JPH0153949B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a confidential communication device, and for example, to a communication device such as a cordless telephone device that prevents wiretapping of communication contents.

Conventionally, confidential communication methods in various communication devices are as follows:
A complex modulation method is used depending on the degree of confidentiality.
The modulation frequency is also high, and the frequency band tends to be wide.

For example, in the conventional phase modulation method, the modulation frequency is set at 10 to 30kHz, and a considerably wide exclusive band is required.

It is inappropriate to use such a confidential communication method in a simple communication device such as a cordless telephone device from the standpoint of effectively using the frequency allocation range.

By the way, in a cordless telephone device, a base unit is installed adjacent to a telephone set, and one or more handset units are installed in response to the base unit, and the handset allows the telephone to receive and send calls from the phone. This is done at a remote location. That is, in such a cordless telephone device, it is sufficient to have a confidential conversation with another person's adjacent telephone.

Hitherto, a confidential communication device that performs phase inversion at the zero-crossing point of the audio signal has been proposed. Although this confidential communication device has the advantage of easily enabling confidential communication in a narrow band, transmission distortion can cause signal distortion. This occurs at the phase switching part.

FIG. 1 shows the occurrence of transmission distortion due to this phase inversion. A shows the audio signal waveform, and B shows the received waveform when the signal is transmitted by alternately repeating phase inversion based on its zero-crossing point. In this received waveform, the phase switching portion b becomes slow. Therefore, when this is phase-inverted and changed to the normal phase, the waveform of the phase switching portion b is lost, as shown in C, and a normal signal cannot be reproduced.

SUMMARY OF THE INVENTION Therefore, the present invention aims to provide a confidential communication device that compensates for transmission distortion when phase inversion is performed at a zero-crossing point in confidential communication using phase inversion, and reproduces a normal audio signal. shall be.

That is, the confidential communication device of the present invention includes a transmitter that selectively inverts the phase of an audio signal in synchronization with a synchronization signal and transmits an audio signal having a phase inversion section together with the synchronization signal; and a reception unit configured to invert the phase of the phase inversion section of the audio signal in synchronization with the signal to reproduce the audio signal of normal phase, the transmission unit configured to transmit the audio signal to be transmitted. and a reference level set within the amplitude range of the audio signal to generate an intersection detection output between the two, and a high level section and a low level section are determined from the intersection detection output generated by the comparator. a frequency dividing means for forming the set synchronization signal; and inverting any section of the audio signal in the high level section or the low level section of the synchronization signal, and converting it into an audio signal having the phase inversion section. and a first phase inversion means,
The receiving section includes a waveform shaping means that moderates the rise or fall of the synchronization signal sent from the transmission section, and a waveform shaping means that changes the phase of the phase inversion section of the received audio signal into an output synchronization signal of the waveform shaping circuit. and second phase inverting means for reproducing the audio signal having a normal phase.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 2 shows an embodiment of the transmitting section in the confidential communication device of the present invention, and FIG. 3 shows an embodiment of the receiving section in the confidential communication device of the present invention.

In FIG. 2, the audio input from the microphone 2 is amplified by an amplifier 4 and then applied to a synchronizing signal generating circuit 6 and a phase inverter 8 as a first phase inverting means. The synchronization signal generation circuit 6 is
Generates a synchronizing signal pulse that is synchronized with the intersection of the audio signal and a reference level set within the amplitude range of the audio signal, that is, the zero cross point, and has a high level section and a low level section that differ by a certain ratio. It is something to do. Therefore, this synchronization signal generation circuit 6 is equipped with a low-pass filter 10, a comparator 12, a differentiating circuit 14, a waveform shaping circuit 16, T flip-flop circuits 18 and 20, and an AND circuit 22 as a logic circuit. .

A low-pass filter 10 removes high-frequency components from the audio signal component, a comparator 12 compares the low-frequency components with a reference level, and the output is sent to a differentiating circuit 1.
After being differentiated by 4, the differentiated waveform is waveform-shaped by a waveform shaping circuit 16, and T is used as a pulse generation circuit.
It is added to flip-flop circuit 18. A first pulse is obtained from the T flip-flop circuit 18 as a detection output of a zero-crossing point synchronized with the zero-crossing point of the audio signal, and this pulse is applied as a trigger input to the T flip-flop circuit 20 set as frequency dividing means. , a second pulse with a period twice that period is obtained. These first and second pulses are applied to an AND circuit 22 which constitutes frequency dividing means together with a T flip-flop circuit 20, and a synchronizing signal as a frequency divided output is formed by taking the logical product of both pulses.
This synchronization signal is a pulse signal of two levels, high and low, in which high-level sections and low-level sections are alternately set according to the comparison output of the comparator 12.

This synchronization signal is applied to the FS modulator 24 together with a phase inverter 8, and the phase of the synchronization signal is selectively inverted in its high level section in synchronization with the synchronization signal. Further, the FS modulator 24 generates an FS signal (f±Δf) having a frequency deviation Δf with respect to the reference frequency f in response to the synchronization signal.

