Abstract: Telephone call management is provided via a computer network (web) facility which can be remotely accessed by subscribers using web browsers. The web facility includes an information database for storing personal telephone directories and call logs, and a telephone call control system coupled to a telephone switch via a switch-computer interface. Information on calls to and/or from telephone numbers of subscribers is communicated from the switch to the web facility to be stored in the database without requiring the subscribers' browsers to be active. Subscribers can make telephone calls and control telephone communications via the browsers and the web facility. Subscribers do not require any hardware or software in addition to a telephone and web browser.

Abstract: A SAW device has tapered trasnsducers each of which is divided into two or more tapered transducer parts, which are arranged in line with one another in one or more SAW tracks with the tapers of adjacent tapered transducer parts complementary to one another to provide a compact arrangement. The tapered transducer parts can be symmetrically or asymmetrically tapered to provide different frequency bands for band or bandwidth switching of the SAW device. Input and output impedances of the SAW device can be maintained during such switching by switching of dummy transducer parts also provided on the same piezoelectric substrate.

Abstract: A full bridge DC-DC converter has four switching devices in two switching legs each of two devices connected in series between two supply voltage terminals, junction points of the legs being connected to a primary winding of a transformer, from a secondary winding of which an output voltage of the converter is derived by rectifying and filtering. The output voltage is regulated by phase shift control of the switching devices. Zero voltage switching (ZVS) of the switching devices under potentially all converter load conditions is provided by snubber capacitors, connected in parallel with the switching devices, in conjunction with two inductors each connected between the junction point of a respective one of the switching legs and a point at a voltage midway between the voltages of the supply voltage terminals, which can be provided by a capacitive voltage divider between the supply voltage terminals. The inductors typically have different inductances, and one of the inductors may be omitted.

Abstract: AMPS (Advanced Mobile Phone System) ST (signalling tone) is detected by a tone detector in which samples of a demodulated signal are amplitude limited to remove click energy, and the limited signal is bandpass filtered, using a notch filter and summer, to limit it to the range of possible ST frequency. Power of the bandpass filtered signal is detected, and compared with detected power of a version of the bandpass filtered signal from which any sinusoidal signal has been eliminated, independent of frequency, to provide for ST detection. A function [x(k)+x(k-2)]x(k-2)-[x(k-1)+x(k-3)]x(k-3) for successive samples x(k) of the bandpass filtered signal is used for the sinusoidal signal elimination. The invention can also be used to detect other tones.

Abstract: A flyback converter has a main switch coupling a primary winding of a transformer between supply terminals, a duty cycle of the main switch controlling an output of the converter derived from a secondary winding of the transformer. Soft (zero voltage) switching of the main switch is facilitated by a snubber capacitor in parallel with the main switch. An auxiliary circuit coupled in parallel with the snubber capacitor and main switch includes a series-connected auxiliary switch, capacitor, and inductor coupled via another inductor to a full wave rectifier arrangement for recovering energy from the snubber capacitor. Resonant circuits provided by the auxiliary circuit facilitate soft switching of the auxiliary switch for low power loss and high frequency operation. The switches can be MOSFETs with reverse-poled diodes in parallel with their drain-source paths.

Abstract: Diversity path signals, each comprising time division multiplexed symbols in a time slot including known symbols constituting a reference signal, are combined with respective weights to reduce co-channel interference. The weights are determined, from a correlation matrix and a reference signal correlation vector, using a sliding window starting with synchronization symbols and/or CDVCC (coded digital verification color code) symbols as the known symbols. SINR (signal to interference plus noise ratio) is determined for each window position from elements of the correlation matrix and the reference signal correlation vector. The determined SINRs are averaged through the time slot, over a plurality of time slots, and for the diversity paths to provide an accurate determination of SINR within a short period. The SINR provides a reliable signal quality parameter that is useful in a cellular communications system for procedures such as hand-off, adaptive channel allocation, dynamic power control, and cell tiering.

Abstract: A current mirror circuit comprises first and second resistors for conducting first and second reference currents dependent upon a supply voltage, and first and second current mirrors coupled to the first and second resistors, the second resistor being in series with a voltage reference. The second current mirror mirrors the second reference current, and its mirrored current output is subtracted from the first reference current, the difference current being mirrored by the first current mirror to produce a controlled output current. The circuit can be arranged so that the controlled output current is independent of changes of the supply voltage, or, optionally with further current mirrors and voltage references, so that the controlled output current has a desired relationship with the supply voltage.

