Showing papers on "Biasing published in 1983"

Microwave Characteristics of an Optically Controlled GaAs MESFET

Abstract: This paper presents the results of an experimental investigation of microwave characteristics of a GaAs MESFET under optically direct-controlled conditions. The gain, drain current, and S-parameters were measured under various optical conditions in the frequency region from 3.0 GHz to 8.0 GHz, and it was found that they can be controlled by varying the incident light intensity in the same manner as when varying the gate bias voltage. As applications of this phenomenon, optical/microwave transformers and an optically switched amplifier were investigated.

Series current limiter

Abstract: Field effect transistors are used in a series current limiter circuit. The field effect transistors are depletion type transistors and are interconnected in a manner to decrease conduction when an overvoltage or overcurrent condition is sensed. Biasing resistors are used to maintain the transistors in a non-conductive state until the overvoltage or overcurrent condition is removed.

Presence of mobility-fluctuation 1f noise identified in silicon P+NP transistors

Abstract: The magnitude and location of mobility-fluctuation 1f noise sources have been identified by means of biasing a PNP transistor in a common emitter configuration with first a high and then a low source resistance. Comparison of the two noise spectra at the same base currents shows the low source resistor bias isolates the collector noise sources, and the high source rsolates base noise sources. The magnitude of the observed collector 1f noise gives an α − 2 × 10−6 from Kleinpenning's mobility-fluctuation theory. The base 1f noise gives an α ∼- 10−7 due to an impurity mobility reduction factor of about 100.

Measurement of series resistance in IMPATT diodes

Abstract: A new method is given for determining the electrical series resistance of an IMPATT diode. The measurement is based on observation of the oscillation threshold bias current for a diode in a standard circuit. The method is applied to GaAs diodes near 40 GHz. The values obtained are used to quantitatively explain other performance characteristics of the diodes.

Analog telemetry system for biomedical implant

Abstract: An analog data transmission circuit for a biomedical implant employs a linear amplifier to modulate the impedance of a resonant circuit tuned to an externally generated constant carrier frequency. The resonant circuit comprises a tuned coil in circuit with a linear modulating switch and a digital modulating switch. The digital switch is gated by the digital data output from digital control circuitry within the implant. The linear amplifier output drives the linear modulation switch. The switches are preferably matched pairs of MOSFET's of opposite polarity having complementary parasitic diodes which form a phantom diode bridge. The bridge acts as a full wave rectifier and boosts the bias voltage on the sources of the FET pair forming the linear modulation switch such that the radiated amplitude is independent of the distance of the programming head. A timed power-up circuit supplies power to the amplifier and starts a square wave calibration period in response to the approach of the programming head. For ICEG transmission, a charge dump circuit depolarizes the lead before it is coupled to the amplifier.

Substrate bias control circuit and method.

Abstract: An integrated circuit and method includes a substrate bias voltage control circuit (20) formed on a common substrate therewith for ensuring that the substrate has a voltage (VCC or VBB) applied thereto while a semiconductor device on the substrate has a supply voltage (VCC) applied thereto which includes means for providing sources of bias (30) and supply (28) voltages to the substrate with means for firstly coupling the bias voltage to the substrate when the bias voltage is present and means for secondly coupling the supply voltage to the substrate when the bias voltage is not present.

Method for eliminating short and latent short circuit current paths in photovoltaic devices

Abstract: Systems and methods for detecting and eliminating latent and existing short circuit current paths through photovoltaic devices of the type including at least one semiconductor region overlying a substrate and a layer of conductive light transmissive material overlying the at least one semiconductor region are disclosed. The latent paths are first converted to existing short circuit current paths by applying a bias voltage to the devices. The short circuit current paths which are eliminated extend through the at least one semiconductor region from the substrate to the layer of conductive light transmissive material. The resistivity of the short circuit current paths is increased substantially at the interface between the conductive light transmissive material and the semiconductor region by isolating electrically the conductive light transmissive material from the short circuit current path. The isolation can be provided by removing the transparent conductive material from electrical contact or connection with the short circuit current path. The isolation also can be provided by depositing a body of insulating material onto the semiconductor region over an area including a short circuit current path prior to the deposition of the conductive light transmissive material. Further, the short circuit current path can be detected and located by applying a voltage to discrete areas of the device through a conductive solution which path then can be eliminated as described above.

