Showing papers on "LC circuit published in 1971"

Circuit for coupling radio receiver and radio transmitter to a common antenna for duplex operation

Abstract: Antenna coupling circuit for duplex radio transmission and reception by use of a common antenna (duplexer), including plurality of helical resonator sections provided within conductive enclosures in a conductive housing. A helical winding is provided in each enclosure having one end connected to the housing, and an adjustable conductive stud forms a capacitor with the other end of the winding. The winding and enclosure form a parallel tuned resonator, and the series capacitor forms therewith a series tuned circuit. One series tuned circuit at the receiver frequency is coupled to the antenna by a transmission line having a length equal to an odd multiple of a quarter wave length at the transmitter frequency, and this junction is connected to the transmitter through a circuit which may include additional tuned circuits. A second series tuned circuit at the transmitter frequency is coupled to the antenna by a transmission line having a length equal to an odd multiple of a quarter wave length at the receiver frequency, and this junction is connected to the receiver through a circuit which may include additional tuned circuits. A reactance may be connected in parallel with the first series tuned circuit to provide an anti-resonant circuit at the transmitter frequency, and a different reactance may be connected in parallel with the second tuned circuit to provide an anti-resonant circuit at the receiver frequency. Additional resonator sections can be connected in the transmitter and/or receiver branches of the circuit.

Method and apparatus for actuating an electric circuit

Abstract: A field of electrostatic, electromagnetic or high frequency radiant energy is provided on a predetermined intermittent cycle in a confined space through which persons are directed. A tuned resonant circuit, concealed on merchandise being carried through the space, is activated by the energy field. During the time interval when the energy field is cut off, the decaying electric signal from the tuned resonant circuit is radiated to a receiver. The received electric signal functions to activate an alarm.

Radio capsule oscillator circuit

Abstract: This invention relates to a Colpitts oscillator circuit for a radio capsule of the type adapted to be swallowed by a patient for investigating a condition of the gastrointestinal tract. The circuit includes a transistor as the active element and a parallel resonant LC circuit including the series combination of a variable capacitance diode and first and second capacitors, the capacitance of the second capacitor being the larger of the two in order to provide the minimum amount of positive feedback required to cause stable oscillation. The capacitance of the first capacitor, which is connected between the diode and the transistor emitter, approximates that of the diode at the lowest voltage applied to the diode by a sensor device.

Regulating and filtering transformer

Abstract: Transformer for providing a regulated and filtered output voltage. Input voltage is applied to an input winding which is wound around two magnetic cores. One magnetic core saturates for part of each half-cycle of the induced alternating flux during normal operation. The other magnetic core does not saturate during normal operation and includes air gaps in the legs thereof. An output winding is positioned around the non-saturating core and connected in parallel with a capacitor to form an output tank circuit resonant at the operating frequency of the transformer.

Interference suppression circuits

Abstract: In a thyristor switching circuit which includes an LC filter, means responsive to the collapse of principal current through said thyristor are provided for preventing the thyristor from commutating into an off state during midcycle, said means including an inductance which is also included in the LC filter.

Constant frequency power inverter having silicon controlled rectifier multibridge inputs for output wave shaping with variable phase control for overload conditions

Abstract: A static inverter for converting D. C. power to three phase A. C. power which has a bridge circuit connected to the D. C. power source and including a plurality of silicon controlled rectifiers turned on by logic signals from a logic control circuit. A commutating circuit has silicon controlled rectifiers turned on by logic signals from the logic control circuit to control a single LC network to provide reverse polarity voltages to all the silicon controlled rectifiers in the bridge circuit to turn them off. Three phase A. C. power is provided by transformers having their primary windings connected to the bridge circuits and their secondary windings connected in series. The static inverter may include a plurality of bridge circuits and the relative phases of the logic signals to the bridge circuits is shifted to vary the phase relationship of the currents from the bridge circuits to change the amplitude of the three phase A.C. power from the transformers to avoid overloading the inverter in case of a short circuit in the load.

