Abstract: A voltage controlled oscillator circuit with a high power supply rejection ratio incorporates a clamping transistor with respect to each output terminal which limits the signal swing of the output terminal. The limited voltage swing allows relatively large movements in the power supply and ground voltages without causing significant changes in the frequency of the output signals. Such an oscillator circuit may be incorporated into an integrated circuit characterized by noisy power supply and ground conductors. Additionally, multiple delayed versions of the output frequency may be created using a level shifter circuit and a buffer circuit. The oscillator circuit is relatively quick to react to changes in the controlling voltage, adjusting the oscillation frequency in a relatively short time interval.

Abstract: A voltage controlled oscillator that completely eliminates the need for any externally mounted coil and capacitor includes a first loop and a second loop. The first loop provides band-limiting of an output signal of an amplifier through a bandpass filter to provide oscillation at a frequency of a resonant point of the bandpass filter, and the second loop controls the oscillation amplitude, so that a lowpass filter output with a 90.degree. phase is extracted from the first loop, while a bandpass filter output with a 0.degree. phase is extracted from the second loop. The voltage controlled oscillator may be used in an automatic fine tuning circuit for television.

Abstract: A circuit for causing an element to produce a substantially linear response to an input signal comprising an element for providing a response, a transistor oscillator circuit for providing an electrical output signal of variable amplitude to excite the element in response to the input signal, the transistor oscillator circuit normally causing the electrical output signal to vary non-linearly with respect to the input signal, and microprocessor means for correcting the non-linear relationship between the input signal and the electrical output signal to thereby cause the electrical output signal to vary substantially linearly with respect to the input signal when the input signal is applied to the microprocessor means.

Abstract: An apparatus for providing excitation of a vapor discharge lamp includes a control circuit for controlling an oscillator circuit during an ignition mode of the vapor discharge lamp to establish and maintain a substantially constant DC voltage at an output of an oscillator transistor and to establish a current flow through the oscillator transistor at a first current level sufficient to ignite the vapor discharge lamp, and for controlling the oscillator after ignition of the vapor discharge lamp to maintain the substantially constant DC voltage at the output of the oscillator transistor while reducing the current flow through the oscillator transistor from the first current level to a second current level, and in preferred embodiments, includes circuitry to suppress unwanted blocking oscillations and optimize the dynamic range of the control circuitry.

Abstract: An oscillator comprising an amplifier device, a capacitive divider bridge whose terminals are connected between a control electrode of the device and a reference voltage, the intermediate junction point of this bridge being connected to a principal electrode of the device, and also comprising, in parallel between the control electrode and the reference voltage, a tuning circuit having parallel branches: a first branch with an inductance in series with a variable capacitance, and, a second branch equivalent to a variable capacitance. The tuning circuit has a third branch constituted by a capacitance in parallel with the first branch, while a series inductance whose value is smaller than that of the tuning inductance is arranged between the junction point connecting the two latter branches and the junction point connecting the control electrode of the device to the second branch and to the divider bridge.

Abstract: The disclosure is directed to a Lever oscillator for use in high resistance resonator applications, especially for use with quartz resonator sensors. The oscillator is designed to operate over a wide dynamic range of resonator resistance due to damping of the resonator in mediums such as liquids. An oscillator design is presented that allows both frequency and loss (R.sub.m) of the resonator to be determined over a wide dynamic range of resonator loss. The Lever oscillator uses negative feedback in a differential amplifier configuration to actively and variably divide (or leverage) the resonator impedance such that the oscillator can maintain the phase and gain of the loop over a wide range of resonator resistance.

Abstract: A self-regulating oscillator circuit and method are disclosed. Specifically, a method is described whereby an oscillator having an active device is operated. The oscillator is operated by providing a current through the active device, as well as through a reference device connected in series with the active device of the oscillator. A reference voltage across the reference device is sampled, and a regulated voltage is generated by adding a predetermined voltage to the sampled reference voltage. Finally, the regulated voltage is applied to the active device of the oscillator. In one circuit embodiment, the oscillator as described includes a gallium arsenide FET structure which cooperates with a resonant structure to produce a reflection-type oscillator. In addition, a regulator circuit is described including an isolating op amp which samples the reference voltage from the active device of the oscillator and provides its output to a voltage source device.