High voltage optoelectronic switching in diamond

Abstract: Subnanosecond photoconductive switching has been observed in ultraviolet illuminated type IIa diamonds. Switching efficiencies up to 50% were attainable in coaxially mounted samples for direct current bias voltage as high as 8 kV at room temperature.

Normally-off, gate-controlled electrical circuit with low on-resistance

Abstract: An electrical circuit includes a JFET serially connected to an IGFET, the gate of the IGFET constituting the gate for the circuit. Biasing structure, such as a resistor, is connected between the circuit gate and the gate of the JFET for forward-biasing the P-N junction of the JFET extant between its gate and channel regions. When this P-N junction is biased by more than about 0.6 volts for a silicon JFET, the JFET gate region injects current carriers into the JFET channel region, whereby bipolar conduction occurs in the JFET channel region and low on-resistance for the circuit is achieved. In a preferred circuit the biasing structure comprises an IGFET, which advantageously results in the circuit gate having a high input impedance.

Optical transmission apparatus

Abstract: An optical transmission apparatus is provided which has an LD of single longitudinal mode. A bias current of the LD is set at its threshold current. A current obtained by amplitude modulation of a signal to be transmitted is superposed on the bias current. The LD is then set in the multimode, so that the apparatus can transmit a high-quality signal with reduced modal noise and distortion during multimode fiber transmission.

Stabilized biasing of semiconductor lasers

Abstract: In this paper we analyze the design of biasing and control circuits for semiconductor lasers in a generalized context based on an idealized laser characteristic. In particular, we address three major design considerations: whether to bias the laser above or below threshold, how to stabilize the optical output levels independent of variation in the average output power, and to what degree the output levels can be stabilized relative to various circuit and device parameters. Results of our study indicate that to eliminate from the optical output any dependence on either variation in laser device characteristics or the dc average of the input signal, feedback control of both the prebias and modulation current is necessary.

A numerical analysis of a heterostructure InP/InGaAs photodiode

Abstract: Electrical properties of a heterostructure InP/In 0.53 Ga 0.47 - As photodiode have been analyzed numerically. A device simulator, which can handle a heterostructure up to a high voltage operation, was developed for this work. The numerical simulator explains the experimental results obtained regarding photocurrent. The band-gap discontinuities, i.e., 0.22 eV for the conduction band and 0.37 eV for the valence band, were confirmed to be plausible. The photocurrent switching mechanism in the photodiode by bias voltage was clarified through carrier and potential distributions. It was revealed that the photo-excited holes accumulate at the heterointerface, and the switching voltage for photocurrent varies according to the incident optical power level. It is expected that this simulator will be a powerful tool for optimum heterostructure photodiode design.

Multiple quantum-well infrared detector

Abstract: Alternating layers of N+ GaAs (80 Å) and N+ Ga 1-x Al x As (300 Å), all heavily doped with a uniform flux of Sn, and biased by 2V, provide a multiple quantum-well heterojunction structure for infrared detection with cutoff wavelength established by the choice of the value x which defines the depth of the wells. Fine tuning of the cutoff wavelength may be achieved by varying the bias voltage. By biasing the individual quantum-well layers progressively through a voltage divider, an avalanche mechanism may be achieved in the detector for signal amplification. The detectors may be fabricated in large two-dimensional arrays.

Biasing and fast degaussing circuit for magnetic materials

Abstract: A dual-function circuit is provided which may be used to both magnetically bias and alternately, quickly degauss a magnetic device. The circuit may be magnetically coupled or directly connected electrically to a magnetic device, such as a magnetostrictive transducer, to magnetically bias the device by applying a d.c. current and alternately apply a selectively damped a.c. current to the device to degauss the device. The circuit is of particular value in many systems which use magnetostrictive transducers for ultrasonic transmission in different propagation modes over very short time periods.

