Showing papers on "Rise time published in 1975"

Effect of junction capacitance on the rise time of led's and on the turn-on delay of injection lasers

Abstract: The space-charge capacitance of the forward-biased junction has been found to play a major role in (i) the apparent rise time of the emission from small-area, high-radiance led's and (ii) the apparent turn-on delay of stripe-geometry dh-structure laser diodes. For a zero-bias capacitance of 200 pF, a typical value for such devices made by oxide-masking techniques, the measured rise time of an led that is fully turned on and the turn-on delay time of injection lasers may be as much as twice the limitation imposed by the spontaneous carrier recombination time. A proposed method to reduce these delays by preshaping the driving pulse is analyzed, and a reduction of the delay by a factor of 2 or better is predicted. These results are in agreement with experiments.

Regulation of Transpiration in Avena. Responses to White Light Steps

Abstract: The transient responses in transpiration rate of the primary leaf of 8-days-old oat plants were studied when step changes in the white light irradiance were administered to the plants. A light or dark step was achieved by an instant increase or decrease, respectively, of the irradiance on the leaf surface. Usually the light step responses consisted of one rapid response (rise time 1–2 min) and one slow response (rise time 5–10 min). The dark step response had a fall time of about 10 min. At a high irradiance level and in CO2-free air the slow response disappeared. This could mean that the slow response is CO2-controlled. The rapid response was still present under these conditions and is therefore probably caused by other processes than the slow response. In long time experiments several cycles of a circadian rhythm (period 26–28 h) could be followed in the light step responses. Thus the rapid response was small at that time of the day when the slow response was most pronounced and vice versa. The endogenous nature of the rhythm was established in phase-shift experiments. It is concluded that experiments on stomatal dynamics must take circadian variations into account.

Apparatus for detecting and measuring peak-to-peak values in electrical signals

Abstract: Apparatus is disclosed for detecting and measuring peak-to-peak values in an electrical input signal, the signal comprising at least one positive-going and one negative-going peak and can include waveforms characterized by short duration and fast rise time pulses. In operation, one of the at least one input signal peaks is referenced to a predetermined d.c. voltage level, such as, for example, 0 volts d.c., and an electrical output signal is generated which is representative of the magnitude of the input signal with respect to the predetermined d.c. voltage level. The output signal is generated by electrical circuitry capable of accurately tracking fast rise time pulses and then stretching the other unreferenced at least one peaks to prevent decay thereof.

Printed Low Velocity Delay Lines for Cathode Readout of Proportional Chambers

Abstract: A new type of flat delay line was developed which has a low propagation velocity and very good delay to rise time ratio. It can be constructed by printed circuit techniques without crossovers. The magnetic loops of a shifted periodic structure yield high inductance per unit length. Geometric scaling factors are shown. This line, forming the cathode plane of a proportional chamber, allows simultaneously, a satisfactory induced signal and the readout of the second coordinate by time delay without disturbing the electric field configuration around the anode. Optimization of position resolution vs. noise is discussed. Experimental results are shown. Other properties of such delay lines are discussed.

EMP Coupling Analysis Using the Frequency (Transfer Function) Method with the SCEPTRE Computer Program

Abstract: The availability of digital computer time and scientific programming languages (such as Fortran) has, resulted in the use of the digital computer for electromagnetic pulse (EMP) coupling analyses. This report describes combining complex frequency domain analysis techniques with the SCEPTRE computer program to evaluate the time response of the current induced on a thin-wire scatterer when the scatterer has been excited by an arbitrary shaped electromagnetic pulse. The method is illustrated by performing an analysis for the current which would be induced by a fast rise time EMP (unit step) and a relatively slow rise time EMP (waveshape similar to that produced by a lightning stroke).

Circuit for monitoring temperature of high-voltage equipment

Abstract: This invention relates to an improved circuit for measuring temperature in a region at high electric potential and generating a read-out of the same in a region at lower potential. The circuit is specially designed to combine high sensitivity, stability, and accuracy. A major portion of the circuit situated in the high-potential region can take the form of an integrated circuit. The preferred form of the circuit includes an input section which is situated in the high-potential region and comprises a temperature-compensated thermocouple circuit for sensing temperature, an oscillator circuit for generating a train of ramp voltages whose rise time varies inversely with the thermocouple output, a comparator and switching circuit for converting the oscillator output to pulses whose frequency is proportional to the thermocouple output, and a light-emitting diode which is energized by these pulses. An optical coupling transmits the light pulses generated by the diode to an output section of the circuit, situated in a region at ground. The output section comprises means for converting the transmitted pulses to electrical pulses of corresponding frequency, means for amplifying the electrical pulses, and means for displaying the frequency of the same. The preferred embodiment of the overall circuit is designed so that the frequency of the output signal in hertz and tenths of hertz is equal to the sensed temperature in degrees and tenths of degrees.

