Abstract: An electrosurgical unit including voltage control circuitry which operates to limit the voltage at the electrosurgical electrodes when the unit is not in coagulation mode. The electrosurgical unit includes sensing circuitry for providing a signal representative of the voltage at the electrosurgical electrodes, a mode setting switch or dial for changing between a cut mode setting and a coagulation mode setting, a circuit for producing a mode signal, and an RF power generator responsive to the mode setting switch for providing a cut mode waveform at the electrode outputs when the mode setting switch is in cut mode and a coagulation mode waveform when the mode setting switch is in the coagulation mode setting. A voltage limiting circuit is responsive to the signal from the sensing circuitry and limits the voltage at the outputs when the electrosurgical unit in cut mode. Suppression circuitry responsive to the mode signal prevents the voltage limiting circuitry from operating in coagulation mode.

Abstract: A state variable oscillator with leveler circuit and with a feedforward circuit for improving the oscillator's rejection of leveler-induced distortion. The feedforward circuit combines a signal representative of a leveler-distorted feedback signal with the main oscillator output to reduce the amount of harmonic distortion, below a certain order, appearing in the output.

Abstract: An AC signal source having constant frequency-amplitude product is also easily realizable in hybrid microcircuit form. A square wave oscillator output is rectified and clamped to a feedback control voltage. The resulting controlled amplitude square wave is low-pass filtered to produce a sinusoidal output signal which is typically amplified and applied to a variable-impedance load. The sinusoidal signal is also applied to a similar but simulated load of fixed impedance value and the current flowing through the simulated load is summed with a temperature-compensated reference current producing an error current which is then integrated to produce the feedback control voltage which controls the amplitude of the sinusoidal signal so as to maintain a constant frequency amplitude product.

Abstract: An oscillating circuit includes first and second stage amplifiers, a feedback circuit formed of a capacitor and a resistor and connected between the output terminal of the second stage amplifier and the input terminal of the first stage amplifier and a crystal resonator having a predetermined resonance frequency and being connected to the first stage amplifier, the total gain of the oscillating circuit being selected so that the oscillating circuit initiates its oscillation only when the crystal resonator is connected to the first stage amplifier.

Abstract: A clock source for timing and synchronizing the operation of digital data processing equipment and having automatic duty cycle correction is described. A source of signals provides clock signals at a predetermined frequency. A buffer circuit provides the true and complement clock signals to low pass filters that function to filter the true and complement clock signals to DC levels proportional to the duty cycle of the source signals. The DC voltages represent instantaneous deviation voltages from a known reference and are applied to a differential amplifier circuit for providing a feedback signal for adjusting the duty cycle of the clock output pulses that are available. One embodiment has the source of signals directly coupled to the buffer circuitry and utilizes the feedback signal to adjust the duty cycle of the signal source circuitry. A second embodiment has the source signals capacitively coupled to the self-correcting circuitry and the feedback signals adjust the duty cycle of the clock output signal.

Abstract: There is disclosed a driving and control circuit for a tuning fork resonator also adaptable to rotary motor control wherein an approximately sine wave signal from a motion sensor is applied to an instantaneous level detector which causes a control signal to be generated during that portion of the sine wave signal where the instantaneous level exceeds an adjustable reference level; the control signal causes the application of a current to the tuning fork drive which is in a direction to cause braking and reduction of motion amplitude. A distinctive feature of the instantaneous level detector is the fact that the sine wave signal is not rectified but is rather converted to a fluctuating direct current signal with a DC level accurately determined by an internal semiconductor voltage reference element.

Abstract: A switched capacitor oscillator is constructed by providing a damped resonator network with a comparator as a nonlinear feedback element by connecting the input of the comparator to the output of a first operational amplifier of the resonator network and connecting the output of the comparator to the input of the resonator network. The comparator thus becomes a saturable positive feedback element for the resonator network. Also disclosed is a startup network for the oscillator and an input network which derives an input from a reference voltage in order to eliminate supply voltage noise and provide precision control of amplitude.

