Low-level DC Research Articles

Design of a Switched Capacitor Negative Feedback Circuit for a Very Low Level DC Current Amplifier

To miniaturize a very low level dc current amplifier and to improve its output response speed, the switched capacitor negative feedback circuit (SCNF), instead of the conventionally used high-ohmage resistor, is presented in this paper. In our system, a switched capacitor filter (SCF) and an offset controller are also used to decrease vibrations and offset voltage at the output of the amplifier using SCNF. The theoretical output voltage of the very low level dc current amplifier using SCNF is obtained. The experimental results show that the unnecessary components of the amplifier’s output are much decreased, and that the response speed of the amplifier with both the SCNF and SCF is faster than that using high-ohmage resistor.

Real-time measurement method of dc injection for transformerless PV systems

Measurement of dc injection is crucial for the transformerless PV systems. IEEE Std.929-2000 specifies that the PV systems shall not inject the dc current greater than 0.5% of the full rated output current. Dc injection measurement is not only useful for evaluating whether a transformerless PV system meets IEEE standards, but also for the effective dc suppression with injecting an equal but opposite dc component via a proper control scheme. In practice, however, it is difficult to extract the very low-level (0.5% I rated) dc currents in the presence of high levels of ac currents in transformerless PV systems. In order to overcome the limitation, this paper presents a real-time dc injection measurement technique. Some major issues such as the basic operating principle, frequency excursion effect mitigation and discrete-domain implementation of the proposed method are discussed. Theoretical analysis and performance evaluation results verify the effectiveness of the proposed dc injection measurement technique.

Caracterização inorgânica de cinza volante de uma estação de incineração de resíduos sólidos urbanos com vista à sua eventual reciclagem

Fly ashes from municipal solid waste incinerators (MSWI) are considered hazardous waste. In Portugal, they are expected to increase over time which poses a growing concern about the waste management issue they represent. The use of landfills for fly ash disposal is currently the main option in many countries. Since a variety of heavy metals concentrate in fly ash, mainly deposited on the surface of particles, making them more apt to leach, the ash need to be stabilized prior to disposal, to reduce their environmental impact, which is done by the addition of cement. The electrodialytic process (ED) promisingly removes heavy metals from fly ash, enabling their further valorisation (e.g. as a soil amendment or for incorporation in construction products) and the recovery of heavy metals for further reuse. The ED uses a low-level dc current as the cleaning agent, combining the electrokinetic movement, with the principle of electrodialysis. The Project POCTI/AGG/45073/2002, currently being carried out, aims at studying the application of the ED, in order to maximize heavy metals removal from this contaminated media. In this work the inorganic fraction of fly ash are characterized.

Electric-field-induced magnetization in Pb(Zr,Ti)O3/Terfenol-D composite structures

We report the electric-field-induced magnetization (EIM) in the composite structures made by combining Pb(Zr0.52Ti0.48)O3 (PZT) and Tb0.30Dy0.7Fe2 (Terfenol-D). The results showed that the EIM could be generated in the composite structures due to the efficient stress-mediated electromagnetic coupling interaction between the piezoelectric PZT and magnetostrictive Terfenol-D. This EIM effect depended significantly on the driving electric field frequency and was highly sensitive to the dc magnetic bias, which exhibited a promising potential in the low-level dc magnetic field detecting application.

Double-Type Photocoupler Negative Feedback Circuit for Very Low Level DC Current Amplifier

To obtain fast response in a very low level dc current amplifier, the amplifier using a single-type photocoupler negative feedback circuit has been developed; however, it has an offset drift problem because of the electrical property of the photocoupler. In this study, we proposed a very low level dc current amplifier using a double-type photocoupler negative feedback circuit that has two functional parts, that is, a negative feedback part and an offset controller. The experimental results show that the response speed of this amplifier is as high as that of the amplifier using the single-type circuit, and that the offset voltage drift of the amplifier using the double-type circuit is markedly improved.

