Output Current Signal Research Articles

High frequency current mode oscillator employing fT integration technique

A low distortion high frequency oscillator is described, which is a development of the recently proposed fT-integrator, in which an amplitude control circuit is embedded inside the integrator. Simulation results suggest that, for the oscillation range 1–2.6 GHz, the total harmonic distortion (THD) of the output current signal is well below 0.5% for the output current level at 50% modulation depth (peak-to-peak). The phase noise of the oscillator is simulated to be –72 dBc/Hz at 1 MHz offset for 1% THD output current.

Spatially integrated speckle intensity: maximum resistance to decorrelation caused by in-plane target displacement

Laser speckle produced from a diffuse object can be used in determining the angular position of a rotating object. When the object rotates the backscattered speckle pattern, which changes continuously but repeats exactly with every revolution, is sampled by a suitably positioned photodetector. The photodetector output signal is periodic, and one period is stored in the memory as a reference. Shaft position can then be determined by the comparison of this stored reference signal with the current photodetector output signal. When the shaft is axially displaced, for example, by vibration, the backscattered speckle pattern changes on the photodetector and the similarity between the reference signal and the current signal is reduced. We examine the cross correlation of the real-time photodetector output signal and the stored reference signal as a function of axial shaft position. Use of a rotating shaft when collecting data is shown to be an efficient means by which to make effectively several thousand independent estimates of the maximum axial displacement tolerable before decorrelation of the photodetector output. Theoretical results and experiments conducted show that the decorrelation displacement varies, according to optical configuration, to a maximum value of 0.7 of the beam diameter. This has important implications for a proposed laser torquemeter as well as additional applications in which changes to the sampled speckle pattern, including decorrelation, are either desirable or undesirable.

Modalities of Distortion of Physiological Voltage Signals by Patch-Clamp Amplifiers: A Modeling Study

An extensive evaluation of the possible alterations affecting physiological voltage signals recorded with patch-clamp amplifiers (PCAs) working in the current-clamp (CC) mode was carried out by following a modeling approach. The PCA output voltage and current signals obtained during CC recordings performed under simplified experimental conditions were exploited to determine the equations describing the generation of error currents and voltage distortions by PCAs. The functions thus obtained were used to construct models of PCAs working in the CC mode, which were coupled to numerical simulations of neuronal bioelectrical behavior; this allowed us to evaluate the effects of the same PCAs on different physiological membrane-voltage events. The models revealed that rapid signals such as fast action potentials are preferentially affected, whereas slower events, such as low-threshold spikes, are less altered. Prominent effects of model PCAs on fast action potentials were alterations of their amplitude, duration, depolarization and repolarization speeds, and, most notably, the generation of spurious afterhyperpolarizations. Processes like regular firing and burst firing could also be altered, under particular conditions, by the model PCAs. When a cell consisting of more than one single intracellular compartment was considered, the model PCAs distorted fast equalization transients. Furthermore, the effects of different experimental and cellular parameters (series resistance, cell capacitance, temperature) on PCA-generated artifacts were analyzed. Finally, the simulations indicated that no off-line correction based on manipulations of the error-current signals returned by the PCAs can be successfully performed in the attempt to recover unperturbed voltage signals, because of alterations of the overall current flowing through the cell-PCA system.

Current mode chaos generator

A new chaos generator that uses the second generation current conveyor (CCII) as the active building block and produces a chaotic current output signal is introduced. The procedure of obtaining the generator by modifying a current mode sinusoidal oscillator using a nonlinear resistor of antisymmetrical current-voltage characteristics is emphasised. The small input resistance associated with the CCII inverting input terminal is found to be responsible for stimulating the circuit's chaotic nature. Experimental results, PSPICE simulations and numerical simulations of the derived mathematical model are included.

High-Spatial-Resolution Medical-Imaging System Using a HARPICON Camera Coupled with a Fluorescent Screen

A high-sensitivity HARPICON camera was developed for medical X-ray imaging using a fluorescent screen. It is an avalanche-multiplication-type image pick-up tube and is 32 times more sensitive than conventional tubes. The camera also has a wider dynamic range than conventional medical-imaging cameras because a maximum output signal current of 2.3 muA is obtained and, in high-illumination-intensity regions, photocurrent is not proportional to illumination intensity. The fluorescent screen is an intensifying screen of the type used for radiographic screen-film combinations in medical examination. An X-ray image on the screen is focused on the photoconductive layer of the pick-up tube using a coupling lens with f/0.65. Experiments were performed using monochromated X-rays at the Photon Factory. An image of a spatial resolution test chart was taken in a 525 scanning-line mode of the camera. The chart pattern of 5 line-pairs mm(-1 )(spatial resolution of 100 mum) was observed at an X-ray input field of 50 x 50 mm. Real-time digital images of the heart of a 12 kg dog were obtained at a frame rate of 60 images s(-1) after injection of a contrast medium into an artery. The images were stored in digital format at 512 x 480 pixels with 12 bits pixel(-1). High-spatial-resolution and high-contrast images of coronary arteries were obtained in aortography using X-rays with energy above that of the iodine K edge; the image quality was comparable with that of conventional selective coronary angiography.

