Showing papers on "Rise time published in 1983"

Effects of propagation on the rise times and the initial peaks of radiation fields from return strokes

Abstract: The theoretical solution to the problem of radiation from a pulsed vertical dipole over a flat homogeneous earth is employed to study the changes in rise times and the attenuation of the initial peaks of the radiation fields from lightning constructed according to the most recent experimental data on lightning return stroke radiation fields Expected changes in rise times and the attenuation of the initial peaks for different values of distances and conductivities are presented It is shown that for a given initial rise time there is a spread in distant rise times due to the variability of the shapes of the radiation fields The expected spread in distant rise times for different values of distances and conductivities is calculated The results show the importance of taking into account the propagation effects in any attempt to estimate return stroke current parameters such as rise time, rate of rise, and peak current from radiation fields which propagated over land The predictions are compared with the available experimental data, and a good agreement is found between them

New graded band-gap picosecond phototransistor

Abstract: We demonstrate the first phototransistor with a graded band‐gap base. The AlGaAs/GaAs wide gap emitter molecular beam epitaxial structure, when operated at zero bias, behaves as an ultrahigh speed photodetector. The pulse response is symmetric with an intrinsic rise time ≤20 ps and a full width at half‐maximum ≤40 ps. When operated at reverse bias the detector behaves as a phototransistor. The response time of this device demonstrates that the base transit time is greatly reduced by the quasi‐electric field in the base. This feature combined with the abrupt wide gap emitter may be used to implement new high‐speed transistors.

Apparatus for simultaneous temperature and heat‐flow measurements under transient conditions

Abstract: In this paper, it is shown how a heat‐flow transducer and a digital electronic unit can be used together for simultaneous measurements of heat flow and temperature The electrical output of the sensor consists of a voltage generator (whose open circuit voltage is proportional to the rate of the heat flow to be measured) The electrical output of the sensor acts as a single battery and metallic resistors were disposed between the terminals The open circuit voltage is proportional to the rate of heat flow to be measured The value of the resistor is controlled by temperature The procedure for simultaneously measuring heat flow and temperature is made straightforward by including a balanced Wheatstone bridge driven by an ac carrier as an integral part of the design To solve the difficult problem of precise detection and maintenance of the balance, the classical Wheatstone bridge configuration has been slightly modified by adding a capacitor to smooth the phase variations around the balance The discrete time feedback loop used for automatically balancing the bridge includes a digital integrator which sums the phase errors and provides the required voltage As a result, temperature measurements were made with a linearity better than 1% in the measuring range and the digital readout is obtained with a rise time of 10 ms

Temperature and end‐plate currents in rat diaphragm.

Abstract: 1. Spontaneous miniature end-plate currents (m.e.p.c.s.) were recorded in rat diaphragm at 7, 22 and 37 degrees C at -80 mV. The onset rate, measured as 20-80% rise time, was sensitive to temperature with activation energy 14 kcal mol-1 deg-1, and was not sensitive to membrane voltage between -60 and -130 mV. 2. The rise time recorded by external electrodes was 144 microseconds at 37 degrees C (6) and was similar to that found by internal electrodes. 3. The fall time was temperature-sensitive with activation 18 kcal, and was prolonged when the end-plate was hyperpolarized. 4. With acetylcholine (10 microM) the current increased to a peak and then fell within 30 s to a value which declined slowly. From fluctuation analysis the channel open time of 237 microseconds (7) at 37 degrees C was estimated. External recording gave comparable values (4). Comparison of the initial estimates with those obtained after 3-6 min of continued application showed no consistent change. The channel conductance was 26 pS at 37 degrees C. 5. The time constant of m.e.p.c. decay was consistently longer than the channel open time obtained from noise analysis. 6. With carbachol (40 microM) the current increased to a peak and then declined to a steady value. Fluctuation analysis by internal and external recording gave an increase of 5% in root mean square current with channel open time of 83 microseconds (6) at 37 degrees C, and channel conductance 17 pS.