Surface-tension-driven nanoelectromechanical relaxation oscillator

Because of its linear dependence on length scale, surface tension can be a dominant force for small systems. Properly harnessed, this force is uniquely suited for nanomechanical applications. We have developed a nanoelectromechanical relaxation oscillator with a surface-tension-driven power stroke. The oscillator consists of two liquid metal droplets exchanging mass, and its frequency is directly controlled with a low-level dc electrical voltage.

Optical transmission of low-level DC, slowly varying and pulsed current signals using the optically coupled current mirror architecture

The optically coupled current mirror (OCCM) is a novel optoelectronic architecture that replicates at ground potential a current flowing in an isolated conductor. The mirroring action is done without need to bring any power to the potential of the conductor where the current flows, as its input stage is completely passive. This feature is particularly important when the conductor is at high voltage (HV), a typical case being the photomultiplier tubes (PMTs) biased with positive HV, or when the number of channels is very large as it is the case of many particle physics experiments. The OCCM has been used to equip the two prototype telescopes, each one comprising 440 PMTs, of the ultra-high-energy cosmic-ray experiment Pierre Auger. Despite that the PMT's anodes were at HV, the DC or slowly varying component of the anode current was measured with high resolution, clearly revealing the presence of faint stars, planets, and other similar objects which determine the sky background light. In this paper we describe the principle of operation of the OCCM and its application to the measurement of the anode current of PMTs biased with cathode grounded, as well as the first results obtained with the OCCM on linear transmission of 2-/spl mu/s-width pulses, via fiber optics.

Organic light-emitting diode fabricated on a polymer substrate for optical links

An organic electroluminescence diode (OLED) fabricated on polyimide substrate has been investigated to realize a flexible electro-optic device for optical links. The device fabricated on polyimide substrate shows similar device characteristic to that on glass substrate. The modulation performance of the OLED was significantly improved by applying a positive, low-level DC bias, which results in a slower falling time. An undershoot voltage applied to the falling edge of the input voltage pulse results in faster falling time and a decrease in intensity of the optical output. We demonstrate that the OLEDs can be applied to short-range optical communication fields, such as electro-optical conversion devices for optical links.

Frequency-controlled low-level current source based on charge pumping

The use of the charge pumping in MOSFETs as a low-level DC current source is proposed. Such a current source has some superior characteristics: namely, its output current is proportional to the frequency of input pulses; the output is insensitive to the drift of the pulse voltage (i.e. the drift of the pulse base/top levels); and it has an extremely high input resistance.

Analysis of a very low‐level DC current amplifier with allowance for the distributed ground capacitance of a high‐ohmage feedback resistor

AbstractWhen the response speed of a very low level dc current amplifier is increased with a shield, especially with a shielding pipe of small diameter, distortion of its output waveform increases. To elucidate the phenomenon, the new concept of distributed ground capacitances, in addition to the stray capacitances across the terminals of the high‐ohmage resistor, is taken into consideration for the circuit analysis. This paper shows that the output waveforms of the very low level dc current amplifier are distorted when Cin < KCa (where Cin, K, and Ca are the effective input capacitance, the amplification of the high‐input‐resistance amplifier and the distributed capacitance to ground, respectively) and that the distortion on its output waveforms is mainly caused by Ca.

A Very Low Level DC Current Amplifier Using Photocoupler Negative Feedback Circuit

In order to improve the response speed of a very low level dc current amplifier, we propose a novel method in which a photocoupler, instead of a high resistor (1010 Ω), is employed for the negative feedback circuit. In this paper, it is shown experimentally that with the proper use of positive feedback, the rise time t r of 10 µs is obtained for this circuit at the current sensitivity of 10 pA. In comparison, the t r with the use of the high resistor with the shielding plate is 120 µs. (Here, the current sensitivity is the minimum measurable input signal current that produces an output signal voltage of a very low level dc current amplifier equal to its output noise voltage, or that leads to a signal-to-noise ratio of unity.)

