JPH11187077A - Signal output device with echo check function, circuit and method for demodulation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal output device with echo check function, a circuit and a method for demodulation with which a signal modulated by a two-phase phase shift keying(PSK) system can be demodulated through a simple data processing with a small scale circuit. SOLUTION: A band pass filter 11 removes higher harmonic wave components and PCM modulated signal components such as noises in a two-phase PSK modulated signal 21 and converts the signal into a two-phase PSK modulated signal 22. A comparator 12 compares the two-phase PSK modulated signal 22 with a reference value S. When the occurrence of an suspension period (m) in a binary signal 23 is judged, a monostable multivibrator 13 outputs one rectangular wave. When a change point of an output signal 24 from the monostable multivibrator 13 is detected, a toggle flip-flop 14 inverts the level of its own output signal 25 and generates a demodulated signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a two-phase PSK (Phas
e Shift Keying) The present invention relates to a demodulation circuit and a demodulation method suitable for demodulating a modulated signal, and it is possible to confirm by echo back whether or not a command signal transmitted to an artificial satellite or the like has been normally transmitted. The present invention relates to a signal output device with an echo check function.

[0002]

2. Description of the Related Art There is a command signal output device for outputting a command signal for controlling the attitude of an artificial satellite. As such a command signal output device, as shown in FIG.
Phase PSK modulation circuit 51, output circuit 52, input circuit 5
3 and a demodulation circuit 54.

A two-phase PSK modulation circuit 51 is a PCM (Puls
The digital signal modulated by e Code Modulation (pulse code modulation) is modulated by two-phase PSK and
The phase PSK modulation signal 41 is output via an output circuit 52 to a subsequent device such as a transmitter.

[0004] The input circuit 53 re-inputs the two-phase PSK modulated signal 41 that is folded at the end of the two-phase PSK modulated signal output to the antenna of the transmitter. The demodulation circuit 54 demodulates the re-input two-phase PSK modulation signal to obtain a PCM digital signal 46.

The command signal output device is a two-phase P
The PCM digital signal before the SK modulation is compared with the PCM digital signal demodulated after the PCM digital signal is modulated and input again from the antenna end.

On the basis of the result of the comparison, the command signal output device confirms whether or not the two-phase PSK modulated signal has been transmitted normally.

[0007] As a result of the comparison, the case where the two digital signals of the PCM system coincide with each other is the case where a signal which has been normally subjected to two-phase PSK modulation is transmitted. On the other hand, when they do not match, it means that a normal two-phase PSK modulation signal could not be transmitted.

A conventional two-phase PSK demodulation circuit 54 used in such a command signal output device will be described below.

The conventional two-phase PSK demodulation circuit 54 includes a band-pass filter 31, a sample-and-hold circuit 32, a phase tracking circuit 33, and an A / D converter 34.
And an arithmetic circuit 35.

The band-pass filter 31 allows only a signal in a predetermined frequency band to pass. The phase tracking circuit 32 outputs 0 degree, 90 degree, 180 degree,
A timing signal indicating the time point of 70 degrees is output.

The sample-and-hold circuit 33 converts the signal passed through the band-pass filter 31 into a phase tracking circuit 3
The sampling is performed at the timing indicated by the timing signal output from the counter 2, and the sampled value is held.

The A / D converter 34 converts an analog signal held by the sample and hold circuit 33 into a digital signal.

The arithmetic circuit 35 sequentially compares the value indicated by the digital signal output from the A / D converter with a predetermined reference value, and inverts the level of its own output signal according to the comparison result.

That is, the arithmetic circuit 35 sequentially compares the digital signal output from the A / D converter 34 with the reference value, and when the digital signal gradually increases and exceeds the reference value, and When the digital signal gradually decreases and becomes smaller than the reference value, the level of its own output signal is inverted.

Next, the operation of the conventional demodulation circuit shown in FIG. 3 will be described with reference to FIG. First, a two-phase PSK signal 41 shown in FIG. 4A is input to a conventional demodulation circuit. The two-phase PSK signal 41 is a signal echo-backed out of the two-phase PSK signals modulated and output by the command signal output device.

The two-phase PSK signal 41 has its noise removed by the band-pass filter 31 and is output as a two-phase PSK signal 42 shown in FIG.

