Abstract: A description is given of a communication set for connection to a communication line such as a telephone line, which communication set includes means for detecting set functions such as ringing signal detection, and a rectifier circuit which is connected to a common output which is coupled to a scanning device included in the set function detection means, which scanning device detects the line conditions. A large number of line conditions may be detected with a minimum of components required, among which an analog/digital converter for which only a single input pin on a chip is necessary.

Abstract: In known telephone subscriber end stations a caller_ID IC detects a tone alerting signal TAS alerting that successive caller_ID information can be received for displaying on a display of the phone. The known station applies narrow frequency band filters to detect tones indicating the end of TAS. Such a detection is not flexible as it can only be used for a specific caller_ID signal protocol. A flexible detector is proposed which can easily be adapted to widely varying protocols and which can also be used for other purposes such as the detection of power drops in an FSK signal. The detector comprises means for determining a time-domain signal representing the signal energy of a signal on the subscriber line in a predetermined time interval.

Abstract: A keyboard has key positions providable with keys. A number of the key positions are actually provided with keys, whereas at least one other key position has a mode setting option. The mode setting option provides a feature that is readable by a microprocessor connected to the keyboard. Such features include pulse dialing parameters such as a pulse rate, a pulse width, and a pulse pause, or tone dialing parameters, or the like.

Abstract: A control circuit for controlling a DC current and an AC current through an acoustic transducer such as a ringer or a buzzer in a telephone. The control circuit comprises a current controlled output stage with an output terminal for the acoustic transducer, and a driver transistor of which a main current path drives the output stage. The driver transistor has a single control input for controlling both the DC current and the AC current through the acoustic transducer.

Abstract: For the generation of a junction voltage with a negative temperature coefficient, a band gap reference circuit includes a first semiconductor element (T) and a voltage divider (R3, R4) adapted to generate a measure of the junction voltage across a main current path of a second semiconductor element (T5), a current source (J1) being adapted to generate a reference current with a positive temperature coefficient by means of a resistive element (R1) coupled in series with the main current path. Since the reference current generates a compensation voltage with a positive temperature coefficient across the resistive element (R1) the sum of the measure of the junction voltage and the compensation voltage yields a reference voltage with a specific temperature coefficient, the presence of the voltage divider (R3, R4) inter alia enabling a reference voltage with a temperature coefficient of zero volts per temperature unit to be obtained at comparatively low supply voltages.

Abstract: An amplifier circuit includes a driver stage made up of a differential pair and which is coupled to an output stage consisting of a first output transistor and a second output transistor having a common terminal coupled to the output signal terminal of the amplifier circuit. The driver stage provides class AB operation of the output transistors at a comparatively low supply voltage. In order to obtain such operation, a translinear network including the differential pair and a diode-connected transistor is coupled directly to a current mirror which includes the second output transistor. The translinear network and the current mirror dictate the setting of the first and the second output transistor, respectively.

Abstract: A controlled current supply circuit for semiconductor logic circuitry, such as I.sup.2 L, which has an unscaled part (10) which remains continuously active and a scaled part (12) which, when not in a data processing mode requiring a high current can be operated at a much lower curent so that the data therein is preserved and power is saved. Unless switching between the low and high currents is carefully controlled then there is a risk of data being lost. A curernt supply circuit (14) responds to a data input signal of the unscaled logic to cause the current supply to the scaled logic (12) to increase or decrease in a number of steps, there being a sufficiently long time delay between steps to allow the scaled logic to settle. The rate of increase or decrease of the injected current is such that there are smaller increments or decrements when the overall current is low causing the scaled logic to be slow and larger increments and decrements when the overall current is high causing the scaled logic to be fast.

Abstract: A infra-red receiver for use in applications such as remote control of consumer equipment and receiving audio signals modulated on an IR carrier. The receiver comprises an IR diode (10) which is operated in its forward mode so that it constitutes a current source. The IR diode (10) is connected in an amplifying circuit which includes means (16) for detecting low frequency interference components in the signal and in response to the detection of these interference components temporarily shorts out the IR diode.