Showing papers on "Rise time published in 1992"

Nanosecond transient electroluminescence from polymer light‐emitting diodes

Abstract: The transient electroluminescence from polymer light‐emitting diodes is reported. When the devices are mounted on a microstrip transmission line, the temporal response is limited by the electrode geometry, with rise and fall times below 50 ns. With low duty‐cycle pulses (0.5%) the electroluminescence intensity remains proportional to the current at values up to 10 A/cm2, two orders of magnitude greater than possible under direct current operation. Since the spectral blue‐shift observed at high current levels (with power dissipation above 1 W/cm2) indicates significant sample heating, still higher levels should be possible with proper thermal management.

Characterization of a microsecond-conduction-time plasma opening switch

Abstract: This paper presents data and analyses from which emerges a physical picture of microsecond‐conduction‐time plasma opening switch operation. During conduction, a broad current channel penetrates axially through the plasma, moving it toward the load. Opening occurs when the current channel reaches the load end of the plasma, far from the load. During conduction, the axial line density in the interelectrode region is reduced from its value with no current conduction as a result of radial hydrodynamic forces associated with the current channel. A factor of 20 reduction is observed at opening in a small, localized region between the electrodes. When open, the switch plasma behaves like a section of magnetically insulated transmission line with an effective gap of 2 to 3 mm. Increasing the magnetic field in this gap by 50% results in an improvement of 50% in the peak load voltage and load current rise time, to 1.2 MV and 20 nsec, respectively. An erosion opening mechanism explains the inferred gap growth rate using the reduced line density at opening. Improved switch performance results when the maximum gap size is increased by using a rising load impedance.

Stacking power MOSFETs for use in high speed instrumentation

Abstract: A reliable circuit configuration is described for stacking power metal–oxide semiconductor field effect transistors (MOSFETs). The resulting circuit has a hold off voltage N times larger than a single power MOSFET, where N is the number of power MOSFETs used. The capability to switch higher voltages and thus greater amounts of power, into a 50 Ω load, in approximately the same time as a single device is realized. Design considerations are presented for selecting a power MOSFET. Using the design method presented, a 1.4 kV pulse generator, into 50 Ω, with a 2 ns rise time and negligible jitter is designed.

Temperature rise and thermal rise‐time measurements of a semiconductor laser diode

Abstract: A novel method is presented for measurement of the rise in temperature and thermal rise time of a semiconductor laser diode (LD) under pulsed operation. The technique employs the shift in LD threshold current which occurs with a rise in junction temperature. Practical results are given, showing a rise time of about 10 ns.

Investigation of In0.53Ga0.47As/AlAs resonant tunneling diodes for high speed switching

Abstract: We report an investigation of In0.53Ga0.47As/AlAs resonant tunneling diodes designed for high speed switching applications. Experimental peak current densities are observed to increase with decreasing AlAs barrier thicknesses, in good agreement with a two band tunneling calculation, which includes the effects of strain and band bending. Swing voltages over the range 0.5–1.0 V are demonstrated to be controllable via the thickness of a lightly doped depletion layer. Estimated RC time constants are compared with intrinsic tunneling times for the samples studied. A sample with 6 monolayer AlAs barriers yields devices with peak current densities of 3.1×105 A/cm2 and peak‐to‐valley current ratios of 6:1. The minimum rise time in this sample is calculated to be limited by RC switching delays to 1.6 ps.

Comparison of signal-to-noise ratio of myoelectric filters for prosthesis control.

Abstract: A comparison of signal-to-noise ratios and rise times was performed on several myoelectric filters used for muscle-force estimation and prosthesis control. Linear, averaging, and adaptive filters were compared using single as well as multiple electrode pairs (spatial filtering). The filters were matched for having the same rise time (0-95%) and the signal-to-noise ratios were measured off-line using the same myoelectric signal recording. The linear filter was a low-pass filter with a time constant of 80 ms. The averaging filter had an averaging time of 250 ms. The adaptive filter was the same as is used in the Utah Artificial Arm. The adaptive filter varied its time constant according to the rate of change of the signal mean. If the rate was high, the time constant was set low. If the rate was low, the time constant was set high. Spatial filtering is where the myoelectric signals from four cutaneous sites over the same muscle were summed, that is, spatially filtered, and the resultant signal was smoothed by the linear, averaging, or adaptive filter. Significant improvement in the signal-to-noise ratio has been shown over conventional linear or averaging filters when using spatial and adaptive filtering, both when used separately and when used together.