The two-phase PSK signal 42 is supplied to the phase following circuit 32
And input to the sample and hold circuit 33.

The phase follow-up circuit 43 includes a two-phase PSK signal 42
A timing signal 43 indicating each time point of 0 °, 90 °, 180 °, and 270 ° in the phase is output to the sample-and-hold circuit 33.

The sample and hold circuit 33 converts the two-phase PSK modulation signal at the timing indicated by the timing signal 43 output from the phase tracking circuit 32, that is, at the sample point in the two-phase PSK modulation signal 42 shown in FIG. Sample and hold the sampled value.

The sample value 44 held by the sample and hold circuit 33 is output to the A / D converter 34.

The sampled value 44 is stored in the A / D converter 34
And sequentially converted into a digital signal 45 shown in FIG.

The digital signal 45 is sequentially transmitted to the arithmetic circuit 3
5 to be operated. When the results of the sequential calculations are arranged in time series, for example, a waveform indicated by a broken line in FIG. 4D is obtained.

The arithmetic circuit 35 determines whether the calculated value exceeds a preset reference value (K1 in FIG. 4D) (time points T1 and T3 in FIG. 4D) or the calculated value. Is the reference value K
When it falls below 2 (time points T2 and T4 in FIG. 4), it inverts the level of its own output signal and outputs it as a two-phase PSK demodulated signal 46 shown in FIG.

A conventional demodulation circuit is disclosed in
-279050.

The demodulation circuit described in Japanese Patent Application Laid-Open No. 2-279050 detects a phase change point by digitally correlating a coherent two-phase PSK input signal with a comparator and a shift register. Japanese Patent Laid-Open No. 2-279
The demodulation circuit described in Japanese Patent Publication No. 050 aims to demodulate any coherent two-phase PSK modulation signal without adjustment.

[0026]

However, in the conventional two-phase PSK demodulation circuit shown in FIG. 3, in order to demodulate a two-phase PSK modulation signal, a band-pass filter 31, a phase tracking circuit 32, a sample and hold A circuit 33;
Since the A / D converter 34 and the arithmetic circuit 35 are required, there is a problem that the data processing process for the demodulation becomes complicated and the circuit scale becomes large.

In the two-phase PSK demodulation circuit described in Japanese Patent Application Laid-Open No. 2-279050, a plurality of comparators, a 4-bit shift register, a decoder, and a flip-flop are essential components. Phase PS
There is a problem that the data processing process for demodulating the K modulation signal becomes complicated and the circuit scale becomes large.

The conventional two-phase PSK demodulation circuit shown in FIG. 3 and the two-phase PSK demodulation circuit described in JP-A-2-279050 both use a band-pass filter as a component, but remove noise. There is a problem that the bandpass filter is used for the purpose, and the function of the bandpass filter is not sufficiently exhibited.

The present invention has been made in view of the above situation, and has a signal output with an echo check function which can demodulate a signal modulated by a two-phase PSK system in a simple data processing step and by a small-scale circuit. An object is to provide a device, a demodulation circuit, and a demodulation method.

Further, the present invention provides a signal output device with an echo check function which can demodulate a two-phase PSK modulated signal by effectively utilizing the effect of extracting a phase change point of the two-phase PSK modulated signal by a band-pass filter. An object is to provide a demodulation circuit and a demodulation method.

[0031]

To achieve the above object, a demodulation circuit according to a first aspect of the present invention comprises a filter for passing a signal in a predetermined frequency band, an amplitude of a signal passing through the filter, and A comparator for comparing a signal with a predetermined reference value and outputting a signal of a level corresponding to the comparison result; detecting means for determining whether an output signal of the comparator has become constant over a predetermined time or more; Output means for changing an output level when the means determines that the output level has become constant for the predetermined time or more.

According to such a configuration, the modulation signal input to the filter can be demodulated and output from the output means, so that the circuit scale of the demodulation circuit can be made very small.

[0033] The output means may have a binary output level, and invert the output level when the detection means determines that the output level has become constant for the predetermined time or more.

[0034] The filter may be a band-pass filter, and the band-pass filter is a signal to be a signal to be demodulated by the present demodulation circuit, and is a two-phase modulation modulated by a two-phase modulation. The modulation frequency of the signal may be included in the pass band, and the frequency of the modulated signal component of the two-phase modulated signal may be included in the non-pass band.