Picosecond correlation measurements of indium phosphide photoconductors

Abstract: The response times of InP photoconductors under picosecond optical illumination are observed to differ widely depending on whether the electrical bias is dc or a short pulse. The use a pulsed bias gives a slower response (>100 ps) which is more characteristic of the intrinsic material properties, than a dc bias which gives a very fast (<15 ps) response and can be attributed to imperfect contacts.

Programmable MOS transistor

Abstract: @ Each transistor of an array is selectively programmable with a laser beam which is precisely directed to the transistor. The laser beam and the biasing voltage on a control electrode common to all transistors causes charge to be selectively placed in a trapped-charge region. In one embodiment of the invention, the laser beam is incident on a floating gate and the control electrode to provide photoelectrons which, depending on the bias potential on the control electrode, produce a net negative or positive charge in the floating gate. In another embodiment, the laser beam is incident on the control electrode to heat underlying insulator material and provide a conductive path for charge between the trapped-charge region and the appropriately biased control electrode.

System for resist defect measurement

Abstract: A non-destructive test system for determining the number, size and location of pinhole defects in insulative coatings on a semiconductor substrate employing photocathodic current measurement at the semiconductor surface. This current is produced by contacting the coated semiconductor with an aqueous electrolyte, applying a small electrical bias with respect to a metal electrode, and scanning a small, focused light beam over the semiconductor surface. The frequency of current peaks produced is proportional to defect density. Current peaks provide data relative to defect size and location is correlated relative to scanning data to determine defect location.

A comparison of etched-geometry and overgrown silicon permeable base transistors by two-dimensional numerical simulations

Abstract: Etched-geometry and overgrown Si permeable base transistors (PBT's) are compared by using two-dimensional numerical simulations. Because of the asymmetry of the etched structure, two biasing conditions are possible (etched-collector and etched-emitter) and both are considered. The base-to-collector transfer characteristics of PBT devices have two regions of operation. At low base-to-emitter voltages, barrier-limited current flow is observed, The two-dimensional nature of the depletion region near the Schottky-contact base grating results in a smaller electron barrier and thus a larger collector current in the etched structures than in the overgrown structure. At high base-to-emitter bias levels, charge is limited from entering the base region of the etched-emitter structure and from leaving the base region of the etched-collector device. The resulting parasitic feedback effects lead to a deviation from the square-law behavior found in the collector characteristics of the overgrown PBT. Because of the absence of semiconductor material directly above the base grating lines in the etched devices, these structures have lower device capacitances. They also have smaller transconductances at high base-to-emitter voltages. The important consequence of this is that overgrown and etched structures have comparable predicted maximum values of the small-signal unity short-circuit current-gain frequency and maximum frequency of oscillation. Fabrication-related effects are discussed qualitatively and GaAs PBT operation is considered in light of the present simulations.

Discharges on a negatively biased solar array in a charged particle environment

Abstract: The charging behavior of a negatively biased solar cell array when subjected to a charged particle environment is studied in the ion density range from 200 to 12 000 ions/sq cm with the applied bias range of -500 to -1400 V. The profile of the surface potentials across the array is related to the presence of discharges. At the low end of the ion density range the solar cell cover slides charge to from 0 to +5 volts independent of the applied voltage. No discharges are seen at bias voltages as large as -1400 V. At the higher ion densities the cover slide potential begins to fluctuate, and becomes significantly negative. Under these conditions discharges can occur. The threshold bias voltage for discharges decreases with increasing ion density. A condition for discharges emerging from the experimental observations is that the average coverslide potential must be more negative than -4 V. The observations presented suggest that the plasma potential near the array becomes negative before a discharge occurs. This suggests that discharges are driven by an instability in the plasma.