Abstract: An apparatus suitable for use as a local oscillator is disclosed, which includes (a) a tank circuit operatively associated with an FET to generate a fundamental frequency oscillating signal at an output of the FET and (b) a bi-directional clamp circuit coupled at a junction between the tank circuit and a gate of the FET to limit a swing of the gate of the FET, preventing the gate of the FET from entering either a saturation region or a cut-off region. The bi-directional clamp includes a first diode coupled to allow positive current to flow to the junction and a second diode coupled to allow positive current to flow away from the junction. The oscillator produces an output with a reduced level of radiation-prone harmonics.

Abstract: A variable reluctance transducer system incorporating digital control of parallel resonant circuits including two inductive sensors L1 and L2 on each side of a flat diaphram. The dual variable reluctance elements provide dual frequency signals for digital calculation to obtain a quotient of the frequencies, thereby substantially eliminating the resonant frequencies as a variable in the accuracy of the device. Manipulation of the produced quotient by a micro-controller 10 employing digital calibration tables stored in a programmable read only memory 14 allows calibration reponsive to a temperature sensor 16, thereby substantially eliminating temperature induced errors in the system, further increasing accuracy.

Abstract: A ceramic resonator, a variable reactance circuit, and a limiter circuit are connected to the output of an amplifier having an output that is fed back to the positive phase-sequence input, and the frequency of oscillation is controlled by varying an equivalent capacitance of the reactance circuit with a control voltage applied to the reactance circuit. The limiter circuit ensures a variable frequency range on the high frequency side, and the symmetry of the capture range when this system is applied to a PLL can be improved.

Abstract: A self-excited solid-state oscillator for supplying a high-power RF inductive load. The oscillator includes at least one MOSFET transistor connected in a self-excited oscillator configuration, an output tuned circuit including an inductive load and a tank circuit connected to the load, the tank circuit having a resonant frequency determined at least in part by the inductance of the load, an RF feedback transformer coupling the tank circuit to the gate of the MOSFET for providing a switching signal to the MOSFET for causing the MOSFET to alternate between the on state and the off state at a frequency equal to the resonant frequency of the tank circuit, and a bias circuit for superimposing a forward bias voltage on the switching signal.

Abstract: The present invention comprises an oscillator including a transformer having a first winding with a power feed to the center tap. A first pair of transistors in a push-pull configuration are connected at the emitter electrodes across the second winding of the transformer. A center tap on the second winding is provided for a negative polarity power return. The base electrodes of the transistors are commonly connected to receive a control current and the collector electrodes of the transistors are connected across a first winding of the transformer. A capacitive element is connected across the first winding to create a tuned circuit within an oscillator.

Abstract: The output of the first CMOS inverter, connected as an oscillator, is applied to the inputs of second and third CMOS inverters that have logic threshold voltages higher and lower than the logic threshold voltage of the first inverter. The outputs of the second and third CMOS inverters are connected to an output circuit via a logic output circuit. The output of the logic output circuit is shorted by an output control circuit, under the control of the outputs of the second and third CMOS inverters, when the output of the oscillator is between the logic threshold voltages of the second and third inverters.

Abstract: An actively biased oscillator (200) includes a set of current sensing components (214,216) for sensing the amount of current flowing into the first terminal of the amplifier; and a differential amplifier (212) responsive to the current sensing components for automatically adjusting the amount of current flowing into the second terminal of the amplifier.

Abstract: A resonant circuit comprises first and second amplifiers. An input of the second amplifier is coupled to an output of the first amplifier, and an output of the second amplifier is cross-coupled to an input of the first amplifier. The first amplifier has a first gain and a 90 degree phase shift between its input and its output at a resonant frequency of the resonant circuit. The second amplifier has a second gain and a 90 degree phase shift between its input and its output at the resonant frequency of the resonant circuit. The second gain is different from the first gain. The resonant circuit can have a first port and second ports coupled to an input and an output respectively of one of the first and second amplifiers. Because the gains of the first and second amplifiers differ, the gain from the first port to the second port of the resonant circuit will differ from the gain from the second port to the first port.