Inductively coupled metal detector arrangement

Abstract: A metal detector arrangement for detecting the presence of a metal object in proximity thereto. A case means is provided in which there is a cavity. An electrically operated detector circuit is positioned within the cavity and the detector circuit generally comprises a search coil connected to an oscillator. The oscillator has a tank circuit and the inductor of the tank circuit is connected to the primary of the transformer. The search coil is connected to the secondary of the transformer. The oscillator generates an output at a preset frequency. When a metal object is in proximity to the metal detector the impedance to the signal radiated by the search coil is changed thereby changing the inductance of the tank circuit. The change in inductance of the tank circuit in the presence of a metal object raises the frequency of the oscillator output signal. A receiver coil is positioned within the search coil and receives the radiated signal from the search coil. The receiver coil is connected to an amplifier and the response of the amplifier is such that the increase in frequency of the radiated oscillator output signal changes the magnitude of the amplifier output signal. An indicator, such as a light bulb, is coupled to the amplifier through a switch means and the light bulb changes in intensity in proportion to the change in the magnitude of the amplifier output signal. The switch means turns off the indicator for the amplifier output having a preselected magnitude. A sensitivity control means is also provided to increase the magnitude of the amplifier output signal for the condition of the presence of a given mass of metal at a given distance from the detector and, thus, provide a variable sensitivity to aid in the detection of very small metal objects.

Phase shifter having at least one t-section lc circuit

Abstract: THE PRESENT INVENTION SETS FORTH DESIGN CRITERIA AND GENERIC LC CIRCUIT CONFIGURATIONS FOR TWO TYPES OF PHASE SHIFTERS. THE FIRST TYPE ACCOMPLISHES VARIABLE PHASE SHIFTING BY EMPLOYING A T-SECTION CIRCUIT USING FIXED INDUCTORS AND VARIABLE CAPACITORS IN THE SERIES LEG OF THE CIRCUIT WHILE A PARALLEL CONNECTION OF FIXED INDUCTOR AND VARIABLE CAPACITOR EXISTS IN THE SHUNT LEG OF THE CIRCUIT. IN THE SECOND TYPE, DIGITAL PHASE SHIFT IS ACCOMPLISHED BY SEQUENTIALLY SWITCHING BETWEEN LOW AND HIGH PASS T-SECTION FILTERS.

A fail-safe electronic comparator circuit

Abstract: This disclosure relates to a fail-safe comparator circuit having a free-running multivibrator powered by two separate d.c. supply voltages. A resonant circuit is coupled to the output of the multivibrator and tuned to the normal resonant frequency of oscillation of the multivibrator so that oscillations having the normally resonant frequency will be induced into the resonant circuit when and only when the two d.c. supply voltages are in agreement and no critical component or circuit failure is present.

Voltage controlled oscillator

Abstract: An oscillation circuit loop includes two phase shifters for advancing and delaying the phase of an input signal respectively, an adder for obtaining the vector sum of the output signals of these two phase shifters, and feedback means for the positive feedback of the output signal of the adder to an oscillation amplifier through a tank circuit. An external control voltage is applied to the adder so as to continuously vary the relative magnitude of the two signals added to each other by the adder. With an oscillator having such a construction, the degree of phase shift by the phase shifters and the value of Q of the tank circuit can be freely selected, and as a result, any desired sensitivity and phase control range can be freely obtained.

Oscillator with a piezo-mechanical vibrator

Abstract: Improved oscillator including an oscillator element, amplifier, amplitude limiter and tuned output circuit. A feedback path is provided between the tuned output circuit and the oscillator element. The amplitude limiter is connected between the amplifier and the tuned circuit to provide a constant amplitude signal to the tuned output circuit notwithstanding variations in the output from the amplifier caused by variation in the ambient temperature and aging. Further, by providing a resistance between the amplitude limiter circuit and the tuned circuit the resonance Q of the tuned circuit can be made high without producing an adverse effect on the amplitude limiter circuit.

Rf/dc generator for quadrupole mass analyzer

Abstract: The specification discloses an improved radio frequency-direct current (RF/DC) generating circuit for use with a quadrupole mass analyzer. A free-running oscillator is employed to generate the radio frequency signal, the oscillator having diode means in the feedback circuit for limiting the dynamic range over which the oscillator must operate. The output of the oscillator is connected through a coil to the rods of the quadrupole mass analyzer which, in conjunction with the coil function as a tuned circuit, thereby the magnitude of the radio frequency applied to the rods is obtained by Q multiplication. A detector circuit is connected to the output of the coil for producing a feedback signal which is compared with a ramp voltage for driving the output of the oscillator as a function of the control ramp input. The detector output is also fed back to the input of two similar circuits for generating equal magnitude with opposite polarity direct current potentials which magnitude varies as a function of the output of the detector and thereby under control of the input control ramp. Additional diodes are provided in the detector circuit to enable the detector to operate near zero volts.