According to such a configuration, the two-phase modulation signal modulated by the two-phase modulation method is demodulated by effectively using the action of extracting the phase change point of the two-phase PSK modulation signal by the band-pass filter. A demodulation circuit capable of performing the above can be realized by a small-scale circuit.

[0036] The filter may be a band-pass filter, and the band-pass filter is a signal to be a signal to be demodulated by the present demodulation circuit, and is a two-phase modulated signal modulated by a two-phase modulation method. An attenuation band that includes a modulation frequency of a signal in a pass band and includes a frequency of a modulated signal component of the two-phase modulation signal and a frequency higher than the modulation frequency of the two-phase modulation signal, the attenuation ratio being larger than the pass band. And may have characteristics.

According to such a configuration, the band-pass filter can remove noise included in the two-phase modulated signal and having a frequency higher than the modulation frequency of the two-phase modulated signal. The modulated signal component of the two-phase modulation signal can be extracted. Therefore, according to such a configuration, it is possible to configure a demodulation circuit that effectively uses the action of extracting the phase change point of the two-phase PSK modulation signal by the band-pass filter, without increasing the circuit scale of the demodulation circuit. In addition, a demodulation circuit resistant to noise can be configured.

The reference value of the comparator is a value smaller than the maximum amplitude value of the modulation frequency component of the signal that has passed through the filter, and is the value of the modulated signal component of the signal that has passed through the filter. The value may be larger than the maximum amplitude value.

The detecting means detects a period during which the level of the output signal of the comparator is substantially constant,
A monostable multivibrator for outputting one pulse when the fixed period exceeds the predetermined time, wherein the output means has a binary output level of a high level and a low level; And a toggle flip-flop for inverting the output level each time the pulse output from the monostable multivibrator is input.

According to such a configuration, a demodulation circuit capable of demodulating a two-phase PSK modulated signal can be realized with a very simple circuit configuration.

A signal output device with an echo check function according to a second aspect of the present invention includes a modulating means for modulating an input signal by a two-phase modulation method, and a two-phase signal which is a signal modulated by the modulating means. Output means for outputting a modulation signal; and demodulation means for demodulating the two-phase modulation signal output from the output means. The signal to be modulated by the modulation means, and the demodulation means modulated by the modulation means. In the signal output device with an echo check function that performs an echo check by comparing the signal with the signal demodulated by the filter, the demodulation unit includes a filter that passes a signal in a predetermined frequency band, and an amplitude of the signal that has passed through the filter. And a comparator that outputs a signal having a level corresponding to the comparison result, and that the output signal of the comparator exceeds a predetermined period. Detecting means for judging whether or not it has become constant, and output means for changing the output level when the detecting means judges that the constant has been maintained over the predetermined time or more, I do.

According to such a configuration, an echo check function is provided which modulates the input signal by the two-phase modulation method, outputs the modulated signal, echoes back the output modulated signal, demodulates the output signal, and performs an echo check. The demodulation means of the signal output device can be constituted by a simple and small-scale circuit. Therefore, according to such a configuration, the signal output device with the echo check function can be made simple and small.

[0043] The output means may have a binary output level, and invert the output level when the detection means determines that the output level has become constant for the predetermined time or more.

A demodulation method according to a third aspect of the present invention comprises:
A signal selecting step of passing a signal component of a predetermined frequency band in the analog signal, attenuating and passing a signal component other than the predetermined frequency band, and an amplitude of a signal processed in the signal selecting step and a predetermined A comparison step of sequentially comparing a reference value and sequentially outputting a signal corresponding to the comparison result, and detecting a comparison result of the comparison step, and determining whether the comparison result has been constant for a predetermined period or more. Controlling the demodulated signal component detecting step of determining whether the output means has a binary output level, and determining that the demodulated signal component detecting step has become constant over the predetermined period or more. And an output control step of inverting the output level.

According to such a configuration, the modulated signal can be demodulated using a very simple data processing process.

