SE7504909L - MODULATOR - Google Patents

Abstract

1505750 Multiplex system COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 28 April 1975 [29 April 1974] 17492/75 Heading H4M In a digital multiplex system on which digital data q 1 -q n on n channels is to be transmitted in frequency multiplex, the digital data is sampled successively at 1 and the samples are used to modulate a base frequency carrier Fo. Thereafter the modulated base frequency is passed to a unit 21, which produces: (a) n coded words representing the phase change #i for a given sample as compared with the phase of the previous sample of the same channel and (b), interleaved with these words, n words representing the phase increments #i of the respective transposition frequencies. These words pass to an adder 23, where they are combined with the output of a memory 24 containing the information from the previous sample of the same channel. The adder output is fed to change the memory and also to control a read-only memory 25 which contains a table of digitally encoded sine and cosine values. The values related to the particular phase are read out to a time shared band limit recursive filter 3 whose output is passed to one input of a transposition circuit 4. This receives at its other input an n interleaved series of digitally coded transposition samples, such that there is produced Si sin (#i+#i) where Si is the maximum amplitude. The transposed outputs are passed to a combining or multiplexing circuit 5 in which the various signals are frequency multiplexed, after which they are passed through a D/A converter 6, and a low pass band limiting filter to the system output.