Analysis of laser induced acoustic pulse probing of charge distributions in dielectrics

Abstract: Some features of the laser induced acoustic pulse method for the determination of electric field or charge distributions in dielectrics are analysed. Three aspects of this method are described. 1) The electric field can be derived by a numerical method whose resolution depends essentially on the rise time of the pressure wave. Measurements are described which support this analysis. 2) The mechanisms of generation of the pressure wave are studied; a method is described which allows the production of hundreds of pulses without noticeable alteration, with a good energy conversion efficiency. 3) The influence of the elastic properties of the material on the attenuation and dispersion of the wave is considered. Measurements performed on Polyfluoroethylenepropylene (FEP) samples show that one has to take these parameters into account if the rise time of the pressure is much shorter than the transit time.

Avalanche InP/InGaAs heterojunction phototransistor

Abstract: We report on the characteristics of an avalanche InP/InGaAs heterojunction phototransistor. Below the turnover voltage, the gain is bias dependent and avalanching can be used to achieve significant ( \sim5\times ) improvement in the gain-bandwidth product. The noise current in this bias region has been measured and is shown to be predominantly shot noise of the photocurrent and the leakage current. Above the turnover voltage, negative resistance is observed and extremely high gains (>104) are achieved. In this mode, the pulse response is a narrow spike (rise time ≃ 20 ns) whose width is independent of the width of the incident optical pulse.

Bistable operation of two semiconductor lasers in an external cavity: Rate-equation analysis

Abstract: The steady-state and dynamic behavior of a bistable laser resonator containing two semiconductor elements is examined theoretically. We derive necessary conditions for the bistable operation of the cavity and the constraints on the amplifier and absorber element characteristics imposed by these conditions. Our rate equation model demonstrates turn-on and turn-off of the output via current pulses, overshoot and ringing using fast rise time pulses, and critical slowing down when either the absorber or amplifier is switched. We give numerical results on switching.

Rise time of silicon p-n-p photodiodes

Abstract: Exact analytical expressions are derived for the short circuit photodiode currents excited by light pulses, under the assumption that the drift carrier velocity linearly depends on the electric field in the depletion layer. Reflection from the back surface of the photodiode is taken into account. Using the obtained expressions it is possible to establish a connection between the rise time t rise and the product αW eff of the absorption coefficient α(λ) and effective depletion layer width W eff ( W ) at various ratios of the diode thickness and the effective depletion layer width. The influence of the RC -constant (where C is the photodiode effective capacity and R is the sum of the diode series and loading resistances) on the rise time is also analyzed. One of the most important conclusions is that generally the rise time is larger for p - n - n + photodiode configurations than for n - p - p + configurations at the same substrate resistivity.

Investigation of the radiation emitted by metal-barrier-metal structures

Abstract: An investigation was made of the visible radiation emitted by planar metal–barrier–metal structures as a result of decay of plasma oscillations. A method was found for increasing the intensity of the output radiation using a barrier in the form of a multilayer insulator consisting of different oxides evaporated consecutively. It was found experimentally that the efficiency of emission by these structures was twice that of structures with a simple barrier. The rise time of an optical response of such metal–barrier–metal structures to a single short voltage pulse was at least 4 nsec. The output radiation intensity increased under the additional action of a microwave field of frequency up to 1.2 GHz. This property could be used for the purpose of fast-response visualization of microwave fields with a sensitivity threshold of ~1 mW/cm2.

Floating limiter circuit

Abstract: A floating limiter circuit for reducing interference from high frequency, very large pulses or fast rise time pulses, without distorting the desired signal. The reference voltage for the limiter circuit is established by the envelope of the desired output signal, thereby allowing the desired signal to vary over a wide dynamic range.

Knocking control system in engine

Abstract: In a knocking control apparatus for a spark-ignition internal combustion engine, the full-wave rectified output from a vibration sensor is integrated and summed with a constant offset voltage to provide a variable reference signal. The integration time constant is selected to be no more than approximately five times the rise time from inception to maximum value of each knocking occurrence, such that the reference value can remain above the envelope of the background vibrations of the engine, which have a much longer rise time than do the knocking vibrations, without being set too high to detect knocking in a cylinder remote from the location of the vibration sensor. The rectified output of the vibration sensor is directly compared with the reference signal to generate a knocking control pulse each time the alternating sensor output exceeds the reference value.

X-ray generator with phase-advance voltage feedback

Abstract: An X-ray generator system is provided with a high-voltage feedback loop for controlling the output of an inverter to thereby maintain a desired output voltage level. The voltage-feedback loop is provided with a phase-advance network to selectively vary the gain of the system in such a way as to provide for high gain during the initial stage so as to obtain a short rise time, while subsequently reducing the gain so as to clamp the kV overshoot at the end of the rise time. A phase-lag network is also included to effectively eliminate noise that is introduced by the phase-advance network.

