PURPOSE: To directly make TDM-FDM conversion and to simplify the constitution of a converter, by reducing the amount of operation together with an FIR filter and a modulation section.
CONSTITUTION: An inputted 1 TDM multiplex signal is separated at 2 and a signal corresponding to each channel CH is inputted to a multiplying circuit 3. An odd channel CH is shifted by -2kHz at circuits 6-1∼6-11 through a cyclic type digital filter 4 in 8kHz operation and a noncyclic type digital FIR filter 5 of 16kHz operation, and an even channel is shifted by +2kHz at circuits 6-2∼ 6-12. Next, additions 7-1∼7-6 are made, and through an FIR filter 8 of 32kHz operation, -4kHz shift is made at 9-1∼9-5 circuit and +4kHz shift is made at 9-2∼ 9-6 circuits and additions 10-1∼10-3 are made. Through FIR filters 11-1∼ 11-3 of 224kHz operation, a real part is picked up at filter 15 via multiplication circuits 12-1, 12-2 and an addition circuit 13, and a digital FDM signal is outputted at 16.
MURANO KAZUO
SOEJIMA TETSUO
AOYAMA TOMONORI
YOSHIMURA HIROSHI
WAKABAYASHI KIYOHISA
NIPPON TELEGRAPH & TELEPHONE