Active tuned circuit

Abstract: Active tuned circuit configurations particularly suitable for microelectronic construction as filters, amplifiers, and oscillators for operation near the Ft of the transistors employed. A high Q, tunable network at a frequency near Ft is provided by coupling a second bipolar transistor configuration to the emitter of a first bipolar transistor in order to provide negative resistance and capacitive reactance as necessary to tune the low Q inductive value of the first bipolar transistor.

Tuned oscillator circuit for providing a rotating magnetic field

Abstract: A tuned field drive circuit for use in magnetic domain apparatus is provided for generating a reversible, rotating, magnetic field in a plane. The circuit is capable of initiating, maintaining and terminating the rotating field with a predetermined phase and with a field strength envelope having a substantially constant amplitude. The basic circuit includes a high-speed transistor switch, a tuned L-C resonant circuit, and a feedback field current amplifier, for compensating for resistive loss in the resonant circuit. Two of the basic circuits are "slaved" together to form the resultant field drive circuit, each basic circuit providing one of two normal magnetic vector components comprising the rotating field.

Pulsed resonance spectrometer system employing improved radio frequency pulse turn-off method and apparatus

Abstract: A magnetic resonance spectrometer system wherein a pulse of driving radio frequency signal is transmitted to the resonant circuit coupled to the sample under analysis to produce magnetic resonance therein, the free induction decay signal from said sample being induced in said resonant circuit and delivered to the receiver circuitry after said pulse termination, the ringing signal induced in the receiver circuitry due to energy decay in the resonant circuit after the radio frequency pulse termination being substantially reduced by reversing the phase of the radio frequency transmitter signal just prior to said pulse termination, and then terminating the pulse when the radio frequency transmitter voltage at said resonant circuit is at the zero crossing value.

Weak Link Point Contact Devices

Abstract: Recent progress in our laboratory on permanently adjusted niobium point‐contact superconducting devices is reported. We describe an rf noise‐biased magnetometer obtained by appropriate tuning and adjustment of the point contact in a superconducting ring that is coupled to an LC tank circuit which provides an rf noise‐bias excitation at its resonant frequency. Thus, the rf oscillator normally used is eliminated although the magnetometer noise increases somewhat. In addition, mechanically stable, room‐temperature‐helium‐temperature‐cyclable insulated double and single point contacts have been obtained by use of an insulating glass with thermal expansion matching that of niobium. When two of these contacts are connected in parallel the resultant device works quite well as a cyclable dc‐biased magnetometer. Study of the temperature dependence of the critical current is facilitated by the stable configuration. Preliminary measurements showed sharp rises of the critical current with decreasing temperature similar to those observed with S‐N‐S sandwiches. Properties of these devices are discussed.

Emergency fluorescent lighting apparatus

Abstract: Fluorescent lamp apparatus for emergency lighting comprises a battery-operated low-impedance transistor network which when energized develops square waves of voltage. The generated voltage is applied across an LC circuit. The lamp is connected in parallel with one of the elements of the LC circuit. The very high voltage initially generated across the individual elements of the LC circuit causes the lamp to strike, and after operation of the lamp is initiated, the current through the lamp is constant for any given applied battery voltage.

The use of resonant circuits in power conditioning equipment

Abstract: Four different power conditioning circuits are described showing how the series resonant circuit can be used instead of the saturating transformer to determine opeating frequency. These circuits are a dc-to-squarewave inverter and an ac-to-ac frequency sextupler, both fully qualified for aerospace, a dc-to-dc converter and a dc-to-sinewave inverter, both in the successful prototype stage. Attention is given to the relation betwen damping constants and rejection ratios, and it is shown graphically how to take advantage of these features of the resonant circuit by suitable choice of isolating transformer turns ratios as related to load constants. The four circuits show how the careful use of these principles reult in superior frequency stability and, especially in the sinewave inverter, vitual elimination of high power switching transients, with resultant low generation of electromagnetic interference and extremely low electrical stresses in switching power transistors.

