JPS6228910B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention utilizes two audio carrier waves, first and second.
This invention relates to a stereo demodulator in a two-audio carrier system that transmits FM stereo signals.

2. Description of the Related Art Conventionally, as a method for transmitting stereo left and right signals L and R in a television or the like, there are a stereo multiplex signal method and a two-audio carrier method.

The former modulates the main carrier using a composite wave of the subcarrier frequency modulated (hereinafter simply referred to as FM) by the difference signal (L-R) and the sum signal (L+R).
However, in this method, the stereo left and right signals L and R are mainly transmitted using this main carrier wave.On the other hand, in the latter method, the two audio carrier waves, the first and second audio carrier waves, are FMed with audio signals separately, and these two audio carrier waves are This is a method in which stereo left and right signals L and R are transmitted using audio carrier waves.

Of the above two systems, the present invention relates to a stereo demodulator for the latter two-audio carrier system.Prior to explaining the present invention, a conventional example thereof will first be explained with reference to FIGS. 3 and 4.

The examples shown in FIGS. 3 and 4 show a stereo audio signal transmission/reception system circuit in a television, and illustration of a video carrier system circuit is omitted.

First, Figure 3 shows a signal generator in a two-audio carrier type transmission system. In the figure, reference numeral 6 is a matrix circuit, and 7 and 8 are input terminals for the left signal L and right signal R, respectively, in the stereo signal. , this matrix circuit 6 causes one output terminal 9 to output 1/2 (L+R), and the other output terminal 10 to output a right signal R. sign
r ₃ and r ₃ are resistance elements forming the matrix circuit 6.

Then, one output terminal 9 sets the oscillation frequency to the first
A first audio frequency modulation oscillator ₁₁ whose oscillation frequency is the frequency F 1 of the audio carrier wave is connected to a superimposer 13, and the other output terminal 10 is connected to a second audio frequency modulation oscillator 12 whose oscillation frequency is the frequency F ₂ of the second audio carrier wave.
It is separately connected to a superimposing device 13 via the.

The first audio carrier wave F ₁ ±ΔF{ _{1/2(L+R) } which is FMed by the audio signal 1/2 (L+R)} in the first audio frequency modulation oscillator 11 and the second audio frequency modulation oscillator 12 FM by right signal R at
The second audio carrier F ₂ ±ΔF _(R)
3, the stereo left and right signals L and R are
Output terminal 1 is carried by two audio carrier waves F ₁ and F ₂
Sent from 4.

Next, FIG. 4 shows a stereo demodulator in the receiving system, which is used in correspondence with the signal generator in the above-mentioned transmitting system.

In FIG. 4, reference numeral 15 is an input terminal,
FM first and second audio carrier signals extracted through a filter (not shown) provided in the receiving system are introduced into the input terminal 15.

Next, this introduction line is divided into two, and one line is 1.
6 is connected to a dematrix circuit 20 via a third bandpass filter 18 whose center frequency is the frequency F ₁ of the first audio carrier wave and a third audio frequency discriminator 19, and the other line 17 is connected to the dematrix circuit 20 whose center frequency is the frequency F 1 of the first audio carrier wave. It is separately connected to the dematrix circuit 20 via a fourth bandpass filter 21 with the frequency F ₂ of the audio carrier wave and a fourth audio frequency discriminator 22 . The dematrix circuit 20 is composed of an operational amplifier 20', resistors r ₄ , r ₄ and the like.

Then, it is extracted through the third bandpass filter 18.
The FM first audio carrier signal is discriminated by the third audio frequency discriminator 19 and the audio signal 1/2 (L+
R), and on the other hand, the FM second audio carrier signal extracted through the fourth bandpass filter 21 becomes the fourth
The right signal R is discriminated by the audio frequency discriminator 22.
becomes. Next, this audio signal 1/2 (L+R) and right signal R are processed by the dematrix circuit 20 by 2×
After the calculation of {1/2(L+R)}-R=L, both output terminals 23 and 2 in this dematrix circuit 20
4, a left signal L and a right signal R are separately taken out.