The signal combiner 26 combines the phase inverted output and the FS signal to obtain a combined signal. This composite signal is applied to the FM modulator 28, and the FM modulator 28
Then, a transmission signal is generated by subjecting a carrier wave to frequency modulation using a composite signal. This transmission signal is transmitted from the antenna 30 toward the receiving section.

Next, in FIG. 3, the transmission signal from the transmitter is received by the antenna 32 of the receiver, demodulated by the FM demodulator 34, and then applied to the synchronization signal detection circuit 36 and the notch filter 38.

The synchronization signal detection circuit 36 detects a synchronization signal from the demodulated output of the FM demodulator 34, and is composed of a tone synchronization circuit 40 and an FS demodulator 42. That is, the tone synchronization circuit 40 detects the FS signal of the FS modulator 24 and applies it to the FS demodulator 42,
The FS demodulator 42 detects a synchronizing signal pulse from the frequency deviation of the FS signal, slows the rise and fall of this synchronizing signal through a time constant circuit 44 as a waveform shaping means, and then converts the synchronizing signal into a second phase signal. It is added to a phase inverter 46 as an inverting means.

On the other hand, the demodulated output from which the FS signal component has been removed by the notch filter 38 is applied to the phase inverter 46. The phase inverter 46 performs a linear phase inversion operation in response to a synchronization signal pulse applied from the time constant circuit 44, and inverts the phase of the phase inversion section of the demodulated output to convert it into a normal phase. This normal phase audio signal is applied to an amplifier 48 and amplified, and then applied to a speaker 50.

Based on the above configuration, its operation will be explained in detail with reference to FIGS. 4 and 5.

FIG. 4A shows a signal waveform obtained by amplifying the output signal of the microphone 2 with the amplifier 4, and the high-frequency vibration component of this signal waveform is removed by the low-pass filter 10, as shown in FIG. 4B. is added to comparator 12. A reference level V _REF is set in the comparator 12, and the intersection of this reference level V _REF and the audio signal shown in FIG. 4B is detected, the output is inverted, and the pulse shown in FIG. 4C is generated. When this pulse is differentiated by the differentiating circuit 14, the pulse shown in FIG. 4D is obtained, and when this pulse is waveform-shaped by the waveform shaping circuit 16 and the negative component is inverted, the pulse shown in FIG. 4E is obtained. . Using this pulse as a trigger input, T
When added to the flip-flop circuit 18, FIG.
A first pulse shown in FIG. 4 is generated, and when this pulse is applied to the T flip-flop circuit 20, a second pulse shown in FIG. 4G is generated. That is, the second pulse has a period twice that of the first pulse. By adding these first and second pulses to the AND circuit 22 and performing a logical product, a synchronization signal shown in FIG. 4H is obtained. The synchronization signal pulse is formed such that the ratio of the low level (L) section to the high level (H) section is three times that of the synchronization signal pulse.

When this synchronizing signal pulse is applied to the phase inverter 8, its output becomes as shown in FIG. 4I, the high level section of the synchronizing signal is inverted, and the inversion timing is the zero cross point.

Further, the synchronization signal is applied to the FS modulator 24, and the FS signal shown in FIG. 4J having a frequency deviation corresponding to the synchronization signal is generated. This FS signal and the audio signal with phase inversion are combined, and the combined signal is modulated by the FM modulator 28 and sent to the antenna 3.
0 as a transmission signal.

When this transmission signal is received by the antenna 32,
It is modulated by an FM demodulator 34. This signal is applied to the tone synchronization circuit 40 of the synchronization signal detection circuit 36, which tone synchronization circuit 40 is shown in FIG. 5K.
The FS signal is detected, and the FS demodulator 42 demodulates the synchronization signal pulse shown in FIG. 5L from this signal. The rising and falling pulses are changed into slow pulses and applied to the phase inverter 46.

On the other hand, the demodulated output applied to the notch filter 38 has its FS signal component removed and is shown in FIG.
Only the audio signal components shown in are extracted. and,
In the phase inverter 46, the phase of the phase inversion section is gradually switched by the synchronization signal, and as shown in FIG. 5O, the audio signal is converted into a normal phase audio signal. This audio signal is amplified by the amplifier 48 and then reproduced by the speaker 50.

According to such a configuration, phase inversion is performed in synchronization with the zero-crossing point of the audio signal, so it is possible to easily realize confidential communication, and it also compensates for transmission distortion in the phase switching portion of the audio signal, thereby converting the normal audio signal into a normal audio signal. Can be played.

Next, FIG. 6 shows a specific example of the circuit configuration of the time constant circuit 44 and the phase inverter 46.

The time constant circuit 44 is composed of constant current sources 52, 54, a transistor 56, a diode 58, a resistor 60, and a capacitor 62. A synchronizing signal is applied from the FS demodulator 42 to an input terminal 64 formed at the base of the transistor 56. The drive voltage Vcc is applied to the power supply terminal 66.