Bandwidth and rise time calculations for digital multimode fiber-optic data links

Abstract: The use of multimode fiber in digital fiber-optic data links requires simple and accurate procedures for the calculation of data line component bandwidth and rise time responses. The author investigates source/fiber/detector interactions, to develop a simple model for multimode fiber system information capacity. Simplified expressions for the baseband impulse and frequency responses of each component are given along with relationships between the theoretical impulse response root mean square (RMS) width and the component rise time or bandwidth. The application of the central limit theorem to the system yields expressions for the composite system rise time and bandwidth which contain correction factors to those that would be obtained using the normal Gaussian assumptions. >

Characteristics of current filamentation in high gain photoconductive semiconductor switching

Abstract: Characteristics of current filamentation are reported for high gain photoconductive semiconductor switches (PCSS). Infrared photoluminescence is used to monitor carrier recombination radiation during fast initiation of high gain switching in large (1.5 cm gap) lateral GaAs PCSS. Spatial modulation of the optical trigger, a 200--300 ps pulse width laser, is examined. Effects on the location and number of current filaments, rise time, and delay to high gain switching, minimum trigger energy, and degradation of switch contacts are presented. Implications of these measurements for the theoretical understanding and practical development of these switches are discussed. Efforts to increase current density and reduce switch size and optical trigger energy requirements are described. Results from contact development and device lifetime testing are presented and the impact of these results on practical device applications is discussed.

Electron multiplication and electrostatic discharge wave forms

Abstract: A metal block, immersed in the electric field of an electrode, has been used to study the electrostatic discharge phenomenon. Using a high‐speed transient oscilloscope, current wave forms of air discharge across a small fixed gap between the metal block and a current probe have been measured. The combined bandwidth of the measurement setup, including the oscilloscope, cables, connectors, splitter, and the probe, is above 3.5 GHz. The setup is capable of measuring rise time as fast as 100 ps. Voltage change on the metal block was also measured by a low‐speed transient oscilloscope. For a gap of 0.01 cm and a voltage of 1086 V, the observed current wave form of the discharge exhibits a rise time of 300 ps, a peak current of 5.8 A, and a pulse width at half‐height of 770 ps, about 2.6 times the rise time. The existence of a residual voltage on the metal block after each discharge was also observed. Using the Townsend’s α coefficient for the electron multiplication in air, an analytic model and a one‐dimensio...

CMOS delay line having duty cycle control

Abstract: A delay line having feedback from a control circuit at the output of the delay line controls the delay line duty cycle to within a specified range. The delay line comprises at least one delay unit having control inputs to each delay unit. The output of the delay line feeds to a low-pass filter (LPF). A voltage proportional to the duty cycle of the delay line output is generated within the LPF and fed to a differential amplifier. The differential amplifier is in turn coupled to the control inputs of each of the delay units. When the voltage signal from the LPF is high (duty cycle is high), the differential amplifier will generate a signal causing the fall time of the signal propagating through the delay line to increase and rise time to decrease. This will decrease the high cycle time at the output of the delay line. When the voltage signal from the LPF is low (duty cycle is low), the differential amplifier will generate a signal causing the fall time to decrease and the rise time to increase. This will increase the high cycle time at the output of the delay line.

Low‐noise lumped‐element timing filters with rise‐time invariant crossover times

Abstract: Herein are described low‐noise, lumped‐element pulse‐shaping filters that produce output pulses with zero‐crossing times that are invariant with changes in input pulse amplitude and invariant with changes in input pulse rise time for input pulses with linearly increasing leading edges. Design equations and circuit diagrams are given. In addition, equations are derived that show that, in general, the noise‐caused timing variance is inversely proportional to the crossover time, provided the crossover time occurs during the linearly increasing leading edge. The noise‐caused timing variances of these lumped‐element filters are only a few percent worse than the best that can be achieved for the same crossover time with a conventional delay‐line constant‐fraction filter in cascade with a resistance‐capacitance low‐pass filter. Neither delay lines nor delay‐line approximates are used in these filters.

