Abstract: There is disclosed a call announcement circuit arranged for connection to a communication system via a voice (or data) path and also via a separate control channel. Using this arrangement, the system main processor can control the message delivery capacity of the announcement circuit since the circuit has direct access to the internal system buses. This configuration allows detailed control of the announcement circuit on channels separate from the communication channel.

Abstract: A dual mode disk controller is disclosed for use between a host processor and its storage medium for controlling data transfer to and from the storage medium. The data is formatted on the medium in two distinct formats, one capable of bulk fast transfers useful in a swapping operation, and the other capable of periodic slower transfers as is acceptable for file retrieval. The disk controller is designed having a small fast buffer memory for accepting information from the storage medium. File transfer data is transferred immediately without host CPU intervention, to a larger cache memory. The host CPU accesses the fast buffer memory periodically to retrieve swap transfer data while only accessing the larger cache memory when it needs to retrieve the file formatted information.

Abstract: A time division communication system having peripheral devices controlled om a port circuit is arranged such that the port circuit may have assigned to it a variable number of time slots for any peripheral device associated therewith. Each port circuit has a microprocessor control device which is capable of controlling communication to or from the port circuit over the system time division bus or to and from the port circuit and the peripheral over a variable number of time slots, none of which are preassigned to the port circuit.

Abstract: A technique which improves the accuracy of determining the circuit element values in a three terminal equivalent circuit is disclosed. The improvement results from the use of at least one ratio wherein the numerator and denominator of each ratio is a different function of at least one measurement of the three terminal equivalent circuit. Each ratio is representative of the true value of one preselected circuit element to another preselected circuit element value. This technique can be used for DC or AC analysis of the equivalent circuit and can be adapted for different sources of measurement errors.

Abstract: A novel circuit recovers a carrier signal from a 16 or 64 QAM double sideband suppressed carrier IF signal for use in synchronolus demodulation. A 70 MHz IF signal is fed to a power splitter for distributing the signals to a demodulator and to a quadrupler. The 280 MHz signal from the quadrupler is fed to a surface acoustic wave filter to extract the components of the double sideband suppressed carrier signal and the output therefrom is amplified prior to being divided by four to recover the 70 MHz signal. The 70 MHz signal is delivered to a phase frequency detector which provides an error signal during acquisition to deviate a VCO toward the received frequency and thus obtain very fast acquisition time. When the VCO is locked, the phase frequency detector is disconnected from the summing node of a PLL, and a correlated error polarity adaptive carrier recovery circuit operates the demodulator.

Abstract: There is disclosed a call announcement circuit integrated into the switching network of a PBX switching system such that the announcement board resides in one of the port slots and has direct access to the internal system buses. The circuit can handle many separate announcements each stored at a selectable compression ratio. Each such announcement can be recorded or played in any of the time slots under processor control. This configuration allows tradeoffs between storage capacity and compression ratio (i.e., speech clarity) and also allows messages to be played on any line or to any station via the communication bus and the selected time slot.

Abstract: A bandwidth reduction technique is disclosed for use in digital systems wherein a pair of data signal elements modulate quadrature-related carriers. This modulation, referred to as quadrature amplitude modulation (QAM), phase shift keying (PSK) or amplitude and phase shift keying (APSK), generates a double-sideband signal which is transmitted in a variety of communications systems. In accordance with the present invention, the above-described double-sideband signal is filtered to form either a single sideband or vestigial sideband signal prior to transmission. While this use of a vestigial or single-sideband signal, in lieu of a double-sideband signal, permits the transmission of more information in a given frequency interval, the filtering process contaminates the data signal elements. To recover the data signal elements at the receiver, a pair of received signal elements is formed by extracting the carrier signals.

Abstract: Each multiply-accumulate device, in an adaptive equalizer, multiplies each input signal sample by an associated coefficient in an ensemble, stores the result and periodically outputs the accumulated results as the equalized input signal. A rotating coefficient register in the adaptive equalizer successively associates each coefficient in the ensemble with a different multiply-accumulate device. Coefficient update circuitry is also provided which periodically updates the coefficients in the ensemble so as to optimize equalizer performance.

Abstract: An improved decision-directed control circuit is disclosed which supplies adjustments to adaptive circuitry in a communications system. The improvement is achieved by only supplying adjustments when there is a high probability that the adjustment is correct. In the disclosed embodiments, this high probability equates, at a minimum, to times when the adaptive circuit output has an amplitude which lies outside of a range extending from the largest to the smallest value of the digital signal. This adjustment approach can be used to adjust a variety of adaptive circuits including transversal equalizers, timing recovery circuits, cross-polarization cancellers and carrier recovery circuits.

