JPH0773251B2 - Demodulation circuit for PCM transmission line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has means for detecting a signal disturbance in a PCM transmission line portion in a demodulation circuit of a multi-phase FSK communication system using a PCM transmission line. The present invention relates to a demodulation circuit for PCM transmission line. Especially P
The present invention relates to a PCM transmission line demodulation circuit having line fault detection means, which is suitable for a high-speed FSK modulator / demodulator for system protection using a CM transmission line.

〔Overview〕

The present invention is a PC using a multiplex conversion device for performing digital time division multiplex conversion of voice band analog signals and vice versa.
In the demodulation circuit of the FSK communication system that uses the M carrier line, when the PCM transmission line is disturbed, the unwanted sideband component due to the error PAM pulse generated in the digital-analog conversion of the PCM device is detected and output from the FSK demodulation circuit. The output of unnecessary signals is prevented by limiting the signal.

[Conventional technology]

Conventionally, as the form of the line failure of the FDM transmission line, there are instantaneous interruption (level interruption) and noise generation. Instantaneous interruption can be detected by adding a level drop detection circuit.In noise detection, noise components are evenly distributed to each channel, so by adding a noise detection circuit independent of the signal channel. It was possible to detect each at high speed.

[Problems to be solved by the invention]

However, since there is a conversion process between analog signals and digital signals in the PCM transmission line, when a data error or loss of synchronization occurs in the digital signal part, it occurs in the FDM transmission system when converting to an analog signal. There is a drawback that a drooping signal that does not exist is not always detected by the conventional line fault detection circuit, and an unnecessary signal for a certain time or longer is output at the output of the demodulation circuit.

The object of the present invention is to eliminate PC by eliminating the above-mentioned drawbacks.
Detects line failure in M transmission line at high speed and
Another object of the present invention is to provide a demodulation circuit for a PCM transmission line that detects noise generation in a DM transmission line at high speed and prevents the output of unnecessary signals for a certain period of time or longer.

[Means for solving problems]

The present invention is a PC using a multiplex conversion device for performing digital time division multiplex conversion of voice band analog signals and vice versa.
In the demodulation circuit of FSK communication system using M carrier line,
It is provided for each channel, receives the FSK modulated wave input signal of each channel as an input, detects other signal components mixed in the FSK modulated wave input signal, and generates a control signal for stopping the output of the FSK demodulation circuit. It is characterized by including an unnecessary component detection circuit.

[Action]

Next, the principle of operation of the present invention will be described with reference to the drawings.

FIGS. 6 and 7 (a) to (d) show a block structure on the transmission side, for explaining how signals on the respective channels are multiplexed on the transmission side and transmitted as PCM signals. FIG.

FIG. 6 is a diagram showing an example of a block configuration on the transmission side.
In this configuration example, the inputs of the input terminals 11, 12 and 13 are used as phase comparison signal inputs, and the outputs k, l and m are output.
To the PCM-24 device 17 as input to FSK modulation circuits 14, 15 and
It consists of 16. Reference numeral 18 is an output terminal of the PCM-24 device 17.

The phase comparison signals input to the input terminals 11, 12, and 13 are FS-modulated by the FSK modulation circuits 14, 15, and 16, and the PCM−
24 Inputs to device 17 inputs k, l and m
After being digitally converted, the 24-channel time division multiplexed PCM signal is output to the terminal 18.

7 (a) to 7 (d), FIG. 7 (a) shows PCM-2.
Figure 4 (b) shows the signal input of channel n of 4 devices.
Shows a pulse obtained by sampling the signal input of channel n with an 8 kHz sampling signal every 125 μs, and FIG.
Indicates that the sampling pulse of channel n is encoded into 8-bit data, and FIG. 7D shows that the encoded data of channels 1 to 24 are time-division multiplexed. Note that the signal s in FIG. 7D indicates a multi-frame synchronization bit.

FIGS. 3 (a)-(c), 4 (a)-(c) and 5 (a)-(b) show the PCM as the operating principle of the present invention.
It is an explanatory view for explaining that an unnecessary sideband component outside a signal band occurs at the time of disturbance in a transmission line.

3 (a)-(c), FIG. 3 (a) shows PCM-24.
The input data of the device is shown in FIG.
The PAM pulse is reproduced in accordance with the 8-bit data value of the above, and FIG. 7C shows the PAM pulse converted into the original voice band signal through the low-pass filter.

4 (a) to (c), FIG. 4 (a) shows the normal state.
Shows the PAM pulse, (b) shows a case where PAM pulses h ₁ becomes h _1a by the input data errors. FIG. 11C is a signal obtained by subtracting the signal shown in FIG. 11B from the signal shown in FIG. 11A, and shows that it is considered that a single PAM pulse for the error is added due to an error at the normal time.

5 (a) and (b), the same figure (a) shows a single-shot PA.
The M pulse is shown, and the figure (b) shows the spectrum of a single PAM pulse.

here, Is. From this, data error causes error PAM
It can be seen that when a pulse occurs, a continuous spectrum occurs and falls into the entire voice band.

The present invention has, as an unnecessary component detection circuit, band-pass filtering characteristics that allow the above-mentioned unnecessary sideband components to pass.
At the time of disturbance such as error or loss of synchronization in the PCM transmission line, unnecessary sideband components generated in the process of converting the PCM signal to the FDM signal are detected, and the output of the FSK demodulation circuit is controlled to be stopped.

