Abstract: Dual tone multi frequency signals, such as those used in Touch-Tone.RTM. telephones, are digitally detected. In an eight tone frequency regime of four low frequencies (697 hz, 770 hz, 852 hz and 941 hz) and four high frequencies (1209 hz, 1336 hz, 1477 hz and 1633 hz)) combinations of paired tones, one from each group, are detected. Each received tone is converted to a digital format and thereafter passed through parallel digital filtering in a microprocessor acting as a tone detector. Each suspect tone is examined twice, once for a short time interval in the range of 10 milliseconds and once for a long time interval in the range of 20 milliseconds. The short time span, generally not capable of resolving the discrete tones in each group one from another, only produces a broad power response to the signals present in each group thus giving a wide band filter. The long time examination is sufficient to discretely resolve each of the chosen four discrete frequencies thus giving a narrow band filter.

Abstract: A high speed bus structure is described which employs an ordinary flat ribbon cable. ECL receivers are coupled to conductor pairs of the cable through resistors which change the capacitive load of the ECL receivers to a resistive load. The receivers are coupled to the cable through a plurality of connectors having spaced-apart pins. The pins in each connector engage less than all of the conductor pairs, thus a plurality of connectors are required to completely couple receivers to all the conductors in the cable. This connector arrangement substantially reduces the parasitic capacitance loading on the cable. The invented high speed bus is able to effectively function at 100 MHz with 80 feet of cable and with 16 receivers coupled to each conductor pair.

Abstract: An inductively coupled sensing circuit for use on a common cable communications system is disclosed. When used in conjunction with transceivers on a common cable system, the circuit is capable of both detecting signals and determining the direction of any colliding signals while the transceiver is operating. An inherently balanced bridge is created by coupling the transmitter lead between two elements of the sensing circuit. Each receiver is provided with means for determining the polarity of the sensing circuit, thereby determining the direction of any incoming signal. The use of this sensing circuit in a common cable system allows a hierarchy among cable users to be created thereby optimizing cable use. A left or right priority is determined by the polarity of an end signal transmitted at the end of each transmission.

Abstract: An improved transmitter/receiver for use on a common cable communications system which permits sending and receiving of data at multiple data rates. Each transmitter first transmits a message alerting the intended receiver. The message also informs the receiver of the rate at which data is to be transmitted. This data rate is a function of the available bandwidth between the transmitting transmitter and receiving receiver. Each transmitter includes a memory of such bandwidth for all receivers on the cable.

Abstract: In a digital information transmission system having an analog-to-digital converter (ADC), an information transmission medium, and a digital-to-analog converter (DAC) all located between a transmitting station and a receiving station, signal transmission is improved by injection of a controlled signal in the form of a symmetric triangle wave sweep having a maximum peak-to-peak amplitude exceeding the magnitude of a few quantization intervals of the ADC and the DAC, introducing frequency components concentrated outside the system frequency spectrum. A class of controlled signals is disclosed. In the preferred embodiment, the controlled signal is injected into the analog information input signal prior to conversion to digital form.