JPS5826220B2 - 4 Channel Stereo Adjustment Fukuchiyou Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a demodulation circuit for a four-channel stereo composite signal.

Hereinafter, an embodiment of the present invention will be described. When broadcasting 4-channel stereo FM, signals corresponding to the left front, left rear, right front, and right rear sounds of the listener are
Assuming F t LB and RF t RB, the four-channel stereo composite signal f(t) is frequency-multiplexed as shown by the following equation, and has a frequency spectrum as shown in FIG.

f (t)”A+ Bs stone ωt + Ccos ωt +
Dsin 2ωt +Psm-twhere, the first and second
, the third and fourth matrix signals A-D are A = (LF + LB) + (RF + RB)
B-(Lp+LB)-(Rp+RB)C-(L
FLB) + (Rp-RB)D= (LF
LB) (Rp-RB)ω=2 rf,
f = 38 kHzP, the band of pilot signals A-D is 50H2 to 15kHz2.

Such a composite signal is demodulated by the configuration shown in FIG.

In FIG. 2, 1 indicates the input terminal to which the composite signal f(t) obtained by reception detection in the FM receiver is supplied, and 2 indicates the switching signal 51(t) from the signal f"(t).
This is a switching signal forming circuit that forms ~S, (t).

Each of the switching signals 51(t) to S,(t) has a duty factor of 25% and a repetition period T of (1/f), as shown in FIG. This is a pulse signal with a width of 1.

Therefore, when the switching signals 51(t) to S, (t) are expanded into a Fourier series, they become as follows.

In addition, in FIG. 2, 11 to 14 are composite signals f (t
) to which switching circuits 11 to 14 are supplied with switching signals 51(1) to 51(1) to 14, respectively.
S, (t) is supplied.

, 15-18 indicate switching circuits to which the composite signal f(t) is supplied via a phase inversion amplifier 3 and an attenuator 4.

If the gain of this phase inversion amplifier 3 is assumed to be 1 for simplicity and the attenuation ratio of the attenuator 4 is α, then the switching circuits 15 to
The input signal to 18 is -αf(t).

Further, the switching circuits 15-18 are supplied with switching signals 57t)-57t, which are obtained by passing the switching signals 51(t)-S, (t) through inverters 21-24.

Taking the switching signals 57t) to 84(t) as an example, the waveforms of the switching signals 57t) to 84(t) are as shown in FIG.

The outputs of the switching circuits 11 to 18 described above are e1 to e8.
Then, these outputs will be:

Then, the outputs e1 and e5 of the switching circuit are supplied to the addition circuit 31, the outputs e2 and 2 are supplied to the addition circuit 32, the outputs e3 and e7 are supplied to the addition circuit 33, and the outputs e4 and e
8 is supplied to the adder circuit 34.

Among the outputs e9 to e1□ of these adder circuits 31 to 34, output e9 is supplied to adder circuits 42, 43, and 44, and outputs e1o and e are supplied to each of adder circuits 42, 43, and 44, respectively.
11. Supply e1□.

In this way, the output e13 of the adder circuit 42, 43, 44
t e14 j e15 becomes a matrix signal BCD by selecting the attenuation ratio α.

To explain this using signal B as an example, the output e9 of the adder circuit 31 is as follows.

This output e is, if we focus on the necessary audible band components,
Furthermore, it can be expressed as follows.

This output e1o can be further expressed as follows if we focus on the necessary audible band components.

Here (α %)given that, becomes.

Therefore, the output e13 of the adder circuit 42 is Therefore, only the second matrix signal is obtained.

In addition, the output "11" of the adder circuit 33 is becomes.

This output e1□ can be further expressed as follows if we focus on the necessary audible band components.

Here, if (α=X), becomes.

Therefore, the output e14 of the adder circuit 43 becomes , and only the third I-IJ signal C is obtained.

Furthermore, the output e1□ of the adder circuit 34 is becomes.

This output e1□ can be further expressed as follows if attention is paid to the necessary audible band component.

Here (α 3A), then becomes.

Therefore, the output e15 of the adder circuit 44 is Therefore, only the fourth mixed signal is obtained.

Therefore, by supplying the first matrix signal A separated by the low-pass filter 5 from the second to fourth matrix signals B to D and the composite signal f(t) to the matrix circuit 6, A 4-channel stereo signal Lp j "B, RB y RF can be obtained at its output.