Therefore, when the PCM transmission line is disturbed, the FSK demodulation circuit is prevented from outputting unnecessary signals for a certain period of time or longer.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In this embodiment, the outputs a, b and c of the PCM-24 device 7 are used.
FSK demodulation circuits 1, 2 and 3 which respectively output the outputs d, e and f, an unnecessary component detection circuit 4 which inputs the output a and outputs the control signal g to the FSK demodulation circuit 1, and an output b. To the FSK demodulation circuit 2 and to input the control signal h to the FSK demodulation circuit 2, and to output the control signal i to the FSK demodulation circuit 6 unnecessary component detection circuit 6. 8 is the input terminal of the PCM-24 device 7,
9, 10, and 11 are FSK demodulation circuits 1, 2, and 3, respectively.
Output terminal. Further, as shown in FIG. 2, the unnecessary component detection circuits 4, 5 and 6 include band-pass filtering circuits having band-pass filtering characteristics that allow the unnecessary side-band component to pass by dividing the audio 1-channel band. There is.

The feature of the present invention is that the unnecessary component detection circuits 4, 5 and 6 are provided in FIG.
The output of the K demodulation circuits 1, 2 and 3 is controlled.

Next, the operation of this embodiment will be described. In Fig. 1, if no disturbance occurs in the PCM transmission line, the PCM
-24 The outputs a, b and c of the device 7 are the FSK demodulation circuit 1 and the FS signal which are digital-analog converted accurately, respectively.
2 and 3 are given. FSK demodulation circuits 1, 2 and 3
Respectively frequency-discriminates the FS signal and outputs d, e and f
The phase comparison signal is demodulated to output terminals 9, 10 and 11
Is output to. On the other hand, unnecessary component detection circuits 4, 5 and 6
Since the input has a bandpass filter that passes frequency components outside the signal band, when the PCM transmission line is in a normal state, the FS input signal component does not drop and there are no out-of-band components, so unnecessary components The control signals g, f and i from the detection circuits 4, 5 and 6 are in a state where no PCM transmission path abnormality is detected, and the NOR state signals are given to the FSK demodulation circuits 1, 2 and 3.

Here, if the PCM transmission is disturbed, the data of the PCM signal is erroneous, and the outputs a, b, and c which are digital-analog converted by the PCM-24 device 7 are erroneous. The outputs d, e and f of 2 and 3 are erroneously output, and the PCM-24 device 7
Therefore, there is a possibility that erroneous output continues for a considerably long time until the loss of synchronization is detected and the signal is lost.

Assuming that there is a data error on the PCM transmission line only in the signal of the channel of the output a of the PCM-24 device 7 in FIG. 1, the output a of the erroneous signal is added to the FSK demodulation circuit 1. However, the normal signal outputs b and c are added to the FSK demodulation circuits 2 and 3 using the other channels, and the noise is evenly distributed to each channel like the conventional FDM transmission line. Since the noise does not occur, the noise detection method on the dedicated 1-channel may not detect the data error on the PCM transmission line.

In the unnecessary component detection circuits 4, 5 and 6 in each phase, as described above, the erroneous signal of the channel of the output a is FS.
When added to the K demodulation circuit 1, the phenomenon that an unwanted sideband outside the signal band is generated at the output a is used. The unnecessary component detection circuit 4 detects an out-of-band component, applies an output lock signal as a control signal g to the FSK demodulation circuit, and performs output lock control so as to prevent erroneous output for a predetermined time or longer.

That is, in this embodiment, the unnecessary component detection circuit 4,
When the disturbance of the input signal is detected at 5 and 6, a control signal for stopping the output is given to the FSK demodulation circuits 1, 2 and 3 so that unnecessary signals do not continue to the outputs d, e and f.

In addition, the unnecessary component detection circuits 4, 5 and 6 change the detection sensitivity and the width of the unnecessary signal to detect the FSK.
It is possible to detect only the disturbance that affects the demodulation circuit.

In this embodiment, the signal has three channels, but the same applies even if the signal channel is an N channel. Furthermore, it has a noise detection function in the conventional FDM transmission line, and can be used in a mixed transmission line of PCM and FDM.

〔The invention's effect〕

As described above, according to the present invention, the circuit for detecting the unnecessary sideband component due to the error PAM pulse generated in the process of digital-analog conversion of the PCM-24 device at the time of the disturbance in the PCM transmission line is the FSK demodulation circuit of each phase. With this, it is possible to prevent the FSK demodulation circuit output from outputting an unnecessary signal for a certain time or more when the PCM transmission line is disturbed. Further, it can also serve as a noise detecting means in the conventional FDM transmission line, and it can be an FSK demodulation circuit that can be used in both FDM and PCM transmission lines, and its effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a frequency characteristic diagram of the unnecessary component detection circuit. 3 (a)-(c), 4 (a)-(c), and 5 (a)-(b) are explanatory views of the principle of operation of the present invention. 6 and 7 (a) to 7 (d) are views for explaining the operation of the transmitting side of the present invention. 1-3 ... FSK demodulation circuit, 4-6 ... unnecessary component detection circuit, 7, 17 ... PCM-24 device, 8, 11, 12, 13 ... input terminal element, 9-10, 18 ... output Terminals, ... Input terminals, 14, 15,
16 ... FSK modulation circuit, a to c ... (PCM-24 device) output, d to f ... (FSK demodulation circuit) output, g to i ... control signal, k to m ... (transmitting side) Input (for PCM-24 device).

Claims (1)

[Claims] 1. A multiplex conversion device for performing digital time division multiplex conversion of a voice band analog signal and its inverse conversion is used.
An FSK communication system demodulation circuit that uses a PCM carrier line is provided for each channel and receives the FSK modulated wave input signal of each channel as an input to detect other signal components mixed in the FSK modulated wave input signal. , A demodulation circuit for a PCM transmission line, which includes an unnecessary component detection circuit that generates a control signal for stopping the output of the FSK demodulation circuit.