KR830000789B1 - 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 AM multi-acoustic transmitter in accordance with the present invention.

4 is a pager diagram useful in explaining the amplitude and phase modulated signals of 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.

FIG. 7 is a block diagram showing another configuration for the receiver portion of FIG.

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

의 오디오 위상차를 갖게한다. 발진기(18)로 부터의 반송파 신호는 위상변조기(20)에서 위상 변이된 스테레오 차신호 정보와 함께 위상변이 되고 제한기(21)에서 진폭이 제한된 후, 진폭 변조기(22)에서 위상 변이된 스테레오 합신호 정보와 더불어 진폭 변조된다. 진폭변조기(122)로부터의 출력신호는 독립측파대 AM 신호로서, 이 AM 신호의 하측파대 및 상측파대에는 L스테레오 신호 정보 및 R 스테레오 신호 정보가 각각 분리되어 나타낸다.U. S. Patent No. 3218393 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 LR and L + R signals. do. The phase shift network 14, 16 has the sum signal L + R and the difference signal LR substantially equal to 90.

Let's have the audio phase difference. The carrier signal from the oscillator 18 is phase shifted together 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 summation in the amplitude modulator 22. Amplitude modulated with signal information. The output signal from the amplitude modulator 122 is an independent sideband AM signal, and L stereo signal information and R stereo signal information are separately shown in the lower band and the upper band of the AM signal.

The carrier may be 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 refers to both a transmission frequency signal and a low frequency signal.

의 위상차를 가진 서로 수직한 스테레오 합신호 및 차신호의 벡터에 대해 진폭 및 위상변조를 사용하면 반송파벡터(26)쪽의 시계방향으로 진행하는 합성변조 페이져(phasor) (24)가 얻어지는데, 이것은 단일 측파대신호를 나타낸다.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. Convenient, as shown in FIG.

Using amplitude and phase modulation on a vector of stereo sum signals and difference signals that are perpendicular to each other with a phase difference of, obtains a synthesized modulated phasor 24 running clockwise toward the carrier vector 26. Represents a single sideband signal.

Fig. 4 shows a rational situation in which only the fundamental upper band and the carrier exist, and this signal format is a stereo sum signal (L + R) in which the envelope detection characteristic of the standard receiver is a distorted sinusoidal wave shown as 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 either channel 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.

U.S. Patent No. 3908090, which describes a transmitter for an independent sideband AM stereo system, describes a phase modulation component of a second harmonic present in an independent sideband AM stereo signal generated by a system of fixed second harmonic of a stereo difference signal (LR). An improved transmitter is provided, which is provided to reduce the to a desired value, which is shown in FIG. This improved conventional transmitter comprises components similar to those in the system shown in FIG. 1 and denoted by the same numerals, in addition to adding second harmonic fixation to the stereo difference signal LR prior to phase modulation of the carrier. The circuit includes a phase shift network (32, 34) for imparting a phase between the phase shifted stereo difference signal and the phase shifted stereo sum signal to the L and R stereo signals. 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 a fixed 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 fixed 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 fixed 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.

The phase modulated carrier is then amplitude modulated in modulator 22 by a stereo sum signal L + R phase shifted prior to transmission. However, the second harmonic fixation of such a 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 are LR phase modulation components. Indicates distortion. However, since the monoacoustic receiver essentially ignores the phase modulation of the received independent sideband AM stereo signal, the compatibility of the signal is not affected. Moreover, this L-R distortion is canceled in an independent sideband stereo receiver, resulting in an L-R signal with no real distortion.

However, while this conventional transmitter provides the desired second harmonic fixation for the independent sideband AM stereo signal being transmitted, it is clearly seen from FIG. 2 that the generation of the calibration signal is quite complicated for the harmful transmitter. .