A demodulation method according to a fourth aspect of the present invention comprises:
The modulation frequency of the two-phase modulation signal is passed, and the frequency of the modulated signal component of the two-phase modulation signal is passed with an attenuation ratio larger than the pass band. A signal selecting step of passing a high frequency with an attenuation ratio larger than the pass band; and a value smaller than a maximum amplitude value of a modulation frequency component of the signal processed in the signal selecting step, and the signal selecting step. A reference value that is larger than the maximum amplitude value of the component of the modulated signal of the processed signal and the amplitude of the signal processed in the signal selection step are sequentially compared, and the comparison result is obtained. A step of sequentially outputting a signal having a level corresponding to the period, and detecting a period in which the output level of the comparison step has a constant value, and detecting the period in which the constant level exceeds a predetermined period. A non-fluctuation period detecting step of outputting one predetermined signal; and demodulating the output signal by inverting the level of the outputted signal each time the one predetermined signal is output in the processing of the non-fluctuation period detecting step. And outputting a demodulated signal as a signal.

According to such a configuration, a two-phase PSK modulation signal can be demodulated using a very simple data processing process.

[0048]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A demodulation circuit according to an embodiment of the present invention will be described below with reference to the drawings.

This demodulation circuit is a two-phase PSK (Phase Shift
t Keying) is a circuit that demodulates a signal modulated by the method. The two-phase PSK modulation modulates the wave modulated by the modulation function so that the instantaneous phase of the wave changes between two values.

As shown in FIG. 1, the demodulation circuit includes a band-pass filter 11, a comparator 12, a monostable multivibrator 13, and a toggle flip-flop 14.
And.

The band-pass filter 11 removes high-frequency components such as noise included in the two-phase PSK modulation signal 21 and attenuates a modulated frequency component (PCM modulation signal component) included in the two-phase PSK modulation signal 21. And two-phase PSK
Output as a modulation signal 22. Here, the modulated frequency component attenuated by the band-pass filter 11 is a data rate component of the PCM modulation signal 21 and a component constituting a phase change point of the two-phase PSK modulation signal. The modulated frequency component attenuated by the band-pass filter 11 is a two-phase PS
It has a lower frequency than the modulation frequency of the K modulation signal 21.

That is, the quality factor (Q value), which is a characteristic of the band-pass filter 11, is such that the modulation frequency component of the two-phase PSK modulation signal 21 is not attenuated,
The characteristic is set such that the PCM modulation signal component, which is the modulated frequency component of the modulation signal 21, is greatly attenuated.

The comparator 12 receives the two-phase PSK modulation signal 22 output from the band-pass filter 11,
The two-phase PSK modulation signal 22 is compared with a predetermined reference value (threshold value). Then, the comparator 12
High level or low level 2 according to the comparison result.
The value signal 23 is output.

The threshold value of the comparator 12 is
Band-pass filter 11 of two-phase PSK modulation signal 21
The value is larger than the maximum amplitude of the data rate component of the PCM modulation signal attenuated by the above, and is smaller than the maximum amplitude of the PCM modulation signal 22. Therefore, comparator 1
2 is, for example, the PCM modulated signal 22
Is about 70% of the maximum amplitude.

As a result, the binary signal 23, which is the output of the comparator 12, has a clock period k in which a plurality of square waves appear at a substantially constant cycle, as shown in the binary signal 23 shown in FIG. The level state is constituted by a prolonged period m, which is a period that lasts longer than the period of the square wave.

The monostable multivibrator 13 receives the binary signal 23 output from the comparator 12. Then, the monostable multivibrator 13 detects that the extended period m has occurred in the binary signal 23, and outputs one square wave in response to this detection to obtain the output signal 24.

Specifically, the monostable multivibrator 1
3 detects a level change point (rising edge or falling edge) of the binary signal 23. Then, the monostable multivibrator 13 detects whether the detection interval of the change point is longer than a predetermined reference time,
It is determined whether or not the extension period m has occurred.

The predetermined reference time for determining that the monostable multivibrator 13 has detected the extension period m is, for example,
The time is about twice as long as the cycle of the clock period k of the binary signal 23 output from the comparator 12 (period D shown in FIG. 2D).

The monostable multivibrator 13 is shown in FIG.
When the period D shown in (d) is detected, it is determined that the extension period m has been detected, and one square wave shown in FIG. On the other hand, when the change point detection interval is shorter than the predetermined reference time, a constant low level signal is continuously output.

The toggle flip-flop 14 receives the output signal 24 of the monostable multivibrator 13 and, when detecting a change point (rising edge or falling edge) of the output signal 24, inverts the level of its own output signal 25. .