By the way, in the conventional stereo demodulator, as mentioned above, the audio frequency components 1/2 (L+R) and R are converted into signals by the third and fourth discriminators 19 and 22, and then the dematrix circuit 20 Since the signal is separated into left and right signals L and R by the operation of (L+R) and the right signal R, and the audio signal 1/2 (L+R ) and the right signal R are not exactly the same, both output terminals 23 and 2
As a result, the degree of separation between the left and right signals L and R outputted from 4 is degraded.

That is, if the third and fourth discriminators 19 and 2
Audio signal 1/2 (L+
R) and the right signal R, if the level of the right signal R is greater by ΔR, as a result of calculation by the dematrix circuit 20, the level of the right signal R is
3 outputs a signal of L±ΔR, and the degree of separation deteriorates.

And the audio signal 1/2 (L+R) in the transmission system
In order to make the level ratio between R and the right signal R the same as that in the receiving system, it is first necessary to equalize the modulation sensitivities of both the first and second audio frequency modulation oscillators 11 and 12 in the transmitting system. At the same time, it is necessary to equalize the discrimination sensitivities of both the third and fourth audio frequency discriminators 19 and 22 in the receiving system.

However, it is extremely difficult to maintain the modulation sensitivities of both modulation oscillators 11 and 12 and the discrimination sensitivities of both discriminators 19 and 22 to be the same at all times, and deterioration in the separation of the stereo left and right signals L and R cannot be avoided. .

In this case, the present invention provides that one of the lines into which the two FM audio carrier signals are introduced is divided into two.
An intermodulation circuit, a first bandpass filter adapted to extract a signal of a predetermined third-order frequency component from the output signal from the intermodulation circuit, and a first audio frequency discriminator are interposed in sequence, A stereo demodulator that outputs one of the signals in the stereo signal directly from the first audio frequency discriminator and avoids dematrixing at the audio frequency signal stage, thereby preventing deterioration of separation in the demodulation stage. This is what we tried to provide.

The present invention will be specifically explained below based on the embodiments shown in the drawings.

In Fig. 1, reference numeral 1 is an input terminal, and two FM audio carrier wave signals connected to input terminal 1 [F ₁ ±ΔF{ _1/2(L+R) }] + [F ₂ ±ΔF _(R) ] is divided into _two , and one line _l2 is connected to _an intermodulation circuit _U1 , which will be described later, and a predetermined third-order component signal ( _{2F1- F2} )
a first bandpass filter whose center frequency is the frequency of
After sequentially interposing the BPF ₁ and the first audio frequency discriminator U ₂ , the output terminal 2 of the left signal L is derived.

On the other line _L3 , a second bandpass filter BPF ₂ whose center frequency is the second audio carrier F ₂ and a second audio frequency discriminator U ₃ are sequentially interposed, and then the right signal R is output. Lead out terminal 3.

Next, referring to FIG. 2, the above-mentioned intermodulation circuit U ₁
An example will be explained in more detail.

In FIG. 2, reference numeral 4 is an input terminal of the intermodulation circuit U ₁ , and reference numeral 5 is an output terminal, and the intermodulation circuit U ₁ has two diode elements D ₁ and D ₂ connected in parallel in opposite directions. It is mainly composed of two resistors r ₁ and r ₂ .

If two signals f ₁ and f ₂ with different frequencies are input to the input terminal 4, the input side signals f ₁ and f ₂ will be output from the output terminal 5 due to the nonlinearity of the circuit.
A new odd-order frequency component signal consisting of a combination of f ₁ , f ₂ , _2f 1 - f 2 , 2f _{2 -} f ₁ , 3f ₁ - 2f ₂ , 3f _{2 -} 2f ₁ ...
occurs. In the present invention, among these odd-numbered output signals, the first bandpass filter BPF ₁
A predetermined tertiary frequency component signal (2f ₁ -f ₂ ) is extracted using the following steps.

Next, the operation of the stereo demodulator as an embodiment of the present invention configured as described above will be explained. Before explaining the function, the symbols used in this specification will be explained.

