Abstract: A laser power supply control circuit may, when the power supply is initially turned on, temporarily permit an excessive supply voltage which may damage the laser. To prevent that, but without restricting the operating range or speed of response of the control circuit, the invention provides a sensing circuit for deriving a sensor signal indicative of a change in the loop gain of the control circuit when it departs from its normal operating mode. The sensor signal is used to prevent the power supply control signal from increasing excessively after a temporary reduction in supply voltage, but permits the control signal to operate substantially immediately when the supply voltage returns to its normal operating range.

Abstract: A current amplifier arrangement in which a current-current converter (30) has an input connected to the input (33) of the current amplifier arrangement and a power supply input (34, 35) to which a current source (51-54) is connected a current mirror circuit (31, 32, 42, 44)has an input connected to the output (36-39) current converter and an output (46-49) connected to the output (50) of the current amplifier arrangement. The current converter includes a first output transistor (T1, T3) whose main current path is arranged between the input (33) and the output (37, 39) of the converter and whose base is connected to the power supply input (34, 36), and a diode-connected driver transistor (T2, T4) connected between the base of the first output transistor (T1, T3) and a node (K) which provides a reference potential during operation. The main current path of a second output transistor (T5, T6) is connected to the output of the arrangement and the base of this transistor is connected to said node.

Abstract: The invention relates to a semiconductor device comprising a radiation-sensitive element (A . . . D). The radiation-sensitive element includes a transistor (T) having an emitter region (6), a base region (4) and a collector region (2), and further a radiation-sensitive region (7) having a rectifying junction (5). Due to the presence of the transistor (T), such an element (A . . . D) can supply a considerably larger output signal than a photodiode. On the contrary, however, the first-mentioned element (A . . . D) is comparatively slow as compared with a photodiode due to the parasitic capacitance of the rectifying junction (5). The invention obviates this disadvantage in that according to the invention the radiation-sensitive region (7) has at least a first subregion (71) and a second subregion (72) and the transistor (T) is subdivided into two subtransistors (T.sub.1, T.sub.2), whose base regions (4) are separately connected to the subregions (71, 72).

Abstract: A focus control system for optical record carrier scanning apparatus includes a mechanical actuator (13) for moving the focus of the scanning beam relative to a recording layer of the record carrier, a focus-error detection circuit (15, 16, 17) for generating a focus-error signal (FE), and a control circuit (26) for generating a first control signal (AS') for the actuator (13) which is proportional to the focus-error signal (FE). In order to ensure that the actuator is within its generating range when it locks-in to the focus-error signal, the system also includes a lock-in circuit (20) having a signal generator (21) and an integrator (23) for generating an additional control signal (AS') for the actuator (13) prior to lock-in.

Abstract: A radiation-sensitive semiconductor device, more particularly but not exclusively a photo detection arrangement for determining the postion of a luminous spot, including a semiconductor body having at least two radiation-sensitive diodes and amplifying circuitry for the photocurrent generated by the luminous spot. The amplifying circuitry includes transistors arranged outside the area of the semiconductor body occupied by the radiation-sensitive diodes. Each transistor is assigned to and connected to a radiation-sensitive diode, while at least the active parts of the transistors are arranged more closely to each other in the semiconductor body than the diodes to which they are assigned. A focusing arrangement may advantageously incorporate such as semiconductor photodetector.

Abstract: In full or half DC/AC bridge circuits, the current through the control circuit, by which the power transistors T1,T2 are switched, is derived from the high supply voltage via a resistor. In order to reduce this current and the dissipation associated therewith, the control circuit includes an additional switch, preferably a MOST T4, which is non-conducting when the inverter transistor T3 is conducting and which is conducting when the transistor T3 is non-conducting. The control circuit thus becomes practically currentless. When the control electrode is applied to a suitable voltage, the transistor T4 can be controlled by its source voltage and thus becomes self-controlling. Thus, the circuit can be kept simple. The bridge circuit is particularly suitable for use with gas discharge lamps.

Abstract: A D/A converter providing a binary weighted series of currents (I.sub.3, I.sub.4, I.sub.5) via first current-source transistors (T.sub.3, T.sub.4, T.sub.5) each in a given ratio to a reference current (I.sub.1) in a reference transistor (T.sub.1). The weighted currents are switched to analog output (15) or to positive supply terminal (20) via first switching devices (3.1, 3.2, 3.3). A control device includes a second current-source transistor (T.sub.8) connected to a reference-current source or to the positive supply terminal via a second switching device (4). The current (I.sub.8) in the transistor T.sub.8 has a given ratio to the reference current (I.sub.1). By connecting the second current-source transistor to the positive supply terminal or to the reference current source, the reference transistor carries the full reference current (I.sub.ref) from the reference current source or only a fraction of the full reference current, respectively. As the weighted currents are in a given ratio to the current (I.