The response of a microwave multipolar bucket plasma to a high-voltage pulse with finite rise time

Abstract: A collisional model that describes the response of a microwave multipolar bucket plasma to a high-voltage pulse with finite risetime has been developed for plasma immersion ion implantation (PIII). The agreement between this model and the measurements of the sheath position and target current in a 100 mtorr helium plasma is found to be much improved when the risetime of the pulse and the ion energy distribution during the PIII process is considered. >

Phosphor currents in ZnS:Mn ac thin film electroluminescent display devices

Abstract: Conduction current in the phosphor layer of ZnS:Mn ac thin film electroluminescent (ACTFEL) display device was measured as a function of the amplitude and the rise time of the bipolar voltage pulses: electric field in the phosphor was also determined. It was found that the clamping field of an ac thin film electroluminescent device is not a single‐valued device characteristic. The clamping field depended upon the rise time of the applied voltage pulse increasing in value as the rise time became smaller. These data were interpreted in terms of a nonideal breakdown of the insulator‐phosphor interface and a time delay involved in the emission of electrons from this interface. To account for the nonideality in the interface breakdown the ac equivalent circuit of the ACTFEL device was modified by including a voltage‐dependent resistor in parallel with the phosphor capacitance. The phosphor current measurements, transferred charge measurements and tunneling current calculations indicate that in the nonhystereti...

Power-on-reset circuit

Abstract: A power-on-reset circuit includes a plurality of MOS transistors and a first depletion type N-channel MOS transistor connected in series to an input terminal of a current mirror circuit. A capacitor is connected between the input terminal and a voltage supply terminal. A second depletion type N-channel MOS transistor having a low current driving capacity is connected to an output terminal of the current mirror circuit. The degree of integration can be increased by constituting an integrating circuit with depletion type N-channel MOS transistors in place of a resistor. In addition, the voltage supply voltage is compared to the sum of the threshold voltage of the plurality of MOS transistors. This makes it possible to initialize the internal circuit positively even if the rise time of the voltage supply voltage becomes larger than the time constant of the integrating circuit.

Picosecond time‐resolved measurements of electroabsorption in an InGaAs/GaAs multiple quantum well p‐i‐n modulator

Abstract: We report the first picosecond time‐resolved measurements of electroabsorption in a strained InGaAs/GaAs multiple quantum well p‐i‐n structure as a function of applied bias at various optical excitation densities. The data above 4 V are explained by a model which assumes a rise time dominated by a single carrier sweep‐out time and a decay dominated by lateral diffusion. A bias independent electro‐absorption rise time of 10±2 ps is obtained and appears to be limited by the transit time of carriers across the structure. The decay time is also ≊10 ps. Below 4 V the decay time increased to 80 ps as the bias was reduced to 0 V. This increase may be related to the change in depletion length with bias in the intrinsic region.

Comparison of sonic boom rise time prediction techniques

Abstract: An important quantity in determining the loudness of sonic booms outdoors is the rise time. In the absence of turbulence, the rise time is dictated by frequency‐dependent loss mechanisms in the atmosphere including relaxation, viscosity, and thermal conduction. Two techniques have been used to predict rise times of sonic booms. The technique developed by Pestorius and Blackstock numerically steps a weak shock through the atmosphere accounting for frequency‐dependent absorption and time‐dependent wave steepening independently at each step. This technique has been extended by Bass and Raspet to include absorption and dispersion by the vibrational relaxation of N2 and O2 in the presence of H2O. The second technique is to apply the augmented Burgers’ equation to determine a steady‐state asymptotic shock profile. This approach is strictly valid only for a plane shock wave with a duration much greater than the rise time. This letter compares predicted rise times using these two approaches. The input waveforms were assumed to be N waves with a linear rise at the front and rear of the shock. These calculations show that N waves of duration greater than 100 times the rise time can be treated as steady‐state shocks. The rise time for shock waves of shorter duration cannot be determined using the steady shock assumption.

Measurement of energy transfer in a five-mode gravitational wave bar detector.