Amplitude modulation in U.S. Patent No. 4018994, which describes a conventional independent sideband AM stereo receiver, is a stereo difference received from a second harmonic fixed component generated by an independent sideband AM stereo transmitter described in U.S. Patent No. 3980902. It is used to remove from the signal component (LR), which is shown in FIG. In general, US Pat. No. 4,018,994 describes the amplitude of one or more signals derived from a stereo sum signal component for the purpose of reducing LR distortion resulting from the second harmonic correction component generated by the transmitter. It is described as being modulated.

It is an object of the present invention to provide a novel coexistence of independent sideband multiplexing, e.g., stereo acoustic AM transmitters, in which preferred second harmonic correction of stereo difference signals can be done by simple and economical circuit arrangement.

According to the present invention, an improved independent sideband multiple acoustic system transmitter has finite means for supplying a pair of audio frequency signals L and R for displaying left and right multiple acoustic information, and predetermined from them in response to the L and R signals. Means for generating a sum signal and a difference signal having L and R signal components of the selected amplitude and phase synthesized by the method, and means for generating a phase modulated carrier signal. In this case, the phase modulated carrier signal represents a difference signal modulated by the sum signal according to the first selection modulation function. The transmitter also includes means for amplitude modulating the phase modulated carrier signal by the sum signal so that a composite independent sideband AM multiple acoustic signal is formed.

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 frequency fixed signal is added to the stereo difference signal before the phase modulator 20 phase modulates the carrier signal. However, according to the present invention, as shown in the independent sideband transmitter of FIG. 3, the preferred second harmonic fixing is not performed by adding a fixed signal, but inversely modulating the stereo difference signal component by the sum signal component. Is achieved by This inverse modulation is done in accordance with the optional modulation function described later.

The transmitter of FIG. 3 responds to the L and R stereo signals, which may arise from any stereo signal source, for example, separate microphones 50 and 52, respectively, the stereo difference signal LR and each stereo sum signal L. Synthesizers 10 and 12 generating + R. The stereo difference signal is controlled at an audio frequency of 5 kHz or less by the selective action of the low pass filter 54. As shown in US Pat. No. 3,080,90, it will be appreciated by those skilled in the art that such filtering is performed in the difference signal channel, and that 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 such that a phase difference of 90 ° is generated between them.

According to the third embodiment of the present invention, the stereo difference signal is modulated by the stereo sum signal according to the selected modulation function. This inverse modulation eliminates the need to generate and add a second harmonic correction signal to the difference signal, as is done in the conventional transmitter of FIG. This inverse modulation takes place in the modulator 56. After inverse modulation of the stereo signal in the embodiment of FIG. 3, the difference signal and the sum signal are used to phase modulate and amplitude modulate the conventional carrier, respectively.

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 is modulated by the stereo sum signal according to the modulation function. Those skilled in the art will appreciate that other implementations are possible.

와

의 변조지수를 가진다. 제1도에 도시한 종래의 송신기에 있어 반송파 시간변화를 표시하지 않은(즉, 벡터표 기법을 사용하는) 위상변조기 20의 출력(S₁)은 다음과 같이 표현될 수 있다.Approximate analysis shows that the transmitter arrangements of FIGS. 2 and 3 provide substantially the same harmonic correction, while the arrangement of FIG. 3 results in less complex circuitry and less intermodulation distortion. The following 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 indicate a carrier time change (i.e., uses a vector table technique) may be expressed as follows.

S ₁ = cosψ-j sinψ

sin ω_at) ……(1)(ψ = phase modulation)

sin ω _a t)…. … (One)

If ψ is small in the above formula,

ψ이므로,sin ψ

ψ,

sin²ω_at)-j

sin ω_at ……(2)S ₁ = (1-

sin ² ω _a t) -j

sin ω _a t. … (2)

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

cos ω_at][(1-

sin ω_at)-

-sin ω_at] ……(3)S ₂ = [1+

cos ω _a t] [(1-

sin ω _a t)-

-sin ω _a t]. … (3)