Electron Beam Transport Experimts with Short Duration Pulses

Abstract: This paper describes experiments designed to extend the simulation of IEMP effects by fast pulse ( 700 cm2) and greater total currents (~9 kA) than heretofore. Both charge and current neutralization as a function of pressure from <10-2 mTorr to 700 mTorr were determined with an electron-beam facility that generated an injected pulse with rise time ~l.5 ns and a peak intensity of 12.5 A/cm2. The results indicate that for such large time rate of change of total currents, the necessary pressure to achieve space-charge barrier dissipation before the peak of the pulse will also lead to avalanche breakdown of the ambient gas, occurring at almost the same time and thus reducing the net transmitted current.

Signal conditioning circuit

Abstract: A signal conditioning circuit for a fixed rise time, variable amplitude receiving system (TACAN) that digitizes the time of arrival and samples the pulse amplitude at the receiver's last intermediate frequency (IF) stage before video detection. The time of arrival measurement is performed by counting a fixed number of successive threshold crossings of the IF carrier, utilizing a pair of comparators having two inputs each. One input of each comparator is coupled to the IF stage. The other input of each comparator is coupled to a point of reference potential, one comparator being referenced to ground and the other being coupled to a small positive threshold voltage level. The output of the grounded comparator is delayed, and the delayed output is used as a clock signal to the remaining circuitry. The output of the threshold comparator provides data pulses, one data pulse being generated each time that the IF signal goes above the threshold value. The data pulses, along with the clock pulses, are applied to an up down shift register which acts as a digital flywheel. The output of the digital fly-wheel enables and disables a counter. Two signal conditioning circuits are described, one which extracts time information, and one which extracts amplitude information from a fixed rise time, pulse-amplitude modulated carrier as is found in a typical TACAN receiver at the last intermediate frequency (IF) stage. The time of arrival of the leading edge 50% voltage point is determined in real time with virtually zero delay, and therefore does not rely on conventional approaches which must first wait until the full unknown amplitude of the pulse is determined before a 50% detector is enabled. The technique is based on the fact that there are a fixed number of cycles of IF carrier under the leading edge of the pulse regardless of its amplitude and that therefore the 50% voltage point is determined by counting in an electronic counter a fixed number of "consecutive" cycles that exceed a pre-determined noise threshold as determined by a comparator set at that threshold. The technique operates on the signal one stage before conventional video detection. Erroneous false alarm and false dismissal threshold crossings are rejected by a digital up-down shift register which acts as a fly-wheel. The peak amplitude of the IF pulse-amplitude modulated carrier is detected, sampled, amplified, and buffered in one efficient circuit. The detection function is performed by charging a capacitor, which is isolated from the raw IF by a differential amplifier stage, up to a voltage proportional to each successive carrier cycle peak by a closed loop means. Since the capacitor can only charge in one direction, it charges up to a voltage proportional to the most positive peak of the pulse-amplitude modulated carrier, with a fixed amount of rate limiting for noise immunity. Two logic signals, a Track/Hold command and a Dump command are used to respectively hold the peak amplitude for subsequent analog to digital conversion and digital signal processing, and to reset the detector prior to encoding another pulse.

Short pulse generator

Abstract: A device for achieving a narrow high voltage output pulse having a rise t essentially limited only by the rise time of the switching means.

Traveling‐wave electron‐beam–semiconductor system for picosecond rise‐time pulse generation

Abstract: This paper describes a powerful pulse generation technique based on the use of a swept electron beam to excite traveling waves on a stripline semiconductor target. A simplified wave analysis of the swept stripline target shows that the pulse rise time is not restricted by the effects of carrier transit time or target capacitance which typically limit the rise time of other beam‐semiconductor devices. The swept stripline is thus capable of rise times approaching the very short time required for equilibration of the carrier pair creation process in the electron‐bombarded semiconductor. The output capability of the swept stripline is discussed, and a near‐optimum design method is presented for long uniform striplines. It is estimated that output levels of 100 V with output/rise time values of 10 V/psec and 10 A/psec are feasible. An experimental result from a short nonoptimum silicon stripline target shows a 5‐V 2‐A pulse with a rise time estimated to be ∼10 psec.