Group delay time correcting circuit including a toulon circuit for use in an intermediate-frequency amplifying circuit

Abstract: A group delay time correcting circuit including a toulon circuit for use in an intermediate-frequency amplifying circuit The intermediate-frequency amplifying circuit is comprised of an amplitude limiter, a group delay time correcting circuit and a detector circuit coupled to the output of the group delay time correcting circuit The group delay time correcting circuit includes a differential amplifier for converting the input signals thereto from the amplitude limiter into two signals equal in amplitude but opposite in phase The output of the differential amplifier is applied to a Toulon circuit comprised of a series connected reactance circuit and a resistor The output of the Toulon circuit is taken at the junction between the reactance circuit and the resistor The reactance circuit of the Toulon circuit is constructed so as to have at least one resonance point and one anti-resonance point

Voltage controlled crystal oscillator

Abstract: A voltage-controlled crystal oscillator circuit for use in various kinds of electronic apparatus is shown. The preferred embodiment consists of voltage sensitive capacitor, as a varactor, in circuit with a crystal and a compensating tuned circuit, the latter being adjustable as desired to eliminate the effects of nonlinearity in the impedance characteristics of the crystal and the varactor as the voltage across the varactor is varied.

Self-excited composite capacitance and interlocking inductance oscillator

Abstract: A self-excited, self-tuning and self-loading generator in which the load electrode is an inherent part of the capacity and inductance of the generator tank circuit. The generator is automatically, instantly and steplessly self-tuning with respect to wide variations in load characteristics. A maximum power input to the load is maintained by the generator and this is in proportion to changes in the loss factor of the load. A composite or interlocked inductance is used for the load electrode and the tank circuit. Series coupling condensers are used in the load circuit and leads from these coupling condensers are crossed and their terminals are connected to the composite inductance thus interlocking the composite inductance with the load circuit. This is why I term the composite inductance an interlocked inductance.

Negative-Impedance Converters (NIC) for VHF Through Microwave Circuit Applications

Abstract: The negative impedance converter (NIC) is an active circuit element which has been increasingly useful in low frequency applications. It is a 2 port device which converts any load impedance at one port to an input impedance -Z as seen at the other port. The NIC can be used to synthesize negative impedances and admittances which are then used to generate transfer functions or impedance functions which are not physically realizable without active circuits. We have developed two types of NIC circuits suitable for VHF and microwave applications. The first type of NIC is based upon the idealized circuit shown in Fig. 1. Particular care has been taken in the design and layout of this circuit to minimize stray reactance which might reduce the frequency response of this NIC realization. The transistors used in this circuit are NEC 2SC 989's which are relatively inexpensive and have an f/sub T/ of 3 GHz. Figure 2 is a sketch of the layout of a practical realization of the RF portion of this NIC. Figure 3 demonstrates that the NIC can indeed neutralize a 22 pf capacitor up to 120 MHz. Figure 4 shows the effect of temperature variations on a lossless single-pole L-C filter which used an NIC to generate a -R which cancelled the loss in the inductor. The loaded Q of the tuned circuit is 100. Without the NIC, the loss of the tuned circuit was 8 dB. The noise figure of the filter and NIC was 17 dB and the in-band third order intercept was -12 dBm.

Pulsed vhf radio spectrometer for investigation of nuclear quadrupole resonance in solids

Abstract: A pulsed VHF radio spectrometer for the invenstigation of nuclear quadrupole resonance (NQR) in solids, in which the tuning arrangements of the anode and grid tanks in a double-tank r.f. pulse oscillator are kinematically linked to each other and to the tuning arrangement of the tuned circuit of a local oscillator by means of a drive having a programmer. The latter is made such that the grid tank in the r.f. pulse oscillator and the localoscillator tuned circuit are swept in frequency in a predetermined manner. The radio spectrometer disclosed herein has an inductance coil to enclose the solid test specimen, which is electrically connected to the r.f. pulse oscillator through a matching means which matches the impedance of the inductance coil to the impedance of the anode tank in the r.f. pulse oscillator. The circuit parameters of the matching means and the circuit parameters of the inductance coil determine the above-mentioned manner for frequency sweeping.