Abstract: For detecting whether an input signal is above or below a reference level in such a way that brief signal interruptions and negative spurious pulses are not interpreted as decreases below the reference level, the detector includes an input comparator, a first delay circuit, a second delay circuit and an output circuit. The first delay circuit comprises a first integrator comprising a first transistor and a first capacitor, a first current source and a second comparator. The second delay circuit comprises a second integrator with a second transistor and a second capacitor, a second current source and a third comparator. The first delay circuit and the second delay circuit have equal delay times.

Abstract: An apparatus is described for reading optically coded discs. In this apparatus the photodiode signals are amplified by current amplifiers which are biased by the unipolar photodiode signal currents, so that offset-free class-B operation is obtained.

Abstract: A four-wire communication line circuit for two or more two-wire subscriber lines, comprising a pair of amplifiers respectively connected in the line pairs of the four-wire line for each direction of transmission and a transmission direction detection circuit connected to each line pair. The detection circuit generates a control signal from the voltage signals transmitted on the line pairs, and which is dependent on the direction in which the net energy of such voltage signals is transmitted over the two-wire subscriber lines. The control signal is applied to control circuitry which switches the gain factors of the line amplifiers between a high and a low value, as determined by the direction of net energy transmission.

Abstract: An amplifier circuit for supplying output voltages which are much higher than the breakdown voltage of the individual components forming the amplifier comprises a control circuit (1) and an amplifier stage (2). The amplifier stage (2) comprises 2n transistors (7-12) where n is an integer greater than one, having their main current paths serially connected between two supply terminals (3, 4). The bases of the transistors (7-12) are connected to tapping points on a series chain of diodes (34-41) in the control circuit (1). Further supply sources (13-16) apply an incrementally decreasing sequence of voltages to transistors (8, 9) and (10, 11) so that the voltage across any of the transistors (7-12) is limited to one increment of the sequence of voltages.

Abstract: A conference system comprises a conference circuit to which a plurality of participants are connected via terminals respective connecting circuits having input and output circuits, the signal from the output circuits being fed to the connecting circuit and signals from the conference circuit being fed lines to the input circuits. The conference circuit has summing amplifiers (10 to 13) whose inputs are connected to the outputs of the connecting circuits so that the output signals from the connecting circuits are algebraically summed. The signs of the signals to be summed are determined from the relationship E-S* S=O where E is the unity matrix and S* is the transposed complex conjugate matrix of S.

Abstract: A conference system for establishing simultaneous interchange of information among a plurality of participants (E.sub.o -E.sub.k) comprises a conference network (CN). Each participant is connected to a terminal (n.sub.o -n.sub.k) which is connected to a hybrid network (CS.sub.o -CS.sub.k). The output (SW.sub.o -SW.sub.k) from the hybrid networks (CS.sub.o -CS.sub.k) are fed to summing amplifiers (SA.sub.o -SA.sub.k) in the conference network CN. The outputs of the summing amplifiers are fed to the participants via the hybrid networks (CS.sub.o -CS.sub.k).The summing amplifiers (SA.sub.o -SA.sub.k) are arranged so that the signals contributed by the participant to which the particular summing amplifier output is connected is multiplied by a factor .beta. while the signals contributed by the other participants are multiplied by a factor .alpha..

Abstract: An amplifier for a subscriber's line circuit comprising an extra transistor whose base-emitter junction is connected across a resistor which is arranged in series with the main current path of the output transistor of the amplifier. Furthermore, a supply source is connected to the output terminal of the amplifier via the main current path of the additional transistor and an impedance for supplying at least a portion of the line current of a subscriber's line connected to the output terminal, in order to reduce the dissipation in the semiconductor elements of the amplifier.

Abstract: Current detection circuit arrangement for an automatic telephone exchange for detecting currents in a system of two conductors having earth as the common return conductor. This circuit arrangement comprises a pair of measuring resistors R.sub.1, R'.sub.1 and a pair of voltage dividers R.sub.2, R.sub.5 and R.sub.3, R.sub.4 which are connected cross-wise and form a bridge. The loop current I.sub.d can be detected with this circuit arrangement. It is also desirable for the circuit arrangement to enable the detection of the longitudinal currents in the conductors. The present circuit arrangement comprises a pair of connecting points for a detector for the longitudinal currents, one point of which is connected to the tapping point of one and to the tapping point of the other voltage divider, respectively, by way of separate resistors, the other point being a point of reference potential.