JPH0648829B2 - Signal loss detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a digital carrier transmission type demodulator,
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, an input break detection circuit detects the presence or absence of a signal by detecting a demodulated baseband signal. For example,
FIG. 2 shows an example of a demodulation device using a conventional detection circuit.

In FIG. 2, the modulated wave input to the signal input terminal IN is multiplied by the reproduced carrier wave input to the local oscillator input terminal LO by the multiplier 1, and also passes through the phase shifter 3 to obtain a phase difference of 90 °. Is multiplied in the multiplier 2 by a reproduced carrier having Then, each signal passes through the 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 have an appropriate amplitude by amplifiers 6 and 7, and the analog-digital converter 1
It is made a digital signal by 0 and 11. At the same time, the clock components are extracted by the non-linear circuits 8 and 9 and the band pass filter 12 and input to the clock synchronization circuit 13.

In such a demodulator, the signal c from the amplifier 7 which is obtained by amplifying the demodulated baseband signal to an appropriate amplitude is detected by the detector 14 and converted into a direct current by the low-pass filter 15 so that the presence or absence of the modulated wave is detected. Is detected.

Therefore, when there is no input modulated wave or no modulation, no signal component appears in the outputs of the amplifiers 6 and 7,
The DC voltage output from the low-pass filter 15 changes with respect to the case where there is a modulated wave, and a signal break is detected based on this change.

[Problems to be Solved by the Invention]

In the above-described conventional detection circuit, since the demodulated baseband signal has a low frequency component, if the time constant of the low pass filter 15 is small, the circuit may malfunction in response to the low frequency component. is there. 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 as described above, it takes time to detect the presence or absence of a modulated wave and to detect a signal break, and the detection result is used as an alarm for the device or various controls. There is a problem that the operation is too slow to reset the circuit.

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

[Means for Solving the Problems]

The signal loss detection circuit of the present invention is a non-linear circuit that performs a non-linear operation on a demodulated baseband signal obtained by demodulating an input signal with a reproduction carrier and band-limiting, and a band for extracting a clock frequency component from the output of the non-linear circuit. It has a pass filter, a detector for detecting the output of the band pass filter, and a low-pass filter for converting the output of the detector into a direct current.

[Action]

In the above-mentioned configuration, the clock component extracted from the demodulated baseband signal is detected to detect the signal disconnection, so a high frequency component is detected, and the time constant of the low-pass filter is reduced, and the detection time is reduced. Can be shortened.

〔Example〕

 Next, the present invention will be described 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 description thereof will be omitted. That is, 1 and 2 are multipliers, 3 is a 90 ° phase shifter, 4 and 5 are low-pass filters, 6 and 7 are amplifiers, 8 and 9 are non-linear circuits, 10 and 11 are analog-digital converters, Reference numeral 12 is a bandpass filter, and 13 is a clock synchronization circuit.

Further, here, a detector 16 and a low-pass filter 17 are connected between the band pass filter 12 and the clock synchronization circuit 13 to detect a signal break. In other words,
In this embodiment, the circuit composed of the detector 16 and the low-pass filter 17 has a configuration in which the clock component extracted from the demodulated baseband signal is used as the input signal.

According to this configuration, the demodulated baseband signal demodulated by the reproduced carrier wave as in the conventional case is amplified to an appropriate amplitude, then subjected to the nonlinear operation by the nonlinear circuits 8 and 9, and is clocked by the bandpass filter 12. Only the components are extracted.
The extracted signal serves as an input signal to the clock synchronization circuit 13 and is detected by the detector 16 and then converted into a direct current by the low-pass filter 17 to become a signal indicating the presence or absence of a modulated wave.

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

Therefore, this signal loss detection circuit uses the extracted clock component at the input of the detection circuit as well as the one that can distinguish the normal state from the case where the input modulated wave is disconnected or non-modulated, A high frequency component is detected as compared with a conventional circuit using a baseband signal, and the time constant of the low pass filter 17 can be reduced.

As a result, the signal disconnection detection circuit can easily form a detection circuit having a short detection time, and does not malfunction because it does not have a low frequency component unlike the conventional circuit.

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

〔The invention's effect〕

As described above, the present invention can configure a signal loss detection circuit that does not malfunction and has a short detection time by detecting the clock component extracted from the demodulated baseband signal. Further, regardless of the bit rate of the modulated wave, detection can always be performed faster than the conventional detection circuit.

[Brief description of drawings]

FIG. 1 is a block diagram of a demodulator having a signal loss detection circuit according to the present invention, and FIG. 2 is a block diagram of a demodulator having a conventional signal loss detection circuit. 1, 2 ... Multiplier, 3 ... 90 ° phase shifter, 4, 5 ... Low-pass filter, 6, 7 ... Amplifier, 8, 9 ... Non-linear circuit, 1
0, 11 ... Analog-digital converter, 12 ... Band pass filter, 13 ... Clock synchronization circuit, 14 ... Detector, 15 ... Low-pass filter, 16 ... Detector, 17 ... … Low-pass filter.

Claims (1)

[Claims] 1. A signal loss detection circuit for detecting a signal loss by identifying a demodulation baseband signal obtained by demodulating an input signal in a digital carrier wave transmission system by a reproduced carrier wave and band-limiting, to obtain the demodulation baseband signal. A non-linear circuit that performs non-linear operation, a band-pass filter that extracts the clock frequency component from the output of this non-linear circuit, a detector that detects the output of this band-pass filter, and a DC output of this detector. And a low-pass filter that operates.