A dual digital signal processor (DSP) provides real time links between multiple time division channels of a digital carrier system (e.g. T-1) and a host data processor. Operating only on digital signals, internally and at its interfaces to the carrier and host systems, the DSP exchanges data and control signalling information with the carrier system and data and control information with the most processor, converting the data in passage to different digital forms. At the interface to the carrier system, signals are received and transmitted in a form adapted to diverse terminal equipment of users remotely linked to the carrier system via the switched public network. At the host interface, signals are transferred and received in a form suited to the data process requirements of the host system (e.g. data bytes directly representing alphanumeric characters). Thus, the DSP acts as the equivalent of multiple different types of modems in performing required conversions. The DSP may also perform processing services in order to reduce the processing burden on the host system (e.g. parity checking of data, detection of specific character functions in data or specific tones in audio signals, selective routing of voice to host storage for voice mail applications, etc.).

Real-time digital signal processing relative to multiple digital communication channels

A multifrequency tone receiver (100) for detecting simultaneous tone signals in a sampled digital signal. The tone receiver (100) includes a microprogrammed sequence controller (101 and Fig. 3B), a time-multiplexed digital filter (102 and Fig. 3C) and a signal processing microcomputer (103 and Fig. 3A). For each sample of the digital signal, the sequence controller (101) is programmed to time multiplex the digital filter (102) for performing three cascaded second order filtering operations (two bandpass filter operations and one low pass filter operation as shown in Fig. 2) for each of six tone signals to provide corresponding energy estimates and one additional filtering operation to provide a total energy estimate. The signal processing microcomputer (103) processes (per flowchart in Fig. 7) a number of sets of the seven energy estimates and provides an indication when a multifrequency tone pair has been detected. The digital filter (102), when enabled by a filter start signal from the sequence controller (101), asynchronously performs a signal multiplication-like filtering operation to implement each second-order filter, and provides a filter done signal upon completion of the filtering operation. Full-wave rectifying capability is provided during low pass filtering operations by logically complementing (gate 361 in Fig. 3C) the digital filter input signal. Limit cycles may be suppressed in the digital filter output signal by rounding the output signal and clamping (gates 365-368 in Fig. 3C) positive and negative overflows to the largest allowable positive and negative signals, respectively. The tone receiver (100) may be advantageously utilized in a PCM communication system for detecting multifrequency tone signalling used for dialing and supervisory control. Moreover, the inventive tone receiver (100) may be adapted to receive many different types of tone signalling simply by changing firmware (Tables I and IV) therewithin.

Programmable multifrequency tone receiver

A call progress signal monitor includes a translation circuit for generating data signals indicative of predetermined signal characteristics in a TDM PCM signal channel. A processor implemented detection circuit is responsive to the data signals for detecting call progress tones and silence. The translation circuit includes a translation ROM for assigning PCM signal samples with code values in a range with maximum and minimum limits. A comparator generates a comparison value signal in response to the code values of an instant sample and an immediately previous sample. An encoding ROM generates a trend data byte in response to an instant comparison value signal and a plurality of consecutive previous comparison value signals. The instant code value and the instant trend data byte comprise data signals for identification of the progress tones and silence occurrences by the detection circuit. In the detector a first frequency is derived from an average period of time between code values corresponding to extreme or peak code values in a direction of one of the limits. In a case where the peak code values are dissimilar an envelope frequency is derived from a period of time between peak code values of a greatest dissimilarity. A second frequency is derived as a difference of the envelope frequency being subtracted from the first frequency.

Call progress signal monitor and method for telephone systems

An optical disk player provided with a digital servo circuit uses a time-sharing multifunctional digital filter, in which a plurality of filter functions are realized with a single filter. By lowering the sampling frequency of the plurality of digital filter functions than the master clock of the signal processing circuit and operating the plurality of digital filters on a time-sharing basis, the number of steps of the signal processing command can be decreased and the circuit scale can be reduced. By constructing a High Pass Tracking Zero Cross HPF and an anti-shock BPF of a digital filter using the same step, reduction in the circuit scale and increase in the sampling rate can be attained.

Optical disk player with a digital servo-control circuit incorporating a time sharing multifunctional digital filter

A system and method for use in a network of the type including a bus which carries a plurality of digital, multiple bit time divided channels of information including audio information provides for the decoding of digital audio within one of the channels to analog audio signals, the coding of analog audio to digital audio and the placing of the digital audio onto the bus within one of the channels, and the generation of internal or localized analog tones in an improved and efficient manner. A decoding means is provided for converting a digital multiple bit word to analog form. A control means which includes tone generating means adapted for providing digital multiple bit tone words controls a select means which selectively couples the decoding means to the bus to enable decoding of the digital audio or to the tone generating means for providing the analog tones in response to digital data received from the bus within a preselected channel. The decoding means if further capable of converting analog audio to digital audio to be placed upon the bus. The control means further is adapted to convey digital data to the bus within the preselected channel.

System for producing encoded and decoded voice, internal audio tones, and data communication within a time division multiplex network

A digital signalling receiver translates pulse code modulated (PCM) tone signalling into a signal format compatible with a controller in an associated time division multiplex (TDM) telephone switching facility. In the receiver, steering signals are generated in synchronism with the operation of the switching facility to direct the operation of a time shared filter. The filter performs a plurality of filter functions with a series of PCM signals received from the TDM switching facility and generates therefrom series of filter signals relative each of the filter functions. A translator identifies two filter signals having larger amplitudes than the others and if the two signals persist substantially uninterrupted (a) through a predetermined period of time, (b) within a predetermined relative amplitude range and (c) one of the two signals having at least a predetermined signal to noise ratio relative another filter signal corresponding to an allpass filter function, the translator indicates the receipt of multifrequency signalling by generating the appropriate signals in the required signal format.

Daniel J. Doyle

Papers

Digital signalling receiver for receiving PCM tones