JPH048681Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial field of application] The present invention relates to an AM stereo signal transmission device, and is particularly compatible with conventional monaural receivers and has a narrow bandwidth occupied by sidebands. The present invention relates to a signal transmission device.

[Conventional technology]

Currently, various methods for transmitting AM stereo signals have been proposed and are in practical use in the United States. One method has good compatibility with monaural receivers, but has the disadvantage that the occupied bandwidth of sidebands is wide; the other method has a narrow occupied bandwidth of sidebands, but The disadvantage is that it is not compatible with Therefore, the present applicant previously proposed an AM method that solved the above-mentioned drawbacks in Japanese Patent Application No. 59-6174.
A stereo transmission method and device were proposed. The gist of the method is that the left audio signal L and the right audio signal R are S = Acos (ωt + φ), where A: amplitude ω: carrier wave angular frequency φ: phase angle (=tan ^-1 L-R/1+L+R) When transmitting AM stereo signals, A=1+L+R for low-frequency audio signals, and A=√(1++) ² +(-
R) This is an AM stereo transmission method characterized by transmission with ^two amplitudes.

FIG. 2a shows a modulator included in a transmitter to implement the above transmission method. In the figure, 1
is an input terminal into which the left audio signal L is input, 2 is an input terminal into which the right audio signal R is input, 3 is a matrix circuit that creates a signal of the sum and difference of the left and right audio signals, and 4 is a quadrature modulator, its output. is Acos(ωt+φ) AM
It is a stereo signal. 5 is an amplitude controller for changing the amplitude A of the signal; 6 is its input terminals 7 and 8;
The amplitude controller 5
9 is a low-pass filter that passes the low-frequency component of the amplitude control signal, and 10 is an output terminal for the AM stereo signal S to be transmitted.

Left and right audio signals L input from input terminals 1 and 2
and R are converted by the matrix circuit 3 into a sum signal (L+R) and a difference signal (L-R). In the quadrature modulator 4, the sum signal (L+R) amplitude modulates the carrier wave of angular frequency ω to become (1+L+R) cosωt, and the difference signal (L−R) amplitude modulates the carrier wave with a phase difference of 90° from the carrier wave with carrier suppression. Do-(L-R)
sinωt, and both are combined and output. Therefore, this output signal is (1+L+R)cosωt−(L−R)sinωt =√(1++) ² +(−) ² cos(ωt+φ)
...(1) becomes. here It is. A signal of (1+L+R) is applied to the input terminal 7 of the amplitude control signal generation circuit 6. This signal is, for example, the (1+L+
R) Obtained by detecting the envelope of cosωt.
The input terminal 8 has, for example, √(1++) ² +(-) ² obtained by envelope detection of the signal of equation (1).
signal is added. In the amplitude control signal generation circuit, the signal applied to the input terminal 7 is divided by the signal applied to the input terminal 8 and output. Therefore, this output signal is It is. For example, the frequencies of the left and right audio signals L and R are
When the frequency is low below 3KHz, the amplitude control signal
cosφ passes through the low-pass filter 9 and then the amplitude controller 5
added to. In the amplitude controller 5, the quadrature modulator 4
The signal of equation (1), which is the output of , and the signal of equation (3), which is the output of the low-pass filter 9, are multiplied, and the multiplied signal S is led to the output terminal 10. That is, the signal S in this case is S=(1+L+R) cos(ωt+φ) (4).

When the frequency of the left and right audio signals L and R is higher than 3KHz, the amplitude control signal cosφ is passed through the low-pass filter 9.
The output of the low-pass filter 9 is 1.
Therefore, the output of the quadrature modulator 4 is directly guided to the output terminal 10. The signal S in this case is S=√(1++) ² +(-) ² cos(ωt+φ)
...(5).

The characteristics of the above AM stereo signal are as follows. The frequency of the left and right audio signals is low, and the signal S
When is transmitted in the form of equation (4), there are high-order sideband waves, but the bandwidth below the third harmonic, which accounts for most of the energy, is at most ±9KHz, and the amplitude A is (1+L+R), so it is compatible with monaural receivers. For an audio signal of 3KHz or higher, the signal S is transmitted in the form of equation (5), so the sideband wave is only the fundamental frequency, so if the frequency of the audio signal is, for example, 10KHz, the bandwidth occupied by the sideband wave is ±
It is 10KHz. In this case, when receiving with a monaural receiver, some distortion occurs, but since the frequency of the harmonics that are distortion components is high, there is no problem in terms of hearing. In other words, the AM stereo transmission method described above is compatible with monaural receivers, and
It is characterized by a narrow occupied bandwidth of sideband waves.