Abstract: On an integrated circuit, a power limiting circuit is added to a crystal oscillator for limiting power dissipation in the crystal to a prescribed safe power dissipation range. The power limiting circuit includes a Pierce design crystal-controlled oscillator coupled to a self-stabilizing circuit. The self-stabilizing circuit detects the oscillation amplitudes of the crystal controlled oscillator. The self-stabilizing circuit prevents the oscillations from exceeding a predetermined maximum power dissipation level for the crystal. The self-stabilizing circuit includes a means for detecting oscillation amplitudes and means for limiting the gain of the crystal controlled oscillator circuit. Therefore, independent of manufacturing tolerances from integrated circuit to integrated circuit, the self-stabilizing circuit assures that the maximum power dissipation level of the crystal is not exceeded.

Abstract: An oscillator includes at least one oscillator transistor having collector, emitter and base leads, a controllable current source connected between the emitter lead of the at least one oscillator transistor and a supply potential, and a frequency-determining element, such as an oscillating circuit, connected at least to the base or collector lead of the at least one oscillator transistor. A method for controlling the amplitude of the output signal of the oscillator includes supplying a direct voltage variation at the emitter lead of the at least one oscillator transistor resulting from a change in amplitude of a signal applied to the base lead of the at least one oscillator transistor as a controlled variable for the current of the controllable current source. The oscillator may also include a control amplifier. The emitter lead of the at least one oscillator transistor is connected to one input of the control amplifier and the other input of the control amplifier is connected to a reference potential.

Abstract: A voltage controlled oscillator circuit including an oscillator circuit having first and second terminals to which an external inductance is connected. A frequency control voltage (V.sub.F) is applied through a bias circuit to the second terminal for varying the center frequency. The oscillator circuit may have an AGC circuit or a modulation circuit connected to it. An output amplifier is connected with the first terminal and has an adjustable output impedance for matching the input impedance of a load circuit.

Abstract: A crystal oscillator uses automatic gain control to minimize the operating current through its inverting amplifier. The power supply potential to switching transistors of the amplifier is reduced by the automatic gain control to a level substantially equal to the sum of the switching thresholds thereof which minimizes simultaneous conduction through the switching transistors and associated operating current. The low level output signal of the amplifier becomes sinusoidal about a DC bias point operating at the resonant frequency of the crystal which eliminates undesirable harmonicas interfering with the crystal's natural vibration. The sinusoidal output signal may be buffered and level-shifted to a useable state.

Abstract: Controllable oscillator circuit comprising a regenerative loop which incorporates a cascade circuit of first and second sections each having a controllable gain and a phase shift which is 90.degree. at the oscillation frequency, and an amplitude detection arrangement which is coupled between an output and a control input of at least one of the two sections.

Abstract: An integratable amplitude-regulated oscillator circuit includes a resonator element, a control element having a control input, an inverter having an output and an input coupled to one another through the resonator element and having a quadrature-axis current component being variable by the control element, an amplitude regulating circuit having an input connected to the input of the inverter and an output connected to the control input of the control element, and an output stage having an input connected to the input of the inverter. The amplitude regulating circuit includes a differential amplifier having an inverting input and a non-inverting input, a first peak value rectifier connected upstream of the inverting input, and a second peak value rectifier connected upstream of the non-inverting input.

Abstract: An improved control circuit for maintaining constant amplitude of the sinusoidal output signal of an oscillator circuit by synchronously demodulating the signal using a push-pull transistor pair operating in saturation to generate a control signal for comparison with a reference voltage in a direct coupled negative feedback loop to the oscillator. The configuration of the feedback loop provides effectively instantaneous control response to eliminate low frequency modulation propagated internally in the oscillator due to noise generation in circuit components.

Abstract: A heterodyne stage of a receiver which includes a conventional mixer circuit and local oscillator circuit further includes a differential amplifier circuit which measures the amplitude of the injection signal generated by the local oscillator circuit and controls it precisely to a desired reference level by adjusting the current bias supply to the local oscillator circuit within a banded range to ensure start-up of the local oscillator upon energization and to protect against loss of injection signal under all operating conditions. The differential amplifier circuit provides for a precise amplitude reference setting and sufficient closed-loop gain for controlling the amplitude of the injection signal with a minimum of error between the measured and reference values.