Abstract: A 1400‐kg five‐mode bar detector has been constructed and tested at room temperature. Detailed calculations and computer simulations have been performed to optimize the design and study the dynamics of the system. The tests have confirmed the analytical prediction that a large fraction (67% in this experiment) of the energy deposited into the bar is transferred to the last resonator. The rise time of the energy at the last resonator is short (≂2 ms), and corresponds to an effective detector bandwidth of ≂500 Hz.

Picosecond large‐signal switching characteristics of a pseudomorphic AlGaAs/InGaAs modulated doped field effect transistor

Abstract: We present the first comprehensive study of the large‐signal switching characteristics of an AlGaAs/InGaAs modulation‐doped field‐effect transistor on a picosecond time scale. Electro‐optic sampling is used to measure drain voltage response to a steplike gate input with a 2.8 ps rise time, at various dc biases. A large‐signal switching time of 6.2 ps is obtained. Features deleterious to high‐frequency device operation are observed, related to equivalent circuit parameters, and reduced by appropriate choice of operating point.

Simulation and interpretation of fast rise time light-activated p-i-n diode switches

Abstract: A simulation program and a comprehensive physical interpretation for risetimes and output powers of the long transit p-i-n diode under high and low optical-pulse excitations as well as at various impedances are presented. The physical interpretation explains the mechanisms of the switch risetime limitation in terms of the cancellation electric field due to separated photocarriers, the induced electric field with various RC time delays, and the optical-pulse energy risetime. Under high optical excitations and long circuit risetimes, the output risetime is determined only by the electric field cancellation time associated with the collapse of the total electric field and decreases with increasing optical-pulse excitation. This is in contrast to the case of low optical-pulse excitations where the risetime is determined by both the circuit risetime and the optical-pulse energy risetime. >

ECL driver with adjustable rise and fall times, and method therefor

Abstract: An ECL driver, such as an ECL cut-off driver, is provided with settable output rise time and settable output fall time, in order to reduce noise at the output of the driver while limiting the delay resulting from such noise reduction. A method is also provided for so controlling an ECL driver. The driver includes a current switch and a current source. The current switch includes a NOR side including one or more transistors, and an OR side including one or more transistors. The input to the NOR side can be buffered with an input emitter follower, and the output from the current switch can be buffered with an output emitter follower. A capacitance is connected across the collector(s) and emitter(s) of the NOR side transistor(s) of the current switch, and a capacitance is connected at one electrode both to the collector(s) of the OR side transistor(s) and to the base(s) of the output emitter follower transistor(s). In one embodiment, the remaining side of the other capacitance is connected to ground and to the collector(s) of the output emitter follower transistor(s). In another embodiment, the other side of the other capacitance is connected to the collector(s) of the NOR side transistor(s). In still another embodiment, the other side of the other capacitance is connected to the emitter(s) of the OR side transistor(s), and to the current source.

Color signal contour compensator for matching the rise times of color and luminance signals of a video signal to produce sharper images

Abstract: A color signal contour compensator includes an A/D converter, signal processors for processing the digital composite video signal output from the A/D converter into separate color and luminance signals, a color signal rise time compensator for detecting the rise time of the color signal output from the signal processors so as to output a delay control signal, a D/A converter for converting the color signal of the color and luminance signals output from the color signal rise time compensator into an analog signal during a period corresponding to a specific level of the delay control signal output from the color signal rise time compensator, a microcomputer including a memory device for storing a predetermined amplitude absolute value of the color signal, a rise time value of the luminance signal, and a delay value for delaying the luminance and color signals. The compensator matches the rise time of the color signal to the relatively short rise time of the luminance signal, thereby sharpening the contour of a picture during playback and improving the picture quality.

High speed bus

Abstract: PURPOSE:To suppress ringing in a transmission line so as to transmit a waveform whose frequency is high by using an open collector element where rise time is delayed for more than 3ns as a bus driver element in a bus. CONSTITUTION:The end of the bus is connected to a first potential 1 through resistance parts 11 and 12, a reflection coefficient is regulated by the resistance values of the resistance parts 11 and 12, and the characteristic impedance of the transmission line 3 of a high speed bus and the reflection of the waveform is suppressed small. Thus, ringing at the time of raising the output waveform at the high speed bus can be suppressed small by using open collector output where rise time in output is delayed for more than 3ns as the bus driver element 4 at the high speed bus. Thus, the rise waveform at the high speed bus can speedily be stabilized.