FIG. 2b shows a demodulator included in a receiver for implementing the above-described AM stereo transmission method.
In the figure, 11 is an input terminal into which the signal S is input, 12 is an amplitude controller for controlling the amplitude A of the signal S, and 13 is an amplitude controller for controlling the amplitude by signals inputted through input terminals 14 and 15, which will be described later. 12 is an amplitude control signal generating circuit that generates an amplitude control signal to be added to the amplitude control signal, and 16 is a low-pass filter that passes a low-frequency component of the amplitude control signal. A quadrature demodulator 17 outputs a sum signal (1+L+R) and a difference signal (L-R) of left and right audio signals L and R. 18 is a matrix circuit for adding and subtracting the sum signal and the difference signal, and 19 and 20 are output terminals from which left and right audio signals L and R are respectively output.

One input terminal 1 of the amplitude control signal generation circuit 13
A signal called cos(ωt+φ) is input to 4. This signal is obtained, for example, by passing the signal S=Acos(ωt+φ) applied to the input terminal 11 through a limiter. A signal cosωt is input to the other input terminal 15. This signal is derived, for example, from a carrier wave generator used for demodulation. The above two signals input to the amplitude control signal generation circuit 13 are multiplied in the amplitude control signal generation circuit, and frequency components higher than the carrier wave angular frequency ω are removed. As a result, the amplitude control signal generation circuit 13 outputs a signal cosφ. The frequency of the left and right audio signals is
When it is lower than 3KHz, the signal S applied to the input terminal 11 is S = (1 + L + R) cos (ωt + φ) ... (6), and the output signal of the amplitude control signal generation circuit
cosφ passes through a low pass filter 16 and is applied to the amplitude controller 12. In the amplitude controller 12, the signal S is
Divided by cosφ. Therefore, the amplitude controller 1
From 2, √(1++) ² +(-) ² cos(ωt+φ)
...(7) is output and applied to the orthogonal demodulator 17. The orthogonal demodulator 17 demodulates the signal expressed by equation (7) using carrier waves cosωt and sinωt generated by a carrier generator provided therein. As a result, the quadrature demodulator outputs a sum signal (1+L+R) and a difference signal (L-R), which are added and subtracted by the matrix circuit 18. The left audio signal L is sent to the output terminal 19, and the right audio signal is sent to the output terminal 20. A signal R is output.

When the frequency of the left and right audio signals L and RMP is 3KHz or higher, the signal S is S=√(1++) ² +(-) ² cos(ωt+φ)
...(8), and since the output of the low-pass filter 16 is 1, the signal S is directly applied to the quadrature demodulator, and the left and right audio signals L and R are output to the output terminals 19 and 20.
are output respectively.

[Problem that the invention attempts to solve]

In the modulator and demodulator shown in FIGS. 2a and 2b, the amplitude controllers 5 and 12 are located between the orthogonal modulator 4 and the orthogonal demodulator 17, so that the signals handled are of high frequency. Generally, there is a problem that the higher the frequency, the more difficult it is to handle, so the present invention aims to perform amplitude control in the low frequency portion. [Means for Solving the Problem] The present invention provides a modulator with first and second multipliers as amplitude controllers between a matrix circuit and a quadrature modulator, and one output circuit of the matrix circuit. A first multiplier is disposed in the other output circuit, a second multiplier is disposed in the other output circuit, and in the demodulator, first and second dividers are disposed as amplitude controllers between the orthogonal demodulator and the matrix circuit, A first divider is arranged in one output circuit of the orthogonal demodulator, and a second divider is arranged in the other output circuit. As another means, first and second dividers are provided on the output side of the matrix circuit in the demodulator, the first divider is provided in one output circuit of the matrix circuit, and the second divider is provided in the other output circuit of the matrix circuit. This is where a divider is placed.

[Effect]

With the above configuration, amplitude control is performed in the low frequency signal portion.