Output signal 2 of toggle flip-flop 14
5 is a signal obtained by demodulating the two-phase PSK modulation signal 21.

The case where this demodulation circuit is used instead of the demodulation circuit 54 of a command signal output device for outputting a command signal as shown in FIG. 3, for example, will be described below.

The two-phase PSK modulation circuit 51 of the command signal output device further modulates the digital signal shown in FIG.
It is output as a two-phase PSK modulation signal shown in (b). The two-phase PSK modulated signal is output to the transmitter antenna via the output circuit 52.

The input circuit 53 of the command signal output device is
A part of the two-phase PSK modulation signal output to the antenna, and the two-phase PSK modulation signal folded at the antenna end is input. This demodulation circuit demodulates the two-phase PSK modulation signal output from the input circuit 53, and outputs the PSK signal shown in FIG.
It is a digital signal of the CM system.

The command signal output device is a two-phase P
The digital signal shown in FIG. 2 (f) demodulated after SK modulation and output, and the digital signal shown in FIG.
An echo check is performed to confirm whether a normal command signal has been output by comparing the digital signal shown in FIG.

That is, the command signal output device, by observing the result of the comparison,
It is confirmed whether or not the two-phase PSK modulated signal has been transmitted normally.

As a result of the comparison, the case where the two digital signals of the PCM system coincide with each other is the case where the two-phase PSK modulated signal is normally transmitted. On the other hand, when they do not match, it means that a normal two-phase PSK modulation signal could not be transmitted.

Next, the operation of the demodulation circuit when demodulating a two-phase PSK modulation signal will be described with reference to FIG.

First, the demodulation circuit shown in FIG.
The two-phase PSK modulation signal 21 shown in (b) is input to the band-pass filter 21. Two-phase PSK shown in FIG.
The modulation signal 21 is obtained by converting the digital signal shown in FIG.
Modulated by the phase PSK modulation method.

High-frequency components such as noise included in the two-phase PSK modulation signal 21 are removed by the band-pass filter 21. In addition, P included in the two-phase PSK modulation signal 21
The low frequency component, which is the data rate of the CM modulation signal component,
It is removed by the band pass filter 21.

Therefore, the two-phase PSK modulation signal 22 output from the band-pass filter 11 has the attenuated portion H which forms the phase change point of the two-phase PSK modulation signal 21 attenuated as shown in the waveform of FIG. The resulting waveform is obtained.

The two-phase PSK modulation signal 22 is input to the comparator 12 and compared with a predetermined reference value S. The comparator 12 outputs a two-phase PSK modulated signal 22
When the value is larger, the output is set to a high level, and when the two-phase PSK modulation signal 22 is smaller than the reference value S, the output is set to a low level to obtain a binary signal 23 shown in FIG.

As shown in FIG. 2D, the binary signal 23 output from the comparator 12 has a clock period k in which a plurality of square waves appear at a substantially constant cycle, and a low level state of the square wave. An extended period m is a period that lasts longer than the cycle.

The binary signal 23 is input to the monostable multivibrator 13. Monostable multivibrator 13
Monitors the time during which the binary signal 23 is at a low level using a timer. Note that this timer is configured by a simple circuit such as charging a predetermined capacitor with a current of a predetermined value when the binary signal 23 is at a low level and checking the potential of the capacitor.

When the time during which the binary signal 23 is at the low level exceeds the predetermined time D, the monostable multivibrator 13 determines that the extension period m has occurred. Here, the predetermined time D for determining the extension period m is two-phase PS.
The time period is longer than the modulation period of the K modulation signal 21 and shorter than the extension period m, for example, twice as long as the modulation period of the two-phase PSK modulation signal 21.

The multivibrator 13 has the extension period m
When it is determined that the occurrence of has occurred, one square wave is output, and an output signal 24 as shown in FIG.

The output signal 24 output from the monostable multivibrator 13 is input to the toggle flip-flop 14. The toggle flip-flop 14 changes the output signal 24 of the monostable multivibrator 13 (only one of the rising edge and the falling edge).
Is detected, the level of its own output signal 25 is inverted as shown in the waveform of FIG.

Output signal 2 of toggle flip-flop 14
5 is a signal obtained by demodulating the two-phase PSK modulation signal 21 shown in FIG. 2B, and is the same signal as the digital signal modulated by the PCM method shown in FIG.