Memory switching effects in a-Si/c-Si heterojunction bipolar structures

Abstract: The authors report a three-terminal undoped amorphous silicon (a-Si)/p-n crystalline silicon (c-Si) structure, which exhibits OFF and ON states. An OFF state is characterized by a current in the structure in the low nanoampere range due to the large resistance of the undoped a-Si layer, while in the ON state the structure exhibits a large conductance and its current is determined in practice by the load resistance. Reversible switching between the two states with a rise time of about 40 ns and a fall time of about 200 ns was achieved by applying appropriate positive or negative current pulses to the base of the c-Si p-n junction. The structure can be integrated into a standard bipolar process, and, being of a size suitable for VLSI applications, may be useful as a basic three-terminal memory cell. >

High-frequency response piezo-electric film type pressure transducer

Abstract: The utility model relates to a pressure transducer for measuring the dynamic and quasi-static pressure of fluid, particularly a high-frequency response piezoelectric film type pressure transducer, mainly comprising a shell, a cone-shaped core rod, an insulating medium, a piezoelectric film sheet, an electric pole film sheet, and a screw-threaded joint provided with core threads. With high sensitivity without oscillation, simple structure, and low cost, the utility model is particularly suitable for measuring pressure pulse with short rise time (< 1 mu s) as well as measuring the pressure of the shock wave of various fluids.

High current back lighted thyratron switch

Abstract: High current operation of the back lighted thyratron, an optically triggered, low pressure diffuse discharge closing switch that operates with a self heated, super‐emissive cathode, is reported. Repetitive operation at 5 Hz, 17.5 kV, 60 kA, with 500 ns pulse length has been achieved. The switch exhibits no high current limit up to 82 kA. High dI/dt≳1011 A/s and <45 ns rise times have been obtained. The high current and short rise time capabilities make this switch a possible replacement for spark gaps and multiple parallel thyratron switches in accelerator and laser applications.

An optimum gate drive for high power GTO thyristors

Abstract: The description and design of an optimum gate/base drive for current-controlled-type self-commutated semiconductor switches such as gate turn-off thyristor (GTO) or bipolar transistors are presented. The major disadvantages of the conventional gate/base drive circuits are that they impose timing limitations (such as minimum off-time and maximum on-time), have poor efficiency, and use a reduced DC supply which adversely affects the current rise/fall times. To overcome these problems, a special MOSFET-based current shaping circuit is introduced which minimizes the rise time, significantly reduces the switching losses, is nearly lossless, and does not suffer from any timing limitations. Experimental results verify the performance of the proposed gate/base drive. >

High Tc superconducting switch

Abstract: We report the results of an experimental and modeling investigation of a high‐temperature superconducting opening switch using optical and current switching The switch was fabricated using a thin film of YBaCuO on a SrTiO3 substrate A Nd:YAG pulsed laser, operating at the fundamental frequency, and the signal current was used as a triggered source The results of optical switching indicates that the switching is due to the heating of the superconductor by the laser from its superconducting to the normal state Switching using current pulses shows a thermal hysterisis effect The dependence of the switching characteristics (rise time and delay) on the bias (temperature and current) and trigger intensity is discussed Also, the results of a model based on heat equations is presented

High-voltage spheres in an unmagnetized plasma: long-term evolution and rise-time effects

Abstract: A fluid model was used to study the response of a nonmagnetized plasma to a high-voltage sphere for a time interval up to 20000 plasma periods. Different applied voltages, background plasma densities and voltage rise times were considered. It was found that after the transient response to the applied voltage the system evolves to a steady state. In the steady state, the ion density satisfies the Boltzmann relation. The thicknesses of both the electron sheath and the presheath increase with the applied voltage. The sheath thickness, estimated from the electron and ion density profiles, agrees with the simple Langmuir-Blodgett (LB) theory, but the simulation current is 2-5 times higher. If the voltage is applied according to an exponential law with a rise time tau , only the electron motion at very early times is affected if tau