KR860000232B1 - Compatible am stereo broadcast system - Google Patents

Abstract

This compatible AM stereo broadcasting system is one in which the signal carrier has an amplitude directly variable with monoral or sum (L+R) information and has an instantaneous phase which varies as a function of the resultant amplitude of the sum information (L+R) and difference information (L-R). These are established in preselected phase relationship(quadrature). In a stereo receiver, L and R or the sum and difference signals may be restored by dividing the signal by the cosine of the angle φ, and in a monoral receiver, the sum signal is onlu detected.

Description

Compatible AM stereo broadcasting system

1 is a block diagram of a conventional broadcast system for transmitting and receiving two signals that are amplitude modulated at quadrature with a single carrier signal.

FIG. 2 is a phasor diagram showing the carrier and sidebands of the transmission signal of the system shown in FIG.

3 is a block diagram of an AM stereo system constructed in accordance with the present invention.

4 is a pager diagram showing a transmission signal of the system shown in FIG.

5 is a block diagram of a transmitter that meets the operational requirements of the present invention.

6 is a block diagram of a preferred receiver that meets the operational requirements of the present invention.

FIG. 7 is a circuit diagram of a portion of the receiver shown in FIG.

8 is a block diagram showing another embodiment of a receiver suitable for the system of the present invention.

9 is a block diagram showing another embodiment of a receiver.

10 is a block diagram of an SSB system with left-right inputs.

FIG. 11 is a block diagram of a receiver suitable for the system shown in FIG.

12 is a spectrum configuration diagram of a transmission signal of the system shown in FIG.

13 is a block diagram of another SSB system.

14 is a spectrum configuration diagram of a transmission signal of the system shown in FIG.

The present invention relates to an AM stereo broadcasting system for transmitting two kinds of signals on a single carrier, and in particular, a system for transmitting and receiving AM stereo signals that are sufficiently compatible in the AM broadcasting bands of mono and stereo receivers without introducing substantial distortion. It is about improvement of.

Several systems for transmitting and receiving stereo signals are known in the art. The simplest system is probably unchanged, carrying two kinds of signals A and B, eg left (L) and right (R) signals, on two carriers of equal frequency but 90 ° out of phase. (unmodified) A system that uses right angle signals. This system is similar to the system used for carrying two color signals on one carrier in the NTSC standard for color television broadcasting in the United States. However, when a signal current rectifier is used to induce an audible frequency signal to the existing mono receiver, there is a double frequency distortion proportional to the amount of stereo difference (L-R) signal. This distortion is due to the fact that this signal consists essentially of the following equation.

cos(ωt+ψ)

cos (ωt + ψ)

In this equation, the term in the radical is amplitude, and ψ is tan ^-1 (LR) / (1 + L + R). However, in a mono receiver, the amplitude of the received signal should be substantially equal to the carrier plus the audible frequency signal (1 + L + R). Therefore, the term (LR) represents distortion, which is a square term, resulting in double frequency distortion. The pi term represents phase modulation. The pi term indicates no output from an envelope detector commonly used in monophonic receivers when there is little amplitude or phase distortion in the transmission signal of a broadcast system. Do not create.

In another conventional system, a technique of transmitting a single carrier is used, which is amplitude modulated with information L + R and frequency modulated with information L-R. If any frequency or phase distortion occurs in the received signal, the complex spectrum of the transmitted signal may cause unnecessary distortion in mono and stereo receivers. When the signal LR contains low frequency components, the emitted spectrum may contain multiple sideband frequencies with distorted phase and amplitude, which leads to spurious conversion of the FM components to amplitude modulation components. do.

로 변환시키고 직각 성분의 크기를 변화하지 않게 유지시킴으로써 이루어진다. 따라서 위상 혹은 스테레오 정보 신호가 왜곡되었고 유효 측파대(significant sideband)의 수가 증가하게 됨에 따라, 단청 및 스테레오 수신기의 잠재적인 왜곡이 증가되었었다.Another system transmits a synthesis and difference signal with a phase angle of 90 °, but corrects the amplitude of the envelope and distorts the component (L + R) to make it compatible. This is done by adding the frostbite component from the component (1 + L + R)

By conversion to and keeping the size of the rectangular component unchanged. As the phase or stereo information signal was distorted and the number of significant sidebands increased, the potential distortion of mono and stereo receivers increased.

Accordingly, an object of the present invention is to provide an AM stereo broadcast system that can be received by existing AM monolithic receivers, minimizes circuit changes of existing transmitters, and minimizes the complexity of receiver circuits designed for stereo decoding. To provide.