Thus, the demodulation circuit includes one band-pass filter 11, one comparator 12,
A two-phase PSK modulation signal 21 that is a signal modulated by a two-phase PSK modulation method is demodulated while having a small-scale circuit configuration including one monostable multivibrator 13 and one toggle flip-flop 14. can do.

Further, the demodulation circuit can demodulate a two-phase PSK modulation signal while performing a simple signal processing step.

Therefore, the demodulation circuit can contribute to downsizing and low power consumption of a command signal output device for performing an echo check and the like using the demodulation circuit.

This demodulation circuit extracts the phase change point of the two-phase PSK modulation signal using a band-pass filter and removes noise included in the two-phase PSK modulation signal using the band-pass filter. A two-phase PSK modulation signal containing a large amount of noise can be demodulated with a small-scale circuit configuration.

In the above embodiment, the monostable multivibrator and the toggle flip-flop are used to detect the extension period m from the output signal of the comparator 12 and to form a demodulated signal based on the detection. The invention is not limited to this, provided that it detects the extension period m and generates a demodulated signal based on the detection.
Means other than the monostable multivibrator and the toggle flip-flop may be used. For example, instead of the monostable multivibrator 13 and the toggle flip-flop 14, a circuit that changes its own output level when the extension period m is detected may be used.

In the above-described embodiment, the monostable multivibrator 13 outputs one square wave when the extension period m is detected. The present invention is not limited to this, and the monostable multivibrator 13 only needs to output one pulse when the extension period m is detected.

Also, in place of the monostable multivibrator 13, a binary signal 23 output from the comparator 12 is output.
Is alternately changed to a high level and a low level within a predetermined time interval (when the delay period m does not occur), the output is set to the low level, and the level of the binary signal 23 is changed at the predetermined time interval. Does not fluctuate (the extension period m
), A circuit for setting the output to a high level may be used.

The multivibrator 13 operates when the binary signal 23 output from the comparator 12 alternately changes between high level and low level within a predetermined time interval (when the extension period m does not occur). ) May set the output to a high level, and set the output to a low level when the level of the binary signal 23 does not fluctuate at the predetermined time interval (when the extension period m occurs).

The band pass filter 11 of the above embodiment
May be realized by an electronic circuit using a resistor, a capacitor, a coil, and the like, or may be realized by a digital filter by digital signal processing.

The digital filter can be realized with a simple configuration of the A / D converter, the CPU and the memory. First, a two-phase PSK modulation signal (analog signal) is converted into a digital signal by an A / D converter. The digital signal is processed by the CPU and the memory.
This signal processing is an arithmetic processing for realizing the frequency selection function of the bandpass filter 11 described above. By performing this signal processing, the waveform shown in FIG.
A signal corresponding to the waveform shown in FIG.
Note that a DSP (Digital Signal Processor) is used instead of the CPU.
ssor) may be used.

Also, A /
By making the D converter, the CPU, and the memory function as the comparator 12, the monostable multivibrator 13, and the toggle flip-flop 14 of the present embodiment, the scale of the demodulation circuit can be reduced.

[0090]

As described above, according to the present invention,
Since a demodulation circuit can be constituted by the filter, the comparator, and the detecting means, an echo check function can demodulate a signal modulated by the two-phase PSK system in a simple data processing step and by a small-scale circuit. An attached signal output device, a demodulation circuit, and a demodulation method can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a demodulation circuit according to an embodiment of the present invention.

FIG. 2 is a waveform chart showing an operation of each section of the demodulation circuit shown in FIG.

FIG. 3 is a block diagram showing an example of a configuration of a conventional two-phase PSK signal demodulation circuit.

FIG. 4 is a waveform chart showing an operation of each part of the two-phase PSK demodulation circuit shown in FIG.