Abstract: An amplitude stabilized oscillator which includes an amplifier having an input, an output, and a control terminal. The amplifier has a frequency determining feedback circuit connected between its output and input terminals, and has a control voltage produced by two opposite current sources applied to its control terminal. An amplitude detector detects the oscillator output amplitude during at most one half of each oscillation period and produces an amplitude stabilizing signal which is applied to one of the two current sources.

Abstract: A monolithically integrable amplitude-controllable oscillator amplifier circuit includes a differential amplifier having capacitors and transistors, some of which form a cascode circuit and some of which are connected to various potentials, as well as a frequency-determining circuit element connected to the oscillator amplifier, amplifier outputs providing output signals and resistors connected to the transistors. A first current source is formed of a series circuit of a second current source, a constant current source and a circuit node. A control circuit for the oscillator amplifier controls amplitude as a function of the output signal and has a control element with a first voltage-controlled current source. A controller provides an actual-value detection by rectification, an input signal mean-value suppression with a differential amplifier, and a set-point setting. The controller feeds a control variable to the first voltage-controlled current source.

Abstract: A monolithically integrable amplitude-controllable oscillator amplifier circuit includes a differential amplifier. The bases of first, second and third transistors are acted upon by a direct voltage. A first capacitor connects the base of the second transistor to a reference potential. A frequency-determining circuit element is connected to the base of a first transistor, the collector of the second transistor and the oscillator amplifier. The collector of the first transistor is connected directly to the emitter of the third transistor forming a cascode circuit. The collector of the third transistor is connected to a first potential. The collector of the second transistor forms an amplifier output. A first resistor is connected between the collector of the second transistor and a second potential.

Abstract: A crystal oscillator circuit having an accurate duty cycle at very high frequency is provided. An oscillator stage is provided which receives regenerative feedback from an inverter to sustain oscillation. The oscillator stage provides an AC output signal having a first average DC value determined by the regenerative feedback. The AC signal is coupled to a clipping circuit which symmetrically clips the AC signal about a predetermined second average DC level at first and second predetermined voltage levels. The inverter receives the clipped signal and provides an oscillating clock signal with an accurate duty cycle in response thereto.

Abstract: An oscillator circuit which includes a differential amplifier in combination with a negative feedback network and a positive feedback network connected to the amplifier. One of these networks determines the frequency of the generated oscillation. In order to obtain an oscillation of constant amplitude, the negative feedback network comprises a current limiter active as a controllable one-port network which is connected between the negative feedback input of the differential amplifier and a fixed potential.

Abstract: The present invention provides an alternative circuit for microwave oscillators. The invention consists of an amplifier, signal divider, filter(s), and optional limiter. The feedback path is external to the amplifier, allowing direct access and control of the loop phase and loop gain. Control of the loop gain can be used for applications such as amplitude modulation of the oscillator's output or control of the oscillator's output power. Control of the loop phase can be used to frequency modulate the oscillator or to create a voltage-controlled oscillator. Dynamic control of the loop gain with a limiter enables one to maintain linear operation throughout the oscillator. Linear operation is often desirable to eliminate the 1/f noise contributions at the frequency of operation and to enable the use of small signal s-parameters in the design and analysis.

Abstract: A voltage controlled oscillator circuit of a type having a tank circuit for generating oscillations which includes a means for establishing a fixed bias voltage with respect to ground at a bias end of said tank circuit, means for drawing current from an a.c. end of said tank so as to control the tank gain, and an AGC capacitor. A constant current source is coupled to the AGC capacitor for supplying it with a constant charging current. Means are provided for discharging the AGC capacitor at a voltage level determined by a ratio of resistors and a transistor emitter-base ratio.

Abstract: A switchable microwave oscillator is disclosed that includes a quenching circuit for switching, attenuating, modulating, or otherwise controlling the output amplitude of frequency-stabilized, transistor-based, microwave-frequency oscillators. The quenching circuit includes a diode that is coupled to the transistor at the same port that reactive feedback is present, and includes diode biasing means for selectively applying a bias voltage to the diode. The quenching circuit selectively diverts some of the current flowing through the transistor of the oscillator to control the output thereof.