Theoretical study of the response of InGaAs metal-semiconductor-metal photodetectors

We present a theoretical investigation of the response of metal-semiconductor-metal (MSM) photodetectors made of InGaAs lattice-matched to InP using a two-dimensional drift-diffusion model with a thermionic-field emission boundary condition for the heterojunctions. The effect of including a top InAlAs layer to increase the effective barrier height of the metal fingers on the InGaAs active layer is thoroughly examined and found to limit the collection of the photocurrent signal due to the electron and hole barriers that it forms with InGaAs. Due to the thickness and height of the InAlAs barrier layer in existing designs, the tunneling current obtained from the model is found to be negligibly small to significantly affect the output signal current. In an attempt to obtain a better response, different design structures including one where a quasi-Schottky contact is utilized are studied and their speed of response, breakdown voltage, and dark current are compared to that of the usual InGaAs device. >

Proportional regime of a double superconducting tunnel junction detector

The proportional regime of a double superconducting tunnel junction detector is described in terms of the diffusion equation of the nonequilibrium quasiparticles excited in the absorber by the impinging radiation. The expression of the output current signals through the junctions is obtained. Some numerical results are shown and discussed also in connection with the operation of the detector in the charge collection mode.

Theoretical study of the effect of an AlGaAs double heterostructure on metal-semiconductor-metal photodetector performance

The impulse and square-wave input response of different GaAs metal-semiconductor-metal photodetector (MSM) designs are theoretically examined using a two dimensional drift-diffusion numerical calculation with a thermionic-field emission boundary condition model for the heterojunctions. The rise time and the fall time of the output signal current are calculated for a simple GaAs, epitaxially grown, MSM device as well as for various double-heterostructure barrier devices. The double heterostructure devices consist of an AlGaAs layer sandwiched between the top GaAs active absorption layer and the bottom GaAs substrate. The effect of the depth of the AlGaAs layer on the speed and responsivity of the MSM devices is examined. It is found that there is an optimal depth, at fixed applied bias, of the AlGaAs layer within the structure that provides maximum responsivity at minimal compromise in speed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pituitary Microcirculation: Physiological Aspects and Clinical Implications. A Laser-Doppler Flow Study during Transsphenoidal Adenomectomy

The anterior and posterior pituitary lobes (AL and PL, respectively) are assumed to differ in the type of vascular supply and structure of their microvascular networks. Animal experiments have shown that the pituitary microvascular flow differs between the two lobes, being extremely high in the PL and low in the AL. For technical reasons, it has hitherto not been possible to study pituitary microflow in humans. Laser-Doppler flowmetry (LDF) is now a well-established method for real-time monitoring of microcirculation, applicable also in humans. In a prospective clinical study, the microflow in the AL and PL was measured during transsphenoidal microsurgery in 52 patients with adenomas of different size, growth characteristics, and endocrinological activity. The mean microflow in the PL (177.7 +/- 12.6 [flux]) was found to be about six times higher than that in the AL (27.4 +/- 2.7 [flux]). No difference in the laser-Doppler fractional volume of the lobes could be detected (0.73 +/- 0.06 [] vs. 0.77 +/- 0.07 [], where [] designates the ratio of the alternating current output to the direct current output signals). Microflow within the pituitary lobes was influenced neither by the histological type nor the size of the adenoma. Additionally, LDF signal-averaging triggered by the electrocardiogram allowed detection of different characteristic pulsatile microvascular flow patterns in the AL and PL. Our findings provide strong physiological support for the idea that the angioarchitecture of the pituitary lobes differs. With this method, the AL and PL can be identified objectively during surgery. LDF might provide useful information concerning intraoperative surgical approach.

New physical timing models of bipolar nonsaturation logic using current-domain analysis technique

A new large-signal equivalent circuit with input and output current signals for a nonsaturated bipolar junction transistor has been developed. Based upon this equivalent circuit, physical timing models of direct-coupled transistor logic (DCTL) and nonthreshold logic (NTL) have been derived through a general modeling methodology. It is shown from extensive comparisons with SPICE simulation results that the models have a maximum error of 25% in single-stage delay calculation and 10% in multi-stage delay calculation. Experimental results on NTL ring oscillators also partly substantiate the developed current-domain large-signal equivalent circuit and physical timing models. Good accuracy, wide applicable ranges of device/circuit parameters and input waveforms, and less CPU time and memory consumption than full transient simulations make the physical timing models feasible in optimization and CAD of high-speed bipolar ICs.

Current mode allpass/notch and bandpass filter using single CCII

A current mode second-order allpass notch and bandpass filter using a single CCII, two grounded capacitors and four resistors is proposed. The allpass and notch output current signals, taken out through port z of a CCII and having high output impedance, can be obtained by tuning a resistor in the proposed network. The resonance angular frequency and quality factor of the new network have the advantages of low passive sensitivities and are insensitive to the current tracking error of the nonideal CCII.

