JPS61198840A - Privacy call equipment - Google Patents

Abstract

PURPOSE:To obtain a privacy call equipment inexpensively with high privacy call performance through a simple constitution by using an output signal from an exclusive OR circuit so as to control a clock generating circuit thereby changing the period of a clock signal controlling a storage circuit. CONSTITUTION:As the storage circuits 7, 8 of a modulation section and a demodulation section, n-stage of charge transfer elements are used. A clock frequency generated from a clock generating circuit 8 is controlled to f1 or f2 by using a signal from an exclusive OR circuit 11. A privacy call signal H (inputted to a terminal 17) inputted to a storage circuit 18 comprised of n-stage of charge transfer elements is produced at the output I of the storage circuit 18 with the delay of n-pulse's share of a clock signal (b). When the clock signal is a signal having a period change taking 2n-pulse as the basic period, the privacy call signal H being the output of a modulation section 14 is a signal with privacy call. When the modulation section 14 and the demodulation section 16 are synchronized and the mode for code setting switches S1, S2 and S3, S4 is matched and the same waveform as a sound signal (g) is obtained at the output I.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a confidential communication device that can be used in a voice transmission device such as a cordless telephone.

゛Prior Art In recent years, cordless telephones have come into widespread use. In such cordless telephones, there is a problem in that the contents of telephone calls may be intercepted by a third party, and a confidential communication device for this purpose has been desired.

Conventionally, various devices have been proposed as such confidential communication devices. For example, there are devices that use a method to invert the frequency spectrum of audio, or a method that divides the frequency band and swaps it and inverts the spectrum, but these require various filters, modulators, demodulators, etc. It has the disadvantage of being complicated and large. Another method is to perform analog-to-digital conversion of the audio signal, perform one-hour swapping, and then perform digital-to-analog conversion, or use a charge transfer element to temporally swap the analog signal. Further, devices have been proposed that use methods such as applying frequency modulation or amplitude modulation to audio signals. (JP-A-54-26604, JP-A-54-53903, JP-A-58-210732, etc.) A conventional confidential communication device will be described below with reference to the drawings.

FIG. 4 shows a block diagram of a conventional secret communication device. In FIG. 4, 1 is an audio signal input terminal, 2 is an analog-to-digital converter, 3 is a digital memory, 4 is a digital-to-analog converter, 6 is a control section, and 6 is an output terminal.

The operation of the confidential communication device configured as described above will be explained below.

First, the signal input from audio input terminal 1 is analog-
A digital converter 2 quantizes it into a digital quantity and stores it in a digital memory 3.

When the signals have been accumulated for a certain period of time, they are outputted in the order controlled by the control section 5, and are outputted to the digital-to-analog converter 4.
The analog signal is output from the output terminal 6. FIG. 6 is an explanatory diagram showing the state of input and output signals, where (a) shows signals input to the audio input terminals 1 arranged in a normal order.

(b) shows the signal output to the output terminal e after time swapping, and t and -tn each mean a signal for a certain period of time. The receiving device inputs signals from the audio input terminal 1 shown in FIG. 4, and can output the signals in the normal order by controlling the signals in a manner completely opposite to that of the transmitting device. On the other hand, the time reference for time swapping in the receiving device is created by processing the synchronization signal sent from the transmitting device separately from the polarized analog signal.

Problems to be Solved by the Invention However, the above configuration requires an analog-to-digital converter, a digital-to-analog converter, and a large-capacity digital memory, resulting in an expensive device. Was.

Means for Solving the Problems In order to solve the above problems, the confidential communication device of the present invention includes: a storage circuit that stores and holds audio signals; a clock generation circuit that generates a clock signal to control the storage circuit; a frequency dividing circuit that divides the frequency of a clock signal output from the clock generation circuit; a code generator that generates a code based on the signal from the frequency dividing circuit; and a signal from the code generator and the frequency dividing circuit. and an exclusive OR circuit that receives a signal from the circuit, and controls the clock generation circuit by the output signal from the exclusive OR circuit, and changes the period of the clock signal that controls the storage circuit. It has the following configuration.

Operation The present invention achieves privacy by phase-modulating the audio signal with the signal from the exclusive OR circuit, and provides a privacy device with a simple configuration and a high degree of confidentiality at low cost. It is something that can be done.