The above-mentioned object is achieved by the system of the present invention (the transmitted signal includes mono information and phase or stereo information necessary for separating the stereo signal, but the mono signal does not include information LR or difference signal). You can. Therefore, there is no difference in the signal from the normal AM mono signal transmission to the mono receiver circuit. There are not many circuit changes necessary in the transmitter of the present invention, and the AM stereo receiver circuit is not complicated. In essence, the concept of the present invention is to multiply the quadrature signals by a factor related to the stereo information phase at the transmitter, and split the signal received at the stereo receiver by the same coefficients to recover the original original quadrature signal.

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

The conventional AM right angle broadcasting system (see FIG. 1) and the compatible system configured by the present invention (see FIG. 3) describe stereo signals with left (L) and right (R) program channels for the sake of brevity. However, it should be noted that this limitation does not mean that there is an inherent vulnerability, and that the system can be applied to send and receive any two signals on a single carrier.

The system of the present invention shown in the form of a block in FIG. 3 can be easily understood by referring to the block diagram of FIG. 1. The system of FIG. 1 is an incompatible quadrature system without performing circuit changes. . In the right-angle transmitter partitioned by the number 10 in FIG. 1, the signal 1 + L + R is introduced from the input terminal 11 to the modulator 12. The first program signal path and the input terminal 13 A second program path for introducing the signal LR to the modulator 14 is configured. The carrier signal of the RF exciter 15 is applied to the modulator 12, and this carrier signal is also applied to the modulator 14 via a 90 ° phase shifter 16. The outputs to these two modulators 12 and 14 are combined with the signal adder 17 and then transmitted in any manner. The transmission signal is described mathematically as follows.

cos(ωt+ψ)

cos (ωt + ψ)

In this equation, ψ is tan ⁻¹ (LR) / (1 + L + R). When this signal is received by the stereo receiver indicated by number 18 in FIG. 1 and then demodulated by the red detector or divider 20, 21, the signals (1 + L + R), (L You get + R). However, in the envelope detector 22 of the mono receiver indicated by the dashed line 23, the demodulated output is expressed by the following equation.

From the above equation, it can be seen that only when L = R, i.e., a mono signal, it is compatible.

FIG. 2 shows a trace 24 of a modulated transmission signal for a broadcast system in which a phase diaram of FIG. 2 is shown in FIG. The phaser 25 represents an unmodulated carrier, i.e., 1 cos ωt, the phaser 26 represents an in-phase modulation signal L + R, and the phaser 27 represents a linear value signal LR. Denotes the ordered phase angle of the composite phaser 28, which cannot exceed ± 45 °, as trajectory 24 shows.

을 체배시킨것과 등가적이다. 이 송신 신호는 완전히 양립적인데, 즉 이 신호가 단청 수신기(23')에 수신되어 포막선 검파기(22')로 복조될때, 그 출력은 (L+R)에 비례한다. 송신 신호가 파선(33)으로 표시한 스테레에수신기에 수신될 때 제한기(34)에서 제한된다. 제한기(34)에서 출력된 스테레오 정보는 체배기(35)에서 VCO(voltage controlled oscillator)(36)로부터 인가된 cosωt의 위상과 비교되는데, 이 위상은 후술하는 바와같이 송신기(30)의 RF여진기(15')의 위상으로 고정되어 있다. 이때 위상차는 cosψ이고, 채배기(35)의 출력은 cosψ에 비례한다.The compatible AM stereo broadcast system of the present invention is shown in block diagram in FIG. 3, which has two input terminals 11, 13 ', and signals (1 + L + R) and (LR). Through these input terminals 11 'and 13', it is applied to the two modulators 12 'and 14' of the transmitter shown by the dashed line 30, respectively. The operating functions of the RF exciter 15 'and the ideal phase 16' are the same as those in FIG. The outputs of the modulators 12 ', 14' are synthesized at the adder 17 ', where the amplitude variation is removed by the limiter 31, leaving only phase information. Therefore, the phase modulated carrier output from the limiter 31 is amplitude modulated in the high level modulator, that is, the multiplier 32 by the signal component 1 + L + R. Transmitted signal (1 + L + R) cos ψ, which is cos ψ (1 + L + R) / to the original stereo signal output from adder 17 '.