Photon generation in forward-biased silicon p-n junctions

Abstract: Photons are generated by forward biasing a silicon p-n junction at 10-5∼ 10-4quantum efficiency through radiative recombination. At large distances from the forward-biased junction, leakage currents of magnitudes significant for some VLSI circuits can appear due to the substrate minority carriers generated by the photons. The effective decay length of the measured leakage current is about several hundred to one thousand micrometers. The effects of forward biasing an input node or a parasitic lateral bipolar transistor are, therefore, longer ranged than commonly assumed.

Traveling-wave electrooptic modulator

Abstract: An integrated-optics Mach-Zehnder interferometric modulator in LiNbO3 has been designed and fabricated. The electrodes are 3-μm thick asymmetric coplanar striplines formed by ion-beam etching techniques. The push–pull design and the r33 electrooptic coefficient of LiNbO3 are utilized for efficient modulation. Complete modulation is achieved with 6.5 V for the 6-mm long device at 0.83-μm wavelength and with 18 V at 1.3-μm wavelength. The 3-dB bandwidth of the modulator is 3.5 GHz, being limited by the excessive resistive loss of the stripline electrodes. Since this particular modulator retains a dc electrical bias, it performs either as an intensity modulator by applying a π/2 dc phase bias to achieve maximum linearity or as a frequency shifter by changing the dc bias point to π. In addition, we analyzed the principle of operation of the Y junction by observing both the in-phase and the out-of-phase modes of a multimode waveguide modulator.

Ionization probe interface circuit with high bias voltage source

Abstract: The primary winding of an engine ignition coil is coupled to an ionization probe detecting cylinder combustion in order to apply a bias voltage.

Analog switch device

Abstract: PURPOSE:To obtain an output signal of less distortion, by supplying a voltage, which corresponds to an input analog signal voltage, to the substrate electrode of an N-channel MOS transistor TR to make the resistance value between input and output terminals constant. CONSTITUTION:Enhancement N-channel MOSFET1 and P-channel MOSFET2 are connected in parallel to constitute an analog switch, and the output voltage of a voltage buffer circuit 5 which consisting of an enhancement N-channel MOSFET7 and a depletion P-channel MOSFET8 and outputs a voltage corresponding to an input analog signal voltage IN is supplied to a substrate electrode B of the N-channel MOSFET1. Thus, the back gate bias voltage of the MOSFET1 is always held in an approximately constant value, and the change due to the variance of the threshold of the on-state resistance of the MOSFET1 is eliminated, and the output signal of less distortion is obtained.

Voltage and current expressions for a two‐junction superconducting interferometer

Abstract: The average voltage and circulating current of a superconducting interferometer containing two Josephson junctions (a dc SQUID) are calculated analytically, in various approximations, as functions of bias current and applied magnetic field or control current. The results are useful in calculations of the noise characteristics of the dc SQUID, as well as in other applications.

Linear sense amplifier

Abstract: A sense amplifier suitable for use with a source of binary signals, where one of the signals is "well" defined and the other is "poorly" defined includes a current source for producing a bias current which is of the same polarity as the current produced by the ill defined signal and of amplitude intermediate the amplitude of the currents produced by the ill and well defined signals. The bias current and signal source currents are summed and when applied to an inverter which is precharged to, or close to, its transition point cause the inverter output to respond with approximately equal speed to either of the two binary conditions.

Analytical Solutions of Traveling Fluxon Waves on a Josephson Transmission Line with Shunt Conductance and Uniform Bias Current

Abstract: Traveling-wave type solutions describing the fluxon motion on an infinite Josephson transmission line with shunt conductance and uniform bias current are derived analytically by approximating the sinusoidal current vs. phase-difference relation of the Josephson junction by a triangular saw-tooth like relation. From the result, the relation between the velocity of the waves and the bias current is obtained numerically, and the dependence of the phase and voltage upon space and time is also obtained. Finally, the energy flow of the waves along the line is expressed by a simple formula.