Abstract: Voltage controlled oscillator provided with a resonant network, an amplifier and a reactive network, all incorporated in an oscillator loop, the reactive network having one or more reactive components whose values depend on a control signal fed to a control input, so that the oscillator frequency can be regulated with said control signal. A control loop is provided between the resonant network and the reactive network, with which control loop the difference is determined between a measure of the imaginary part of the impedance or admittance of the resonant network and the control signal acting as reference quantity. The imaginary part of the impedance or admittance of the reactive network is regulated with said difference. The control loop contains a derivation circuit for deriving said measure and a differential amplifier, to one input of which the output signal of the derivation circuit is fed and to the other input of which the control signal is fed.

Abstract: Inductive proximity sensor for detecting an object having electrical conductivity comprising a sensor housing, a measuring coil and reference coil placed on either side of a plane of symmetry through the sensor housing. Each coil is partly surrounded by a piece of magnetic material which leaves the measuring coil or reference coil respectively free at the front which faces the direction of the object to be detected or a reference member. An electronic circuit is provided for supplying both coils with an AC signal and for measuring the change in a specific property of the measuring coil with respect to that of the reference coil when object approaches and determining therefrom the distance or the presence of the object. The pieces of magnetic material around the two coils are formed essentially from the same homogeneous material forming a block. Means are provided in the sensor housing for screening magnetic fields produced by both coils in order to suppress thereby mutual crosstalk.

Abstract: Voltage-controlled oscillator provided with a frequency-determining element and an oscillator loop having a phase-rotating network, in which the value of one or more elements depends on a control signal which is fed to a control input and with which the phase rotation and thereby the oscillator frequency can be changed. The oscillator is further provided with a phase control loop, at least comprising a phase-rotating network to the input of which the oscillator signal is fed, a phase detector to the two inputs of which the input signal and the output signal of said phase-rotating network are fed, and an amplifier which amplifies the output signal of the phase detector and feeds it to the control input of the phase-rotating network of the oscillator loop. The phase detector has an accurately known and temperature-independent input-output relation. The phase-rotating network of the phase control loop may be formed by the phase-rotating network of the oscillator loop (FIG. 2).

Abstract: Envelope detector comprising a differential amplifier (A), a full-wave rectifier circuit and a smoothing filter (AF), which differential amplifier (A) converts an input voltage into a pair of current signals in phase opposition and which full-wave rectifier circuit comprises a pair of half-wave rectifiers (HWR1, HWR2) for half-wave rectifying the said pair of current signals, coupled to a first combining stage (S) for combining the output signals of the two half-wave rectifiers (HWR1, HWR2) with like polarity, which first combining stage (S) supplies a full-wave rectified signal. In order to reduce d.c. offsets, the detector comprises a frequency-dependent negative feedback loop which comprises a second combining stage (D) coupled to the outputs (R.sub.o1, R.sub.o2) of the pair of half-wave rectifiers (HWR1, HWR2) for combining the output signals of the pair of half-wave rectifiers (HWR1, HWR2) with opposite polarity, said second combining stage (D) being negatively fed back to the input (I.sub.

Abstract: An oscillator circuit comprising a feedback amplifier circuit having a power supply terminal, a resonant circuit comprising a crystal, and a differential amplifier which is coupled to a bias current source which is switchable stepwise by means of a level detector for the stepped excitation of the resonant circuit from a predetermined potential at the power supply terminal. When switching on the power supply voltage, the level detector insures that the resonance of the oscillator circuit is achieved in a defined and a reproducible way.

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: AM receiver comprising a tuning oscillator (T0), a first phase detector (PD1) and a first loop filter (LP1) successively arranged in a first phase control loop. The tuning oscillator (T0) is synchronized with a reference oscillator (VCX0) coupled to the first phase detector (PD1) and applies a mixing frequency to a mixer stage (M) for conversion of a received AM signal into an IF-AM signal. The mixer stage (M) is coupled to an AM demodulator (SD) for demodulation of the base-band modulation signal. The reference oscillator (VCX0) is controllable and is disposed between a second loop filter (LP2) and a second phase detector (PD2) of a second phase control loop coupled to the mixer stage (M) for applying a local detection carrier synchronized with the IF-AM signal carrier to the AM demodulator (SD).

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: Gain-controlled amplifier arrangement with a cascade arrangement of first and second gain-controlled amplifier stages, an AM-detection circuit and an integrating arrangement for generating a control voltage for the two stages and a threshold circuit for generating first and second threshold voltages, for delaying at an increasing input level the start of the control of the first stage (1-8) relative to that of the second stage (19-28). So as to prevent the gain control of the first stage from starting, for example because of an unwanted variation of the threshold voltages, before the gain control of the second stage has ended, the control ranges of the two stages are separated from each other by a separation area in which no gain control is effected.

Abstract: A transmitter employing a light-emitting diode as an output element, this element being included in series with a resistor in the output circuit of a difference amplifier the inverting input of which is coupled to the junction point of the diode and resistor, includes a network for compensating for the non-linear output power versus energizing current characteristic of the diode. This network comprises a field effect transistor (fet) biased to operate in the pre-pinch-off region and having its source-drain path connected to the diode. The source-drain path of the FET may shunt the diode and a further resistor in series therewith, or alternatively may be included in a feedback path to the inverting input of the amplifier.