Multilevel signal transmission system

Claim 2

Apparatus for transmitting a multilevel signal having a given number of levels over a transmission line having input and output terminals said apparatus comprising: transmission means coupled to the input terminal of the transmission line, said transmission means including reference means for providing a reference level signal having a fewer number of levels than the given number and for inserting the reference level signal in a train of the multilevel signals at predetermined time intervals, the levels of the reference level signal being of predetermined level values; and receiving means coupled to the output terminal of the transmission line, said receiving means including detecting means for detecting an error difference between the levels of the transmitted reference level signal sampled at predetermined time positions thereof and the predetermined level values, and adjustment means responsive to the detected error difference for varying the DC level of the transmitted signal.

Claim 3

Apparatus as claimed in claim 1, wherein said adjustment means is responsive to the detected error difference for adjusting the amplitude of the transmitted multilevel signal to compensate for variations in the gain of the transmission line.

Claim 4

Apparatus as claimed in claim 1, wherein said transmission means includes means for removing the DC component from the multilevel signal and the inserted reference level signal to be transmitted, said receiving means including restoring means responsive to the detected error difference for restoring the removed DC component into the transmitted multilevel signal.

Claim 5

Apparatus as claimed in claim 1, wherein said transmission means includes: storage means; clock means for generating a first, repetitive clock signal at intervals of T/m where T is a predetermined interval of time and m is a predetermined interger and for generating a second, repetitive clock signal at an interval of T/(m+1); means responsive to the first clock signal for stOring in said storage means a train of the multilevel signals; means responsive to the second clock signal for retrieving from said storage means a train of the multilevel signal; and means for inserting at the time intervals of T the reference level signal into the train of multilevel signals retrieved from said storage means.

Claim 6

Apparatus as claimed in claim 1, wherein each level of the multilevel signals to be transmitted is representative of a binary number of n bits where n is a predetermined integer, said transmission means including means for providing the levels of the reference level signal of a selected magnitude at the transition points of binary digit of a selected position.

Claim 7

Apparatus as claimed in claim 5, wherein said detection means detects the error difference between the levels of the transmitted reference level signal and the predetermined level values as determined by the binary digit of the selected position.

Claim 8

Apparatus as claimed in claim 6, wherein said detection means detects the error difference between the levels of the received reference level signal and the predetermined level values for at least two level values and said adjusting means combines at least two binary digits of the selected position, to correct for a change in the DC level of the transmission line.

Claim 9

Apparatus as claimed in claim 6, wherein said detection means detects the error difference between the levels of the transmitted reference level signal and the predetermined level values by extracting at least two levels, and said adjusting means effects correction in the gain of the transmission line by combining at least four binary digits of the selected position and a more significant position.

Claim 10

Apparatus as claimed in claim 6, wherein said detection means determines the error difference between the levels of the transmitted reference level signal and the predetermined level values with respect to the binary digit of the selected position to provide signals 1 and 0 of the binary digit, said detection means including filter means for integrating the binary signals; and said receiving means further includes differential amplifier means responsive to the integrated output signal of said filter means, for varying the DC level of the transmitted multilevel signal to compensate for variations in the DC level of the transmission line.

Claim 11

Apparatus as claimed in claim 6, wherein said detection means detects the difference between the levels of the received reference level signal and the predetermined level values, with respect to the binary digit of the selected position and that digit of a more significant digit, to provide output signals indicative of the difference in the form of a 1 and 0, the binary output signals corresponding to the two binary digits; said receiving means further includes coincidence means responsive to the two output signals for deriving an output signal indicative of the coincidence of the two output signals; integrating means for averaging the output signal derived from said coincidence means; and attenuator means for varying the level of the transmitted multilevel signal in accordance with the averaged output signal derived from said integrating means.

Claim 12

Apparatus as claimed in claim 1, wherein said receiving means includes attenuator means coupled to receive the transmitted multilevel signal; differential amplifier means coupled to receive the transmitted multilevel signal; a multilevel decoding circuit for receiving and detecting the levels of the received multilevel signal and for converting the detected levels into binary digit signals of n bits; first logic means coupled to said multilevel decoding circuit for providing signals indicative of the conditions 1 and 0 of the binary digits of the selected position of the reference level signal; first integrating means coupled to said first logic means for providing a first averaged signal thereof to said differential amplifier; seCond logic means coupled to said multilevel decoding circuit for providing output signals indicative of the conditions 1 and 0 of the binary digit of the selected position of the reference level signal and the binary digit of a more significant position; second integrating means coupled to said second logic means for providing a second averaged signal thereof to said attenuator means to thereby adjust the amplitude of the transmitted multilevel signal dependent upon the second averaged output signal.