JPH02260846A - Signal interruption detection circuit - Google Patents

Abstract

PURPOSE:To shorten the detection time by providing a nonlinear circuit, a band pass filter, a detector and a low pass filter. CONSTITUTION:A demodulated base band signal demodulated by a regenerative carrier is amplified into a proper amplitude, the resulting signal is subject to nonlinear processing by nonlinear circuits 8, 9 and only a clock component is extracted by a band pass filter 12. The extracted signal is an input signal of a clock synchronizing circuit 13, is detected by a detector 16 and processed into a DC signal by a low pass filter 17 to be a signal representing the presence of a modulation wave. Since the clock component extracted from the demodulation base band signal is detected to detect the signal interruption, a high frequency component is detected and the time constant of the low pass filter is decreased to shorten the detection time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a demodulator for a digital carrier wave transmission system, which includes:
The present invention relates to a signal disconnection detection circuit that detects the presence or absence of an input modulated wave and outputs an alarm.

[Conventional technology]

Conventionally, a human power failure detection circuit has determined the presence or absence of a signal by detecting a demodulated baseband signal. for example,
FIG. 2 shows an example of a demodulator using a conventional detection circuit.

In FIG. 2, the modulated wave input to the signal input terminal IN is combined with the reproduced carrier wave input to the local oscillator input terminal LO to the multiplier 1.
The multipliers are combined, and the multipliers are combined in the multiplier 2 with the reproduced carrier wave that passes through the phase shifter 3 and has a phase difference of 90°. Then, each signal passes through low-pass filters 4 and 5, respectively, and becomes demodulated baseband signals a and b.

The demodulated baseband signals a and b are amplified to an appropriate amplitude by an amplifier 6.7, and then sent to an analog-to-digital converter 1.
0.11, it is a digital signal. At the same time, a clock component is extracted by the non-linear circuit 8.9 and the bandpass filter 12 and inputted to the clock synchronization circuit 13.

In such a demodulator, the signal C from the amplifier 7, which amplifies the demodulated baseband signal to an appropriate amplitude, is detected by the detector 14 and converted to direct current by the low-pass filter I5, thereby determining the presence or absence of a modulated wave. is detected.

Therefore, if there is no input modulated wave or if there is no modulation, no signal component will appear in the outputs of the amplifiers 6 and 7.
The DC voltage output from the low-pass filter 15 changes when there is a modulated wave, and signal interruption is detected based on this change.

[Problem to be solved by the invention]

In the conventional detection circuit described above, since there are low frequency components in the demodulated baseband signal, if the time constant of the low-pass filter 15 is small, the circuit may malfunction in response to the low frequency components. be. Therefore, conventionally, the time constant of the low-pass filter 15 is made sufficiently large. However, if the time constant of the low-pass filter 15 is made sufficiently large, it will take time to detect the presence or absence of a modulated wave and detect a signal interruption, and the detection results may be used to generate alarms for equipment or perform various controls. The problem is that the operation is too slow to reset the circuit.

An object of the present invention is to provide a signal disconnection detection circuit with short detection time.

[Means to solve the problem]

The signal disconnection detection circuit of the present invention includes a nonlinear circuit that demodulates an input signal using a regenerated carrier wave and performs a nonlinear operation on a demodulated baseband signal obtained by band limiting, and a band that extracts a clock frequency component from the output of this nonlinear circuit. It includes a pass filter, a detector that detects the output of the band pass filter, and a low pass filter that converts the output of the detector to DC.

[Effect]

In the above configuration, a clock component extracted from the demodulated baseband signal is detected to detect a signal interruption, so a high frequency component is detected, and the time constant of the low-pass filter is made small to shorten the J detection time. It can be made shorter.

〔Example〕

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

FIG. 1 is a block circuit diagram of an embodiment of the present invention. In this figure, reference numerals 1 to 13 are the same as those shown in FIG. 2, and detailed explanation will be omitted.

That is, 1.2 is a multiplier, 3 is a 90° phase shifter, 4.5 is a low-pass filter, 6.7 is an amplifier, 8.9 is a nonlinear circuit, and 10
．． 11 is an analog-to-digital converter, 12 is a band pass filter, and 13 is a clock synchronization circuit.

Here, a detector 16 and a low-pass filter 17 are connected between the bandpass filter 12 and the clock synchronization circuit 13 to detect signal interruption. In other words,
In this embodiment, a circuit including a wave detector 16° and a low-pass filter 17 is configured to receive a clock component extracted from a demodulated baseband signal as an input signal.

According to this configuration, the demodulated baseband signal demodulated by the regenerated carrier wave is amplified to an appropriate amplitude as in the conventional case, then subjected to nonlinear operation by the nonlinear circuits 8 and 9, and clocked by the bandpass filter 12. Only the components are extracted.

The extracted signal becomes an input signal to the clock synchronization circuit 13, is detected by a wave detector 16, and then converted to a direct current by a low-pass filter 17, and becomes a signal indicating the presence or absence of a modulated wave.

This clock component is obtained from the baseband signal obtained by demodulating the input modulated wave as described above, so when the input modulated wave becomes no signal or no modulation, the clock component is not extracted. Since the waveform after detection by the wave detector 16 is different from that of a normal input modulated wave, the output DC voltage of the low-pass filter 17 changes.

Therefore, this signal disconnection detection circuit can not only distinguish between the input modulated wave being disconnected or unmodulated and the normal state, but also because it uses the extracted clock component at the input of the detection circuit, it can demodulate Compared to conventional circuits using baseband signals, higher frequency components are detected, and the time constant of the low-pass filter 17 can be made smaller.

As a result, this signal disconnection detection circuit can easily be constructed with a short detection time, and unlike conventional circuits, it does not malfunction because it does not have low frequency components.

It goes without saying that the signal disconnection detection circuit of the present invention can be applied to all demodulators that extract a clock from a demodulated baseband signal, and is independent of the modulation method.

[Effects of the Invention] As described above, according to the present invention, by detecting the clock component extracted from the demodulated baseband signal, it is possible to configure a signal disconnection detection circuit that does not malfunction and has a short detection time. Furthermore, detection can always be performed faster than conventional detection circuits regardless of the bit rate of the modulated wave.

[Brief explanation of drawings]

FIG. 2 is a block diagram of a demodulator including an output circuit.

Claims (1)

[Claims] 1. In a signal disconnection detection circuit that detects signal disconnection by demodulating an input signal using a regenerated carrier wave and band-limiting the input signal in a digital carrier wave transmission system and identifying the demodulated baseband signal obtained by band-limiting, a nonlinear operation is performed on the demodulated baseband signal. a band-pass filter that extracts a clock frequency component from the output of this non-linear circuit, a wave detector that detects the output of this band-pass filter, and a low-frequency filter that converts the output of this detector into direct current. A signal interruption detection circuit comprising a filter.