Embodiments Hereinafter, secret communication devices according to embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a secret communication device in one embodiment of the present invention. In FIG. 1, 1 is an audio input terminal, 7 is a memory circuit, 8 is a clock generation circuit, 9 is a frequency dividing circuit, 1o is a code generator, 11 is an exclusive OR circuit, 12 is a secret signal output terminal, 13 is a synchronization signal output terminal, and the modulation section 1
4. 16 is a transmission line, and the transmission line 16 also includes a device for transmitting and receiving electromagnetic waves. 16
is a demodulating section, and its configuration is the same as that of the modulating section 14.

17 is a confidential signal input terminal, and 18 is a memory circuit.

19 is a clock generation circuit, 20 is a frequency dividing circuit, 21 is a code generator, 22 is an exclusive OR circuit, 23 is an audio output terminal, and 24 is a synchronization signal input terminal.

Note that the memory circuits 7 and 18 are charge transfer elements (BB
D) is used.

The operation of the security device configured as described above will be explained below with reference to FIGS. 1 and 2.

FIG. 2 is an explanatory diagram of the operation of the embodiment shown in FIG. 1. FIG. 2 (&) is a simplified block diagram of FIG.
A stage charge transfer element is used.

The clock frequency generated by the clock generation circuit 8 is controlled to either fl or f2 by a signal from the exclusive OR circuit 11. FIG. 2Cb) shows the state of the clock signal. This clock signal is input to the memory circuit 7 and is also applied to the divide-by-one circuit 9 for frequency division. Figure 2 (C)
and (d) shows the outputs C and d of the frequency dividing circuit 9. That is, the output C of the frequency dividing circuit 9 is an output that is inverted every time n pulses of the clock signal are input, and the output d is an output that is inverted every time n/2 pulses of the clock signal are input. The output d of the frequency divider circuit 9 is applied to a code generator 10. The code generator 10 has code setting switches S1 and S2. Either one of the switches S1 and S2 is connected to the output e of the code generator 1o. Each time the bit of the output signal d of the frequency dividing circuit 9 is inverted, the connection state between the switch 31°S2 and the output e of the code generator 10 is changed. That is, when the output signal d of the branch circuit 9 is at a high level, the switch S1 and the output e are connected, and when the output signal d of the branch circuit 9 is at a low level, the switch S2 and the output e are connected. For example, switch S
When both 1 and S2 are ON, the output e is always at a low level. The state of the output e is shown in FIG. 2(e). Four states can be created by setting the switches 81 and 82. Output C of frequency dividing circuit 9 and output e of code generator 10
is added to the exclusive OR circuit 11. Therefore, the output f of the exclusive OR circuit 11 is as shown in FIG. ), the frequency changes to f and f2.

Now, the audio signal g input to the memory circuit 7 is shown in Fig. 2(g).
Think like this. The audio signal g is output after being delayed by n pulses by a memory circuit 7 composed of n stages of charge transfer elements. That is, the audio signal g input during the period T1 is output as an output H ((H) in FIG. 2) during the period T2. Therefore, the signal has an extended time axis as shown in FIG. 2 (6).

Similarly, the audio signal g input during period T2 becomes an output H and is output during period T3. Therefore, the signal becomes a signal whose time axis is compressed as shown in FIG. 2 (6). This is repeated below.

Therefore, the output H becomes a signal for repeating companding as shown in FIG. 2(6), and becomes a signal different from the original audio signal g, and becomes a confidential signal. This secret signal H is transmitted to the transmission line 16 along with the output G of the frequency divider circuit 9 used as a synchronization signal.
The signal is applied to the demodulating section 16 via. The demodulating section 16 has the same basic configuration and operation as the modulating section 14. Modulation section 14
The difference between the demodulating section 16 and the demodulating section 16 is that the frequency dividing circuit 20 is reset at the rising edge of the synchronizing signal from the modulating section 14 (inputted to the terminal 24), that is, the signal shown in FIG. 2(C). This reset operation synchronizes the signals b to f of the modulator 14 and demodulator 16. Now, if the code setting switches S3 and 54 are in the same mode as the code setting switches 51 and 52 of the modulator 14 (in the example of FIG. 2, both switches 83 and 84 are ON), the memory is stored as described in The output from the circuit 18 has the same waveform as the original audio signal C, as shown in FIG. 2(I), and is demodulated into the correct sound.