It is equivalent to multiplying. This transmission signal is completely compatible, i.e., when this signal is received at the mono receiver 23 'and demodulated to the envelope detector 22', its output is proportional to (L + R). When the transmission signal is received at the stereo receiver indicated by the broken line 33, it is restricted at the limiter 34. The stereo information output from the limiter 34 is compared with the phase of cosωt applied from the voltage controlled oscillator (VCO) 36 in the multiplier 35, which phase is the RF exciter of the transmitter 30 as described below. It is fixed at the phase of 15 '. At this time, the phase difference is cosψ, and the output of the distributor 35 is proportional to cosψ.

The signal received at the receiver 33 is divided by the output of the multiplier 35 in the correction circuit 37 (described in detail later), which is shown in detail in FIG. 7, so that the original stereo output of the adder 17 ' Recover. The cosωt signal applied from the VCO 36 is phase shifted by +/- 45 DEG from the phase shifters 38 and 39, and then introduced into the output of the correction circuit 37 and the multipliers 40 and 41. Therefore, the outputs of the dividers 40 and 41 are signals obtained by applying the DC term to L and R.

4 is a phaser diagram of the transmission signal of the system shown in FIG. 3, and has a modified trajectory 45. As shown in FIG. Points in trajectory 45 correspond to points, or values, in trajectory 24 multiplied by cosψ, respectively. Multiplying by cos ψ produces a minimum number of higher order sidebands where distortion is compatible with at least compatible mono signal transmission.

In Figure 5 the transmitter is shown in some detail. In a mono transmitter, the carrier frequency output from the crystal oscillator 15 is usually coupled to the modulator 32.

In the transmitter of the present invention, the modifying circuit 49 necessary for converting the oscillation frequency of the crystal oscillator is indicated in the dashed line 44. The carrier frequency output from the oscillator 15 'is divided and the phase shifter The carrier frequency 90 ° through (16 ') is phase shifted, and then two perpendicular carriers are applied to the modulators 12' and 14 ', which are applied to the modulators 12' and 14 '. The output is coupled at the adder 17 'and also a portion of the carrier that is not phase shifted is applied to the adder 17' via a carrier level adjustment circuit 50 to set the level of the unmodulated carrier. The output of the adder 17 'is limited by the limiter 31, so the amplitude modulation component is removed, leaving only the carrier with phase or stereo information, which is coupled to the high level modulator 32. L (52) has a program level limiter (54), A monitor instrument 56 is configured, and a program level limit gib 55 and a monitor instrument 56 are configured at the input terminal R 52. The signals L and R are added by the adder 58 to the signal L +. R), and then coupled to modulator 12 '. Signal R is also inverted at inverter 60, synthesized to signal LR at adder 61, and then applied to a multiplier or modulator 14'. The second output of the (L + R) adder 58 is applied to the high level modulator 32 via the time delay circuit 62. The time delay circuit 62 is equal to the delay time of the change circuit 49. The same delay is provided, where the output of the high level modulator 32 is an amplitude modulated signal (L + R) and a phase modulated signal for stereo information.

FIG. 6 shows the stereo receiver 33 of FIG. 3 in more detail. The signal received at the antenna is passed through the RF mixer and IF amplifier 65, which is the same as any RF mixer and IF amplifier except for the fact that the reception bandwidth is somewhat larger, even if the operation is not further explained. Those of ordinary skill in the art can readily understand this circuit. The amplitude modulation component of the output signal 66b output to the preference 66b of the RF mixer and amplifier 65 is removed at the limiter 34. The output of the limiter 34, which can be expressed as cos (ωt + ψ), is applied to one input terminal of the multiplier 35, which is an in-phase detector, and to one input terminal of the multiplier 70, which is a quadrature detector. The multiplier 71 forms an integral component of the phase locked loop 71. Low pass filter 72 allows phase drift to pass through this filter while rapid phase changes do not reach VCO 36. At this time, the output of the VCO 36 is adjusted very precisely, and the output of the VCO 36 is at right angles to the output signal of the oscillator 15 'of the transmitter. Combined. The output cosωt output from the phase shifter 73 is applied to the second input terminal of the multiplier 35, and the output 74 of the multiplier 35, which may be denoted by 10 cos phi, is applied to the correction circuit 37. In the correction circuit 37 (the embodiment of this circuit is shown in detail in FIG. 7), since the signal appearing on the line 66a is divided by the output of the multiplier 35, the quadrature signal is recovered. The rest of this circuit is practically the same as described with respect to FIG.

