JPS643104B2 - - 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 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 at 10 to 30 KHz, 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.

Cordless telephone equipment consists of a base unit installed adjacent to a telephone set, one or more handset units installed for this base unit, and telephone receiving and sending operations performed remotely from the telephone set. It is done in position. That is, in such a cordless telephone device, it is sufficient to have a confidential conversation with another person's adjacent telephone.

An object of the present invention is to provide a simple communication device that allows confidential communication and has a narrow dedicated 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 to hundreds of hertz, and the phase inversion timing is formed by this synchronization signal. Therefore, the phase of the audio signal is alternately inverted in synchronization with this 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 combiner 10,
It is combined with the FS signal (f±Δf) from the FS modulator 12. The FS modulator 12 is a means for increasing or decreasing the frequency deviation Δf (f±Δf) with respect to the center frequency f in response to the synchronizing signal from the synchronizing signal generator 8, and outputs, for example, 20 KHz±50 Hz.

Then, the output of the signal synthesizer 10 is frequency modulated by the FM modulator 14 and converted into a high frequency signal,
It is transmitted from 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 FS modulator 12 and applies it to the FS demodulator 28, and the FS demodulator 28 detects a synchronization signal from the frequency deviation of the frequency signal, and outputs the synchronization signal to the timer circuit 30 and the phase signal. Add to 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 and converts it into a normal phase.
added to.

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 transmitter circuit in 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 synchronization signal waveform. Each signal is applied to the phase inverter 6, and its phase is inverted in synchronization with the synchronization signal at time intervals of the high level of the synchronization signal, as shown in FIG. 3C. 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 FIG. 3D, the frequency of the frequency deviation Δf (f +
An FS signal of Δf) is formed.

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.

FIG. 4 shows the operating waveform of the receiving circuit shown in FIG. 2, F is the demodulated output waveform of the FM demodulator 20,
This is the received waveform of the transmitted signal shown in FIG. 3E.

This signal is given to the tone synchronization circuit 26 of the synchronization signal detection circuit 22, and this tone synchronization circuit 26
detects the FS signal and outputs the pulsed FS signal shown in FIG. 4C. 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,
This synchronization signal is applied to a timer circuit 30 and a phase inverter 32.

On the other hand, the demodulated output applied to the notch filter 24 is converted into an audio signal by removing its FS signal component, and the output signal waveform becomes as shown in FIG. 4I. 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 processed by a phase inverter 3.
2, it is inverted in synchronization with the synchronization signal, and as shown in FIG.
Convert to a normal phase signal as shown in . In this case, this signal component includes steep signal components as shown by j ₁ to j ₄ just at the time of phase switching, and in particular, pulse-like signal components shown as j ₃ and j ₄ . If you play it as is, it 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. 4K shows a 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 hold circuit 34
When the reproduced signal shown in FIG. L is generated and compared with the waveform shown in FIG. 4J, the signal components shown at j ₁ to j ₄ are removed, and the previous signal components are maintained in that portion. 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 by 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 range of the audio signal frequency, the waveform distortion at the time of phase switching is
By holding the immediately preceding signal component by sample and hold, it is possible to effectively remove abnormal sounds and improve the fidelity of the reproduced signal.

In this embodiment, the signal synthesizer 10 synthesizes 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, 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, and includes a pair of transistors 40, 4.
A differential amplifier 44 is constructed by connecting the two emitters in common, and a constant current source 45 is connected between the emitters of the transistors 40 and 42 and a reference potential point (ground).
is connected. The bases of the transistors 40 and 42 are commonly connected via a resistor 46, and the input terminal 5 is connected via a capacitor 48.
0 is formed and the audio signal is added.

On the collector side of each transistor 40, 42,
Switching circuits 52 and 54 are installed separately,
The switching circuit 52 is composed of a pair of transistors 56 and 58 having a common emitter, and the other switching circuit 54 is composed of transistors 60 and 62 connected in the same manner. The bases of transistors 56 and 62 and the transistors 58 and 60
are commonly connected to the bases of the two through a resistor 64, and an input terminal 68 is formed through a capacitor 66 to which a synchronizing signal is applied.

The collector of each transistor 56, 60 is connected to a power line on which a power supply terminal 70 is formed, and the collector of each transistor 58, 62 is connected to the power line via a resistor 72, and the collector has a phase inverter. An output terminal 74 from which output is taken out is formed.

A constant potential obtained by dividing the power supply voltage Vcc by resistors 76, 78, and 80 is applied to the base of each transistor 40, 56 as a bias. A capacitor 82, 84 is connected between the base of each transistor 40, 56 and the reference potential point.
is installed.

According to such a configuration, the current of each transistor 40, 42 of differential amplifier 44 is alternately applied to each switching circuit 52, 54 in response to the audio signal input. On the other hand, the switching circuits 52, 5
4 transistors 56, 62 and transistor 5
8 and 60 perform switching operations in response to the synchronization signal alternately, so the output terminal 74 responds to the positive and negative sections of the synchronization signal and easily extracts audio signals in normal phase and inverted phase alternately. be able to.

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

It also distinguishes audio signals in synchronization with synchronization signals,
Even in confidential communication where the order of the divided signals is changed alternately or with a certain jump, when removing unnecessary signals that occur at the signal switching part,
This 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 drawings]

FIG. 1 is a block diagram showing an embodiment of the transmitting circuit of the confidential communication device of the present invention, FIG. 2 is a block diagram showing an embodiment of the receiving circuit of the confidential communication device of the present invention, and FIG. 3 is the operation of the transmitting circuit. An explanatory diagram showing waveforms,
Figure 4 is an explanatory diagram showing the operating waveforms of the receiving circuit, Figure 5
The figure is a circuit diagram showing a specific example of the circuit configuration of the phase inverter of the transmitting circuit. 6, 32... Phase inverter, 8... Synchronous signal generator, 22... Synchronous signal detection circuit, 34... Sample hold circuit.

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; In a confidential communication device comprising a receiving section that reproduces an audio signal by restoring the audio signal to
A confidential communication device characterized by being equipped with a sample hold circuit that holds a sample for a minute time. 2. Claim 1, characterized in that a frequency signal having a specific frequency deviation is synthesized with the audio signal to be transmitted having the phase inverted portion and transmitted.
Confidential communication device as described in section.