The secret signal H (input to the terminal 17) input to the memory circuit 18 composed of n stages of charge transfer elements is outputted from the memory circuit 18 with a delay of n pulses of the clock signal. Figure 2 @) and (1) respectively show the state of the secret signal H2 output I. In FIG. 2, the memory circuit 18
The confidential signal H inputted into the next period T3 is outputted in a time-compressed form.

Similarly, the secret signal H in the period T5 is time-expanded and output in the next period T4. Similarly, the confidential speech signal H is time-compounded and demodulated, and the original audio signal g is converted to 2 of the clock signal.
This occurs after a time delay corresponding to n pulses.

As is clear from the above explanation, if the clock signal has a periodic change with a basic period of 2n pulses, then
The secret signal H, which is the output of the modulation section 14, becomes a signal with secret speech added. The modulation section 14 and the demodulation section 16 are synchronized, and the code setting switch 81, S2 and S3
．． If the mode of S4 is appropriate, it is possible to obtain the same waveform as the audio signal g.

Now, the function of the exclusive OR circuit, which is the most distinctive feature of the present invention, will be explained in more detail with reference to FIG. In FIG. 3, FIG. 3(1) shows signal C. Figure 3 (2)? (3) P (4) t (5)
is the signal e depending on the mode of code setting switches S1 and 82.
This shows the state of signal f. When the signal f is high level, the frequency of the clock signal is f, and when it is low level, it is f2.
becomes. The mode shown in FIG. 3(2) is the mode explained in FIG. As explained in FIG. 2, the pulse interval of the clock signal is different when the signal f is at a high level and when it is at a low level. However, in FIG. 3, the pulse intervals are shown at equal intervals for the sake of clarity. Third
In figure (2), the pulse interval is 1/f in 5 periods T, T2.
1, the signal stored in the n-stage charge transfer element is transferred to the next period T3. At T4, the pulse is output at a pulse interval of 1/f2.

Therefore, as explained in FIG. 2, the signal is time-expanded. Similarly, in FIG. 3 (3), the input signal has a pulse interval of 1/f during one period T1.

In 1 period and 2, the pulses are stored in n stages of charge transfer elements with a pulse interval '/f2. Then, during the period T1, the signal that is observed in the n-stage charge transfer element is transmitted at a pulse interval of 1 during the period T3.
/f2 is output. Similarly, the signal in period T2 is
It is output at a pulse interval of 1/f. Therefore, the period T
The signal input to 1 is time-expanded, and the signal input to 2 is compressed in time and output.

In the following steps (4) and (5) in FIG. 3, the input signal is outputted as a signal that has necessarily been subjected to time companding.

In this embodiment, two code setting switches are used to create four states, but it is also possible to provide a larger number of switches to create a larger number of states.

Furthermore, although charge transfer elements are considered as the storage circuits 7 and 18, they may be elements that perform analog-to-digital conversion of audio signals and store them digitally.

Effects of the Invention As described above, by using an exclusive OR circuit, the secret output H is always a signal that is compressed 100% of the time, no matter what mode the code generation circuit is in. You can obtain the secret effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a secret communication device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. 1, and FIG. 3 is an explanatory diagram of the operation of the exclusive OR circuit 11. FIG. 4 is a block diagram of a conventional confidential communication device, and FIG. 6 is an explanatory diagram of the operation of FIG. 4. 1...Audio input terminal, 2...Music/D converter, 3...Digital memory, 4...
...D/mu converter, 5...Control unit, 6...
・・Secret message output terminal, 7, 18・・・・Memory circuit, 8
, 19... Clock generation circuit. ” 9, 20... Frequency divider circuit, 10, 21...
... Code generator, 11, 22 ... Exclusive OR circuit, 12 ... Confidential output terminal, 13.
... Synchronous output terminal, 14 ... Modulation section, 1
6...Transmission line, 16...Demodulator, 17
...Secret speech human power terminal, 23...Audio output terminal. 24...Synchronization input terminal. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 3

Claims (1)

[Claims] a memory circuit that stores and holds audio signals; a clock generation circuit that generates a clock signal that controls the memory circuit;
a frequency dividing circuit that divides the frequency of a clock signal output from the clock generation circuit; a code generator that generates a code based on the signal from the frequency dividing circuit; and a signal from the code generator and the frequency dividing circuit. and an exclusive OR circuit that receives a signal from the circuit, and controls the clock generation circuit by the output signal from the exclusive OR circuit, and changes the period of the clock signal that controls the storage circuit. A confidential communication device characterized by being configured as follows.