JPS60117932A - Privacy communication device - Google Patents

Abstract

PURPOSE:To attain the privacy communication and also to reduce the width of an exclusive band with a simple device by providing a sample holding circuit at a reception part to hold the final value of a normal phase for a slight period of time when switching modes of normal and reverse in phase of a sound signal. CONSTITUTION:A signal containing a frequency deviation is synthesizdred with a sound signal containing a phase inverted part and to be transmitted. This synthetic signal is transmitted. A reception circuit obtains a demodulation signal F, an FS signal G and a synchronizing signal H through an FM demodulation circuit 20, a tone detecting circuit 26 and an FS demodulator 28 respectively. While the demodulation output is converted into a sound signal I by a notch filter 24. The phase inverted part of the signal I is inverted by a phase inverter 32 and converted into a signal J of a normal phase. This reproduction signal is applied to a sample holding circuit 34 together with the output pulse of a timer circuit 30. The circuit 30 produces a pulse K having the duty of a slight period of time in response to the signal H, and the sample point of an input waveform is decided by the front edge of the pulse K. Then the pulse width time is equal to the holding time. As a result, the pulses J1-J4 are deleted from the reproduction signal L of the circuit 34 at a phase switching time point.

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 communication contents from being decoded.

Conventionally, confidential communication methods in various communication devices have used complex modulation methods depending on the degree of confidentiality, and the modulation frequency tends to be high and the frequency band tends to be wide.

For example, in the conventional phase modulation method, the modulation frequency is set to 10 to 30 KI1g, 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.

A cordless telephone device has a base unit installed adjacent to a telephone set, one or more handset units installed for this base unit,
Receiving and transmitting operations on the telephone are performed using a handset at a location remote from the telephone.

That is, in such a cordless telephone device,
Confidential conversations between adjacent telephones of other people are sufficient.

An object of the present invention is to provide a simple communication device that enables confidential communication and has a narrow exclusive bandwidth.

The present invention includes a transmitter that alternately inverts the phase of an audio signal at predetermined time intervals in synchronization with a synchronization signal, and transmits the inverted phase part of the audio signal in synchronization with the received synchronization signal. It consists of a receiving section that restores the normal phase and reproduces the audio signal, and a sample hold circuit that holds the final value of the normal phase for a short time when switching between the normal phase and inverted phase of the audio signal is installed in this receiving section. It is characterized by

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

1 and 2 show an embodiment of the confidential communication device of the present invention, with FIG. 1 showing its transmitting circuit and FIG. 2 its receiving circuit, respectively.

In FIG. 1, an audio signal generated by a microphone 2 is amplified by an amplifier 4 and then applied to a phase inverter 6. A synchronizing signal is applied to the phase inverter 6 from a synchronizing signal generator 8, and a phase inverting operation is ensured in response to this synchronizing signal. This synchronization signal is set as a pulse having a specific period given at a low repetition frequency of the audio signal frequency, for example, a frequency of several tens of two to several hundred Hz, and the phase inversion timing is formed by this synchronization signal. Therefore, the phase of the audio signal is alternately inverted in synchronization with the synchronization signal, and the audio signal is converted into a signal that alternately repeats positive phase and negative phase at predetermined time intervals.

This synchronization signal is applied to the signal synthesizer 10 and is combined with the FS signal (f±Δf) from the FS modulator 12. F.S.
The modulator 12 increases or decreases the frequency deviation Δf (f±Δ
f) A means for
Output.

Then, the output of the signal synthesizer 10 is frequency modulated by the FM modulator 14 and converted into a high frequency signal, which is transmitted from the antenna 16.

Next, in FIG. 2, the high frequency signal received by the antenna 18 is demodulated by an FM demodulator 20 and then applied to a synchronization signal detection circuit 22 and a notch filter 24.

The synchronization signal detection circuit 22 detects a synchronization signal from the demodulated output of the FM demodulator 20, and is composed of a tone synchronization circuit 26 and an FS demodulator 28. That is, the tone synchronization circuit 26 detects the FS signal of the FSS opener 2 and applies it to the FS repeater 28, and the FS repeater 28 detects a synchronization signal from the frequency deviation of the frequency signal and sends it to the timer circuit. 30 and phase inverter 32. This timer circuit 3
0 is composed of a one-shot timer circuit and outputs a minute width pulse in synchronization with a synchronization signal.