Inverter commuting capacitor charge control circuit

Abstract: An inverter commuting capacitor is connected in shunt with a series combination of an inductor and a controlled rectifier to limit the transient time of the commuting capacitor during commutation. Energy stored in the commuting capacitor is used to commute the inverter''s power controlled rectifiers at predetermined times, and energy stored in the motor windings is transferred to the capacitor during the transient period of commutation to prepare the capacitor for the subsequent commutation. The inductor connected in shunt with the commuting capacitor increases the natural frequency of the LC circuit comprised of the commuting capacitor and the motor winding when the controlled rectifier connected in series with the inductor is gated conductive. In this manner, a reduction in the transient time of the capacitor is effected.

Voltage controlled oscillator having two phase-shifting feedback paths

Abstract: A voltage controlled oscillator having a pair of active elements operating differentially with respect to DC inputs and differentially as amplifiers with respect to RF feedback currents. Separate feedback paths having + OR - 45* phase shift are associated with each active element so that the sum of the phase shifts depends on the differential DC inputs to the active elements. A tuned circuit in the common feedback loop changes frequency to compensate for the phase shift, thus providing frequency control in response to the differential DC inputs.

Gyromagnetic resonance spectrometers

Abstract: In a gyromagnetic resonance spectrometer where the specimen is rotated about an axis, and where the polarization field is modulated at a low angular frequency OMEGA , the synchronous detection of the HF components, in phase with the excitation, of the output signals from the resonant detector circuit gives a signal at the frequency OMEGA , a d.c. component, and a component at the rotation speed which, by means of filters, are respectively directed to the recorder, to a circuit correcting the resonance frequency of, or the coupling in, the resonant detector circuit, and to a rotation speed measurement system.

Image-rejecting frequency selective apparatus

Abstract: A frequency-selective network includes a circuit parallel resonant at a desired frequency for effectively transmitting signals at the desired frequency and a circuit series resonant at an undesired frequency for effectively attenuating signals at the undesired frequency. A variable tuning capacitor is connected in both the parallel resonant circuit and the series resonant circuit for selectively determining the desired frequency and the undesired frequency. The resonant circuit components are chosen such that the undesired frequency always differs from the desired frequency by a substantially constant frequency. Further, the resonant circuit components are chosen such that the frequency selective network tracks as a conventional tank circuit at the desired frequency.

Frequency discriminator circuit including piezoelectric resonator providing coupled resonant circuit

Abstract: 1,271,049. Frequency discriminators. MOTOROLA Inc. 26 Nov., 1970 [15 Dec., 1969], No. 56281/70. Heading H3A. A frequency discriminator comprises a piezoelectric element 10 having two pairs of plates 12, 13; 16, 17 forming part of first and second tuned circuits tuned to the same centre frequency of an angle modulated carrier wave and coupled via the element 10 to produce signals of opposite phase at 16, 17, the second tuned circuit being also coupled e.g. via a capacitor 20 to the input circuit to produce a signal nearly in phase quadrature for combination with the above signals (Fig. 3, not shown), and the combined signals applied to a detector circuit 25, 28 to develop a demodulated output e.g. across a capacitor 30. A variable inductor 18 is provided for tuning out the self-capacitance of element 10 and for precise control of the resonant frequency. The capacitor 19 may be replaced by two capacitors (39, 40, Fig. 2) to the junction of which the input circuit is connected. Resistors 26, 29 provided for the signal return path may be connected in parallel or cross-wise across the diodes 25, 28.

Railroad track circuits

Abstract: A crossbond with a tuned circuit portion, matching the impedance of the rail circuit, is connected across the rails at each location between adjoining noninsulated track sections. A track circuit transmitter is so connected to each crossbond that its output divides equally between the tuned circuit and rail circuit paths. A hybrid coil arrangement couples a track circuit receiver to each crossbond, the coupling being so balanced between tuned and rail circuit paths that each receiver is responsive only to received rail current and not to output of collocated transmitter. All transmitters have a common output frequency for train detection, with each being approach controlled to supply cab signal current which also resets the track circuits after passage of a train.

Second Harmonic Tuning Effects on IMPATT Diode Oscillator Noise Characteristics

Abstract: A method of controlling the conventionally noisy FM characteristics of an IMPATT diode oscillator by properly terminating the second harmonic frequency is described. The result is also characterized by a self-locking mechanism with a resulting mechanical tuning range, via the second harmonic circuit, of up to 100 MHz at lower X-band. Effects of second harmonic tuning on IMPATT reflection - type amplifier operating bandwidth is also discussed.