Showing papers on "Relaxation oscillator published in 1989"

Delay-controlled relaxation oscillator with reduced power consumption

Abstract: A delay-controlled relaxation oscillator includes a capacitance in the oscillator which is alternately charged and discharged. The change-over from charging to discharging is controlled by means of a comparator which compares the capacitance voltage with a reference voltage. The oscillator also includes switching means for reducing the power consumed by switching the power supply for the comparator from the power supply mode into a stand-by mode between two change-overs.

Are relaxation oscillators an appropriate model of gastrointestinal electrical activity

Abstract: Mathematical models based on relaxation oscillators have heavily influenced the terminology and experimental designs of investigations in gastrointestinal motility for nearly two decades. Relaxation oscillator equations have been used to stimulate the electrical activities of the esophagus, stomach, small intestine, colon, and rectosigmoid region. It has been suggested that many attributes of gastrointestinal electrical activity cannot be adequately explained by classic "core-conductor" or "cable" models of excitation and conduction. This article critically reviews the relaxation oscillator model and provides an explanation for each of the putative inadequacies of core-conductor theory. Furthermore, we question whether relaxation oscillator equations are able to simulate the waveforms of gastrointestinal slow waves, alterations in waveform in response to drugs or electrical stimulation, patterns of slow-wave activity when stimulated at physiological frequencies, prolonged periods of constant resting membrane potential between gastric slow waves and electrotonic spread into inactive regions. We conclude that the relaxation oscillator equations do not fully describe gastrointestinal electrical activity; excitation and propagation can be modeled by a theory that provides for morphological features, ionic conductances, and other elements included in the cable equations.

Frequency fluctuations of a diode-pumped Nd:YAG ring laser

Abstract: The spectral density of the frequency fluctuations of a diode-pumped single-mode monolithic Nd:YAG ring laser was measured by locking a Fabry-Perot resonator to the laser frequency. The fluctuations approach the limit due to spontaneous emission (the Schawlow-Townes limit) at frequencies above 80 kHz. The inherent frequency stability of these lasers makes them attractive as a potential light source for gravitational-wave interferometers.

Simple DC-SQUID system based on a frequency modulated relaxation oscillator

Abstract: Nanobridges with hysteretic I-V (current-voltage) characteristics can be operated as relaxation oscillators when connected to an R-L shunt. A DC SQUID (superconducting quantum interference device) configuration results if two such oscillators are incorporated in a superconducting ring. Operating such a self-oscillating SQUID (SOS) with a suitable bias current leads to an output signal of the order of 10 mV, whose frequency depends on the magnetic flux through the SQUID ring modulo Phi /sub 0/. Due to this large output voltage, no impedance matching or special low-noise preamplifier is needed for the readout scheme. Standard integrated circuits for FM (frequency modulated) signal processing can be used, leading to matchbox-size electronics. Such DC SQUIDs have been made of thin Nb, NbN, and Nb/sub 3/Ge films. The highest sensitivity achieved so far is Nb devices with a white flux noise below 10/sup -5/ Phi /sub 0// square root Hz at 4.2 K. >

Rectifier-inverter circuit with low harmonic feedback, particularly for operation of fluorescent lamps

Abstract: To ensure synchronous operation of push-pull connected oscillator transistors (T1, T2), receiving rectified power via a rectifier (GL) from a power network (U), in which the circuit includes an elevated voltage maintenance or step-up converter circuit having a choke (L2), a switching transistor (T3) and a diode - capacitor circuit (D5, C2), the switching transistor (T3) is controlled from the same source of control voltage as the push-pull connected oscillator transistors (T1, T2), for example by coupling the base of the switching transistor (T3) to receive control energy from a feedback coil (RK3) of a feedback transformer (RK1, RK2, RK3) also supplying feedback energy to the push-pull oscillator transistors (T1, T2). The switching transistor (T3) can be controlled by a controllable resistor (R2) connected to its base, which may receive a control voltage through a control amplifier (FIG. 3: RV) representative of voltage levels in the circuit. A further transistor (T4) can be connected serially between the rectifier (GL) and the choke (L2) of the step-up converter circuit which improves approximation of sinusoidal wave form and voltage level maintenance of the circuit, the further transistor (T4) being likewise controlled from the same energy source as the switching transistor (T3).