F ₁ ±ΔF{ _1/2(L+R) } (=f ₁ ): First audio carrier wave FMed by audio signal 1/2(L+R) F ₂ ±ΔF _(R) (=f ₂ ): 2nd audio carrier wave FMed by right signal R. The FM signal extracted from the input terminal 1 in Figure 1 through a filter (not shown) for extracting the audio carrier wave in the receiving system. When two audio carrier wave signals [F ₁ ±ΔF{ _1/2(L+R) }] + [F ₂ ±ΔF _(R) ] are input, first, on one line _l2 side, these two audio carrier wave signals For the intermodulation circuit U ₁ , as shown in Figure 2, there are two input signals with different frequencies, f ₁ = F ₁ ±ΔF{ _1/2(L+R) }, and f ₂ = F ₂ ±ΔF _(R
) , the intermodulation circuit U ₁ generates a new odd-order frequency component signal f ₁ , f ₂ , 2f ₁ −f ₂ , 2f ₂ − consisting of a combination of these two input signals.
f ₁ ... is output. Of these output signals, _the third-order component signal _{2f 1 -f 2 =} 2 [F ₁ ±ΔF{ _1
/2(L+R) }]−{F ₂ ±ΔF _(R) } is taken out,
This third-order component signal is transmitted to the next stage, the first audio frequency discriminator.
It is discriminated by U ₂ and a discrimination output of 2{1/2(L+R)}-R is obtained.

And this discrimination output is 2{1/2(L+R)}-R
=L, the left signal L is output from the output terminal 2 as it is.

On the other line _l3 side, the second bandpass filter BPF ₂ with the second audio carrier F ₂ at its center frequency passes the FM-resulted second audio carrier F ₂ ±ΔF _(R) to the next stage's second band filter BPF 2. The right signal R is taken out from _{the second audio frequency discriminator U 3 and} output from the output terminal 3.

As described above, in the present invention, after becoming an audio frequency signal, the signal is outputted from the output terminals 2 and 3 as it is without being subjected to arithmetic processing by a dematrix circuit or the like at this frequency stage.

As described in detail above, according to the present invention, the introducing line for two audio carrier signals is divided into two, and one line has a
An intermodulation circuit, a first bandpass filter that extracts only a predetermined third-order frequency component from the output signal from the intermodulation circuit, and a first audio frequency discriminator are interposed in sequence, and the other The line includes a second bandpass filter having a center frequency at the second audio carrier;
The left signal L and right signal R are output directly from both branch lines by sequentially interposing a second audio frequency discriminator, and dematrixing is avoided at the audio frequency signal stage, so the separation is achieved. This provides an extremely excellent effect in that the stereo left and right signals L and R can be output stably at all times without causing any deterioration in the quality.

Furthermore, since the stereo demodulator according to the present invention does not cause any deterioration in the degree of separation,
It has the excellent effect of being able to be used as a standard (reference) stereo demodulator to adjust the modulation sensitivity of the FM modulator to achieve the best separation characteristics.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a stereo demodulator according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing an example of an intermodulation circuit applied to the same demodulator, and Fig. 3 is a conventional two-audio carrier system transmission. FIG. 4 is a block diagram showing a signal generator for two audio carrier waves in the system, and FIG. 4 is a block diagram showing a stereo demodulator in a receiving system corresponding to the transmitting system. 1: Input terminal, 2: Left signal L output terminal, 3:
Right signal R output terminal, BPF ₁ : first bandpass filter,
BPF ₂ : Second band filter, D ₁ , D ₂ : Diode element, U ₁ : Intermodulation circuit, U ₂ : First audio frequency discriminator, U ₃ : Second audio frequency discriminator, l ₁ : 2 audio Carrier introduction line, l ₂ : one line, l ₃ : other line.

Claims (1)

[Claims] 1 First audio carrier F ₁ and second audio carrier F ₂
In a stereo demodulator using a two-audio carrier system that transmits a stereo signal by frequency-modulating each audio signal separately, the frequency-modulated carrier signal [F ₁ ±△F ₁ { _1/2(L+R) }＋F ₂ ±△F _2(R) ] The introduction line is divided into two, and one line has an intermodulation circuit and a predetermined third-order component signal (2F ₁ −F ₂ ) A first bandpass filter and a first audio frequency discriminator whose center frequency is the frequency of A second bandpass filter having a center frequency of the second audio carrier _F2 and a second audio frequency discriminator are sequentially connected to the line, and the R signal in the stereo signal is outputted from the second audio frequency discriminator. A stereo demodulator characterized by: