JPH06132937A - Voice scrambler applying inversion of frequency - Google Patents

Abstract

PURPOSE:To provide a voice scrambler which applies the inversion of frequency and requires no high-order LPF. CONSTITUTION:A voice scrambler consists of a pair of phase shift circuits 2 and 3 which relatively shift the phases by 90 deg. against an input signal, a pair of both side band signal generators 4 and 5 which receive the output signals of both circuits 2 and 3 and produce the both side band signals, an adder means 6 which adds together the output signals of both generators 4 and 5 and attenuates the upper side band signal USB, and an LPF 7 which receives the output signal of the means 6 and attenuates the remaining upper side band signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice scrambler by frequency inversion, which is suitable for use in cordless telephones and the like.

[0002]

2. Description of the Related Art A voice scrambler by frequency inversion used for a cordless telephone or the like has been previously proposed (Japanese Patent Laid-Open No. 60-39941).

To explain this, a voice signal in a cordless telephone has a frequency band of 300 Hz to 3 kHz as shown in FIG. 3A, and this voice signal is first frequency-converted by a carrier signal of frequency fc. At this time, as shown in FIG. 3B, the upper sideband signal USB and the lower sideband signal LSB are obtained for the frequency fc of the carrier signal.

Here, the frequency fc of the carrier signal is set to 3 kHz.
When z + 300 Hz = 3.3 kHz is selected, the lower sideband signal LSB becomes a signal of 300 Hz to 3 kHz as shown in FIG. 3C, and when only the lower sideband signal LSB is extracted by the low pass filter as shown in FIG. 3D, the voice scramble is performed. Become a signal. This audio scramble signal has a frequency band of 300H.
It is the same as that of the audio signal before scrambling, which is z to 3 kHz, but the frequency is inverted, so it is difficult to understand even if it is heard as it is.

For example, the audio signal of 1 kHz in FIG. 3A becomes a signal of 2.3 kHz in FIG. 3D, and the audio signal of 300 Hz in FIG. 3A is 3 kHz in FIG. 3D.
It becomes kHz, and high and low sounds are exchanged. Generally speaking, words are incomprehensible sounds because they are composed of multiple frequencies.

In the cordless telephone, the voice signal is transmitted with the frequency inverted at the transmitting side as described above, and the frequency is inverted again at the receiving side to obtain the original voice signal.

[0007]

However, in the voice scrambler by such frequency inversion, the lower sideband signal as shown in FIG. 3D is lower than the lower sideband signal LSB and the upper sideband signal USB as shown in FIG. 3C. A high order low pass filter is required to retrieve only the waveband signal LSB.

For example, when the frequency of an audio signal of 300 Hz is inverted, the lower sideband signal LSB is 3 as shown in FIG.
kHz, and 3.6 kHz for the upper sideband signal USB
And the sideband suppression ratio is 20 log LSB / USB is 40
If about dB is required, this lower sideband signal LSB
The low-pass filter for extracting only the high-order low-pass filter as shown in FIG.

This high-order low-pass filter requires the accuracy of the cutoff frequency and has the disadvantage that the number of elements increases. In particular, when the voice scrambler based on the frequency inversion is integrated into an integrated circuit, there is a disadvantage that it is disadvantageous in the above point.

In view of the above, the present invention proposes a voice scrambler by frequency inversion which does not require a high-order low pass filter.

[0011]

An audio scrambler by frequency inversion according to the present invention, as shown in FIG. 1, for example, has a pair of phase shift circuits 2 and 3 which shift the phase by 90 degrees relative to an input signal, and a pair of the phase shift circuits. The output signals of the shift circuits 2 and 3 are supplied to the pair of double-sideband signal generators 4 and 5, which generate double-sideband signals, and the pair of double-sideband signal generators 4 and 5, respectively. The addition means 6 adds the output signals and attenuates the upper sideband signal USB, and the reduction pass filter 7 that is supplied with the output signal of the addition means 6 and attenuates the residual upper sideband signal.

In the voice scrambler by frequency inversion of the present invention, the lower sideband signal obtained at the output side of the adding means 6 is 300 Hz to 3 kHz in the above description.

The voice scrambler based on the frequency inversion of the present invention has the above-mentioned low-pass filter formed by a second-order low-pass filter.

[0014]

According to the above-mentioned structure of the present invention, only the lower sideband signal LSB is obtained at the output side of the adding means 6, so that a high-order low-pass filter is not required.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a voice scrambler according to the present invention will be described below with reference to FIG. Figure 1
1 is 300 Hz to 3 kHz as shown in FIG. 3A.
The audio signal input terminal to which the audio signal in the frequency band of Esinωt, for example, is supplied, is supplied to the phase shift circuit 2 for shifting the phase of the audio signal supplied to the audio signal input terminal 1 by 0 degree, and the 300 Hz The phase of the audio signal in the frequency band of ˜3 kHz is supplied to the phase shift circuit 3 which shifts the phase by 90 degrees. In this case, the gains are the same on the output side of the phase shifts 2 and 3, so that audio signals whose phases differ by 90 degrees are obtained.