Abstract: An RF modulator is characterized by a gain adjusting circuit for gain adjustment incorporated with an RF amplifier for amplifying a carrier wave provided from a carrier oscillator and applying the same to a video signal modulator and to an audio signal mixer so that the gain of the RF amplifier is adjustable so as to adjust a difference in level of the carrier wave provided differently depending upon a resonance element being connected to the carrier oscillator.

Abstract: The output of an alkali vapor lamp for use in an optical pumping system is stabilized by use of a feedback circuit which regulates current flow from a power supply to an electronic power oscillator used to excite the alkali vapor lamp. Starting of the alkali vapor lamp is facilitated by increasing supply current to the oscillator until the alkali vapor lamp is lit.

Abstract: The oscillator circuit comprises an amplifier having a pair of inputs, a positive feedback path producing a positive feedback ratio to one of the inputs, and a negative feedback path including a series resonant circuit producing a negative feedback ratio to the other of the inputs. The positive and negative feedback paths are independent such that the current in each of the paths can be adjusted independently. In this manner, a high Q multiplier effect is achieved. Also, the circuit has an output path which is separate from the input path so that a high output signal level can be achieved while maintaining a low current through the series resonant circuit.

Abstract: An oscillator circuit in a semiconductor substrate of an integrated circuit, includes a gain correction circuit portion connected between the output terminal of the feedback circuit portion and the input end of the amplifier circuit portion composed of MOS transistors. The gain correction circuit portion suppresses the excessive amplitude of the output signal of the feedback circuit portion, so that the characteristic of the waveform of the output signal of the oscillator device is improved.

Abstract: A method and means for reducing noise in a GaAs FET oscillator circuit is described. The circuit of the present invention achieves low noise oscillator operation by driving the gate input of the GaAs FET oscillator circuit with a source of voltage which exhibits a low impedance at baseband frequencies and driving the drain input with a source of current which exhibits a high impedance at said frequencies. The present invention further operates to control the D.C. voltage present on the drain terminal of the GaAs FET device regardless of the drain current, while simultaneously maintaining a constant D.C. drain current at some predetermined value which corresponds to optimum low-noise operation.

Abstract: An electric oscillator comprising a resonant circuit wherein, after switching on the oscillator, it takes a short time to build up to a desired amplitude of oscillation. To reduce the oscillation build-up time of the oscillator, a current supply source is provided along with control elements and switching means for changing the operating mode of the oscillator from a standby mode to an oscillatory mode, and vice versa. During the standby mode a charging current is supplied to the coil of the resonant circuit so that when switching over into the oscillatory mode, the charging current to the coil is interrupted. As a result, the control elements are immediately supplied with oscillations of the desired oscillatory amplitude.

Abstract: Disclosed is a proximity switch which includes an oscillation circuit whose oscillation output is variable depending on the inductance of a coil so that an object in proximity may be detected from the decline in the oscillation output. Further, the oscillation gain of this oscillation circuit is variable according to an input from an external source. Thus, for the purpose of increasing the recovery speed of the oscillation which has dropped as a result of detecting an approaching object, comparison circuits are provided so that upon reduction in the oscillation output of the oscillation circuit a certain signal is applied to the oscillation circuit to increase its oscillation gain. As a result, even when an object in proximity is detected and the oscillation level is maintained at a certain low level so that the oscillation may be resumed quickly when the object has moved away from the proximity switch.

Abstract: An eddy current crack detection system has an inductive probe coil forming part of an oscillatory circuit. The coil voltage is fed to a measuring device a change in amplitude of the coil voltage being used as an indication of a crack. In order to compensate for lift-off in the amplitude of the coil voltage, a control signal is generated related to the magnitude of lift-off, and controls the value of a variable damping resistor in the oscillatory circuit.

Abstract: A voltage controlled oscillator is disclosed wherein a peak detector is used to control the gain of the active device within the oscillator in response to a control signal taken from the resonant circuit. The control signal is a RF potential developed across a voltage divider within the resonant circuit. By controlling the gain of the active device from an RF voltage provided by a voltage divider, the RF output level of the oscillator "tracks" the DC bias level of the steering line. Therefore, varactor diodes rectification is prevented while contemporaniously allowing maximized output power.