Optical comparator: A new application for avalanche phototransistors

Abstract: We describe an InP/InGaAs heterojunction avalanche phototransistor which can be switched from a low-current "off" state to a high-current "on" state with an optical pulse. The transition is characterized by a region of negative dynamic resistance. In the switching mode where the effective current gain is determined by the circuit series resistance, gains exceeding 105have been achieved. The switching rise time is an order of magnitude less (≃20 ns) than the rise time in the normal phototransistor mode. In addition, we show that this type of device can be used as an optical comparator which discriminates between optical pulses relative to a fixed threshold power level. The threshold level can be varied over three orders of magnitude by changing the bias voltage.

Drive method for electromagnetic fuel injector

Abstract: PURPOSE:To improve valve opening-and-closing response characteristics by conducting small currents corresponding to the holding of the state of attraction through an electromagnetic coil when reaching a stroke end corresponding to the full admission of a valve of an armature attracted through the excitation of the electromagnetic coil is detected. CONSTITUTION:When the pulse of valve-opening time tau arithmetically operated by a last arithmetical circuit 12 on the basis of the quantity of air sucked, etc. is inputted to a control circuit 7, a transistor Tr2 is turned ON while an output from a FF1 is inverted through a trigger circuit 15, and transistors Tr3, Tr4 are turned ON. Consequently, the electromagnetic coil 3' of the fuel injector is supplied with large currents through a parallel circuit of resistors RL1, RL2. After the conduction is started, pulses of fixed width are generated from a one- shot circuit 19 through a differentiation circuit 17 and a waveform shaping circuit 18, and the FF1 is reset by a trigger circuit 20 at the rise time of pulses. Accordingly, Tr3 and Tr4 are turned OFF, and currents limited by RL1 are conducted through the electromagnetic coil 3'.

Lumped Circuit Ferrite Pulse Sharpener

Abstract: : Ferrites are frequently employed as an auxiliary component in high voltage pulse circuits. The ferrite has a twofold purpose. One is to improve the pulse rise time in a low inductance circuit where the rise time is limited by the resistive fall time of the switch, typically a thyratron or an SCR. The other purpose is to reduce dissipation in the switch. The ferrite accomplishes these goals by behaving as a nonlinear inductor, or saturable reactor. At about the same time that the switch becomes fully conducting, the ferrite inductance rapidly saturates, i.e., the pulse permeability quickly changes from a large value to a relatively small one.

Level detecting circuit

Abstract: PURPOSE:To enable changing of the rise time constant of an output signal corresponding to the size of a signal level, by a method wherein, when a difference in a level between an input signal and an output signal exceeds a given range, a current, supplied to a capacitor, is caused to change CONSTITUTION:In case the output from a signal source 21 is a low level, only a detecting circuit 261 is brought into an operation condition, and an output current I1 of an operational amplifying circuit 221 is supplied to a capacitor 28 Then, if the output level from the signal source 21 becomes high and a difference between said output level and an output level of an output terminal 25 exceeds the offset level of a detecting circuit 262 specified by a constant-voltage source 271, detecting circuits 261 and 262 are brought into operation state, and output current I1+I2 of them is supplied to the capacitor 28 The aboves are carried out in the followings, or, if the signal level of the signal source 21 becomes high, a detecting circuit positioned at a side in the proximity of a detecting circuit 26n is brought into an operation state in order and the capacitor 28 is charged with a high current, which results in enabling to shorten a time constant

Digital signal reproducer

Abstract: PURPOSE:To change the speed of a recording medium such as pitch control without generating noise, by turning on or off, the operation of a crystal oscillator and a VCO, switching the output, switching the crystal oscillator to the state to make its output to be selectable, and control the timing. CONSTITUTION:Delay times t1, t2 of delay circuits 6, 7 are selected longer than the maximum value of the time until the phase of rotation of a compact disc CD is locked to a reference frame clock RFCK. Further, delays t4, t5 at the rise time of the VCO2 and an oscillator 1 are shorter than the t1, t2 sufficiently. Moreover, the delay time t3 of a delay circuit 10 is made longer than the delays t4, t5 at the start of oscillation. When the voltage P1 falls down, a variable resistor 3 is adjustd at the center position and the output is switched to that of the oscillator 1 after the time t2 after the oscillation frequency of the VCO2 goes to f0. Thus, even if the delay until the phase locks exists, the out of phase-lock is prevented. In case of rise time, since the out of phase-lock hardly occurs, the switch 8 is changed over after the time t3.