Abstract: A surface wave device is made by forming conductors on a surface of a piezoelectric material in a conductor pattern defined by exposing photoresist via a reticle. The conductor pattern is provided on the reticle in two parts each defining a set of substantially alternate fingers of the pattern, and the photoresist is exposed by two overlaid exposures each via a respective one of the two parts of the conductor pattern. Exposed photoresist can optionally be developed between the two exposures, and conductors can optionally be formed on the surface between the two exposures. The method reduces diffraction limits, permitting manufacture of surface wave devices with sub-micron linewidths for filtering at increased frequencies.

Abstract: A power converter forming part of a telephone subscriber line interface circuit selectively generates a ringing signal waveform, for supply to the line, or a supply voltage for a driver circuit for providing loop current on the line. First and second fixed frequency PWM signals are used to control the power converter, and hence the voltage which it generates, for the ringing signal waveform and the supply voltage respectively. The first PWM signal enables the power converter to provide a high power level needed for ringing signals. The second PWM signal has a lower frequency, and hence results in lower switching losses and power dissipation, and a lower duty cycle, suitable for the lower power level needed for the supply voltage, and is conveniently produced by masking pulses of the first PWM signal. The frequency of the second PWM signal is greater than 270 kHz, to avoid transmitting spectral energy to the line below this frequency.

Abstract: Each complex signal sample a(k)+jb(k) of a frequency modulated signal is limited in order to reduce co-channel interference. The limiting is performed efficiently in a digital signal processor by determining a ratio r with a magnitude less than one, equal to b(k)/a(k) in a first case and a(k)/b(k) in a second case, determining from a look-up table a variable p with a magnitude equal to 1/.sqroot.(1+r.sup.2), and determining a number equal to sgn(a(k))p(1+jr) in the first case and sgn(b(k))p(r+j) in the second case as the limited output signal sample.

Abstract: For combining diversity path signals comprising symbols each modulated in accordance with one of a plurality of orthogonal (e.g. Walsh) functions, a diversity combiner includes, for each path, a demodulator to demodulate each modulated signal symbol in accordance with a selected one of the orthogonal functions, a phase estimator to estimate a phase rotation and amplitude of the diversity path signal from the demodulated signal, and a complex signal multiplier to derotate the phase and weight the amplitude of the diversity path modulated signal in dependence upon the estimated phase rotation and amplitude. The combiner sums real parts of the phase-derotated and weighted modulated signals of the diversity paths, demodulates the combined signal in accordance with all of the orthogonal functions, and selects the maximum demodulated signal for each symbol thereby to determine for the symbol the selected one of the orthogonal functions.

Abstract: A surface wave device comprises first and second SPUDT (single phase unidirectional transducer) resonator filters each comprising first and second transducers, which are preferably RSPUDTs (resonant SPUDTs), the resonator filters being the same except that one transducer of the second resonator filter is a mirror image of the corresponding transducer of the first resonator filter to provide a phase difference of 180.degree.. The surface wave device serves as a balun by having an unbalanced signal connection to the first transducers, and a balanced signal connection comprising signal connections to the second transducer of each of the first and second resonator filters. The resonator filters can be arranged side by side on a common piezoelectric substrate.

Abstract: In a hybrid fiber-coax distribution network, communications between a central station and particular end stations are encrypted using a working key (WK) of a symmetric encryption scheme. The central station has a public and private key (PPK) of a PPK encryption scheme, and some of the end stations can also each have a respective PPK. To provide secure communications for each end station, if the end station has a PPK, then the respective WK is generated in the central station and communicated, encrypted using the end station's public key (PK), to the end station. Otherwise, the WK is generated in the end station and communicated, encrypted using the central station's PK, to the central station. An individual identifier for each end station, and a cryptographic signature at least for end stations not having a PPK, can be communicated to the central station for authentication of the end stations.

