JP2637624B2 - Transmission / reception control circuit of cordless telephone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention includes a transmission / reception circuit of a cordless telephone, in particular, a function of changing transmission power, and a circuit for scrambling a transmission signal to prevent eavesdropping. The configuration of the transmitting and receiving circuit.

[Prior art] A generally used cordless telephone has a communication distance of up to about 100 m. However, there is a problem that the contents of the telephone call can be eavesdropped on by another person. When the power is strong, a circuit system for reducing transmission power and preventing eavesdropping, and a scrambler (a confidential device) for converting a transmission signal into a signal that cannot be intercepted are provided.

FIG. 3 shows a configuration of a slave unit [FIG. (A)] and a master unit [FIG. (B)] in a conventional cordless telephone. In FIG. 3 (a), the slave unit is also called a handset, Receiving circuit 11 and transmitting circuit 12 to which antenna 10 is connected
The receiving circuit 11 is connected to a speaker 14 via a scrambler 13a, and the transmitting circuit 12 is connected to a microphone 15 via a scrambler 13b.

On the other hand, in FIG. 2B, the master unit is also called a base set, and the receiving circuit 21 and the transmitting circuit
The receiving circuit 22 is connected to a speech network circuit 24 via a scrambler 23a, and the transmitting circuit 22 is connected to a speech network circuit 24 via a scrambler 23b. Above speech network 24
Is connected to a telephone line and performs 2-wire to 4-wire conversion.
Adjusts the level of the audio signal.

FIG. 4 shows an example of a scrambler in a conventional circuit. The operating characteristics of the scrambler 13 (23) are shown. When the audio signal 100 of 0.3 to 2.7 kHz is transmitted and received, as shown in FIG. Mix to 100. Then, signals 200 and 201 different from the audio signal 100 appear on both sides of the carrier signal 101 as shown in FIG. Therefore, by extracting the audio signal 200 using a bandpass filter having the characteristic shown by the dotted line 300 in the figure, it is possible to form an audio signal completely different from the original audio signal shown in FIG. This audio signal 200
To prevent others from intercepting the signal.

[Problems to be Solved by the Invention] However, in the above-described transmission / reception circuit of the cordless telephone, the scrambler 13 (2
In order to operate 3), there was a problem that the speech quality deteriorated due to the signal conversion of the scrambler 13 (23).

In an actual call on a cordless telephone, the slave unit and the base unit are often used at a relatively short distance, so that the transmission power is reduced and the scrambler is operated even though there is no possibility of eavesdropping, the communication quality is There is a problem in the point.

In a cordless telephone, the output is increased in order to enable communication within a radius of about 100 m, and performing communication at a high output when the distance is short is wasteful in terms of power consumption.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to perform a call at a short distance (high electric field strength), reduce transmission power, and eliminate the possibility of eavesdropping. It is an object of the present invention to provide a transmission / reception control circuit for a cordless telephone that does not operate a scrambler and improves call quality. Another object of the invention is to provide a transmission / reception control circuit that can achieve the above object and reduce power consumption. It is in.

[Means for Solving the Problems] In order to achieve the above object, there is provided a master unit connected to a telephone line, and a slave unit wirelessly communicated with the master unit. In a transmission / reception circuit of a cordless telephone equipped with a scrambler for scrambling a signal, a circuit for reducing transmission power to prevent eavesdropping, an electric field intensity detection circuit for detecting an electric field intensity of a radio wave, and an electric field intensity detection circuit. When the electric field strength is low based on the output, a transmission / reception signal is passed through the scrambler, and when the electric field strength is high, the transmission power is reduced, and at the same time, a switch is provided to switch so that the transmission / reception signal does not pass through the scrambler. It is characterized by having.

[Operation] According to the above configuration, when the detected electric field strength is small, the cordless telephone is being used at a relatively long distance, so that the scrambler is operated by switching the switch, so that another person can use the cordless telephone. A signal that cannot be heard even if intercepted is transmitted. On the other hand, when the detected electric field strength is high, the transmission power is reduced because the telephone is used at a relatively short distance, and further switching is performed by the switch so as not to use the scrambler, High quality audio can be maintained.

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

FIG. 1 shows a transmission / reception control circuit of a slave unit [FIG. 1A] and a master unit [FIG. 2B] in a cordless telephone according to an embodiment. The description is omitted here.

In FIG. 7A, the output of the receiving circuit 11 is scrambled (demodulated and decoded) by the scrambler 13a.
A switch 16a for selecting whether or not to input,
A switch 16b for selecting whether to scramble (modulate, encrypt) the output of the microphone 15 by a scrambler 13b
Provided, connected to the receiving circuit 11, an electric field intensity detection circuit comprising a detection circuit 17 for detecting the electric field intensity and a comparator 18 for comparing the detection value from the electric field intensity detection circuit 17 with a predetermined value set in advance, A control circuit 19 is provided for controlling the switching of the switches 16a and 16b, controlling the transmission power, and the like based on the output of the comparator 18. The detection circuit 17 is a commonly used electric field strength measuring device or the like, detects the intensity of a signal received from the master unit, and the comparator 18 determines that the electric field intensity indicates that the distance between the slave unit and the master unit is short. When the value exceeds the value, a signal to that effect is output. Then, the control circuit 19 receives the output of the comparator 18 and outputs a switching control signal to the transmission circuit 12 when the electric field strength becomes equal to or more than a predetermined value.

