Abstract: By placing the riser card comprising connectors for both ISA and IPC expansion cards in a connector arranged on the side of the motherboard of a computer of the AT type rather than in a connector arranged centrally of the motherboard, a large number of advantages are obtained: the routing of PCI signals is shortened; the cooling within the computer housing is improved; the components on the PCI expansion cards come to lie at the top of the card; the case for the computer can be simplified and there is no longer any connector arranged centrally of the motherboard which made the through-connection between components on opposite sides thereof rather difficult.

Abstract: Method and device for enciphering data words of a word width of n bits, in particular data words to be written in a computer storage, wherein a product cipher circuit comprises alternately one from a plurality of permutation boxes with n inputs and n outputs and one from a plurality of substitution boxes with n inputs and n outputs, each of these boxes being under the control of a specific part of an m-bits key. In the product cipher circuit the data words are consecutively enciphered in whole and the enciphering device can be regarded as a delay line. The data words to be enciphered can be combined with coding words which depend on the specific sector of the computer storage, in particular a hard storage disk unit, where the data words are stored. The sector-specific coding words and/or the m-bits key can be combined with a key to be entered by a user.

Abstract: A frequency multiplying circuit comprises a differential amplifier formed by two transistors whose emitters are connected by a current source to a low voltage supply rail, collector resistors are connected to a higher voltage rail as is also done with the base electrode of one of the transistors, the base electrode of the other of the transistors has an oscillator connected thereto. An LC resonant circuit coupled between the collectors of the two transistors and is tuned to select either the basic frequency of the oscillator or an odd harmonic thereof.

Abstract: For receiving frequency shift keyed data, a local oscillator generates a signal which is frequency shifted through a fixed frequency relative to the carrier signal, and is mixed with the received FSK signal. A circuit processes the mixer output to emphasize the energy content of signals located at the ends of the receiver passband, over signals located toward the center of the pass band. The output of that circuit is integrated to provide the AFC signal to the voltage-controlled local oscillator.

Abstract: A frequency doubling circuit for doubling the fundamental frequency of a signal wave, comprising a pair of full-wave rectifier circuits which produce output signals which are subtracted to derive the second harmonic of the fundamental frequency. The direct current component and unwanted harmonics produced by the rectifier circuits are suppressed by capacitive loading which establishes a phase-quadrature relationship between the fundamental signal waves applied to both rectifier circuits, and adaptively maintaining the amplitudes of the fundamental frequency signals produced thereby equal by means of a negative feedback gain control loop.

Abstract: A voltage controlled oscillator having an electrical means of frequency control which is able to operate from a supply voltage which is lower than is desirable to use with a "VARICAP" diode. The oscillator comprises a pair of transistors whose base and collector electrodes are connected together, the base electrodes being connected to a supply rail and the collector electrodes are connected to a tunable parallel LC resonant circuit. A frequency determining device, e.g. a crystal, is connected between a tapping of the resonant circuit and the emitter of one of the transistors to form a first feedback path. The crystal together with an integratable small value capacitor connected between the emitters of the two transistors form a second feedback path. The phase shifts due to the first and second feedback paths are summed vectorially at the collectors of the two transistors. By varying the gain of each of the two transistors then the resultant phase shift, and thereby the frequency of oscillation, are varied.

Abstract: Oscillator circuit comprising an amplifier arrangement being connected to a reference level an output and an input thereof being coupled via a single signal-carrying terminal to a resonant network which is connected to the same reference level as the amplifier arrangement, the resonant network comprising a crystal resonator. A stable oscillation at a higher order crystal resonant frequency is provided by means of an LC-network which selects said higher order crystal resonant frequency and a resistor connected in parallel across the crystal resonator, which prevents parasitic oscillations at the resonant frequency determined by the components of the LC-network and the case or holder capacitance of the crystal resonator.