Use of inhibited enzyme electrode for estimation of PEA diamine oxidase inhibitors

A biosensor consisting of a Clark type oxygen electrode and immobilized pea diamine oxidase makes it possible amperometrically to quantify, on the basis of an inhibition effect, substrate analogues of the enzyme (aliphatic amino ketones and monoamines, aromatic diamines), some alkaloids (cinchonine, lobeline, norsedamine) and drugs (1-phenylcyclopropylamine, naphazoline). The output current signal of the inhibited bioelectrode is influenced by the thickness of the membrane and its enzyme content as well as by the sort of the substrate and oxygen concentration in the reaction medium. With most of the tested substances, the response time τ90 is 20-100 s and the linear concentration range about 10-6-10-3 mol l-1 can be observed. The inhibitor concentrations causing a change of the initial current by 50% correspond mostly to the published values of inhibition constants for soluble enzyme. The most efficient inhibitor of the pea diamine oxidase is 1,5-diamino-3-pentanone, for which the accuracy of the method was 5.6%, its reproducibility 7.2%, and detection limit 5 . 10-9 mol l-1.

Fourier Transform Methods in Hydrodynamic Modulation Voltammetry

A theoretical analysis of fast Fourier transform methods in hydrodynamic modulation voltammetry (HMV) is presented for the determination of frequency response spectra. The speed of a rotating disk electrode is modulated in a manner that simultaneously excites many frequencies so that Fourier decomposition of the mass‐transfer limited current output signal gives the system response (amplitude and phase) over the entire frequency spectrum. Nonlinear harmonic interactions that can give rise to significant deviations from linear system response are discussed in detail. Existing linear theories are compared with the numerical results, and upper bounds are established for the modulation amplitudes that give linear response in HMV systems. Results are presented for large amplitude sinusoidal, square root, and triangular modulations in the speed of a rotating disk electrode.

A channel electron multiplier and optically coupled amplifier used as an incident flux monitor

A system is described that performs monitoring of the incident photon flux for synchrotron radiation experiments. The system uses a channel electron multiplier whose output signal current in the high voltage line is accurately measured with an optically coupled isolation amplifier.

Epitaxial silicon avalanche photodiode

Preparation of silicon avalanche photodiodes by a planar method in epitaxial PP+ silicon slices limited charge collection to carriers generated in or close to the depletion region. Reducing the effective size of the zero-field absorption region surrounding the depletion region by this method, resulted in the output signal current of the device reproducing the input light pulse shape, within 15 ns. When illuminated with monochromatic radiation, the shot noise of a detector prepared in epitaxial material was less than that observed with a device fabricated in homogeneous material, due to the reduced signal current.

Precision Electronic Switching with Feedback Amplifiers

Electronic-switching signal transmission devices have been, until recently, used principally for the simultaneous display of more than one waveform on a cathode ray oscillograph. During the past few years, however, in the field of electronic analog computers, several applications have required the development of electronic switches which have transmission characteristics consistent with the performance of precision computing elements. These precision switches utilize highly stabilized feedback amplifiers with the switching elements included in the forward gain portion of the loop to minimize the nonlinear characteristic effects. Multiple output switches, which provide either current or voltage output signal transmission from a single input voltage source, are available. Precision electronic time-division multipliers have been developed which utilize both current and voltage type switching circuits. Modulators and demodulators, utilizing voltage type switched-feedback amplifiers, have been developed with a linearity of 0.1 per cent. A multiple input switch has also been developed which involves an unusual circuit design. This design incorporates two separate input stages and a common output stage with separate feedback paths provided between the common output and the two inputs. With a square wave keying voltage alternately activating the two input stages, signals applied to the two input stages can be alternately connected to the output. The transmission stability and precision are largely dependent on the feedback loop gain of the amplifier and the switching speed on the amplifier bandwidth.

Magnetic amplifiers

D.C. controlled, saturable-core reactors were used successfully by Germany during the 1939–45 War for the amplification and mixing of powers down to a microwatt. Typical performance figures are quoted.An explanation of transductor action is given, and the turns-ratio law relating output current and input signal excitation is derived for a core of infinite permeability. Transductor behaviour on short-circuit is treated analytically, and the non-dimensional plotting of characteristics is discussed. The effect of permeability on the performance with self-excitation is illustrated with curves for Mumetal, Radiometal and Stalloy, and arrangements of transductors to give duo-directional magnetic amplifiers are dealt with. After some notes on selenium rectifier behaviour, fundamental design principles are developed in which power output, amplification and time lag are related to supply frequency, core area and self-excitation or feedback.Transductor time-constants are directly proportional to power amplification, and inversely proportional to supply frequency and positive feedback. Therefore, to obtain a high amplification/time-constant ratio, the correct design procedure is to use a high supply frequency and to connect in cascade a number of stages having positive feedback.It is concluded that transductors are a valuable addition to circuit technique for the amplification of d.c. powers down to about 10−9 watt.