Abstract: An amplitude control circuit of the invention includes a vector composition circuit (18) for composing a cosine-wave signal (e3) from a sine-wave signal (e1) and a control signal generation circuit (20) for providing a control signal (e4) from the sine- and cosine-wave signals (e1, e3) which the control signal (e4) has substantially no ripples. DC level of the control signal (e4) is varied proportional to the amplitude of the sine-wave signal (e1) regardless of the frequency of the sine-wave signal (e1). The amplitude of an amplification control circuit (12) is controlled by the control signal (e4) so that the amplitude of the oscillation output signal (e1) derived from the oscillation circuit (16) is constant.

Abstract: A harmonic frequency generator responsive to an input signal of frequency f hich changes slowly in both frequency and amplitude and characterized in that (1) the output signal (harmonic) amplitude remains proportional to the input signal amplitude and (2) the output frequency nf of the output signal consists soley of one integral (n>1) multiple of the input signal frequency.

Abstract: A transformer coupled, resonant feedback, tuned oscillator circuit in which the output current to a low power variable load is maintained constant by incorporating into the circuit an additional feedback circuit which provides a DC error voltage to the oscillator circuit enabling it to compensate for variations in core loss resistance, variations in load, and variations in other circuit parameters. The feedback circuit includes two separate electronic switches both of which are connected to a voltage averaging circuit and an error amplifier which compares the voltage of the averaging circuit against an adjustable reference voltage whereby the DC error voltage is generated and supplied to the center tap of the transformer feedback winding. Because oscillator transformer core resistance variations can be compensated for, the design of the oscillator transformer can be simplified and readily available, not specially designed, transformers can be utilized.

Abstract: The digital oscillator includes a memory which stores 12 bit words representing sampling points of the analog waveform to be produced and a D/A multiplying converter which receives the bit words and converts them to an analog values, the amplitudes of which are controlled by a reference voltage. The analog output is monitored and compared to a stable reference source in order to generate the controlling reference voltage thus maintaining a constant amplitude digital oscillator output.

Abstract: A mechanical oscillator of the type which includes a mechanical resonator and a resonator driver connected in a regenerative signal loop in which the driver receives the resonant frequency signal of the resonator and provides, in response thereto, a constant magnitude drive signal of equal frequency and supporting phase to the resonator to maintain a minimum amplitude for the resonant frequency signal, is provided with dual resonator drivers actively connected in parallel in the regenerative loop, each providing through a load sharing network a proportionate amount of the total drive signal magnitude in complement with that provided by the other, and each providing the full drive signal magnitude in the presence of a failure of the other.

Abstract: A piezo-electric crystal vibrating in several modes controls several frequencies generated by voltage controlled oscillators simultaneously. The output of each voltage controlled oscillator is fed to a summing amplifier which drives the crystal. The output of the crystal is fed to individual phase detectors; each phase detector is also supplied with the output of a voltage controlled oscillator and generates a voltage proportional to the phase difference between the voltage controlled oscillator and the crystal output for correcting the output frequency of each oscillator.

Abstract: A metal detector is disclosed. The detector comprises oscillator circuit means comprising a first transistor, a second transistor, adjustable resistor means coupled to the emitter of the first transistor, and inductor means arranged to control the conductive state of the second transistor. The oscillator circuit means is arranged to generate an electromagnetic field and the second transistor is arranged to provide an output signal in response to and corresponding to any disturbance of the electromagnetic field caused by the presence of a metal article in the electromagnetic field.

Abstract: A field effect transistor is used in the bias circuit of an oscillation transistor of a piezo-electric oscillator, and a diode is connected between the gate electrode of the field effect transistor and the base electrode of the oscillation transistor with a polarity to pass current from the gate electrode to the base electrode. The source electrode of the field effect transistor is connected to the base electrode of the oscillation transistor and the drain electrode of the field effect transistor is connected to a power source.

Abstract: Method and system for the constant amplitude control of an electromechanical oscillator utilizing a phase locked oscillator to generate a secondary a-c setpoint which is compared to the oscillator output to provide a difference signal which is passed as a fast-acting negative feedback signal to stabilize the amplitude.

Abstract: A variable sinusoidal oscillator comprised of an operational amplifier connected in a unity-gain configuration, with a positive-feedback capacitor connected between the output and the noninverting input of the amplifier, and a resistor between the noninverting input and circuit ground, either in the form of an external resistor or simply in the form of the input resistance of the amplifier. A linear attenuator may be connected in the negative-feedback circuit, and a nonlinear attenuator may be connected in tandem with the capacitor, or vice versa.