Measurement of low level DC magnetic fields using a synchronous demodulation technique

A simple, yet accurate, method for the measurement of low-level DC magnetic fields is proposed. Since a synchronous demodulation technique is used, only incremental field values are directly measured. Absolute values require knowledge of a reference value for the field. An implementation of the method for measuring the magnetic field in soft magnetic materials is also presented. >

Magnetic fields and intracellular calcium: effects on lymphocytes exposed to conditions for 'cyclotron resonance'

There are a number of claims in the literature that specific combinations of low level DC and AC magnetic fields can cause biologically significant effects. The combinations of fields required to elicit these responses fulfil the theoretical conditions for classical cyclotron resonance of the selected ion. Because of the biological importance of calcium ions any effects on them are of particular interest, for instance the claimed increase in calcium uptake by electromagnetically exposed lymphocytes. The authors have measured the intracellular calcium concentration, by means of a sensitive fluorescent probe, during a 60 min exposure of mouse lymphocytes to 'cyclotron resonance' conditions for calcium ions. 'Resonance' conditions at two frequencies (16 Hz and 50 Hz) were tested, with a range of DC field amplitudes used to shift the frequency up to 25% either side of the calculated optimum. No change in intracellular calcium concentration could be detected when lymphocytes were exposed to 'cyclotron resonance' conditions or to the other magnetic field combinations used.

Corner currents in rectangular diffused p+-n-n+diodes

The low-level injection dc characteristics of rectangular p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -n-n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> diodes are discussed, and the vertical, lateral, and corner current components are analyzed and measured. It is shown that the corner current can be a significant fraction of the total current and a simple analytic expression is given.

Stepped Voltage Dc/Ac Inverter --Part I: Analysis

A DC/AC inverter whose voltage is constructed from discrete low level DC sources to form a stepped sine-wave-like output is introduced. The criterion of optimal approximation of the stepped waveform to a sinewave was the minimum mean square error. The internal resistance of the generated source voltage is time varying since the total series resistance changes with the wave shape. When a constant resistive load is connected to such a load, the load voltage shape does not follow the source voltage and the optimal approximation to a sinewave of the two voltages will depend on two different switching policies: one adaptive to the source voltage and the other adaptive to the load voltage'. The inverter operation for both cases is analysed, and the main harmonic voltage and power, harmonic spectrum and distortion are obtained. The proposed inverter has superior properties characterized by its low distortion and high efficiency.

A low-level DC current amplifier for p-n junction radiation detectors

A design study on the amplification of the direct current from transducers of low internal impedance was carried out by this author (1976). The practical implementation of this work in the design of an amplifier for use with p-n junction radiation detectors operated in the direct current mode is described. The circuit affords a high degree of linearity, wide dynamic range and sensitivity of the order of the inherent noise of the radiation detectors.

Transistor used as an adjustable bipolar low-level DC source

The use of a saturated transistor with a collector current opposite to the usual leads to a versatile, stable, and easily adjustable dc source with an EMF ranging from -10 to +10 mV and a low temperature drift. This source may be used to compensate the input offset voltage of a monolithic opamp whenever the impedance must be kept near zero or as low as 1 /spl Omega/. It can be built into an IC design with only a single-pin control line.

The effects of low level DC scalp positive and negative current on the performance of various tasks.

Recently increased interest has been shown in the physiological and behavioural consequences of DC polarization of the brain.

アナログICを用いた計測制御用mV入力直結直流増幅器

アナログICを用いた計測制御用mV入力直結直流増幅器

A Nonsuperconducting Detection System for Low Level dc Voltages

A low level dc detection system with an attainable precision of 25 pV is described. The system uses only normal metal components and commercially available equipment. Measurements can be made automatically, in the presence of large (microvolt) spurious voltages, with switched inputs, and in a non ``null'' configuration. A typical application is described in detail.