-

cos 2ω_at를 사용하면,sin ² ω _a t =

-

If you use cos 2ω _a t,

cos ω_at][(1-

)+

cos 2ω_at-j

sinω_at] ……(4)S ₂ = [1+

cos ω _a t] [(1-

) +

cos 2ω _a tj

sinω _a t]... … (4)

sin 2ω_at를 사용하고,cos ω _a t sin ω _a t =

using sin 2ω _a t,

Since X> 2, ignoring the terms of m ^X (approximate analysis)

Equation (5) is an approximate output from transmitter 22 that illustrates a signal component having a real width. 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 operation 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 variability of the system in which the phase-modulated carrier is amplitudeed (PM x AM system). By adding the sub-correction signal to the stereo difference signal in the conventional transmitter of FIG. 2, the PM term and AM term of the second harmonic are equal, and a single sideband calculation for the fundamental term and the second harmonic term is achieved.

According to the present invention, a predetermined second harmonic correction may be performed 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 synthesized output signal mainly causing the phase modulation can be expressed as follows.

Here the modulation function is chosen as follows.

=1-y+y²……here,

= 1-y + y ² ... …

Using a general relationship called

sin ω_at[1+

cos ω_at][1-m_t

cos ω_at……] ……(8)Q = -j

sin ω _a t [1+

cos ω _a t] [1-m _t

cos ω _a t. … ]… … (8)

sin ω_at-j

sin ω_at(

-

)cos ω_at+…… ……(9)= -j

sin ω _a tj

sin ω _a t (

-

) cos ω _a t +... … … … (9)

을 선택하면 위상변조항은 다음과 같이 표현될 수 있다.Select the phase modulation constant equal to the amplitude modulation constant and m, and the modulation coefficient m _t =

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

sin ω_at -j

sin 2ω_at ……(10)Q = -j

sin ω _a t -j

sin 2ω _a t. … 10

임을 유의해야 한다. 결과적으로 근사분석은 제3도의 송신기에서 구체화된 역변조 기술을 사용하여, 이러한 역변조가 AM의 증배효과를 부분적으로 나마 보상하므로써 합성신호의 PM항을 수정하여 제2조파 PM 및 AM항을 일치시키고 단일 입력스테레오 신호 L에 대하여 실제의 단측파대 신호를 제공해준다는 것을 가르쳐준다. 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 the inverse modulation technique embodied in the transmitter of FIG. 3 to correct the PM terms of the synthesized signal by matching the second harmonics PM and AM terms by partially compensating the multiplication effect of AM. And a single input stereo signal L for the actual single sideband signal. 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 m_a=m_p=m=1일때 제1측파대 성분의 진폭의 1/8인 진폭을 가지는 제2조파 성분에 의해 위상변조항이 수정되었다는 사실을 고려하므로써 알 수 있다. 이 진폭은 미합중국 특허 제3908090호에 기술된 바와같은 제2도의 종래 전송기에 사용된 고정신호의 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 can be seen by considering the fact that the phase modulation term is modified by a second harmonic component having an amplitude equal to 1/8 of the amplitude of the first sideband component when m _a = m _p = m = 1. This amplitude corresponds to 13% of the maximum amplitude of the fixed signal used in the conventional transmitter of FIG. 2 as described in US Pat.

FIG. 6 shows the second harmonic correction component generated by the independent axial band AM stereo transmitter of the type shown in FIG. 2 or 3 of the inverse modulation of the stereo difference signal component by the stereo sum signal component according to the selected nonlinear modulation function. One embodiment of a simplified independent sideband AM stereo receiver used to substantially cancel out the difference signal components is shown. This inverse modulation eliminates the L-R distortion resulting from the insertion of this second harmonic correction component.

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

이다.In the receiver of FIG. 6, a single inverse modulator 63 having a non-linear selection modulation function replaces the elements 40, 52, 54, 44 and 28 shown in FIG. 1 of U. S. Patent No. 4018994. Note that the embodiment of FIG. 6 is less complex than the receiver shown in FIGS. 1, 2 and 3. The general form of the desired nonlinear modulation is

to be.

