KR830000788B1 - Independent Sideband Amplitude Modulation Multiple Acoustic System - Google Patents

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Description

Independent Sideband Amplitude Modulation Multiple Acoustic System

1 is a block diagram of a conventional independent sideband AM stereo transmitter.

2 is a block diagram of an improved conventional independent sideband AM stereo transmitter.

3 is a block diagram of an independent sideband multiple acoustic transmitter for explaining the present invention.

4 is a pager diagram useful in explaining amplitude and phase modulated signals to illustrate the present invention.

5 is a signal diagram showing the amplitude of the signal shown in FIG.

6 is a block diagram of an independent sideband AM stereo receiver according to the present invention.

FIG. 7 is a block diagram showing another configuration of the receiver portion of FIG. 6 according to the present invention. FIG.

The present invention relates to an independent sideband AM multiple acoustic system, such as a stereo acoustic system.

US Patent No. 321839 describes a system for transmitting stereo information of an AM broadcast signal, which can be used in conjunction with existing AM receivers. According to such a conventional system, in the transmitter shown in the block diagram of FIG. 1, the L and R stereo signals are synthesized in the subtracting circuit 10 and the adding circuit 12 of FIG. 1, respectively, to form L-R and L + R signals. Is formed. The phase shifting networks 14 and 16 cause the sum signal L + R and the difference signal L-R to have substantially 90 ° audio phase difference. The carrier signal from the oscillator 18 is phase shifted with the stereo difference signal information phase shifted in the phase modulator 20 and the amplitude is limited in the limiter 21, followed by the phase shifted stereo sum in the amplitude modulator 22. Amplitude modulation with signal information. The output signal from the amplitude modulator 22 is an independent sideband AM signal, and L stereo signal information and R stereo signal information appear separately in the lower band and the upper band of the AM signal.

The carrier may be generated and modulated at the frequency to be transmitted. Typically, such a transmitter modulates the low frequency carrier and then increases the carrier frequency to the frequency to be transmitted. As a result, the term " carrier signal " herein relates to both a transmission frequency signal and a low frequency signal.

To explain the equation of the conventional AM stereo system transmitter shown in FIG. 1, it is assumed that the R signal has zero amplitude when the stereo sum signal L + R is equal to the stereo difference signal LR. It is convenient. As shown in FIG. 4, when amplitude and phase modulation are used for a vector of stereo sum signals and difference signals that are perpendicular to each other with a phase difference of 90 °, the synthesized modulation phaser proceeds clockwise toward the carrier vector 26. A phasor 24 is obtained, which represents a single sideband signal.

Fig. 4 presents an ideal situation in which only the fundamental upper band and carrier are present. This signal format is a stereo sum signal (L + R) whose envelope detection characteristic of a standard receiver is a distorted sinusoidal wave shown at 28 in Fig. 28. It is not suitable for AM stereo system which can be used together because it will be demodulated. The ideal detected signal is a sinusoidal wave 30 as shown in FIG. 5 when a single tonal sinusoid is made only on one of the stereo channels L or R by modulation.

The actual synthesized signal generated by the conventional transmitter shown in FIG. 1 is the second harmonic amplitude modulation and phase modulation component generated by the coupling parts 21 to 22 of the limiter and the amplitude modulation period due to the doubling of the amplitude modulation process. Include them. The second harmonic amplitude modulation components cause the signals detected by the envelope detector of a conventional AM receiver to be relatively free of distortion. Such a monoacoustic receiver essentially ignores the phase modulation component, so that the compatibility of the transmitted independent sideband AM stereo signal is not affected. However, the second harmonic phase modulation components are nearly doubled as compared to the actual single sideband signal.

In US Patent No. 390890, which describes a transmitter for an independent sideband AM stereo system, a phase modulation component of a second harmonic in which the second harmonic fixation of a stereo difference signal (LR) is present in an independent sideband AM stereo signal generated by the system is disclosed. An improved transmitter is provided, which is provided to reduce the to a desired value, which is shown in FIG. Such an improved conventional transmitter includes components similar to those in the system shown in FIG. 1 and denoted by the same numerals, in addition to adding second harmonic correction to the stereo difference signal LR prior to phase modulation of the carrier. Circuitry, which includes phase shifting networks 32, 34 for imparting phases to the L and R stereo signals between the phase shifted stereo difference signal and the phase shifted stereo sum signal. Constant Gain Frequency The multipliers 36 and 38 are used to double the frequency of the L and R stereo signals. Doubled frequency signals are combined in the subtractor 40. The variable gain amplifier 42 supplies the corrector signal to the adder 46 in response to the amplitude of the phase shifted stereo difference (L-R) signal as detected by the rectifier 44. This calibration signal is proportional to the square of the amplitude of the stereo difference signal and has a frequency that is twice the audio frequency of the stereo difference signal. The maximum amplitude of the calibration signal is about 13% of the maximum amplitude of the stereo difference signal. The modified stereo difference signal generated at the output of the adder 46 is supplied to the phase modulator 20 to modulate the carrier wave. This phase shifted carrier is then amplitude modulated in modulator 22 by the stereo sum signal L + R phase shifted before transmission.