Pulse distributing circuit

Abstract: PURPOSE:To supply a control signal whose delay time is set to a necessary minimum, to a switching element, by using an (n) stage shift register, and forming an on-control signal to an off-control signal by delaying it by a constant interval of time CONSTITUTION:When an original signal is applied to an input point (a) of an (n) stage shift register 31, and a clock pulse having sufficiently high frequency and high accuracy, comparing with the original signal is applied to a point (g), the original signal is delayed by time td of (n) times of the clock period, and is outputted to an output terminal (b) A signal from the point (a) and a signal of the point (b), and signals which have inverted the signals from the point (a) and the point (b) by invertor gates 32, 33 are converted to AND signals by an AND gate 34 and an AND gate 35, respectively, and become outputs (e), (f) having a rise delay time td in which a rise time point of one signal is equal to (n) times of the clock pulse period, to a fall time point of the other signal

Frequency Response of Finite Aperture Sample-and-Hold Systems

Abstract: Sampling systems frequently store the collected samples in the form of a series of numbers in the memory of a digital computer. Ideally, the stored number represents the magnitude of the sampled function at one instant of time. Practically, the stored number is the result of some weighted averaging of the sampled function during a finite time interval. As this acquisition time interval becomes a significant fraction of the sample period, the averaging process degrades the sample-system frequency response. The procedure is reviewed whereby one calculates the frequency response for the class of systems that are linear and time-varying or constant during the acquisition interval. The transfer function is calculated for a sampler that first acts as an RC integrator during the acquisition time, then transfers the accumulated charge to some holding circuit (for A-D conversion), and finally begins to acquire the next sample. Tradeoffs between overshoot and rise time in the design of the system transfer function are shown along with an example of how one can arrive at the desired transfer function by convolution of the samples with a proper waveform.

High performance and gate having an "natural" or zero threshold transistor for providing a faster rise time for the output

Abstract: A "natural" threshold device is serially connected between the gate of an output depletion mode FET device and the input node to an FET device so as to provide current flow from the input node to the gate of the FET device as the input waveform begins to rise, and yet to provide sufficient resistance in the gate circuit of the depletion mode device so as to prevent backward flow of current from the gate as the potential of the output node rises. This increases the conductivity of the output load device, thereby providing a faster rise time for the output waveform.

Power-on resetting circuit

Abstract: PURPOSE:To reset assuredly a digital circuit for a fixed time regardless of the rise time of a power supply, by detecting that the power supply voltage is equal to the allowable working voltage and then detecting a fixed subsequent time with the forward voltage of a constant voltage diode and a transistor. CONSTITUTION:The emitter of a pnp transistor TRQ2 is connected to the power supply voltage VCC; the collector of the TRQ2 is grounded via a resistance R2; and the base of the TRQ2 is connected to the VCC via a constant voltage diode D2 and a capacitor C1. Then the collector of an npn TRQ1 is connected to the joint between the capacitor C1 and a diode D2 via a resistance R1; and the emitter of the TRQ1 is grounded. Furthermore the base of the TRQ1 is connected to the VCC via a resistance R3 and a constant voltage diode D1. Then the allowable working voltage VA of the VCC is detected by a circuit consisting of a diode D1, the TRQ1 and the capacitor C1, and a fixed subsequent time (t) is detected by the forward voltage of the diode D2 and the TRQ2. Thus a reset signal is delivered assuredly through a reset terminal 1 and for a fixed time.