Abstract: Complex signal samples of an input signal are supplied to via a frequency down-shifter to a digital filter, and to a time-frequency transform unit which produces a plurality of frequency components each associated with a respective frequency band within a bandwidth of the input signal. The frequency component having the maximum momentary energy is determined to determine the down-shifting frequency for the associated frequency band to be filtered, and to determine a complementary up-shifting following the digital filter to produce an output signal. The filter can be a bandpass filter or a bandstop filter, especially for reducing co-channel interference in different types of wireless communications systems.

Abstract: Diversity path signals, each comprising time division multiplexed symbols in a time slot including known symbols, are combined with respective weights to reduce co-channel interference. Initial weights are determined, using a window on the known symbols, to optimize signal to interference plus noise ratio. These weights are used to determine symbols adjacent to the window, and the window is changed to include determined symbols and the weights redetermined. This process is repeated with the window being moved progressively, preferably with successive positions overlapping, throughout the time slot. The initially known symbols can comprise synchronization symbols and/or CDVCC (coded digital verification color code) symbols. Desirably, both can be used with respective windows being moved in opposite directions through symbols between them to provide two results for each such symbol, the better one of which is selected in dependence upon a monitoring of possibly averaged errors for the symbols.

Abstract: A telephone ringing signal generator includes a DC converter for producing high positive and negative voltages that define peak amplitudes of the ringing signal, which is produced by low pass filtering a generally trapezoidal waveform having these peak amplitudes. The generally trapezoidal waveform is produced by a level-shifting integrator at a frequency determined by a low voltage square wave supplied to the integrator. The integrator comprises a capacitor coupled between a virtual ground point and an output of the integrator and arranged to be charged with two opposite polarities in response to opposite transitions of the square wave, and a resistor via which the square wave is supplied to the virtual ground point. Buffers are provided for buffering the trapezoidal waveform supplied to, and the ringing signal produced by, the low pass filter.

Abstract: A longitudinally coupled double mode surface wave resonator comprises two reflectors, two lateral IDTs (inter-digital transducers), and a centre IDT arranged on a surface of a piezoelectric substrate, for coupling surface waves longitudinally between the IDTs. The two lateral IDTs operate with opposite signal phases by virtue of opposite connections, opposite polarities, or oppositely phased spacings from the centre IDT. Alternatively, or in addition, the centre IDT is divided into two oppositely phased halves. A filter comprising one or more resonators can replace both a filter and a balun in a radio frequency circuit.

Abstract: A surface wave device filter comprises two 2-pole waveguide coupled double mode resonators (WCRs) electrically connected together in cascade. To permit narrowing of the filter passband for improved out-of-band rejection, e.g. for use of the filter as an intermediate frequency channel filter in a wireless communications system, while maintaining good matching for low ripple in the passband, a shunt capacitance is connected in parallel with the static capacitances of the two WCRs. The shunt capacitance is constituted by interdigital fingers provided on the same piezoelectric substrate as one or both of the WCRs, perpendicularly to the WCR fingers to avoid surface wave interference, conveniently in space otherwise used by rails of the WCRs, optionally with oppositely phased fingers to cancel surface waves generated by these fingers. A capacitance can be similarly provided on the same substrate as any other type of surface wave device.

Abstract: A cascaded surface wave device filter comprises two 2-pole surface wave device filters connected in cascade. The 2-pole filters each provide a balun function between balanced and unbalanced signal connections, and have either their unbalanced or their balanced signal connections interconnected in the cascade to reduce electromagnetic feedthrough and improve spurious mode suppression. The 2-pole filters are conveniently longitudinally coupled double mode surface wave resonators which are described, or transversely coupled double mode surface wave resonators. Higher order filters can be provided by connecting further 2-pole filters in the cascade. The cascaded filter is particularly useful for filtering at radio and intermediate frequencies in cellular radio equipment.

Abstract: A distribution network groups television program signals into service tiers. To provide these from unsynchronized MPEG streams without resynchronization, each stream, representing a single program signal is encapsulated into ATM cells with a virtual path (VP) identification of each ATM cell corresponding to the service tier and a virtual channel (VC) identification corresponding to the respective program signal. Payloads in cells having the same VP are scrambled using a scrambling key allocated to that VP and hence to the corresponding service tier, and are unscrambled by entitled subscribers using the scrambling key which is supplied to them individually using public/private encryption techniques.