However, such a second harmonic correction of the stereo difference signal may completely fix the excessive second harmonic phase modulation component inherently generated in the amplitude modulator 22, but the desired second harmonic phase modulation components may not be subjected to LR phase modulation. There is distortion. However, since the monoacoustic receiver essentially ignores the phase modulation of the received independent sideband AM stereo signal, the signal compatibility is not affected. Moreover, this L-R distortion is canceled in an independent sideband stereo receiver, resulting in an L-R signal without actual distortion.

However, while these conventional transmitters provide the desired second harmonic correction for the independent sideband AM stereo signals being transmitted, it is clearly shown in FIG. 2 that the transmitter is extremely complicated to generate the calibration signal. have.

The amplitude modulation in US Pat. No. 40,094,94, which describes a conventional independent sideband AM stereo receiver, is a stereo difference received from a second harmonic correction component generated by the independent sideband AM stereo transmitter described in US Pat. It is used to remove from the signal component LR, which is shown in FIG. In general, U. S. Patent No. 4,018, 994 describes amplitude modulation of a received stereo difference signal component into one or more signals derived from the stereo sum signal component for the purpose of reducing LR distortion resulting from the second harmonic correction component generated by the transmitter. It is written.

An object of the present invention is to reduce the distortion appearing in the stereo difference signal component of the received independent sideband signal by modifying the difference signal component of the received independent sideband AM stereo signal by the sum signal component of the selected nonlinear function. It is to provide a new and improved independent sideband AM multiple sound, such as a stereo acoustic receiver.

을 가지는 선택된 변조함수에 따라서 제1신호(A)가 제2신호(B)에 의해 변조되도록한 공정을 의미한다.As used herein and in the claims, the term "inverse modulation" is used in a monolithic form.

The first signal A is modulated by the second signal B according to the selected modulation function.

According to a feature of the invention, there is provided an apparatus for supplying a received mid-frequency independent sideband AM multi-acoustic signal and inversely modulating the difference signal component of the received signal by the sum signal component in accordance with a second selective modulation function. And a device for deriving a pair of audio frequency output signals therefrom in response to the sum signal component and the inversely modulated difference signal component. Each of the audio frequency output signals represents a corresponding one of the original L and R input signals used at the transmitter to induce the independent sideband AM polyacoustic signal.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

As described above, in the conventional independent sideband transmitter shown in FIG. 2, a second harmonic correction signal is added to the stereo difference signal before the phase modulator 20 modulates the carrier signal. However, in the independent sideband transmitter of FIG. 3, the preferred second harmonic correction is achieved by inversely modulating the stereo difference signal component by the sum signal component without adding the correction signal. This inverse modulation is done in accordance with the optional modulation function described later.

The transmitter of FIG. 3 generates a stereo difference signal LR and a stereo sum signal L + R, respectively, in response to L and R stereo signals that may arise from any stereo signal source such as, for example, separate microphones 50 and 52. It comprises a synthesizer (10, 12). The stereo difference signal is limited to audio frequencies below 5 KHz by the optional action of the low pass filter 54. As shown in US Pat. No. 39,08090, it will be appreciated by those skilled in the art that such filtering is performed in the difference signal channel, it is desirable to have delay equalization in the sum signal channel. The phase shifting networks 14 and 16 act on the stereo sum signal and the difference signal so that a phase difference of 90 ° is shown between them.

According to the third embodiment, the stereo difference signal is inversely modulated by the stereo sum signal in accordance with the selected modulation function. This inverse modulation eliminates the need to generate a second harmonic correction signal and add it to the difference signal, as is done in the conventional transmitter of FIG. This inverse modulation takes place in the modulator 56. In the embodiment of FIG. 3, after the inverse modulation of the stereo signal, the difference signal and the sum signal are respectively used to phase-modulate and amplitude-modulate the carrier in a conventional manner.