Abstract: Apparatus is described for heating tissue and which is particularly useful for treating tumors in humans and animals. An electric field is produced across two electrodes or one electrode and ground, and is passed through both the tumor and the surrounding tissue. The polarity of the electric field is varied at radio frequency. The power of the electric field is efficiently coupled into the tissue being heated. Direct current inverse feedback circuitry enables close control of tissue temperatures.

Abstract: An electrosurgical unit which provides a voltage output to a load. An oscator in the unit produces the output of a given frequency. A switching circuit coupled to the oscillator provides an unmodulated RF carrier from the oscillator for use in cutting procedures and a pulse modulated RF voltage from the oscillator for use in coagulation procedures. A feedback circuit is coupled from the output to the input of the oscillator to maintain the output voltage level from the unit at a substantially constant value independent of the load.

Abstract: A circuit arrangement for combining high frequency power components with the same frequency which come from amplifiers or generators and are fed to a 90.degree. parallel circuit bridge having two substantially decoupled inputs with the input resistance values of these inputs depending on the output load. The operating voltage supplies of the amplifiers or generators are separately controllable and are controlled so that the output powers of these amplifiers or generators, respectively, remain substantially constant even with mismatching.

Abstract: A replica bridge sensing circuit, comprising an amplifier having inverting and non-inverting inputs, which are symmetrically connected to a generator through a bridge circuit that has replica elements in corresponding branches. Replica elements are defined as circuit components which because of identity of the manufacturing process, are nearly identical both physically and electrically. A nearly balanced replica bridge, so connected, between the input and the output of such an amplifier forms a Replica Bridge Oscillator (RBO) circuit. Non-linear elements are included in the oscillator circuit to stabilize the amplifier output amplitude and the phase angles between the inputs and output. Replica Bridge Oscillator operation is substantially immune to changes in environmental conditions and to changes in the power supply voltages.

Abstract: A device for generating a signal varying in frequency from 1 to 18 GHz at a onstant output power. The device utilizes a tracking automatic level loop and reacquire loop which provide automatic alignment of a YIG multiplier filter with a YIG voltage-controlled oscillator (VCO). Adjustability of output power level control is provided in the tracking automatic level loop with a provision for LED display when the device loses lock.

Abstract: An apparatus for treating tumors, both benign and malignant, such as carcinoma, sarcoma, cysts and avascular lesions, in animals, such as humans, by radio frequency heating at the location of the tumor in the host having an adjustable, stable output level with fail-safe feature.

Abstract: An emergency lighting system includes a two-level switching transistor inverter circuit for starting and operating a fluorescent lamp from a battery upon failure of line voltage. One of the switching transistors of the two transistor inverter is arranged for connection first to a tap, then to one of the feed-in terminals of an output transformer coupled with the lamp. A timing controller effects this switching thereby automatically to provide, first, a high power level for starting the lamp, and then, a second lower power level for operating the lamp after starting.

Abstract: The invention relates to an oscillator having a positive feedback amplifier circuit the gain of which is controlled in direct opposite relationship to the amplitude of the oscillatory voltage produced by the oscillator and is especially useful for crystal controlled oscillators. The controlled feedback amplifier comprises a differential amplifier one branch of which feeds a rectifier producing the control voltage and the other branch of which acts as the controlled feedback amplifier.

Abstract: In a signal compressor wherein an amplified and smoothed control signal is employed to control a variable gain or variable impedance device, a switch is provided to connect a positive feedback loop across the control signal amplifier, thereby to place the compressor in an oscillator mode for providing an alignment or calibration signal of stable amplitude.

Abstract: A linear eddy current loss (ECL) proximity distance measuring gauge comprising an ECL oscillator and a linearizing DC feedback circuit is disclosed. As the distance between a magnetic target and the ECL coil increases and changes the impedance of the ECL tuned circuit, the linearizing DC feedback circuit shunts current away from the tuned circuit and controls the rate at which oscillation amplitude varies with a change in target distance. The amplitude control created by the linearizing DC feedback circuit results in oscillation amplitude being linearly related to the distance between the target and the ECL coil. A peak detector circuit detects oscillation amplitude and applies a directly related DC voltage to a buffering emitter follower output circuit. Thus, output voltage is linearly related to target distance.