FIG. 7 illustrates another embodiment of the portion of the independent sideband AM stereo receiver of FIG. In this embodiment, inverse modulation occurs after the stereo difference signal component is detected in the quadrature drum controller 65. However, the result of the circuit is the same. That is, the L-R distortion resulting from the second harmonic correction 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 a system feature of the present invention, when an independent sideband AM stereo signal generated by the transmitter of FIG. 3 is received by an independent sideband AM stereo receiver of the type shown in FIG. 7, the second inverse modulation is actually single sided. The inverse modulator 63 takes place to correct for the distortions that were intentionally present in the transmitter's LR phase modulation to abandon the wave 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.

의 변조함수 형태로 제공되어야만 한다. 예를들면, 제3도의 송신기와 제6도의 수신기에서의 역변조가 둘다

(단, m_t=

)을 갖도록 선택된다면, 전체 시스템 L-R 신호 전달 특성은 거의 직선적이 될 것이며 따라서 사실상 상호 변조 왜곡을 내포한 왜곡이 없어질 것이다. 정확한직선성에 따라서 왜곡이 없는 동작은

의 변조함수를 가진 송신기에서 역변조를 사용하고 또

의 변조함수를 가진 수신기에서 역변조를 사용하므로써 얻어질 수 있다. 그런데 상기한 양 변조함수에서 m_r=m_t이다. 이러한 송신기 변조할수를 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 발전될 수 있다. 그러나, (1+X)가 영에 가까워지는 경우, 하향 AM상에 과도한 잡음이 나타나는 수신기의 L-R채널에서 과잉이득의 문제가 생기게 될 것이다.According to a feature of the overall system of the present invention, the differential signal inverse modulation function of the transmission and the differential signal inverse modulation function of the receiver may be selected such that the entire system has a single propagation characteristic for the stereo differential signal and thus the L and R stereo signals. It is a straight line for the transmission of the L and R signals through the system, from the L and R inputs to the transmitter in FIG. 3 to the L and R outputs from the receivers in FIG. It has a predetermined amount which is independent and independent. The two inverse modulation function 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 LR correction signal that operates effectively in response to L and R individually so that the transmitter produces some intermodulation distortion, especially when strong signals are present at both L and R of different frequencies. It is a multiplication for PMxAM processing in the entire system transmitter, which causes distortion in the stereo differential channel. As a result, the LR signal is not fixed (1 + X), where X is multiplied by the 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.

(Where m _t =

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

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

Can be obtained by using inverse modulation in the receiver with the modulation function of. However, m _r = m _t in both modulation functions described above. With such a transmitter modulator, as X approaches (-1) (1 + X) will be near zero, and 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 can be developed 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 description has been made of 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, different pairs of signals having different information content are present. Modulating may be used. For example, input channels can be connected to audio sources carrying information in other languages. Crosstalks and separation problems that can occur in the case of stereo sound signals will not be scattered or noticeable by 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 are exemplary and not limited.

Claims (1)

Means (LR) for supplying a pair of audio frequency signals representing left (L) and right (R) multi-acoustic information, for example, for use in an independent sideband (ISB) amplitude modulation (AM) multiple acoustic system; Means (10, 54, 12, 14, 16) for inducing a sum and difference signal having a selected amplitude and phase synthesized in a predetermined manner in response to the L and R signals having the L and R signal components therefrom; A transmitter having means 18 for generating a received carrier signal, means 20 for phase modulating a carrier signal, and means for amplitude modulating a phase modulated carrier signal, wherein the transmitter displays and displays the difference signal; Means 56 for inducing a phase modulated signal inversely modulated by the sum signal in accordance with the selected function of 1, wherein the induced signal is applied to a phase modulating means for phase modulating the carrier with the signal; Means for forming a composite independent sideband (ISB) AM multiplexed acoustic signal by applying a sum signal to the amplitude modulating means (22) to amplitude modulate the phase modulated carrier signal. Independent sideband amplitude modulation, characterized in that it can be selected to supply a linear and independent predetermined amount for the transmission of the L and R signals through the antenna, in particular providing a system having a low distortion with low intermodulation distortion Transmitter for multiple acoustic systems.

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