Switching converter with spike limiting circuit

Abstract: A switching circuit which provides excess voltage and a circuit, responsive to the excess voltage, to direct energy related to the excess voltage back to a voltage source coupled to the switching circuit is described. The circuit responsive to the excess voltage includes a capacitor, an inductor, and a transistor to couple and decouple the capacitor and the inductor. The transistor couples the capacitor to the inductor to transfer energy related to excess voltage stored in the capacitor to the inductor for storage, and decouples the capacitor from the inductor to transfer energy stored in the inductor to the voltage source. The circuit also includes a comparator, responsive to the level of the excess voltage, to provide a control signal to the transistor to control the coupling and decoupling of the capacitor and the inductor.

Low-frequency intensity noise resonance in an external cavity GaAs laser for possible laser characterization

Abstract: The dependence of the (low-frequency) resonance of light intensity noise in an external-cavity GaAs laser on cavity length and bias current, combined with the dependence of the threshold current on the magnitude of the light feedback, is used to determine simultaneously the carrier recombination lifetime, the carrier injection at transparency, and the optical loss. The key to this technique is understanding the correction term to the relaxation oscillation frequency due to finite carrier density at transparency and the influence of the long external cavity transit time on the photon lifetime in the three-mirror cavity. The technique uses commercial lasers without modifying them and does not require fast electronics. >

Electronic stimulating device

Abstract: The invention relates to an electronic stimulating device which produces low frequency pulsating signals generated by a relaxation oscillator The electronic circuit board is mounted within a lightweight portable housing to enable a user to conveniently carry the device at all times, if desired

Dual port voltage controlled emitter coupled multivibrator

Abstract: A voltage controlled oscillator includes an emitter coupled multivibrator in which a capacitor determines the frequency of oscillation along with a pair of load resistors and a pair of current sources. A differential amplifier is coupled to operate in parallel with the mutlivibrator and its tail current is operated differentially, with respect to the currents in the pair of sources, in response to the input voltage at a first modulation input port. Thus, a constant current flows in the multivibrator loads even when the frequency is modulated. A second input port is coupled to vary the tail current in the differential amplifier to comprise a dual port control of the voltage controlled oscillator. The circuit can be operated at a relatively low supply voltage and can be temperature compensated. Furthermore, the input ports can include circuitry having a logarithmic response for digital signaling processing.

Precision CMOS oscillator circuit

Abstract: A CMOS relaxation oscillator is disclosed employing a pair of capacitors and individual charging means. A noninverting amplifier comprising two cascaded inverters is provided with a transmission gate input circuit that alternately switches the amplifier input between the two capacitors. A pair of switches coupled respectively across the capacitors alternately discharge them. The resulting oscillator has a frequency determined by the capacitor charging periods. Accordingly, the frequency and duty cycle can be predetermined as desired. The circuit can also be made either power supply tunable or power supply independent.

Nonsaturated multivibrators for sensor signal conditioning

Abstract: Multivibrators based on operational transconductance amplifiers (OTA) are considered. The first is an astable bridge multivibrator with one OTA. This circuit is useful for two-wire bridge-to-frequency converters. The second circuit is an astable multivibrator with two OTAs. This circuit provides a linear dependence of the oscillation frequency on the sensor control current. Both circuits are nonsaturated multivibrators. Calculation of their oscillation frequency involves a linear model which describes the circuit behavior near the transition point from one quasistable state to another. The circuits with bipolar and MOS OTAs are treated. >

Voltage controlled oscillator free from free-run oscillating frequency adjustment

Abstract: A voltage controlled oscillator free from free-run oscillating frequency adjustment is disclosed. This oscillator includes an amplifier having a positive feed-­back loop, a resonator connected to the output of the amplifier, and a variable reactance circuit connected to the output of the amplifier. The reactance circuit presents a reactance value variable by a control voltage to control an oscillation frequency of the oscillator. There is a further provided a low-pass filter which is connected in cascade to the variable reactance circuit. A high-pass filter is preferably inserted in the positive feedback loop.

Hybrid Integrated Ku-Band VCO

Abstract: A hybrid integrated Ku-band voltage controlled oscillator is described. The oscillator design is based upon a linear circuit model of the GaAs-MESFET NE71000. The oscillator circuit is subdivided into two chained twoports, an active twoport containing only the voltage controlled current source modelling the transconductance of the MESFET and a linear feedback twoport containing all the other circuit elements of the transistor as well as the oscillator circuit embedding the FET. Using this model we optimized the oscillator circuit within the whole tuning range. An output power of 12 dBm within a tuning bandwidth of 3 GHz was achieved. High Q-varactors were used in order to obtain good phase noise performance. A phase noise of ?70 dBc/Hz at an offset of 10 kHz of the carrier has been measured.