The combination of elements 56, 18, 20, 21 represented by dashed line 23 represents one particular embodiment of a means for generating a phase modulated carrier signal, wherein the phase modulated carrier signal is selected. The stereo difference signal modulated by the stereo sum signal in accordance with the modulation function. Those skilled in the art will appreciate that other embodiments are possible.

와

의 변조지수를 가진다. 제1도에 도시한 종래의 송신기에 있어, 반송파 시간변화를 표시하지 않은(즉, 벡터표기법을 사용하는) 위상변조기 20의 출력(S₁)은 다음과 같이 표현될 수 있다.Approximate analysis shows that the transmitter arrangement in FIGS. 2 and 3 provides virtually the same type of second harmonic correction, while the arrangement in FIG. 3 results in less complex circuitry and less intermodulation distortion. The next approximation analysis assumes that the signal is supplied to the transmitter via a single stereo channel, e.g., the L channel, and also has a constant amplitude and phase velocity ω _a . For the purpose of normalizing the modulation indices, assume a signal with sufficient amplitude for full modulation when L and R exhibit the same amplitude. If only L or only R is present, the modulation is half of the maximum total modulation that is poor in the stereo system. Thus, for L or R, the resulting signal is for amplitude and phase modulation, respectively.

Wow

It has a modulation index of. In the conventional transmitter shown in FIG. ₁ , the output S ₁ of the phase modulator 20 which does not display the carrier time change (i.e., uses the vector notation) may be expressed as follows.

(1)

(One)

If ψ is small in the above formula,

(2)

(2)

This signal is amplitude modulated by the modulator 22 to be the next output signal S ₂ .

를 사용하고, X>2이므로 m^X의 항을 무시하면(근사분석)

, And ignore the terms of m ^X since X> 2 (approximate analysis)

Equation (5) is an approximate output from transmitter 22 that illustrates a signal component having a real amplitude. All components that contain modulation terms larger than the second harmonic are ignored because they have lower amplitudes. Considering the components of the equation (5), it can be seen that the carrier signal term, fundamental wave term and second harmonic sideband terms are included. The single sideband calculation for the base term is done by m _a = m _p = m, so that the amplitudes of the base AM and PM terms are the same. Thus, the output signal will have a component of the carrier frequency and a component of the fundamental sideband frequency. By making m _a and m _p equal, the AM and PM terms of the second harmonic do not coincide, and the double second harmonic sideband is maintained. In fact, the second harmonic PM term is twice the magnitude needed to produce the single sideband of the second harmonic. This term derives from the multiplication of a system in which a phase modulated carrier is amplitude modulated (PM x AM system). In the conventional transmitter of FIG. 2, the PM term and the AM term of the second harmonic are equalized by adding the sub-correction signal to the stereo difference signal, thereby achieving a single sideband calculation for the fundamental term and the second harmonic term.

In FIG. 3, a predetermined second harmonic correction may be implemented by generating a phase modulated carrier in the stereo transmitter, wherein the phase modulated carrier is inversely modulated by the stereo sum signal according to the selected modulation function. Indicates a signal. In the embodiment of FIG. 3, the quadrature component term of the composite output signal which is mainly the cause of phase modulation can be expressed as follows.

(6)

(6)

Here the modulation function is chosen as follows.

(7)

(7)

=1-y+y²……라는 일반적인 관계를 사용하면,here

= 1-y + y ² ... … Using a general relationship called

을 선택하면, 위상변조항은 다음과 같이 표현될 수 있다.Select amplitude modulation constant and m wave equivalent phase modulation constant, and

If is selected, the phase modulation term can be expressed as follows.

(10)

10

임을 유의해야 한다. 결과적으로, 근사분석은 제3도의 송신기에서 구체화된 역변조 기술을 사용하여, 이러한 역변조가 AM의 증배효과를 부분적으로나마 보상하므로써 합성신호의 PM항을 수정하여 제2고조파 PM 및 AM항을 일치시키고 단일 입력 스테레오 신호 L에 대하여 실제의 단측파대 신호를 제공해준다는 것을 가르쳐 준다. 따라서, 합성 ISB신호는 L 및 R의 두 입력에 대하여 얻어진다.The amplitude of the second harmonic PM term equal to the amplitude of the second harmonic AM term in equation (5) is

It should be noted that As a result, the approximation analysis uses an inverse modulation technique embodied in the transmitter of FIG. And a single sideband signal for a single input stereo signal L. Thus, a composite ISB signal is obtained for two inputs, L and R.

