JPH05110641A - Cordless telephone set - Google Patents

Abstract

PURPOSE:To avoid trouble of interrupting talking by providing a sound and silence detection circuit and switching the frequency for interception prevention only when a voice signal is changed from a sound state into a silence state. CONSTITUTION:A voice signal from a speech line L is inputted to a sound and silence detection circuit 17 via a speech circuit 101, in which detects whether the voice signal is in the sound state or the silence state and the result is outputted to a control section 108. The control section 18 detects it that a detection result signal from the circuit 17 changes from the sound state into the silence state and sends a switching command signal with a voice information channel frequency while using a control information channel to a slave set 2 at this point of time. The slave set 2 receiving the switching command signal from the master set 1 switches the voice information channel frequency for transmission reception and sends the notice signal representing the frequency switching end to the master set 1 through the use of the control information channel. The master set 1 receiving the signal switches the channel frequency to modulate the voice signal from a telephone line L based on the frequency and sends the result to the slave set 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cordless telephone, and more particularly to a cordless telephone having a wiretapping prevention function for communication between a master unit and a slave unit.

[0002]

2. Description of the Related Art A cordless telephone is composed of a base unit and a handset unit, and by replacing a part of the home wiring of a subscriber line with a wireless line, the handset unit can be freely carried and used within a certain range. It is a telephone set.

As a means for preventing eavesdropping on a call between a base unit and a handset in a conventional cordless telephone, there is a system in which the transmission / reception frequency is switched at regular intervals during a call. In this method, the sound is forcibly interrupted when the frequency is switched. Therefore, the telephone emits a warning sound or the like to notify the switching of the frequency. When the caller receives this warning sound, the call is suspended,
The procedure was to restart the call after switching the frequency.

[0004]

In the above-mentioned conventional cordless telephone, the call is forcibly interrupted due to the switching of the transmission / reception frequency during a call. There is a drawback that it is extremely troublesome because it requires a procedure such as a temporary interruption and a call restart after switching the frequency.

[0005]

The cordless telephone of the present invention is a cordless telephone having an eavesdropping prevention function for preventing eavesdropping by switching the frequency for transmission and reception between a master unit and a slave unit during a call. The master unit has a first sound / silence detection circuit for detecting whether the first voice signal received from the slave unit is in a voiced state or a silent state, and a second voice transmitted to the slave unit. A second sound / silence detection circuit for detecting whether the signal is in a sound state or a soundless state, and a sound state of the first sound signal received from the first sound / silence detection circuit. From the first voiced / soundless change, which is a change from the above to the silenced state, and switches the transmission frequency of the slave unit and the reception frequency of the master unit respectively, and receives the output of the second voiced / soundless detection circuit. From the voiced state to the silenced state of the second audio signal It is constituted by a respective control circuit toggle its a reception frequency of the second voice activity change following judgment the slave transmitter and the frequency of the master unit is of.

[0006]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of a cordless telephone according to the present invention.

As shown in FIG. 1, the cordless telephone of this embodiment comprises a base unit 1 connected to a telephone line L and a handset side unit 2 connected to the base unit 1 via a wireless line. Has been done.

The base unit 1 has an antenna 11 and an antenna 11
Transmission / reception duplexer 12 for separating transmission / reception signals for
A demodulation unit 13 for demodulating a reception signal, a modulation unit 14 for modulating a transmission signal, a synthesizer 15 for generating a transmission carrier signal and a reception carrier signal, and an audio signal from the slave unit 2 which is an output of the demodulation unit 13. A sound / silence detection circuit 16 for detecting whether the sound is in a sound state or a silence state,
A sound / silence detection circuit 17 for detecting whether the voice signal from the communication circuit 101 is in a sound state or a silence state;
The synthesizer 15 and the demodulator 1 receive the detection results of the sound / silence detection circuit 16 and the sound / silence detection circuit 17, respectively.
Controller 1 for outputting a frequency switching instruction to the modulator 3 and the modulator 14.
8, a switch 19 for selecting start or stop of the transmission / reception frequency switching function during busy, a communication circuit 101 which is an interface with the telephone line L, and a sound / silence detection circuit 16
And a threshold value setting circuit 102 for setting respective detection threshold values of the sound / silence detection circuit 17.

The handset 2 has an antenna 21 and an antenna 21.
Transmission / reception duplexer 22 for separating transmission / reception signals for
A demodulation unit 23 for demodulating a received signal, a modulation unit 24 for modulating a transmission signal, a synthesizer 25 for generating a transmission carrier signal and a reception carrier signal, and a voice signal from the master unit 2 demodulated by the demodulation unit 23. To a speaker 28 and a voice circuit 27 for outputting an audio signal from a microphone 29 to a modulator 23, a speaker 28, and a microphone 29.

Next, the operation of this embodiment will be described.

First, the operation at the time of calling will be described. The audio signal from the slave 2 received by the master 1 via the antenna 11 and the antenna duplexer 12 is demodulated by the demodulator 13. The demodulated audio signal is input to the sound / silence detection circuit 16. Here, it is detected whether the audio signal is in the voiced state or the voiceless state, and the detection result is detected by the control unit 18.
Output to.