The circuit of FIG. 7 which is an embodiment of a part of the receiver 33 satisfactorily performs the functions of the multiplier 35 and the correction circuit 36 described above. The multiplier 35, which is a phase detector, receives an input signal from the limiter 34 connected to the terminal 80. The output of the limiter 34 switches the pair of transistors 81 and 82 that form a differential amplifier, which pairs the pair of transistors 81 and 82 in synchronization with the carrier signal coming from the limiter 34. It keeps energizing alternately. The reference input signal of the terminal 84 derived from the phase locked loop 71 is supplied to the transistor 83 which is a current source by the output of the phase shifter 73. The phase shifter 73 also acts as a low pass filter to provide the transistor 83 with an essentially sinusoidal reference signal. The DC reference voltage on line 85 is supplied by emitter follower 88, which emits a pair of transistor pairs 81 and 82 as differential amplifiers. Are combined. The current mirror 87 causes the output 74 of the paired transistor pairs 81 and 82 to be balanced at any constant current of the transistor 83, so that the output current of the line 74 is Is proportional to the cosine of the difference angle between the input signals 80,84. The integrating capacitor 86 smoothes the current impulse of the multiplier 35.

In order for the multiplier output 74 to be close to the cosine function, one of the inputs 80 to 84 should be relatively unrelated to higher order harmonics. By making the phase shift network 73 a low pass filter, the odd term harmonics coming out of the square wave of the oscillator are removed.

The correction circuit 37 is primarily composed of a differential amplifier consisting of a pair of amplifiers 100 and 101. Emitter currents of transistors 100 and 101 are supplied from current source 102. Since the two transistors 103 and 104 form a current mirror, the current of the transistor 104 is equal to the current of the transistor 100. When the currents of transistors 100 and 101 are the same, the current of transistor 104 is equal to the current of transistor 101, and the current Io becomes zero.

The signal voltage of the signal input 66a is between the bases of the transistors 100 and 101 via two resistors 108, 109, two diodes 110, 111, and a reference voltage source 112, respectively. Is applied to. Reference voltage source 112 consists of emitter follower 113, which is coupled to a voltage divider consisting of three resistors 114, 115, and 116. The base of transistor 113 is connected to the junction of resistors 114 and 115 so that a reference voltage is provided through this base. The emitter of the emitter follower 113 provides a low impedance voltage reference for the pair of transistors 100 and 101 forming the differential amplifier.

The current Ir flowing through the output terminal 74 of the multiplier 35 flows through the diodes 110, 111, resistors 108, 109, the voltage source 112 and the input signal source 66a. Forward bias is provided for 110 and 111.

As the forward impedance of diodes 110 and 111 performs a voltage division action with resistors 108 and 109, the voltage applied between the base of transistor 100 and the base of transistor 101 causes the resistor 108 to be divided. ), 109 is reduced according to the ratio of the forward resistance of the diodes 110, 111.

The correction circuit 37 will now be described in terms of the output Ir = Imax cos ψ of the multiplier 35 of the current flowing through this circuit. The output current can be expressed as I0 = IlIs / Ir, where I1 is supplied from current source 102. Is is represented by es / 2r as the input signal current at terminal 66a, where 2r is equal to the combined resistance of the two resistors 108, 109, which are the resistors with the highest resistance. es can be expressed as ec (1 + L + R) cos (ωt + ψ), where ec is the amplitude of the unmodulated carrier. Imax is the peak signal current of the transistor 83. Therefore, I2 = [lec (1 + L + R) cos (ωct + ψ) / 2r, I0 = (Ilec (1 + L + R) cos (ωct + ψ)] / 2r Imax cosψ.

이므로, I0는 바람직한 직각 신호로서 I0=(Ilec/2rImax)

cos(ωct+ψ)이다.cosψ = (1 + L + R) /

Since I0 is the preferred quadrature signal, I0 = (Ilec / 2rImax)

cos (ωct + ψ).

8 is a part of another embodiment of a receiver that meets the operational requirements of the present invention, wherein the correction circuit 37 is configured in the audible frequency portion of the receiver, and consists of two substantially identical correction circuits 37a, 37b. . In this circuit, the output 66 of the RF mixer and IF amplifier 65 may be referred to as a single output applied to the multipliers 40 and 41. The output Lcosψ of the multiplier 40 is applied to the correction circuit 37a and divided into cosψ to provide the output at L. The output Rcosψ of the multiplier 41 is applied to the correction circuit 37b and divided into cosψ to provide the R output. The output current at the point 74 of the multiplier 35 is divided and applied to the correction circuits 37a and 37b.