에 해당한 변조계수(m_t)를 갖는

의 변조함수를 사용할때, 제3도의 블록선도에 따라서, 역변조에 의해 생성된 수정된 위상변조신호와 실질적으로 동일하다. 이 변조함수(X)는 합신호를 나타낸다. 이러한 등가는

일 때 제1측파대 성분의 진폭의 1/8인 진폭을 가지는 제2고조파 성분에 의해 위상변조항이 수정되었다는 사실을 고려하므로써 알 수 있다. 이 진폭은 미합중국 특허 제3908090호에 기술된 바와 같은 제2도의 종래 전송기에 사용된 교정 신호의 최대진폭의 13%에 상응한다.According to the block diagram of FIG. 2, the modified phase modulated signal from the limiter 21 generated by adding the correction signal to the stereo difference signal is

Has a modulation coefficient (m _t ) corresponding to

When using the modulation function of < RTI ID = 0.0 >,< / RTI > according to the block diagram of FIG. This modulation function X represents the sum signal. This equivalent

It can be seen by considering the fact that the phase modulation term is modified by the second harmonic component having an amplitude equal to 1/8 of the amplitude of the first sideband component. This amplitude corresponds to 13% of the maximum amplitude of the calibration signal used in the prior art transmitter of FIG. 2 as described in US Pat.

According to the receiver feature of the present invention, FIG. 6 shows that the inverse modulation of the stereo difference signal component is performed by the independent sideband AM stereo transmitter of the type shown in FIG. 2 or 3 according to the selection nonlinear modulation function. This inverse modulation, showing one embodiment of a simplified independent sideband AM stereo receiver used to substantially cancel the generated second harmonic correction component from the difference signal component, results in LR distortion resulting from the insertion of this second harmonic correction component. Eliminate

With the exception of the inverse modulator 63, the rest of the independent sideband AM stereo receiver shown in FIG. 6 is shown in FIG. 1 of U. S. Patent No. 4018994 and described therein. , 30, 34, 68, 60, 64, and 66). For example, elements 60, 61, 62, 64, 66, 65, 67, 68, 69 and 70 of FIG. 6 in FIG. 6 are elements 10, 14 of FIG. , 18, 20, 30, 34, 68, 60, 64 and 66, and need not be described in detail here.

이다.In the receiver of FIG. 6 according to the present invention, a single inverse modulator 63 having a nonlinear selective modulation function replaces the elements 40, 52, 54, 44 and 28 shown in FIG. Please note that the embodiment of FIG. 6 is less complicated than the receivers shown in FIGS. 1, 2 and 3 of the patent. The general form of the desired nonlinear modulation is

to be.

FIG. 7 illustrates another embodiment of the portion of the independent sideband stemeo receiver of FIG. In this embodiment, inverse modulation occurs after the stereo difference signal components are detected in the demodulator 65, respectively. However, the result of the circuit is the same. That is, the L-R distortion resulting from the second harmonic fixed components generated by the transmitters of FIGS. 2 and 3 is virtually eliminated by the inverse modulation of the detected difference signal component occurring in the inverse modulator 63.

According to the system feature of the present invention, when the independent sideband AM stereo signal generated by the transmitter of FIG. 3 is received by the independent sideband AM stereo receiver of the type shown in FIG. The inverse modulator 63 takes place in order to correct the distortions that were intentionally present in the LR phase modulation of the transmitter to induce a single sideband signal as described above. This inverse modulation in the receiver can be done on the synthesized intermediate frequency signal as shown in FIG. 6 or the stereo difference signal can be directly transformed after being demodulated as shown in FIG.

According to a feature of the overall system of the present invention, the difference order inverse modulation function of the transmitter and the difference signal inverse modulation function of the receiver may be selected such that the entire system has a single progression characteristic for the stereo difference signal and thus L and R stereo signals. , It has a linear and independent predetermined amount for the transmission of the L and R signals through the system, from the L and R inputs to the transmitter of FIG. 3 to the L and R outputs from the receiver of FIG. 6 or 7. The two inverse modulation functions can be chosen such that the entire system has a low distortion that implies low intermodulation distortion. The prior art transmitter of FIG. 2 provides an L-R correction signal that operates effectively in response to L and R individually so that the transmitter produces some intermodulation distortion, especially when a strong signal is present at both L and R of different frequencies.