The audio signal obtained at the output side of the phase shift circuit 2 such as Esin ωt is supplied to the multiplication circuit 4 for frequency conversion, and the 90 ° phase shifted audio signal obtained at the output side of the phase shift circuit 3, for example Ecos ωt, is provided. It is supplied to the multiplication circuit 5 for frequency conversion.

[0017] 9 for example shows the carrier signal input terminal to which the carrier signal E ₀ sin .omega ₀ t of 3.3kHz is supplied, multiplying circuit 4 the carrier signal E is supplied to the carrier signal input terminal 9 ₀ sin .omega ₀ t supplying E ₀ cosω ₀ t to the multiplication circuit 5 to the carrier signal of the carrier signal E ₀ sinω ₀ t and 90 degrees phase-shifted through 90 degree phase shift circuit 10 is supplied to the.

In this case, the output side of the multiplication circuit 4 is

[Equation 1] A double sideband signal as shown in FIG. 3C is obtained.

On the output side of the multiplication circuit 5,

[Equation 2] A double sideband signal as shown in FIG. 3C is obtained.

The output signals of the multiplying circuits 4 and 5 are supplied to the adding circuit 6. In this case, the output signals of the multiplying circuits 4 and 5 are the lower sideband signal LSB as shown in Equations 1 and 2.
Have the same phase, and the upper sideband signal USB has the opposite phase.

Therefore, on the output side of the adder circuit 6,

[Equation 3] Such as 300 Hz to 3 kHz lower sideband signal LS
Only B is obtained.

However, in reality, a slight upper sideband signal USB remains as shown in FIG. 2 due to the phase characteristics and gain characteristics of the phase shift circuits 2 and 3. The output signal of the adder circuit 6 is supplied to the scramble signal output terminal 8 through a low-order low-pass filter 7 of the second order as shown in FIG.

In this example, since the lower sideband signal LSB whose frequency has been converted as described above is obtained at the scramble signal output terminal 8, the frequency-inverted voice scramble signal can be obtained at the scramble signal output terminal 8.

In this case, in this example, only the lower sideband signal LSB is obtained at the output side of the adder circuit 6 as shown by the equation 3, and the frequency inversion is performed without the need for a high-order low-pass filter. There is a benefit of being able to obtain a voice scrambled signal according to. Therefore, according to this example, since a high-order low-pass filter is not used, there is an advantage that an integrated circuit can be easily formed by a bipolar process.

In the above embodiment, if a subtraction circuit is used instead of the adder circuit 6 and a high pass filter is used instead of the low pass filter 7, the upper sideband signal USB is SS.
It can be transmitted as a B modulated signal.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various other configurations can be adopted without departing from the gist of the present invention.

[0027]

According to the present invention, only the lower sideband signal LSB can be obtained at the output side of the adder circuit, and a voice scramble signal by frequency inversion can be obtained without the need for a high-order low pass filter. There are benefits that can be. Therefore, according to the present invention, since a high-order low-pass filter is not used, there is an advantage that an integrated circuit can be easily formed by a bipolar process.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a voice scrambler by frequency inversion according to the present invention.

FIG. 2 is a diagram for explaining the present invention.

FIG. 3 is a diagram for explaining a voice scrambler by frequency inversion.

FIG. 4 is a diagram for explaining the present invention.

[Explanation of symbols]

 1 Audio signal input terminal 2, 3 Phase shift circuit 4, 5 Multiplication circuit 6 Adder circuit 7 Low pass filter 8 Audio scramble signal output terminal 9 Carrier wave signal input terminal 10 90 degree phase shift circuit

Claims (3)

[Claims] 1. A pair of phase shift circuits for relatively shifting an input signal by 90 degrees, and respective output signals of the pair of phase shift circuits are supplied,
A pair of double sideband signal generators for respectively generating double sideband signals, an addition means for adding the respective output signals of the pair of double sideband signal generators and attenuating the upper sideband signal, and the adding means An audio scrambler by frequency inversion, which comprises a low-pass filter which is supplied with the output signal of the above and attenuates the residual upper sideband signal. 2. The voice scrambler according to claim 1, wherein the lower sideband signal obtained at the output side of the adding means is 300.
A voice scrambler by frequency inversion, which is set to Hz to 3 kHz. 3. The audio scrambler by frequency inversion according to claim 1, wherein the low-pass filter is a second-order low-pass filter.