Local hysteresis in relaxation oscillators

Abstract: Relaxation oscillations are very commonly found in nature. When modulation by an external force is present, a global hysteresis connected with chaos is often encountered. In addition to this kind of hysteresis a qualitatively different ``local'' form is found in some systems. We describe the circumstances under which one observes local hysteresis. A specific system treated in detail is the Fohlmeister model, originally derived to describe a neuronal encoder. In the limit of small damping an analytical solution is obtained. Furthermore, we derive an upper limit to the hysteresis. The results are compared to numerical calculations on the full system and agree quite well. In contrast to the driven damped-pendulum equation, the hysteresis is limited in size as compared to the phase-locked region.

Jitter in regenerative detectors

Abstract: A method for finding an equivalent noise bandwidth for a regenerative detector which allows the accurate prediction of period jitter with no fitted parameters is reported. The analysis reported is new in several ways. First, the model includes the time constant of the amplifier around which the detector is built ( tau /sub OUT/), even for predicting the oscillator's noise-free period. With tau /sub OUT/ nonzero, the delay between each threshold-crossing and the detector's response lengthens the oscillator's period by the excess period (about four times the delay). Simulations of an emitter-coupled oscillator (ECO), in excellent agreement with measurements, show that the excess period is roughly proportional to tau /sub OUT//sup 2/3/. Second, the noise analysis avoids small-signal bandwidths by using the pulse sensitivity. >

Control circuit for blocking oscillator

Abstract: This invention relates to a blocking oscillating converter for transferring energy from a source of power, such as a vehicle battery, to a storage means, such as an energy storage capacitor in a capacitor discharge ignition system. A novel control and feedback circuit incorporated in the blocking oscillator allows the drive level to the switching transistor to be controlled in response to the peak current in said transistor as well as the output voltage of the blocking oscillator. Furthermore the control circuit allows the blocking oscillator to be turned off during the short period of time after each spark discharge that is needed for turnoff of a switching device used to control that discharge.

Switched-mode power supply for a DC motor

Abstract: Switched-mode power supply for a low-voltage DC voltage motor 8 having a flow-through converter, the power part of which contains a switching transistor 1, a rectifier diode 9 and a transformer 2, the primary winding 21 of which is connected in series with the switching path of the switching transistor 1 and the secondary winding 22 of which is connected in parallel with the series connection of the rectifier diode 9 to the DC motor 8, a freewheeling diode 10 being arranged in parallel with the DC motor 8, the control device of the converter being used for driving the switching transistor 1. The control device contains an astable multivibrator 3 which determines the duty ratio of the switching transistor 1, and a comparator 4 with hysteresis and has the voltage across the DC voltage motor 8 applied to its input side, the output signal of which comparator is delivered at an earlier instant in the event of increasing motor voltage. The outputs of the astable multivibrator 3 and of the comparator 4 with hysteresis are connected to the control terminal of the switching transistor 1 via a logic (switching) element 5.

Balance constant temp. controller

Abstract: The utility model relates to a temperature control device making use of the electrical property of the sensing element or the variation of resistance with temperature to generate the electrical variation, mainly comprising a sensor, an amplifying circuit for the detection signal, a pulse generating circuit and a control circuit. A temperature sensing element of silicon semiconductor material, a control circuit of controlled silicon and a trigger pulse generation circuit of a relaxation oscillator. The utility model has the advantages of high speed, little error, high stability, low cost, simple circuit and wide temperature response range.

Predictions from the van der Pol equation applied to high power microwave phase-locking experiments at Physics International

Abstract: The van der Pol equation has been evaluated as a model for an experiment in which a high-power cavity vircator was driven by a relativistic magnetron. It has been found that Adler's inequality gives a necessary but not sufficient condition for achieving phase locking between the driving magnetron and the driven vircator oscillations. The amplitude of the entrained oscillations has been determined as a function of the injected magnetron power, the initial frequency detuning, and other system parameters. The stability of these oscillation is examined. It has also been found that not all entrained states are stable. Boundaries between stable and unstable states are given. Moreover, the driven oscillator can operate as a beatwave source. Comparison of predictions to measurements has validated the model. A similar analysis has been extended to two coupled van der Pol equations that model phase-locked relativistic magnetron experiments. >

Quartz oscillator circuit for higher frequencies

Abstract: In an emitter-coupled crystal-controlled multivibrator, a difference amplifier stage (T3, T4) is inserted into the feedback branch, as a result of which a higher gain is effected in the oscillator circuit and thus the settled state is achieved faster.