FIG. 5 shows an example of the connection of the part forming the matrix signal B in the above-described embodiment of the present invention. In FIG. 5, 51 indicates a variable resistor corresponding to the attenuator 4, and 2a
, 2b are terminals to which switching signals 51(t) and 52(t) are applied from the switching signal forming circuit 2.

The switching signal 51(t) is applied to the base of the transistor 52 (switching circuit 11), has its phase inverted by the transistor 54 (inverter 21), and is applied to the base of the transistor 53 (switching circuit 15).

Similarly, the switching signal 52(t) is the transistor 55
The signal is applied to the base of the switching circuit 12 (switching circuit 12), and the phase is inverted by the transistor 57 (inverter 22) and applied to the base of the transistor 56 (switching circuit 16).

The emitters of the transistors 52 and 55 are supplied with the composite signal f(t) from the input terminal 1 via the transistors 58 and 59, and the emitters of the transistors 53 and 56 are supplied with the composite signal f(t).
A composite signal -αf(t) passed through the phase inversion amplifier 3 and variable resistor 51 is supplied via transistors 60 and 61.

Since the collectors of the transistors 52, 53, 55, and 56 are commonly connected to the load resistor 62, the outputs of the respective switching circuits are added to the output terminal 63, and only the matrix signal B is obtained.

The circuits for forming other matrix signals C and D can also be constructed in the same manner as shown in FIG.

According to the invention described above, the matrix signal B of the sub-channels (second, third and fourth channels).

Since C and D can be detected independently, subcha,
Even if channel level fluctuations occur, this can be completely corrected.

In general, the switching demodulation power method has the advantage that the circuit configuration is simpler than the frequency division demodulation method, but since it is not possible to detect the matrix signal of the subchannel, it is necessary to correct it when the level fluctuation of the subchannel occurs. This has the disadvantage that separation adjustment becomes troublesome.

However, according to the present invention, by inserting level adjusters between the adder circuits 42 to 44 and the matrix circuit 6, it is possible to easily and completely correct subchannel level fluctuations.

[Brief explanation of the drawing]

FIG. 1 is a frequency spectrum of a 4-channel stereo composite signal, FIG. 2 is a system diagram of an embodiment of the present invention, FIGS. 3 and 4 are waveform diagrams of switching signals, and FIG.
It is a partial connection diagram of the figure. 1 is an input terminal for a composite signal, 2 is a switching signal forming circuit, 3 is a phase inversion amplifier, 4 is an attenuator, and 6 is a matrix circuit. 11-18 are switching

Claims (1)

[Claims] When a signal obtained by matrixing 14 channel stereo signals is used as the first to fourth matrix signals, the first matrix signal and the first subcarrier having a frequency higher than the band of the first matrix signal are used as the second matrix signal. A second channel signal whose amplitude is modulated with a matrix signal, a third channel signal whose amplitude is modulated with a third matrix signal on a second subcarrier in quadrature with the first subcarrier, and a third channel signal whose frequency is twice that of the first subcarrier. In a circuit that demodulates the four-channel stereo signal from a composite signal consisting of a fourth channel signal obtained by amplitude modulating the third subcarrier with a fourth matrix signal and a pilot signal having a frequency of H that is the first subcarrier frequency, First to fourth switching circuits to which the composite signal is supplied and fifth to eighth switching circuits are provided, and the first to fourth switching circuits are provided.
The first to fourth switching signals, which are repeated in the cycle of the first subcarrier and whose phases are sequentially shifted, are supplied to the switching circuit, respectively, and the phases of the first to fourth switching signals are inverted to generate the fifth switching signal. - an attenuator having a predetermined attenuation amount is provided on the input side or output side of the fifth to eighth switching circuits, and the first and fifth switching circuits are supplied with A first addition output is obtained by adding the outputs of the circuits, a second addition output is obtained by adding the outputs of the second and sixth switching circuits, and a second addition output is obtained by adding the outputs of the second and sixth switching circuits. A third addition output is obtained by adding the outputs, a fourth addition output is obtained by adding the outputs of the fourth and eighth switching circuits, and the first and second addition outputs, the first By combining the third addition output and the first and fourth addition outputs, second, third and fourth matrix signals are obtained, respectively, and the combined signal is passed through a low-pass filter to the first This first matrix signal and the second, third and fourth matrix signals are obtained.
A demodulation circuit for a 4-channel stereo composite signal, which obtains the 4-channel stereo signal by matrixing the 4-channel stereo signal.