JPS63263844A - Code conversion circuit - Google Patents

Abstract

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.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a high-quality program signal codec, and in particular performs encoding using the instantaneous companding method in accordance with CCITT Recommendation J41 or J42. 1.544 Mb/s transmission line.

[Conventional technology]

The format of the codec output signal according to CCITT Recommendation J41 or J42 is defined as shown in FIG. Therefore, when considering the correspondence with each bit in the telephone channel, in Varlant A, CHn,
CHn+1. There is a possibility that any of CHn+2 will be all 0s. Also + Mariant B.

There is a possibility that the 8 bits corresponding to CHn+ are all 0s. North American PCM primary group 1,544Mb/s
In the transmission line, it is required that there be a signal at a density of ⅛ or more, that is, the data must be 1 in order to extract the clock. To guarantee this.

In the transmission equipment that interfaces with the North American PCM primary group, each of the 8 bits corresponding to the telephone channel are all '0'.
, the 7th bit out of the 8 bits has no effect on side ringing and has less effect on signal transmission.
Force bit to 1”.

[Problem that the invention seeks to solve]

However, the corresponding bit in the program signal format is the 8th. 10th゜6th
This is the bit, and in VILriant B, it is the A-th pit. These bits include bits that are relatively close to the MSB, so if they are forcibly converted to "1#" as described above, there is a drawback that a large amount of noise will be generated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a code conversion circuit capable of eliminating the above-mentioned drawbacks and outputting a high-quality program signal.

[Means for solving problems]

According to the present invention, CCITT Recommendation J41 or J4
2, the program signal codec using the instantaneous companding method includes an all-O detection circuit that detects all 0s in every 8 bits corresponding to a telephone channel of a program signal converted into a PCM signal and outputs a detection signal; Only when the detection signal is received from the all-O detection circuit, the LSB of every 8 bits is inverted to "IIn" and outputted.

In other cases, a code conversion circuit is obtained which is characterized by having a bit inversion circuit that outputs the program signal as it is.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. In fig.

3 is a PCM program signal input terminal; l is an all-zero detection circuit that detects all 0s in every 8 bits corresponding to the telephone channel of the Pα-encoded program signal and outputs a detection signal;
2 inverts the LSB of the corresponding 8 bits to 1'' and outputs it to the output terminal 4 only when receiving the detection signal from the all-O detection circuit 1, and at other times, outputs the program signal as it is to the output terminal. This is a sign inversion circuit that outputs to 4.

Therefore, at the output of the sign inversion circuit 2, the corresponding 8 bits of the telephone channel will no longer be all O's. Therefore, even if this output is input to a transmission device that interfaces with the North American PCM primary group.

Total O will not be detected and will not generate much noise.

〔Effect of the invention〕

As explained above, one aspect of the present invention is an all-zero detection circuit.

By using the sign inversion circuit, when using a program signal codec that interfaces with the North American PCM primary group, it is possible to avoid the influence of the all-zero suppression circuit included in the interface device and transmit a high-quality program signal.

Note that devices that interface with the European PCM primary group often use HDB-3 as the transmission path code, so the above-mentioned problem does not occur.

[Brief explanation of the drawing]

FIG. 1 shows a code conversion circuit according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the format of a codec output signal according to CCITT Recommendation J413) or J42. l...All O detection circuit, 2...Sign inversion circuit, 3...
・PCM Norogram signal input terminal, 4...P Cvl
Program signal output terminal.

Claims (1)

[Claims] 1. In a program signal codec using the instantaneous companding method in CCITT Recommendation J41 or J42,
an all-zero detection circuit that detects all zeros in every 8 bits corresponding to the telephone channel of a program signal converted into a PCM signal and outputs a detection signal; and an all-zero detection circuit that receives the program signal and outputs the detection signal from the all-zero detection circuit. a bit inversion circuit that inverts the LSB of each of the 8 bits to "1" and outputs it only when the program signal is received, and outputs the program signal as it is at other times. circuit.