Abstract: A technique is presented for simplifying the recovery of two synchronous data signals having a common symbol rate after each signal has respectively modulated a different one of a pair of quadrature-related carrier signals. In the transmitter, the data signal which modulates one of the quadrature-related carrier signals is delayed relative to the data signal which modulates the other quadrature-related carrier signal. This delay is related to an IF frequency chosen at the receiver. After passing through a noisy transmission channel, the quadrature-related carrier signals are coupled in the receiver to a serial combination of an equalizer and analog-to-digital converter. This combination outputs multiple, substantially distortion-free samples of the data signals each symbol interval. The two data signals are then recovered by selecting a subset of the samples provided each symbol interval.

Abstract: A technique is disclosed for equalizing an incoming signal including quadrature-related carrier signals by forming the product of the incoming signal at at least one prescribed time and only one real-valued coefficient associated with each time. In one embodiment of the present invention, the equalized incoming signal is demodulated into a first pair of component signals. At least one of these component signals is then used to generate each coefficient. In another embodiment of the present invention, each coefficient is generated in response to at least one of the component signals in the first pair along with a second pair of component signals which are formed by demodulating the incoming signal. This technique can be advantageously adapted to incorporate a number of coefficient updating algorithms and is suitable for use in a number of modulation formats.

Abstract: The severity of the problems of transmitting high speed data over a regular twisted wire pair are legendary. These problems arise from a variety of conditions, including the capacitance of the wire (which increases with length) and the propensity of unshielded wire to pickup high induced voltages. An arrangement is disclosed that is suitable for short, as well as long, wire distances and which also effectively eliminates the interference problem caused by induced voltages, including those causes by electrostatic discharge. This arrangement passes two twisted wire pairs through a series of ferrite cores. The twisted wire pairs coming out of the ferrite cores are terminated such that one of the pairs is connected to ground while the signal carrying twisted pair is connected to a small signal balun coil, pulse shaping circuit and low pass filter.

Abstract: A second order gradient microphone with unidirectional sensitivity pattern is obtained by housing each of two commerically available first order gradient microphones centrally within a baffle. The baffles have flat surfaces, are preferably square or circular and have parallel surfaces the two baffles being parallel to each other. The rotational axes of the microphones are arranged to coincide. The output signal from one of the microphones is subtracted from the delayed signal output of the other.

Abstract: There is disclosed an asynchronous pulse catching circuit that, for each edge of the variable frequency input, regardless of duty cycle, will provide a pulse, synchronized to a high speed clock. There is also disclosed a pulse comparison circuit consisting of a state machine that provides slip detection between the variable input frequency and a reference input frequency. The circuit provides separate outputs indicating positive and negative slip.

Abstract: This is an improved resistive line battery feed circuit where the improvement consists in establishing a balanced stable power point using an opamp and capacitive input and feeding the AC output to both lines of the tip and ring circuit via opamps and a hybrid for injecting current. In this manner longitudinal balance is maintained. Current is added to the line circuit by a modulated DC current source.

Abstract: A technique for digitally synthesizing the amplitude modulation of one or more carrier signals with a random digital data signal is disclosed. Pursuant to the present invention, a memory unit is addressed by a plurality of binary coded digital symbols in the data signal. For each address, at least two digital representations are read out. Each representation corresponds to a different sample of the carrier signals which has been amplitude modulated by a composite of the spectrally shaped data signal. The disclosed technique can be adapted to synthesize a variety of modulation formats, and can provide compensation for fixed in-rail and cross-rail distortions.

Abstract: A system has been devised that allows commonly used software components to be designed and developed only once, and reused many times in different applications with different operational contexts and requirements. The system includes a language for the specification of software components in a context-independent generic fashion, a compiler for the specification language and a program for generating concrete software components to work in a specific context.

Abstract: A terrestrial radio system which utilizes spot beams, time division multiple access and frequency reuse to provide communications services from a base station to remote customers within a system service region. The base station advantageously is arranged with multistage switching so as to permit the respective sharing of radio transmitters and receivers over larger number of antenna transmitting and receiving ports.

Abstract: A technique for decoding a vestigial sideband signal formed from a double-sideband signal having modulated quadrature-related carrier signals is disclosed. Within the receiver, the vestigial sideband signal is demodulated into a pair of received signals. Each of these received signals comprises a data signal which has been distorted by the double-sideband to vestigial sideband transformation. Pursuant to the present invention, each data signal is recovered in response to the associated received signal and the other data signal. Advantageously, the disclosed technique reduces the bandwidth required to transmit a given amount of information in systems which transmit modulated quadrature-related carrier signals.

Abstract: An improved oscillator circuit utilizing multiple semiconductor devices, such as field-effect transistors or bipolar transistors, is disclosed. To improve the gain of the oscillator circuit corresponding terminals on each device are interconnected via a path which provides a delay equal to an integer multiple of the inverse of the oscillator frequency. This technique can be adapted to provide an oscillator whose nominal frequency is voltage controllable and can be arranged to provide one or more output ports.