The control unit 18 determines that the detection result signal from the sound / silence detection circuit 16 has changed from the sound state to the silence state, and at this time, the control unit 18 uses the control information channel to send a voice signal to the slave unit 2. An information channel frequency switching instruction signal is transmitted. Child device 2 that receives this switching instruction signal from parent device 1
Switches the frequency of the voice information channel for transmission and reception,
A notification signal of frequency switching completion is sent to the master device 1 using the control information channel. Base unit 1 that received this notification signal
Switches the voice information channel frequency for transmission and reception,
Receive the audio signal from.

Next, the operation when receiving a call will be described. The voice signal from the telephone line L is input to the sound / silence detection circuit 17 via the call circuit 101. Here, it is detected whether the audio signal is in the voiced state or in the silent state, and the detection result is output to the control unit 18.

The control unit 18 determines that the detection result signal from the sound / silence detection circuit 17 has changed from the sound state to the silence state, and at this time, the voice signal is transmitted to the slave unit 2 by using the control information channel. An information channel frequency switching instruction signal is transmitted. Child device 2 that receives this switching instruction signal from parent device 1
Switches the frequency of the voice information channel for transmission and reception,
A notification signal of frequency switching completion is sent to the master device 1 using the control information channel. Base unit 1 that received this notification signal
Switches the frequency of the voice information channel for transmission and reception, modulates the voice signal from the telephone line L by the frequency and transmits it to the slave unit 2.

The threshold value setting circuit 102 sets the threshold value of the level of the audio signal which serves as a reference for detecting the voiced state and the voiceless state in the voiced / non-voiced detection circuits 16 and 17. The threshold setting level can be changed arbitrarily.

Further, the operation of the transmission / reception frequency switching function during a call is started and stopped by turning the switch 19 on and off.

As described above, the cordless telephone of this embodiment is provided with the sound / silence detection circuits 16 and 17 so that the transmission / reception frequency is switched only when the change from the sound state to the silence state is detected. Therefore, troublesomeness such as interrupting a call is eliminated.

Next, a second embodiment of the present invention will be described.

FIG. 2 is a block diagram showing a second embodiment of the present invention. In FIG. 2, only the parent device 3 is shown, and the child device 2 is omitted since it is common to the first embodiment described above. The difference of this embodiment from the above-mentioned first embodiment is that
Instead of the master unit 1, the master unit 3 in which the counting circuits 31 and 32 are provided on the output sides of the sound / silence detection circuits 16 and 17 is used.

The counting circuits 31 and 32 have a counter function, and after counting a certain number of changes from the voiced state to the silenced state, output one pulse to the control unit 18 to reset the counters. When the control unit 18 detects this pulse, the control unit 18 sends a voice information channel switching instruction signal to the slave unit 2, as in the case of the master unit 1.

In the present embodiment, the frequency is not switched every time the voice signal changes from the voiced state to the voiceless state, but the voice signal is output at a fixed number of times from the voiced state to the voiceless state. Since the state and the silent state are discriminated and the frequency is switched, there is an advantage that the frequency of generation of the interruption sound during switching is reduced.

[0023]

As described above, the cordless telephone of the present invention is provided with the sound / silence detection circuit so that the frequency switching for preventing wiretapping can be performed when the voice signal changes from the sound state to the silence state. Since it is performed only, there is an effect that the troublesomeness such as interruption of the call every time the frequency is switched is eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a cordless telephone of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the cordless telephone of the present invention.

[Explanation of symbols]

 1,3 Master unit 2 Slave unit 11,21 Antenna 12,22 Antenna duplexer 13,23 Demodulator 14,24 Modulator 15,25 Synthesizer 16,17 Voice / silence detection circuit 18,26 Controller 19 Switch 27,101 Calling circuit 28 Speaker 29 Microphone 31, 32 Counting circuit 102 Threshold setting circuit

Claims (3)

[Claims] 1. A cordless telephone having an eavesdropping prevention function for preventing eavesdropping by switching a transmission / reception frequency between a base unit and a handset during a call, wherein the base unit receives from the handset. A first voiced silence detection circuit that detects whether the voice signal of the voiced state is a voiced state or a voiceless state, and the second voice signal transmitted to the slave unit is a voiced state or a voiceless state. A second sound / silence detection circuit for detecting whether or not the first sound / silence detection circuit receives the output of the first sound / silence detection circuit. From the voiced state of the second voice signal, receiving the output of the second voiced / voiceless detection circuit by determining the voiced / voiceless change and switching between the transmission frequency of the slave unit and the reception frequency of the master unit. The second voiced and silent change, which is a change to a silent state, is determined and A cordless telephone, comprising: a control circuit for switching between a transmission frequency of a master unit and a reception frequency of the slave unit. 2. A threshold value setting circuit capable of varying a threshold value of a voice level when detecting which of the voiced state and the voiceless state in the first and second voiced / unvoiced detection circuits. The cordless telephone according to claim 1, further comprising: 3. A first and second total count value which is a preset count value obtained by respectively counting the first and second voiced / voiceless changes in the outputs of the first and second voiced / voiceless detection circuits. The first and second counting circuits that output numerical values are provided, and the control circuit uses the first and second counting values as the determination of the first and second voiced / silent changes. 2. The cordless telephone according to claim 1, wherein the transmission and reception frequencies of are switched.