[Example of idea]

FIG. 1a shows an embodiment of the modulator of the present invention. In the figure, 21 is an input terminal to which the left audio signal L is input, 22 is an input terminal to which the right audio signal R is input, and 23 is the sum signal (1+L+R) and the difference signal (L-
24 is an amplitude control signal generator that generates an amplitude control signal to be multiplied by the sum signal (1+L+R) and difference signal (L-R) by signals inputted from its input terminals 25 and 26, which will be described later. circuit, 27 is a low-pass filter that passes the low-frequency component of the amplitude control signal, and 28 is a low-pass filter that passes the low-frequency component of the amplitude control signal;
a first multiplier that multiplies R) by the amplitude control signal;
29 is a second multiplier that multiplies the difference signal (L-R) by the amplitude control signal; 30 is a first multiplier 28;
A quadrature modulator 31 performs carrier suppression amplitude modulation in an orthogonal relationship with each other using the output signal of the second multiplier 29 and the output signal of the second multiplier 29 as modulation signals, respectively.
This is an output terminal for AM stereo signal S.

The left and right audio signals L and R inputted from the input terminals 21 and 22 are converted by the matrix circuit 23 into a sum signal (1+L+R) obtained by adding 1 DC component and a difference signal (L-R). A signal of (1+L+R) is applied to the input terminal 25 of the amplitude control signal generation circuit 24.
This signal is led, for example, from one output of the matrix circuit 23. Input terminal 26 has (L-R)
signal is added. This signal is led, for example, from the other output of the matrix circuit 23. The amplitude control signal generation circuit 24 includes a sum-of-squares square root circuit and a divider, and calculates the signals input to the input terminals 25 and 26 to generate the following amplitude control signal. Output. When the frequencies of the left and right audio signals L and R are low, the amplitude control signal cosφ passes through the low-pass filter 27 and is combined with the sum signal (1+L+R) input to the first multiplier 28 and the second multiplier. Each of the difference signals (L-R) input to 29 is multiplied. As a result, the output signal of the first multiplier 28 becomes (1+L+R)cosφ, and the output signal of the second multiplier 29 becomes (LR)cosφ. In the quadrature modulator 30, the signal is (1+L+R)cosφ and (L−
Since the AM stereo signal S output to the output terminal 31 is S=cosφ{(1+L+R)cosωt −(L−R ) sinωt} = cosφ√(1++) ² + (−) ²・cos(ωt+φ) = (1+L+R)) cos(ωt+φ)...(10).

When the frequencies of the left and right audio signals L and R are high,
Since the amplitude control signal cosφ is blocked by the low-pass filter 27, the output of the low-pass filter 27 becomes 1, and the output signals of the first and second multipliers 28 and 29 are the sum signal (1+L+R) and the difference signal (L- R). The orthogonal modulator 30 uses these signals as modulation signals, performs carrier wave suppression amplitude modulation in an orthogonal relationship with each other, and synthesizes them. As a result, the output terminal 31
For S=√(1++) ² +(-) ² cos(ωt+φ)
...(11) AM stereo signal S is output.

As described above, when the frequency of the left and right audio signals L and R is low, the AM stereo signal is transmitted using the signal S of equation (10), and when the frequency is high, the AM stereo signal is transmitted using the signal S of equation (11). The same transmission as explained in section can be performed.

FIG. 1b shows an embodiment of the demodulator of the present invention. In the figure, 32 is an input terminal into which the signal S is input;
33 is an orthogonal demodulator, 34 and 35 are orthogonal demodulators 33
The first and second dividers 36 divide the demodulated signal of 3 by the amplitude control signal.
4 and 35; 39 is a low-pass filter that passes the low-frequency components of the amplitude control signals; 40 is a low-pass filter that generates the output signals of the first and second dividers 34 and 35; Matrix circuits 41 and 42 for addition and subtraction are output terminals to which left and right audio signals L and R are output, respectively.

When the frequencies of left and right audio signals L and R are low (10)
A signal S of the equation (11) is input to the input terminal 32 when the left and right audio signals L and R have high frequencies. One input terminal 37 of the amplitude control signal generation circuit 36 has cos(ωt+
A signal φ) is input. This signal is, for example, a signal S=Acos(ωt+
φ) is obtained by passing it through a limiter. A signal cosωt is input to the other input terminal 38. This signal is derived, for example, from a carrier wave generator used for demodulation. Amplitude control signal generation circuit 36
The above two signals inputted to are multiplied in the amplitude control signal generation circuit 36, and frequency components higher than the carrier wave angular frequency ω are removed. As a result, the amplitude control signal generation circuit 36 outputs an amplitude control signal of cosφ.