[Explanation of symbols]

 Reference Signs List 11 band pass filter 12 comparator 13 monostable multivibrator 14 toggle flip-flop

Claims (10)

[Claims] A filter for passing a signal in a predetermined frequency band; a comparator for comparing an amplitude of the signal passed through the filter with a predetermined reference value to output a signal of a level according to the comparison result; Detecting means for determining whether or not the output signal of the comparator has become constant over a predetermined time; and outputting means for changing the output level when the detecting means determines that the output signal has become constant for the predetermined time or more. A demodulation circuit, comprising: 2. The apparatus according to claim 1, wherein said output means has a binary output level, and inverts said output level when said detection means determines that said output level has become constant over said predetermined time. Item 2. The demodulation circuit according to item 1. 3. The filter according to claim 1, wherein the filter is a band-pass filter, and the band-pass filter is a signal to be a signal to be demodulated by the present demodulation circuit.
The modulation method according to claim 1, wherein the modulation frequency of the phase-phase modulation signal is included in a pass band, and the frequency of the modulated signal component of the two-phase modulation signal is included in a non-pass band. 4. Demodulation circuit. 4. The filter according to claim 1, wherein the filter is a band-pass filter, and the band-pass filter is a signal to be a demodulated signal of the present demodulation circuit, and is a signal modulated by a two-phase modulation method.
The pass band includes the modulation frequency of the phase-phase modulated signal, and the attenuation ratio of the frequency of the modulated signal component of the two-phase modulated signal and the frequency higher than the modulation frequency of the two-phase modulated signal is lower than that of the pass band. The demodulation circuit according to claim 1, further comprising a characteristic included in a large attenuation band. 5. The reference value of the comparator is smaller than a maximum amplitude value of a modulation frequency component of a signal passed through the filter, and a modulated signal of a signal passed through the filter. The demodulation circuit according to claim 1, wherein the value is larger than the maximum amplitude value of the component. 6. The detecting means detects a period in which the level of the output signal of the comparator is substantially constant,
A monostable multivibrator that outputs one pulse when the fixed period exceeds the predetermined time, wherein the output means has a binary output level of a high level and a low level; The demodulation according to any one of claims 1 to 5, further comprising: a toggle flip-flop that inverts the output level each time the pulse output from the monostable multivibrator is input. circuit. 7. A modulating means for modulating an input signal by a two-phase modulation method, and a modulating means which modulates the signal by the modulating means.
Output means for outputting a phase-phase modulation signal; demodulation means for demodulating the two-phase modulation signal output by the output means;
A signal output device with an echo check function that performs an echo check by comparing a modulated signal of the modulation unit with a signal modulated by the modulation unit and further demodulated by the demodulation unit. A filter that passes a signal in a predetermined frequency band, a comparator that compares an amplitude of the signal that has passed through the filter with a predetermined reference value, and outputs a signal having a level corresponding to the comparison result. Detecting means for determining whether or not the output signal has become constant for a predetermined time or more; and output means for changing an output level when the detecting means determines that the output signal has become constant for the predetermined time or more. A signal output device with an echo check function. 8. The apparatus according to claim 1, wherein said output means has a binary output level, and inverts said output level when said detection means determines that said output level has become constant for a predetermined time or more. Item 8. The signal output device with an echo check function according to Item 7. 9. A signal selecting step of passing a signal component of a predetermined frequency band in an analog signal and attenuating and passing a signal component other than the predetermined frequency band; and a signal processed in the signal selecting step. A comparison step of successively comparing the amplitude of the signal with a predetermined reference value, and sequentially outputting a signal corresponding to the comparison result; detecting a comparison result of the comparison step, wherein the comparison result is constant for a predetermined period or more. A demodulated signal component detecting step of judging whether or not the demodulated signal component is detected; and controlling an output means having a binary output level to determine whether the demodulated signal component detecting step has become constant over the predetermined period. An output control step of inverting the output level of the output means. 10. The modulation frequency of the two-phase modulated signal is passed, and the frequency of the modulated signal component of the two-phase modulated signal is
A signal selection step of passing at a higher attenuation ratio than the pass band and a frequency higher than the modulation frequency of the two-phase modulation signal at an attenuation ratio larger than the pass band; and A reference value that is smaller than the maximum amplitude value of the modulation frequency component of the signal and that is larger than the maximum amplitude value of the component of the modulated signal of the signal processed in the signal selection step; A comparison step of sequentially comparing the amplitude of the signal processed in the signal selection step and sequentially outputting a signal of a level corresponding to the comparison result; and the output level of the comparison step becomes a constant value. A non-variable period detecting step of outputting one predetermined signal when the fixed period exceeds a predetermined period; and Demodulation method for each of the at sense one predetermined signal is outputted, and a demodulated signal output step of a demodulated signal by inverting the level of the output signal, characterized in that.