On the other hand, the demodulated output from which the FS signal component has been removed by the notch filter 24 is applied to the phase inverter 32, which inverts the phase of the phase inverted portion of the demodulated output, converts it into a normal phase, and applies it to the sample hold circuit 34. .

The sample and hold circuit 34 performs a sample and hold operation in response to the output pulse of the timer circuit 30, and removes noise components in the phase switching portion of the output audio signal of the phase inverter 32.

This output is amplified by an amplifier 36 and then applied to a speaker 38 to reproduce audio.

Based on the above configuration, its operation will be explained in detail with reference to FIGS. 3 and 4.

FIG. 3 shows the operating waveforms of the transmitting circuit of FIG. 1, A shows the signal waveform obtained by amplifying the output signal of the microphone 2 with the amplifier 4, and FIG. 3B shows the synchronizing signal waveform. Each signal is applied to a phase inverter 6, as shown in FIG.
The phase is inverted in synchronization with the synchronization signal at time intervals when the synchronization signal is at a high level. The waveforms in FIGS. 3A and 3B show the case where an audio signal component with a low frequency, that is, a period with a large period, arrives with respect to the synchronization signal period.

On the other hand, the FS modulator 12 is also given the synchronizing signal shown in FIG. 3B, and the reference frequency signal is modulated with this pulse signal. That is, as shown in the third diagram, an FS signal having a frequency (f+Δf) with a frequency deviation Δf with respect to the reference frequency f is formed corresponding to the high and low level sections of the synchronizing signal.

This signal is combined with the audio signal shown in FIG. 3C by the signal synthesizer 10 to form the signal shown in FIG. 3E. This signal is applied to the FM modulator 14, which modulates the carrier frequency f with the signal, and sends it out from the antenna 16.

4 shows the operating waveform of the receiving circuit shown in FIG. 2, F is the demodulated output waveform of the FM demodulator 20, which is
This is the received waveform of the transmitted signal shown in .

This signal is transmitted to the tone synchronization circuit 2 of the synchronization signal detection circuit 22.
6, this tone synchronization circuit 26 detects the FS signal and outputs the pulsed FS signal shown in FIG. 4G. The FS demodulator 28 demodulates a synchronization signal from this pulsed FS signal. FIG. 4H shows the synchronization signal demodulated by the FS demodulator 28, and this synchronization signal is applied to the timer circuit 30 and the phase inverter 32.

On the other hand, the demodulated output applied to the nonch filter 24 is converted into an audio signal by removing its FS signal component, and the output signal waveform becomes as shown in FIG. 41. In this signal, the gradual rising or falling portion is due to transmission distortion due to air propagation.

The phase inverted portion of this reproduced signal is inverted in synchronization with the synchronizing signal by a phase inverter 32, as shown in FIG. 4J.
Convert to normal phase signal. In this case, there is a steep signal component in this signal component, as shown by j+ to j4, just at the point in time when the phase is switched.
If the pulsed signal components indicated by 3 and j4 are reproduced as they are, they will generate abnormal sounds.

This reproduction signal is applied to the sample and hold circuit 34 together with the output pulse of the timer circuit 30. FIG. 4 shows a hold pulse with a minute duty that is generated by the timer circuit 30 in response to a synchronization signal, the sampling point of the input waveform is determined at the leading edge of this pulse, and the pulse width is the hold time. becomes.

As a result, the sample and hold circuit 34 generates the reproduced signal shown in Figure 4, and when compared with the waveform shown in Figure 4J, the signal components shown from jl to j4 are removed, and that portion replaces the previous signal component. Maintained. This reproduced signal is amplified by an amplifier 36 and then reproduced by a speaker 38.

With the above configuration, the phase of the audio signal is alternately inverted according to the low-frequency synchronization signal period, so that confidential communication can be performed extremely easily and the signal band can be narrowed.

In the embodiment, a communication circuit with an antenna circuit interposed was described, but the present invention can be similarly implemented in a wired circuit. For example, confidential communication is possible even in a communication circuit whose passband is around the voice band. It can be done.

In addition, when the synchronization signal frequency is set to the low frequency part of the audio signal frequency, waveform distortion at the time of phase switching is effectively removed by holding the immediately preceding signal component by sample and hold, and the reproduction signal, such as the occurrence of abnormal sounds, is effectively removed. Fidelity can be improved.