Abstract: Oscillator circuit has a first and second transistors whose emitters are intercoupled and jointly connected to a variable current source, the first transistor being connected in a grounded-base connection. The oscillator current also has a parallel resonant circuit coupled to the collector of the first transistor, this collector being coupled for regenerative feedback of the circuit voltage to the base of the second transistor. Stabilization of the circuit voltage is accomplished by coupling the last-mentioned collector also to a control input of a variable current source, so that the collector current applied to the circuit is modulated in anti-phase with the circuit voltage, that is to say it instantaneously decreases at an increase of the circuit voltage and vice versa.

Abstract: A low noise oscillator is described suitable for use in an AM stereo radio receiver. The oscillator circuit includes means for controlling its amplitude at a constant low level. The oscillator is amenable to electronic tuning and IC construction.

Abstract: A circuit configuration is provided for reducing noise sidebands in the output of an oscillator due to modulation of the oscillation signal by characteristic noise produced by the amplifying element. A gallium arsenide field-effect transistor that produces characteristic noise is operated as a linear amplifier. Positive feedback to the input of the amplifier is provided by a resonator. The amplitude of the oscillation signal is limited by a distinct limiting circuit in the feedback loop, the input to which is isolated from the amplifier by a high pass filter, thereby divorcing the non-linear limiting function of the oscillator from the amplifying function where noise is generated.

Abstract: An electronic drive circuit for driving an actuator mass for a sensor apparatus is disclosed. The driver requires no compensation or bridge elements. The actuator mass is directly driven by a square wave drive signal such that all of the capacitors loading errors associated with the driven actuator means are concentrated in time to that time interval in which the drive signal traverses between its two stable states. A sensor circuit connected to monitor the sensor output response signal is blanked out during the drive signal transition time interval, which effectively eliminates the transition drive noise energy from the sensed output signal.

Abstract: A high-frequency oscillator including an oscillation circuit (1) having a quartz crystal (X) and an amplifying element (Q.sub.2), a power amplifying circuit (3) for amplifying the output of the oscillation circuit, and a control system (Q.sub.7, 6) for varying a bias voltage of the amplifying element to thereby control the output power of the power amplification circuit. The control system comprises an FET (Q.sub.7) connected at the drain thereof to the amplifying element, and a control circuit (6) for applying a control signal to the gate of the FET.

Abstract: There is disclosed a drive regulation and control circuit for a tuning fork resonator also adaptable to other electrical devices wherein an approximately sine wave signal from a motion sensor is applied to an instantaneous level detector which causes a variable width pulse signal to be on during that portion of the sine wave signal where the instantaneous level exceeds an adjustable reference level; a control signal is generated with a magnitude varying as a moving average of the width of the variable width pulses; the control signal causes the reduction of current to the tuning fork drive to cause reduction of motion amplitude. An optional feature provides rapid response by activating a motion braking signal having a duration approximately equal to the variable width pulse "on" period.

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 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: An amplitude modulation circuit wherein a resonant circuit for the determination of the carrier-wave frequency is connected to the collector of one transistor forming a differential pair of transistors forming a differential amplifier having its ground terminal connected to a constant current source while an output terminal of the resonant circuit is coupled to the base of the other transistor forming the differential pair so as to apply a positive feedback to the other transistor thereby forming a carrier wave oscillating circuit, and a constant current adjusting means for dividing by switching the current to be supplied to one of the transistors of the differential pair is connected between the differential amplifier and the constant current source, such that, by supplying a modulating signal to the constant current adjusting means to vary the oscillating level of the carrier wave, a modulated signal at a constant modulation degree can be obtained from the base of the other of the transistors forming the di

Abstract: Transistor oscillator circuit having a resonant-circuit or crystal-controlled oscillator realized by a feedback differential amplifier and provided for driving a mixture stage including a pair of transistors forming the oscillator and having a current-carrying output connected to a respective input of the mixture stage, the latter being of symmetrical construction, a low pass filter also connected to the current carrying output of the oscillator, a common control amplifier having an output, and respective inputs connected to the oscillator via the low pass filter, and means for feeding back the output of the control amplifier to the oscillator in the sense of negative feedback.