Initial clearing circuit

Abstract: PURPOSE:To ensure initial clearing regardless of the rise time of a power supply, by releasing the clear signal with a delay of a certain period after the power supply voltage reaches the prescribed level. CONSTITUTION:A constant voltage diode D41 is not conductive and transistors TRQ41 and TRQ42 are turned off and on respectively at a moment when the power supply voltage VCC is applied. Thus an input VIN of a Schmitt trigger inverter 1 has no rise, and an output inverter 2 delivers a clear signal. When the voltage VCC exceeds the Zener voltage of the diode D41, the TRQ41 and TRQ42 are turned on and off, respectively. Then a delaying circuit consisting of a resistance R44 and a capacitor C41 starts its operation. Thus the voltage VIN of the inverter 1 starts rising. The output of the inverter 1 releases the clear signal delivered from an output inverter 2 after a certain period that is decided by the time constant of the delaying circuit.

Time constant circuit

Abstract: PURPOSE:To obtain a rise time constant and a fall time constant optionally by connecting a resistance to a condenser in parallel through a diode that turns on at the time of discharge. CONSTITUTION:When a constant voltage source ei rises up, a condenser C is charged through a resistance R1 to a voltage divided by resistances R1 and R2. The rise time constant at this time is determined by resistances R1 and R2. When the constant voltage source ei falls, the condenser C discharges through the diode and through resistances R3 and R4, since internal resistance of the constant voltage source ei is small. That is, the resistances R1-R4 are connected in parallel, and fall time constant is determined by resistances R1-R4.

Method of equalizing ink drop flying speed and drive device of ink drop jet means in ink jet printer

Abstract: PURPOSE:To equalize flying speed of ink jet, by a method wherein maximum voltage of drive pulse applied to electro-mechanical converting element installed corresponding to jet chambers of a multi-nozzle injection recording apparatus is adjusted in each jet chamber. CONSTITUTION:If pulse is supplied on signal line S1 from drive pulse control unit, a transistor Tr1 is rendered conductive and then Tr2 is done. If a transistor Tr8 is rendered conductive, voltage adjusted to any amount by a variable resistor RC11 for adjusting piezo-electric element applying voltage is applied to a piezo-electric element 4-1, and ink liquid drop is injected. Then the flying speed of ink liquid drop is adjusted according to amount of voltage applied to the piezo-electric element. Since rise time of pulse applied to the piezo-electric element is determined by variable resistors RC11 and RC21, the variable resistor RC11 is varied to adjust voltage and then the resistor RC21 is varied, thereby rise time of the pulse applied to the piezo-electric element is always set to optimum value.

Experimental and Theoretical Evaluation of Electromagnetic Environment Produced by Direct Electron Injection at AURORA

Abstract: : A mosaic of experimental data accumulated during the last year or two indicates that when operated in the electron injection mode AURORA can produce a very fast electromagnetic response in a large number of sensors. These fast responses are consistent with an electromagnetic environment in the AURORA test cell that has a very fast rise time. The electromagnetic parameters that have been measured and found to have rise times less than 10ns are the electric field and the magnetic field. The rise time of the relativistic electron current has also been found to be approximately 10ns at a number of positions in the AURORA test cell, but not at all positions. Two possible mechanisms that contribute to the fast rise time are: 1) electric field clipping due to conductivity, and 2) beam erosion due to the inductance of the electron beam in the AURORA test cell.

Random Choice Solutions for Weak Spherical Shock-Wave Transitions of N-Waves in Air with Vibrational Excitation.

Abstract: : In order to clarify the effects of vibrational excitation on shock-wave transitions of weak, spherical N-waves, which were generated by using sparks and exploding wires as sources, the compressible Navier-Stokes equations were solved numerically, including a one-mode vibrational-relaxation equation. A small pressurized air-sphere explosion was used to simulate the N-waves generated from the actual sources. By employing the random-choice method (RCM) with an operator-splitting technique, the effects of artificial viscosity appearing in finite-difference schemes were eliminated and accurate profiles of the shock transitions were obtained. However, a slight randomness in the variation of the shock thickness remains. It is shown that a computer simulation is possible by using a proper choice of initial parameters to obtain the variations of the N-wave overpressure and half-duration with distance from the source. The calculated rise times are also shown to simulate both spark and exploding-wire data. It was found that, in addition to the vibrational-relaxation time of oxygen, both the duration and the attenuation rate of a spherical N-wave are important factors controlling its rise time. The effects of the duration and the attenuation rate of a spherical N-wave on its rise time, which are designated as the N-wave effect and the nonstationary effect, respectively, are discussed in more detail pertaining to Lighthill's analytical solutions and the RCM solutions for nonstationary plane waves and spherical N-waves. (Author)