9 is another embodiment similar to the receiver of FIGS. 7 and 8. In this circuit, the inputs 84 and 74 of the correction circuit 37c are supplied from the phase shifter 73 and the multiplier 35, respectively. The output 95 of the correction circuit 37c is applied to the input terminals of the phase shifters 38 and 39, which is a value obtained by dividing the reference voltage output from the VCO 36 by cos ψ. Therefore, the outputs of the multipliers 40 and 41 become the outputs of L and R, respectively.

FIG. 10 is a block diagram of a left and right SSB system having a transmitter similar to that of FIG. 5, that is, a right angle broadcasting system having a cosψ change. Inputs L and R are additively coupled in adder 58 and subtractively coupled in adder 61. The output of the adder 61 is then introduced into the transmitter after phase shifting by 90 ° in the phaser 95. The decoding angle of the corresponding stereo receiver changes to derive the output (L + R) indicated by the number 96 and also to the output (L + R) as indicated by the number 97 and also to the number 97. Induce the same output (LR) / π-2 as indicated. The output L-R / π / 2 (97) is phase shifted by π / 2 in the phase shifter 98 and then enters the receiver matrix circuit 99 together with the output L + R 96. At this time, the output of the receiver matrix circuit 99 becomes L and R.

FIG. 11 shows the receiver shown in FIG. 10 in more detail. The correction circuit 32 is connected to the output terminal 66 of the RF mixer and the IF amplifier 65. The output terminal of the correction circuit 37 is shown in FIG. Is coupled to the multipliers 40 and 41, and the phase locked loop and phase shift network are the same as described with respect to FIG. As described above with reference to FIG. 10, the output of the multiplier 40 is abnormally shifted in the phase shifter 98, and the output LR of the phase shifter 98 and the output L + R of the multiplier 41 are matrix circuits. Applied to 99, output signals L and R are output.

FIG. 12 is a spectrum diagram showing that the L signal of the transmission signal of FIG. 10 is contained in one set of side bands and the R signal is contained in another set of side bands. This signal, of course, contains a higher degree of corrected sideband that will transmit the double sideband.

), (L-R

)이된다. 그후 이들 신호는 코사인 보정 회로를 지닌 송신기에서 반송파에 실려 변조된다. 코사인 보정 회로를 지닌 직각수직기에 이송신 신호가 수신될대, 보정된 신호는 신호 L,R

로 생성되고, R신호는 이상기(98)에서 90°지연된다.FIG. 13 is a block diagram of another single sideband system similar to the system of FIG. In this embodiment, one of the program input signals, for example the R signal, is phase shifted by 90 ° in the phase shifter 95. The phase shifted signal is then introduced into adder 58 or applied to adder 61 via inverter 60. A second program signal is applied directly to the L newlywed adders 58 and 61, for example. The outputs of the adders 58 and 61 are respectively (L + R).

), (LR

Becomes These signals are then carried on a carrier wave and modulated in a transmitter with a cosine correction circuit. When the transfer signal is received in a right-angle weaving machine with cosine correction circuit, the corrected signal is the signal L, R

R signal is delayed by 90 ° in the phase shifter 98.

Therefore, by multiplying the right angle signal by the coin value of the angle ψ and dividing it by the same cosine value at the receiver before transmitting the signal, the system of the present invention is a signal that can be perfectly received at a mono receiver and easily decoded at a stereo receiver Will be provided. Angle ψ is defined as the angle between the vector sum of the initial rectangular carriers and the line dividing the angle between the two rectangular carriers. The transmission signal transmitted in the system of the present invention minimizes the communication distance loss caused by the sky wave distortion in the mono receiver, and at the same time, the stereo performance is optimized. The system of the present invention can be used with an envelope detector or a mono receiver using synchronous distortion. It is preferable to use a correction circuit to obtain excellent performance with a synchronous detector, but good performance can be obtained without changing the circuit of the synchronous receiver.

Claims (1)

In a communication system in which signal information corresponding to first and second information signals is transmitted at right angles and compatible for mono and stereo operation, amplitude modulation is performed according to arithmetic synthesis of the first and second information signals, and tangent. A transmitter 30 for generating a single carrier whose ratio of the difference between the first and second information signals with respect to the envelope of the carrier whose value is amplitude modulated is phase modulated with angle; And a receiver 33 for demodulating the first and second information signals at right angles for stereo operation by receiving the carrier, which is sufficient for reception and direct mono playback without causing actual distortion. Compatible AM stereo broadcasting system with compatible features.

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