Abstract: A single bipolar transistor crystal oscillator with the bias on the base of the transistor fixed and a second transistor coupled in parallel with the transistor of the oscillator for providing an alternate current path when the second transistor is conducting to reduce the current gain of the oscillator transistor, and a diode connected to the base of the second transistor for rectifying the AC output signals of the oscillator and biasing the second transistor into conduction when the output of the oscillator exceeds a predetermined value.

Abstract: A precision crystal-controlled oscillator circuit with provision for separate sinusoidal and square-wave output signals which can be realized as a silicon integrated circuit without the use of external capacitors or resistors is disclosed. Two feedback loops are utilized in addition to the oscillating loop. The first feedback loop maintains the gain of the oscillation loop at substantially unity when the amplitude of the oscillation is at a predetermined level, thereby ensuring both spectral purity and amplitude stability of the sinusoidal output signal. The second feedback loop maintains the duty cycle of the square-wave output signal substantially equal to 50 percent by controlling the circuit operation to equally space the signal zero crossings at the input of the square-wave output stage.

Abstract: The disclosure relates to an amplitude control for controlling the peak amplitude of a transistor oscillator output alternating voltage and to an improved regulating system which includes an oscillator associated with the amplitude control for converting a DC voltage to an alternating output voltage having a regulated or controlled peak amplitude. The amplitude control comprises a control voltage generating means for providing a control voltage and clipping means coupled between the base of the oscillator transistor and the control voltage generator for varying the bias of the oscillator transistor responsive to the control voltage to thereby control the peak amplitude of the oscillator alternating output voltage.

Abstract: A regulated power supply for a laser or gas discharge lamp employs a variable duty cycle oscillator to control the output voltage level. Output current to the laser or lamp load is maintained at a constant value by a feedback loop that controls the oscillator duty cycle. The output current is sensed by a novel circuit which employs a voltage regulator in series with the current return path. A change in output current causes a concomitant change in voltage across a resistor divider that shunts the voltage regulator. The voltage from this divider is a feedback signal that is supplied to a duty cycle modulator which controls the oscillator duty cycle.Another feedback signal is derived in delayed response to voltage output in excess of a certain high value. This feedback signal, which occurs, e.g.

Abstract: A device for maintaining constant the amplitude of the oscillation of an electro-magnetically driven balance wheel of a timepiece, whereby a first voltage is generated of an amplitude proportional to the amplitude of oscillation of the wheel. This is compared with a reference voltage and a signal is derived corresponding in amplitude and sign with the difference. This signal is then used to control the application of driving pulses to the balance wheel. The said driving pulses are preferably much shorter than one half-period of the balance wheel.

Abstract: A noise generator system is described in which the amplitude of a noise source is stabilized by a feedback loop to an automatic gain control circuit, and wherein the output of the system is time controlled by means of a differential pair amplifier.

Abstract: A low frequency oscillator including a pair of novel integrator circuits and a resistive inverter circuit electrically connected together in cascade and having ganged gain control following each integrator. The novel integrator circuit includes an operational amplifier having first and second input terminals, said first input terminal being adapted for connection to a voltage source and including a resistor between said source and terminal. A first negative feedback loop including a capacitor is electrically connected between the output of the amplifier and the first terminal. A second positive frequency independent feedback loop is electrically connected between the output of the amplifier and the second input terminal. The second feedback loop preferably includes a voltage divider having a temperature variable resistor and a pair of independent heaters for varying the resistance of said resistor.

Abstract: A distortion measurement system for measuring distortion as low as 0.002% includes an ultra low distortion oscillator having a relatively fast response which is achieved by switching the time constant of the control loops of the oscillator during settling. The analyzer section included in the distortion system has a unique notch filter which provides low distortion. This is achieved by adding together two 90.degree. all pass phase shifters. In addition, automatic tuning is provided by two feedback control loops; one is responsive to out-of-phase signals which controls the RC filter circuits of the phase shifters and the other responds to the in-phase signals which controls the output summing junction of the notch filter. Finally, a feedforward type of simultaneous tuning is accomplished by ganging the oscillator frequency adjustment with the analyzer.