Further, the phase inverter 46 includes transistors 68,
70, 72, 74, 76, 78, resistance 80, 8
2, 84, 86, 88, 90, 92, 94, 9
6,98,100, capacitor 102,104,
106 and constant current source 108 constitute a double-balanced differential amplifier circuit, and an audio signal to be phase-inverted is applied to an input terminal 110, and a phase-inverted output is taken out from an output terminal 112. .

In this phase inverter 46, a pair of transistors 68 and 70 have their emitters connected to resistors 80 and 82.
The transistors 72 and 74 connect their emitters to the resistor 8 to form a differential amplifier.
4 and 86 to form a switching circuit that performs linear operation. Further, the transistors 76 and 78 have their emitters connected to the resistors 88 and 78, respectively.
They are connected in common through 90 to form a switching circuit that performs a similar linear operation.

Also, resistors 94, 96, 98 and capacitor 1
04 and 106 constitute a bias circuit, and resistor 9
Transistors 68, 4, 96, 98 from the voltage dividing points
72 is given a certain bias.

According to such a configuration, the input terminal 64 has the fifth
When the synchronizing signal pulse shown in FIG. L is applied, the transistor 56 performs a switching operation in response to the pulse. Here, if the output current of the constant current source 52 is 2I, and the sink current of the constant current source 54 is I, then
During the non-conducting period of the transistor 56, the capacitor 62 is charged with a constant time constant by the current I, and
During the conduction period of the transistor 56, the constant current source 52
The current flows through the transistor 56 and the capacitor 6
The second discharge current is sucked into the constant current source 54.

As a result, the bases of the transistors 72 and 78 constituting the switching circuit of the phase inverter 46 have a fifth pulse in response to the low level section of the synchronizing signal pulse shown in FIG.
The voltage in the low level section shown in FIG. The voltage in the high level section shown is applied. The reason why the voltage level changes in FIG. 5M are gradual is that the capacitor 62 has a time constant due to charging and discharging.

Therefore, to the bases of the transistors 72 and 78 and also to the bases of the transistors 74 and 76, as shown in FIG.
Transistors 74 and 76 are conductive in the high level section of FIG. 5M, and transistors 72 and 78 are conductive in the low level section of FIG. Since the voltage rises and falls, each transistor 72, 78 or transistor 74, 76 performs a gentle switching operation.

A transistor 6 constituting the differential amplifier
Each of the currents 8 and 70 is applied alternately to each switching circuit in response to the audio signal input, so that the 5th current
The audio signal having the phase inverter section applied to the input terminal 110 shown in FIG.
As shown in Figure 2, there is no signal dropout in the phase switching part, and a continuous audio signal can be extracted.

As explained above, according to the present invention, confidential communications can be realized with a simple configuration, and when the phase of an audio signal is switched at a zero-crossing point, it is possible to compensate for loss of the reproduced signal due to transmission distortion occurring at that part. , it is possible to reliably reproduce the regular audio signal from the transmitter side at the receiver side.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the generation of transmission distortion due to phase inversion, FIG. 2 is a block diagram showing an embodiment of the transmitter in the secure communication device of the present invention, and FIG. 3 is a diagram of the receiver in the secure communication device of the present invention. 4 is a diagram showing the operating waveforms of the transmitting section shown in FIG. 2, FIG. 5 is a diagram showing the operating waveforms of the receiving section shown in FIG. 3, and FIG. 6 is a block diagram showing the embodiment. 4 is a circuit diagram showing a specific circuit configuration example of a time constant circuit and a phase inverter of the receiving section shown in FIG. 3. FIG. 6... Synchronization signal generation circuit, 8... Phase inverter (first phase inverter), 12... Comparator, 20...
...T flip-flop circuit (frequency dividing means), 22...
...AND circuit (frequency dividing means), 36... synchronizing signal detection circuit (synchronizing signal detecting means), 44... time constant circuit (waveform shaping means), 46... phase inverter (second phase inverting means).

Claims (1)

[Claims] 1. A transmitting unit that selectively inverts the phase of an audio signal in synchronization with a synchronization signal and transmits an audio signal having a phase inversion section together with the synchronization signal, and a transmission unit that is synchronized with the received synchronization signal. and a reception unit that inverts the phase of the phase inversion section of the audio signal to reproduce the audio signal of normal phase, the transmission unit comprising: A comparator that generates an intersection detection output by comparing the signal with a reference level set within the amplitude range of the signal, and a high level section and a low level section are set from the intersection detection output generated by this comparator. a frequency dividing means for forming the synchronization signal; and a first frequency dividing means for inverting an arbitrary section of the audio signal in the high level section or the low level section of the synchronization signal and converting it into an audio signal having the phase inversion section. and a phase inverting section, the receiving section comprising: a waveform shaping section that moderates the rise or fall of the synchronization signal sent from the transmitting section; and a phase inverting section of the received audio signal. A confidential communication device comprising: second phase inverting means for inverting in synchronization with an output synchronizing signal of a waveform shaping circuit and reproducing the audio signal having a normal phase.