ALIASING NOISE ELIMINATING SYSTEM

摘要

PURPOSE:To eliminate aliasing noise generated by out-of-area charging signals in the speech path disk of a PCM terminal station equipment for converting analog audio signals transmitted from a two-wire subscriber's line connected to a public telephone set to PCM codes and converting PAM coded digital signals to analog signals. CONSTITUTION:A rectangular wave oscillation circuit 1 outputs the rectangular wave signals of an out-of-area charging signal frequency. A synchronizing circuit 2 synchronizes the rectangular wave signals which are the output of the rectangular wave oscillation circuit 1 and synchronizing signals inputted to a PCMCODEC 6. A low-pass filter 3 extracts sine signals from the synchronized rectangular wave signals. An analog switch 4 is controlled by an external charging signal control circuit and transmits the output of the low-pass filter 3 to the four-wire reception side terminal of two-wire/four-wire conversion circuit 5 only for the required time. The PCMCODEC 6 is provided with a transmission side A/D conversion circuit 61 and a reception side D/A conversion circuit 62 and performs the analog/digital conversion of transmission/reception signals.