When the frequencies of the left and right audio signals L and R are low,
The signal S input to the input terminal 32 is (1+L+
R) cos(ωt+φ), so the orthogonal demodulator 33
When orthogonal demodulation is performed using carrier waves cosωt and sinωt, signals (1+L+R)cosφ and (LR)·cosφ are output from the orthogonal demodulator 33 and input to the first divider 34 and second divider 35, respectively. be done. Further, the amplitude control signal cosφ passes through a low-pass filter 39 and is input to the first and second dividers,
The above signals (1+L+R) cosφ and (LR)
Since cosφ is divided, the first divider 34 gives (1+L+R), and the second divider 35 gives (L
-R) is output. These signals are added and subtracted in a matrix circuit 40, and output terminals 41 and 4
2, left and right audio signals L and R are output, respectively.

When the frequencies of the left and right audio signals L and R are high,
The signal S input to the input terminal 32 is √(1++) ² +(-) ² cos(ωt+φ), so when orthogonally demodulated, it becomes (1+L+R) and (L-
A signal R) is output from the orthogonal demodulator 33.
The amplitude control signal cosφ is cut off by the low-pass filter 39, and the output of the low-pass filter 39 becomes 1, so the output signal of the orthogonal demodulator 33 is directly input to the matrix circuit 40, where it is added and subtracted. Outputs audio signals L and R. The AM stereo signal S is demodulated as described above.

Incidentally, as shown in FIG. 3, the first and second dividers 34 and 35 of the demodulator may be arranged on the output side of the matrix circuit. In this case, if the output signals of the orthogonal demodulator are (1+L+R)cosφ and (LR)cosφ,
Since the input to the first divider 34 is Lcosφ and the input to the second divider 35 is Rcosφ, cosφ is divided by the first and second dividers 34 and 35, and the left and right audio signals L are obtained. R is output to output terminals 41 and 42.

[Effect of idea]

As described above, according to the present invention, the first and second multipliers and the first and second dividers, which are amplitude control circuits, are arranged before the orthogonal modulator and after the orthogonal demodulator, respectively. Since it deals with low frequency signals, it has the advantage of being easy to design and manufacture.

[Brief explanation of the drawing]

Figures 1a and b show the modulator and demodulator of the AM stereo signal transmission device of the present invention, and Figures 2a and b show the conventional AM stereo signal transmission device.
Modulator and demodulator for AM stereo signal transmission equipment, FIG. 3 shows another embodiment of the demodulator of the present invention. 23... Matrix circuit, 28, 29... 1st
and a second multiplier, 30... orthogonal modulator, 33...
Orthogonal demodulator, 34, 35...first and second dividers, 40...matrix circuit, 24, 36...amplitude control signal generation circuit, 27, 39...low-pass filter.

Claims (1)

[Claims for Utility Model Registration] (1) A matrix circuit that adds and subtracts the left audio signal L and the right audio signal R to generate a sum signal (1+L+R) and a difference signal (LR), and generates an amplitude control signal cosφ. an amplitude control signal generation circuit; a low-pass filter that passes a low-frequency component of the amplitude control signal cosφ;
Output signal of the matrix circuit (1+L+R)
and (LR), respectively, the amplitude control signal
A transmitter includes first and second multipliers that multiply by cosφ, and a quadrature modulator that uses the respective outputs of the first and second multipliers as modulation signals. If the frequency is low, S=
(1+L+R)・cos(ωt+φ), left and right audio signal L
If the frequency of and R is high, S=√(1++)
² + (L-R) ²・cos (ωt + φ) is transmitted as an AM stereo signal, the AM stereo signal is received, and this received signal is S = (1 + L + R) cos
In the case of (ωt+φ), (1+L+R) cosφ and (L
−R) An orthogonal demodulator that demodulates into a cosφ signal, and demodulates into (1+L+R) and (LR) signals when the signal is S=√(1++) ² +(−) ² cos(ωt+φ); An amplitude control signal generation circuit that generates an amplitude control signal cosφ, a low-pass filter that passes a low-frequency component of the amplitude control signal cosφ, and an output signal of the orthogonal demodulator that is (1+L+
R) cosφ and (L-R)cosφ, the first dividing these output signals by the amplitude control signal cosφ
and a second divider, and add and subtract the outputs of the first and second dividers to obtain a left audio signal L and a right audio signal R.
1. An AM stereo signal transmission device, characterized in that an AM stereo signal is received by a receiver comprising a matrix circuit that outputs an AM stereo signal. (2) The AM stereo signal transmission device according to claim 1, wherein the first and second dividers in the receiver are arranged on the output side of the matrix circuit.