| 摘要 |
PURPOSE:To transmit a program signal without generating noise and with high quality, by providing an all zero detection circuit which detects all zeros at every 8 bits corresponding to the telephone channel of the program signal converted to a PCM signal and outputs a detecting signal, and a bit inversion circuit which inverts and outputs an LSM at every 8 bits to (1) only when the detecting signal is received from the all zero detection circuit. CONSTITUTION:The all zero detection circuit 1 detects all zeros at every 8 bits equivalent to the telephone CH of a PCM-encoded program signal, and outputs the detecting signal. A code inversion circuit 2 inverts the LSB out of corresponding 3 bits to (1) only when the detecting signal is received from the all zero detection circuit 1, and outputs it to an output terminal 4, and in other cases, the program signal is outputted to the output terminal 4 as it is. Therefore, it is possible to prevent all of the 8 bits of the corresponding telephone CH from being set at zeros in the output of the code inversion circuit 2. Thereby, even when the output is inputted to a transmission equipment interfaced to the PCM firstorder group of a North American system, no all zeros are detected, and the generation of large noise can be prevent from occurring. |