On the other hand, in FIG. 2B, in the case of the master unit, a switch 26a for selecting whether or not the output of the receiving circuit 21 is scrambled (demodulated) by the scrambler 23a, and the output of the speech network 24 by the scrambler 23b. A switching unit 26b for selecting whether or not to perform scrambling (modulation) is provided, and an electric field intensity detection circuit and a control circuit comprising a detection circuit 27 for detecting the electric field intensity and a comparator 28 as in the case of the slave unit.
29 will be provided. Then, the control circuit 29 outputs a switching control signal to the transmission circuit 22 when the electric field strength becomes equal to or more than the predetermined value.

FIG. 2 shows transmission circuits 12, 2 in the slave unit and the master unit.
2 shows the internal configuration, and the transmission circuits 12 and 22 include a combiner 3
0, a modulator 31 for performing FM modulation, a mixer 32 for converting to an intermediate frequency signal, and an amplifier 33 for determining a transmission output,
The switching control signals of the control circuits 19 and 29 are output to the synthesizer 30 and the amplifier 33. Therefore, the switching control signal input to the synthesizer 30 is modulated together with the audio signal and transmitted from the transmitters 12 and 22 to the other party. When the switching signal is output to the amplifier 33, the transmission output is reduced. Change the amplifier gain to lower.

The embodiment has the above configuration, and its operation will be described below.

In the slave unit and the master unit, when the electric field strength of the received signal is detected by the detection circuits 17 and 27, and when the electric field strength is smaller than a predetermined value set by the comparators 18 and 28, the switching units 16a of both units , 16b, 26a, 26b are connected to the terminal a side, and the transmission / reception signals are scramblers 13a, 13b, 23a, 23b.
Is processed using Therefore, the transmitted voice signal is converted into a signal that cannot be intercepted as in the past, and upon reception, the signal that cannot be intercepted is converted into the original signal, and a good call is performed in a state where eavesdropping is prevented. Will be

On the other hand, the distance between the slave unit and the master unit is shortened, and the detection circuits 17, 2
When the electric field strength detected in step 7 becomes larger than a predetermined value, the switching control signal is sent from the control circuits 19 and 29 to the transmission circuit 1.
Output to 2,22. That is, the switching control signal is
As shown in FIG.
After the modulation, the signal is transmitted to the other party, and this switching control signal is received by the receiving circuits 11 and 21 of the other party.

In the embodiment, when the switching control signal is received from the other party in the control circuits 19 and 29, and the own device determines that the electric field strength has become a predetermined value or more, the switching of the transmission output and the scramblers 13 and 23 is performed. To do. That is, in the slave unit, the detection circuit 17 detects an electric field strength equal to or higher than a predetermined value,
When the switching control signal transmitted from the other party is received by the receiving circuit 11, the control circuit 19
A switching signal is output to the switch 33 and the switches 16a and 16b. The amplifier 33 operates to reduce the transmission power, and the switches 16a and 16b are switched to the terminal b.

In the base unit, when the detection circuit 27 detects an electric field strength equal to or higher than a predetermined value and the reception circuit 22 receives the switching control signal transmitted from the other party, the control circuit 29 A switching signal is output to the amplifier 33 and the switches 26a and 26b. The amplifier 33 operates to reduce the transmission power, and the switches 26a and 26b are switched to the terminal b.

Therefore, when the distance is short, both the slave unit and the master unit process the transmission / reception signal without using the scramblers 13, 23, and it is possible to prevent the deterioration of the communication quality due to the operation of the scramblers 13, 23. it can. Also, by reducing the transmission power at the same time, power consumption can be saved and the battery can be used for a long time.

In the above embodiment, the scramblers 13, 23 are switched when both the slave unit and the master unit detect that the electric field strength is large.However, the present invention is not limited to this. Alternatively, only one of them may be provided with an electric field strength detection circuit to perform switching control.

[Effects of the Invention] As described above, according to the present invention, the electric field intensity is detected by the electric field intensity detection circuit, and when the electric field intensity is large, the transmission power is reduced and switching is performed so as not to use the scrambler. Therefore, it is possible to improve call quality when there is no need to worry about eavesdropping.

[Brief description of the drawings]

FIG. 1 shows a transmission / reception control circuit of a cordless telephone according to an embodiment of the present invention. FIG. 1 (a) is a block diagram showing the configuration of a slave unit, FIG. 1 (b) is a block diagram showing the configuration of a master unit, and FIG. FIG. 3 shows a conventional circuit, FIG. 3 (a) is a block diagram showing a configuration of a slave unit, FIG. 3 (b) is a block diagram showing a configuration of a master unit, FIG. 4 is an explanatory diagram showing an operation of a scrambler It is. 11,21 ... Reception circuit 12,22 ... Transmission circuit 13,23 ... Scrambler 16a, 16b, 26a, 26b ... Switch 17,27 ... Field strength detection circuit 18,28 ... Comparator 19,29 ... Control circuit 30 ... Synthesis Instrument 33 ... Amplifier

Claims (1)

(57) [Claims] A scrambler for scrambling a signal to prevent wiretapping has a master unit connected to a telephone line and a slave unit wirelessly communicated with the master unit. In the transmission / reception circuit of the provided cordless telephone, an electric field intensity detection circuit for detecting the electric field intensity of the radio wave, and if the electric field intensity is low based on the output of the electric field intensity detection circuit, the transmission / reception signal is passed through a scrambler, A transmission / reception control circuit for a cordless telephone, comprising: a switch for switching transmission / reception signals so as not to pass through a scrambler when the strength is high; and controlling to reduce transmission power.