Propagation delay in current-mode switching circuits

Abstract: Propagation delays of current mode switching circuits are computed, taking into account ohmic base resistances as well as gain-bandwidth products and the finite rise time of the input signal. Results are presented graphically for a wide range of circuit parameters.

Feedthrough in TTL circuits under marginal triggering conditions

Abstract: The feedthrough and regeneration action of a TTL circuit under marginal transient conditions such as low input logic levels and slow input signals are studied. The effect of regeneration during rise time and a study of storage delay are presented. An optimized design procedure is described to reduce feedthrough during rise time without endangering the totem-pole inherent reduction of storage time.

Square-Wave Polarography and Related Techniques

Abstract: VI. SUMMARY The theoretical and practical aspects of squarewave polarography and related techniques have been reviewed. From theoretical consideration, the sensitivity of these techniques depends upon the rise time of the cell-potentiostat combination. If this rise time is sufficiently fast, the sensitivity is limited by the DC capacitance current when using the D.M.E. When the H.M.D.E. is used, the sensitivity is limited by the pulse capacitance current or by electronic noise.

Another model for the current pulses of cloud-to-ground lightning discharges

Abstract: A model for the current pulses of cloud-to-ground lightning discharges is proposed. The model is based on an occurence time structure for lightning and includes effects such as time between pulses, decay time and finite rise time. The mean current and power spectral density are calculated using data found in the literature and a numerical technique.

Delay line network pulse modulator for radar - has a thyristorised discharge circuit for the delay line network

Abstract: The network output pulses are used in a magnetron for generation of transmitter pulses of a width shorter than 0.2 us. Each pulse is a pair of pulses consisting of a preliminary and a main component. The preliminary pulse starts the magnetron oscillating, and the main pulse which follows releases the sender pulse proper with a shorter rise time. The delay line network consists of two delay lines, one for the preliminary pulse, and the other for the main pulse, both charged in parallel from the pulse modulator charging circuit. Each delay line is connected in series with one of two delay chokes, whose delay times are different in accordance with the required spacing between the preliminary and the main pulse. The two delay lines discharge circuit has a common thyristor triggered by a single triggering pulse. Both discharge circuits are connected in parallel to the modulator output.

Crystal oscillator circuit

Abstract: PURPOSE:In the crystal oscillator circuit, a CMOS inverter is used as active element and transfer gates are arranged on the same chip Then the resistance of the circuit is so selected that oscillation will become stabilized, thereby improving the characteristics at the rise time of oscillation without adversely affecting the normal oscillating condition

Roots and transient parameters for maximally flat low-pass filters with zeros

Abstract: The poles of the recently discussed maximally flat sharp cut-off low-pass filters were tabulated for various orders of the filter and various values of the parameters. Unfortunately, these tables were incorrect and a new set of poles are presented here, together with the transient response characteristics. All the filter poles and zeros given in this paper have been used to calculate frequency and time-domain characteristics. Tables for rise time, delay time and percentage overshoot are also given.

Dielectric measurements by time domain reflectometry

Abstract: Transient or “time domain” methods have become of considerable interest in the last few years because of the availability of fast pulse generators and sampling oscilloscopes permitting measurements in the range 10−11 to 10−7 seconds, corresponding to frequencies from a few megahertz to a few gigahertz. The voltage pulse reflected from a dielectric sample in a coaxial line after arrival of an incident pulse with short rise time (ca. 40 psec) resembles the dielectric current response to a step voltage, but is distorted by effects of finite amplitude of the reflected pulse, propagation in the sample, and the sample termination, all of which must be taken into account in a proper analysis.

Rise Time of Hard X-Ray Bursts

Abstract: A study was made of the hard X-ray component in the impulsive phase of solar flares. In 36 randomly chosen events the value for the slope in the differential electron power spectrum E−δ electrons cm−2 s−1 keV−1, was related to the 20–32 keV spike rise time (e-folding) as trise=0.56 exp (0.88δ) in the thin target model and trise=0.10 exp (0.88δ) in the thick target picture. In the thin target model, the above empirical relation would imply that the acceleration of electrons can be longer when the acceleration rate is smaller. An alternative interpretation would be that an impulsive hard X-ray burst is a superposition of two components emitted from thin and thick targets; when the former predominates, the duration is longer and the photon spectral index is larger, while when the latter predominates, the duration is shorter and the photon spectral index is smaller; 3≲δ≲4 is required (Figure 1). The uncertainty in δ is 0.5 while that in the rise time is 1 s. Open image in new window Figure 1 Rise-time in 20–32 keV X-radiation versus electron hardness.