의 변조함수형태로 제공되어야만 한다. 예를 들면, 제3도의 송신기와 제6도의 수신기에서의 역변조가 둘다

을 갖도록 선택된다면, 전체 시스템 L-R 신호 전달 특성은 거의 직선적이 될것이며 따라서 사실상 상호 변조 왜곡을 내포한 왜곡이 없어질 것이다. 정확한 직선성의 동작 따라서 왜곡이 없는 동작은

의 변조함수를 가진 송신기에서 역변조를 사용하고 또

의 변조함수를 가진 수신기에서 역변조를 사용하므로써, 얻어질 수 있다. 그런데 상기한 양 변조함수에서

이다. 이러한 송신기 변조함수를 갖는 경우에, X가 (-1)에 접근함에 따라 (1+X)는 영에 가까워지며, 따라서 이득은 무한대로 될 것이다. 그러므로 이러한 비선형 함수에서의 최대 이득(10배보다 작은)에 어떤 실제적인 제한이 가해질 필요가 있다. 상술된 한쌍의 변조함수들은 전송기와 수신기 사이에서 받전될 수 있다. 그러나, (1-X)가 영에 가까워지는 경우, 하향 AM상에 과도한 잡음이 나타나는 수신기의 L-R 채널에서과잉이득의 문제가 생기게 될 것이다.It is a multiplication for PMxAM processing in the overall system transmitter causing distortion in the stereo differential channel. As a result, the LR signal is not fixed and is multiplied by (1 + X), where X is a sum signal. Therefore, for ideal operation, the product of the two inverse modulation functions at the transmitter and the receiver, respectively, cancel out the multiplication effect on the LR channel respectively.

It must be provided in the form of a modulation function of. For example, both inverse modulation in the transmitter of FIG. 3 and the receiver of FIG.

If selected, the overall system LR signaling characteristic will be nearly linear, thus virtually eliminating distortions involving intermodulation distortion. Accurate linearity behavior Therefore, motion without distortion

Inverse modulation is used in a transmitter with a modulation function of

It can be obtained by using inverse modulation in the receiver having a modulation function of. However, in the above-mentioned modulation function

to be. With this transmitter modulation function, as X approaches (-1), (1 + X) will be close to zero, so the gain will be infinite. Therefore, some practical limitations need to be imposed on the maximum gain (less than 10 times) of this nonlinear function. The pair of modulation functions described above may be supported between the transmitter and the receiver. However, if (1-X) approaches zero, there will be a problem of overgain in the LR channel of the receiver where excessive noise appears on the downstream AM.

에 근사할 경우에 전체 시스템에 나타날 것이다. 많은 가능한 조합이 이러한 이상치에 접근하며 본 발명의 취지내에 있는 것으로 생각된다.Good linearity, low distortion, and low cross distortion are ideal functions of the transmitter and receiver modulation functions used for inverse modulation.

If it is approximated to it will appear in the whole system. Many possible combinations approach this outlier and are considered to be within the spirit of the present invention.

Various changes and modifications can be made within the scope of the inventive concept.

Although the specification describes the transmission of stereo sound signals, the application of the inventive concept is not limited to the transmission of a stereo sound signal in which the carrier is phase modulated and amplitude modulated, but in this manner on the carrier a different pair of signals having different information content. It may be used to modulate. For example, input channels can be connected to audio sources carrying information in other languages. Crosstalk and separation problems that may occur in the case of stereo sound signals will not distract or noticeably appear in the listener. However, the concept of the present invention can be used, for example, to transmit signals with full differential information content, and the use of "left" and "right" in the specification and claims is exemplary and not limited.

Claims (1)

A receiver decoder having means (61) for supplying an received intermediate frequency (IF) ISBAM polyacoustic signal for use in an independent sideband (ISB) amplitude modulated (AM) multiple acoustic system, comprising: Means (63) for modifying the difference signal component of the IF signal according to the selected function of the sum signal component; Means (63-64-70) for inducing a pair of audio frequency output signals representing one of the original L and R input signals, respectively, wherein a transform function is provided for the transmission of said L and R signals through said system. A receiver for an independent sideband amplitude modulated multiple sound system, characterized in that it can be selected to supply a linear and independent predetermined quantity, in particular configured to provide a system having a low distortion with low intermodulation distortion.

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