified Howland VCCS [20].…”

Section: Voltage-to-current Conversionmentioning

confidence: 99%

“…In this study the topologies simulated are based on the modified Howland current source, described in [14,20,21]. Specifically, two main approaches have been tested: (a) the grounded load and (b) the mirrored modified Howland VCCS [20]. Their topologies are shown in Figure 1b,c correspondingly.…”

Section: Voltage-to-current Conversionmentioning

confidence: 99%

A Parametric EIT System Spice Simulation with Phantom Equivalent Circuits

2020

View full text Add to dashboard Cite

In this paper a number of LT Spice simulations have been carried out on an Electrical Impedance Tomography (EIT) system, which includes the whole analog and digital circuitry as well as the subject to be examined (phantom model). The aim of this study is to show how the analog and digital parts, the electrodes and the subject’s physical properties may impact the measurements and the quality of the reconstructed image. This could provide a useful tool for designing an EIT system. Special attention has been given to the current source’s output impedance and swing, to the noise produced by the circuits and to the Analog to Digital Converters (ADCs) resolution and sampling rate. Furthermore, some 3D phantom subjects have been modeled and simulated as equivalent circuits, merged with the EIT simulated hardware, in order to observe how changes on their properties interact with the whole circuitry and affect the final result. Observations show that mirrored current sources with z o u t > 350 k Ω and sufficiently high ADC acquisition sampling rate ( f s a m p l e ≥ 16 f i n ) can result to accurate impedance measurements and therefore quality image reconstruction within a frequency span of at least 10 to 100 kHz. Moreover, possible hardware failures (electrode disconnections and imbalanced contact impedances) can be detected with a simple examination of the first extracted image and measurement set, so that by direct modification of the reconstruction process, a corrected result can be obtained.

show abstract

“…First is an AC current source, which must be stable within working frequency range; second is a data acquisition system to record voltage, current, and their phase difference; and third is software for computing and displaying the impedance dispersion curves, which is commonly in the Bode plot or Nyquist plot.Furthermore, in an effort to provide a BIS instrumentation system in good performance, some researchers have offered the new design. Starting from precision AC current sources [26], the high accuracy data acquisition system [27,28], even the whole system device [29][30][31][32][33]. Commonly, the offered BIS instrumentation system is arranged in modular and work separately.…”

mentioning

confidence: 99%

Low-Cost, Compact, and Rapid Bio-Impedance Spectrometer with Real-Time Bode and Nyquist Plots

et al. 2020

View full text Add to dashboard Cite

Bioelectric impedance spectroscopy (BIS) has been widely used to study the electrical properties of biological tissue based on the characteristics of the complex electrical impedance dispersions. One of the problems in using the BIS method is the length of time required for the data acquisition process and possibly data analysis as well. In this research, a compact and work rapidly BIS instrumentation system has been developed at a low cost. It is designed to work in the frequency range of 100 Hz to 100 kHz, which is generally used in the fields of biophysics and medical physics. The BIS instrumentation system is built using several integrated modules. The modules are an AC current source to produce a selectable injection current; a data acquisition system to measure voltage, current, and phase difference rapidly and simultaneously; and software to calculate and display measurement results in the form of Bode and Nyquist plots in real time. The developed BIS system has been validated using a simple RC circuit as the sample being tested. The average time needed in the process of data acquisition and analysis until the formation of impedance dispersion curves in the form of Bode and Nyquist plots, for 54 sample frequencies, is less than one minute. The system is able to identify R and C values of the sample with a maximum error of 1.5%. In addition, some simple application examples are also presented in this paper.

show abstract

High Accurate Howland Current Source: Output Constraints Analysis

Cited by 50 publications

References 12 publications

Analog Front-End for the Integrated Circuit AD5933 Used in Electrical Bioimpedance Measurements

Analog Front-End for the Integrated Circuit AD5933 Used in Electrical Bioimpedance Measurements

A Parametric EIT System Spice Simulation with Phantom Equivalent Circuits

Low-Cost, Compact, and Rapid Bio-Impedance Spectrometer with Real-Time Bode and Nyquist Plots

Contact Info

Product

Resources

About