In this embodiment, the audio signal to be transmitted having the phase inverted portion and the frequency signal having a specific frequency deviation formed by the FS modulator 12 are synthesized by the signal synthesizer 10, so that the degree of secrecy can be reduced. can be increased.

FIG. 5 shows a specific example of the circuit configuration of the phase inverter 6 of the transmitting circuit shown in FIG. In the figure, this phase inverter 6 constitutes a double-balanced differential amplifier circuit,
A differential amplifier 44 is configured by connecting the emitters of a pair of transistors 40 and 42 in common, and the transistors 40 and 42 are connected in common.
．． A constant current source 45 is connected between the emitter of 42 and a reference potential point (ground). Each transistor 40.42
The bases of the transistors 40.42 are commonly connected via a resistor 46, and an input terminal 50 is formed via a capacitor 48. A switching circuit 52.42 is connected to the collector side of each transistor 40.42 to which an audio signal is applied. 54 are individually installed, and the switching circuit 52 includes a pair of transistors 56 having a common emitter.
．． 58, and the other switching circuit 54 also consists of similarly connected transistors 60 and 62.

The bases of transistors 56 and 62 and the transistor 58
．． 60 are commonly connected via a resistor 64, and an input terminal 68 is formed via a capacitor 66 to which a synchronizing signal is applied.

The collector of each transistor 56.6o is connected to the power supply terminal 70.
The collectors of each of the transistors 5B and 62 are connected to the power supply line via a resistor 72, and an output terminal 74 from which a phase-inverted output is output is formed on the collector. .

A constant potential obtained by dividing the power supply voltage Vcc by a resistor 76.78.8o is applied to the base of each transistor 40.56 as a bias. A capacitor 82.84 is individually installed between the base of each transistor 40.56 and the reference potential point.

According to such a configuration, the currents of the transistors 40 and 42 of the differential amplifier 44 are alternately applied to the switching circuits 52 and 54 in response to the audio signal. on the other hand,
Transistor 56.62 of switching circuit 52.54
Since the transistors 58 and 60 perform switching operations in response to the synchronization signal alternately, the output terminal 74 responds to the positive and negative sections of the synchronization signal, and outputs an audio signal of normal phase and inverted phase alternately. can be easily taken out.

Note that a cordless telephone device that uses each transmitting and receiving circuit is composed of a base unit and a handset, and the base unit is connected to the telephone line in parallel with the telephone, but the handset is connected to the base unit by wire or wirelessly. Each circuit unit is installed in each of the master unit and slave unit.

In addition, even in confidential communication where the audio signal is divided in synchronization with a synchronization signal and the order of the divided signals is changed alternately or with a certain jump, this method is used to remove unnecessary signals that occur at the signal switching part. The invention can be applied.

As explained above, according to the present invention, unnecessary signal components can be removed and secret communication can be easily performed in a narrow band.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the transmitting circuit of the secure communication device of the present invention, FIG. 2 is a block diagram showing an embodiment of the receiving circuit of the secure communication device of the present invention, and FIG. 3 is the operation of the transmitting circuit. FIG. 4 is an explanatory diagram showing waveforms of the receiving circuit, and FIG. 5 is a circuit diagram showing a specific circuit configuration example of the phase inverter of the transmitting circuit. □ 6.32... Phase inverter, 8... Synchronization signal generator,
22... Synchronous signal detection circuit, 34... Sample hold circuit. Figure 1 12 Figure 2 Figure 3

Claims (1)

[Claims] +1) A transmitter that alternately inverts the phase of an audio signal in synchronization with a synchronization signal and transmits it together with the synchronization signal, and a transmission unit that normalizes the inverted phase portion of the audio signal in synchronization with the received synchronization signal. In a confidential communication device comprising a receiving section that reproduces an audio signal by restoring the phase, the receiving section receives the final value of the normal phase signal component at the time of switching between the normal phase and the inverted phase of the audio signal. A confidential communication device characterized by having a sample hold circuit for holding data. (2) the audio signal to be transmitted having the phase inverted portion;
The confidential communication device according to claim 1, characterized in that frequency signals having a specific frequency deviation are synthesized and transmitted.