Milgo Electronic Corporation

Novation, Inc.

Robert G Ragsdale

Sang Y Whang

Ran-Fun Chiu

John B Scott

Henry Howard Parrish

Full duplex modems and synchronizing methods and apparatus therefor which allow the relatively low cost realization of full duplex modems compatible with prior art data sets such as the Bell System 212A Data Set. The modems utilize relatively little bandpass line filtering with post demodulation filters which provide normal filtering of second harmonic products, but further also serving to make up for the lack of the ordinarily heavy line or predemodulation filtering commonly used to reject the other channel. In addition, the automatic gain control is provided after the post demodulation filters rather than on the incoming line itself. Carrier sync and timing error corrections are provided under software control, with timing error corrections being achieved by sensing certain phase differences and providing a correction in response thereto. The use of switched capacitor filters, as well as other techniques herein disclosed, allows the use of two identical large scale integrated circuits to provide most of the transmit and receive functions of the modem.

Full duplex modems and synchronizing methods and apparatus therefor

An apparatus capable of transmitting digital data at high data rates over a communication link is disclosed. A carrier signal is modulated by serial groups of digital data signals to be transmitted during a plurality of successively appearing modulation periods. The data-modulated carrier is represented by a unique group of digital signals stored in a memory. The memory upon command, reads out a predetermined sequence of digital signals with each predetermined sequence representing the signal shape of a digital data modulated carrier signal which appears as though it has been passed through a narrow band limited linear phase network. The memory stores a predetermined number of such sequences of digital signals. The number of sequences is four in one preferred embodiment of this invention. In that preferred embodiment, each sequence occupies a spectrum frame which extends in time over four successive modulation periods. Timing at the transmitter insures that the starting time of each frame is successively offset by one modulation period relative to the start of the preceding frame. A summing circuit connected between the memory storage device and an input to the communication link adds the sequences of digital signals as they are read from the memory in a predetermined order. The summing operation generates a composite data modulated signal for application to a communication link.

Integrated circuit modem with a memory storage device for generating a

A data modem that operates to permit the concurrent high speed transmission/reception of digital data over two independent data links or systems, is disclosed. Data bits concurrently applied to a transmitting modem from two independent data sources are interlaced to form a stream of data bits that are effectively grouped as data words to be differentially phase modulated. Modulated data may be transmitted over ordinary voice grade telephone lines to a distant receiver modem at effectively twice the bit rate of the individual data sources. Successive groups of six interlaced data bits are divided into two groups of three bits which are uniquely identified by having a selected phase angle added to or subtracted from the differential phase angle for alternate groups of three bits. The selectively added phase angle is detected at a receiving modem to identify the respective groups of three bits and thereby permit accurate distribution of demodulated data bits to the respective data utilization terminals corresponding to the two data sources.

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Hollywood, FL, United States of America

Robert G Ragsdale