JPS6256705B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a communication system, particularly an AM stereo broadcasting system that transmits two types of signals on a single carrier wave, for example, an AM stereo signal that is completely compatible with the AM broadcast band of a monaural and stereo receiver. The present invention relates to a receiver used in a method for transmitting and receiving data without distortion.

There are various methods for transmitting and receiving AM stereo signals. The simplest method uses two carrier waves with the same frequency and orthogonal phase to generate two types of signals A and B, for example, the left L signal and the right R signal.
It is an unmodified orthogonal signaling method for transmitting signals. This system is similar to the system used to transmit two types of color signals using one type of carrier wave in the NTSC system specified by the US color television transmission. However, in current monaural receivers that extract the audio signal using a signal current rectifier, the stereo difference (LR) signal is proportional to the amount of the stereo difference (L-R) signal.
There is twice as much frequency distortion. This distortion arises from the fact that a stereo signal is basically expressed as:

√(1++) ² +(-) ² cos
(ωt+φ) Here, the term within the radical sign represents the amplitude, and it is assumed that φ=tan ^-1 (L-R)/(1+L+R). However, in a monaural receiver, the amplitude of the received signal must be approximately the sum of the carrier wave amplitude and the audio signal amplitude, that is, (1+L+R).
The (LR) term therefore represents distortion, and therefore the frequency distortion is doubled since this term is a squared term. The φ term also represents phase modulation and will not produce an output from the conventional envelope detector of a mono receiver unless there is significant amplitude or phase distortion in the signal throughout the system.

Other conventional systems employ a technique of transmitting a single carrier wave that is amplitude modulated with (L+R) information and frequency modulated with (L-R) information. In this case, given the presence of frequency or phase distortion in the received signal, the complex spectrum of the transmitted signal causes undesirable distortion in monaural and stereo receivers. If the (L-R) signal contains a low frequency component, the radiated spectrum will contain many sideband frequencies, which will distort the phase and amplitude and thus introduce an FM component to the amplitude modulation. Spurious conversion will be performed.

Still other systems transmit sum and difference signals in an orthogonal relationship, but correct the amplitude of the envelope to distort the (L+R) component that makes them compatible. For this purpose, the in-phase component is changed from (1+L+R) to √(1++) ² -(-) ² , and the magnitude of the orthogonal component is kept unchanged. This distorts the phase of the stereo information and increases the number of sidebands, resulting in a significant increase in distortion in monophonic and stereo receivers. An object of the present invention is to provide a receiver for use in an AM stereo broadcasting system that is compatible with current AM monaural receivers by only slightly modifying the current transmitter and adding only a small number of stereo decoding circuits to the receiver. There it is.

The inventive receiver is amplitude modulated by signal information proportional to the sum of the first and second information signals A and B, and φ=tan ^-1 {C ₁ (A-B)/(C ₂ +A+B)}
In a receiver for receiving a broadcast carrier signal phase modulated by a signal proportional to an angle φ (where C ₁ and C ₂ are constants), an input device for receiving and amplifying the broadcast carrier signal a mixing device for converting into an intermediate frequency carrier signal, an intermediate frequency amplifying device for amplifying the intermediate frequency carrier signal of sufficient bandwidth to carry amplitude and phase modulation information, and demodulation means for extracting a signal proportional to the amplitude and phase of the carrier wave. and a correction signal generating means for generating a correction signal proportional to the phase of the carrier wave from the received signal;
The apparatus is characterized in that it comprises a reproducing means coupled to the demodulating means and the correction signal generating means and generating an output signal substantially equal to the first and second information signals.

The invention will be explained with reference to the drawings.

A communication system comprising a receiver according to the invention shown in FIG. 1 and an unmodified and compatible orthogonal system comprising a conventional receiver shown in FIG. Although the present invention will be explained using a stereo signal having a stereo signal, the present invention is not limited thereto, and can of course be applied to a system of transmitting and receiving two arbitrary types of signals using a single carrier wave.

As is clear from the communication system according to the invention shown in FIG. 3 and the conventional unmodified and compatible orthogonal system shown in FIG.
a program signal path for supplying signal components (1+L+R) from to the first modulator 12 and a second input terminal 1;
3 to the second modulator 14 is provided. Also, the RF exciter 15
The carrier signal generated by the carrier signal is applied directly to the first modulator 12 and via a 90° phase shifter 16 to the second modulator 14. The outputs of both modulators 12 and 14 can be summed in a signal adder 17 to generate a conventionally transmitted signal. This signal can be expressed mathematically as:

√(1++) ² +(-) ² cos
(ωt+φ) Here φ=tan ^-1 (L-R)/(1+L+R)
shall be. This signal is received by a stereo receiver 18, and a multiplier detector or multiplier 20 and 2
When demodulating with 1, special signals (1+L+R) and (LR) can be obtained. However, the demodulated signal output of the envelope detector 22 of the monaural receiver 23 can be expressed by the following equation.

√(1++) ² +(-) ² This output becomes compatible only with L=R, ie monophonic signals.

The phase vector of FIG. 2 shows the trajectory 24 of the modulated and transmitted signal for the communication system of FIG. The phase vector 25 indicates the unmodulated carrier 1cosωt, and the phase vector 26 indicates the in-phase modulated signal (L+
R), and the phase vector 27 represents the orthogonal signal (L-
R). Further, φ represents the instantaneous phase angle of the composite phase vector 28, and as is clear from the locus 24, this angle cannot be greater than ±45°.

Compatible with visible receiver and transmitter of the present invention
Figure 3 shows the AM stereo broadcast system. Also in FIG. 3, two input terminals 11' (1+L+R) and 13' (LR) are connected to two modulators 12' and 14' of transmitter 30, respectively. RF exciter 15' and 90° phase shifter 16' are also connected in the same manner as described with respect to FIG. The outputs of the modulators 12' and 14' are added by a signal adder 17', and amplitude changes are removed by a limiter 31 so that only phase information remains. The phase modulated carrier wave thus obtained is sent to a high level modulator, that is, a multiplier 3.
Amplitude modulation is performed by two signal components (1+L+R). The transmitted signal is (1+L+R)cos(ωt
+φ). This signal is the original stereo signal from adder 17' multiplied by cosφ, i.e. (1+L+R)/√(1++) ² +(-)
It is equivalent to ² . This latter signal will be fully compatible. That is, when this signal is received by the monophonic receiver 23' and demodulated by the envelope detector 22', its output becomes proportional to the signal component (L+R). The transmitted signal is sent to the stereo receiver 3.
3, the amplitude of this signal is limited by a limiter 34. The stereo information thus obtained is compared with the phase of cosωt from the VCO 36 in a multiplier 35. This VCO 36 is synchronized with the phase of the RF exciter 15' of the transmitter 30, as will be described later. Therefore, the phase difference in this case is cosφ, and the output of the multiplier 35 is also proportional to cosφ.

Collector circuit 3 shown in detail later in FIG.
At 7, the signal is divided by the output of multiplier 35, thereby reproducing the original stereo output of adder 17'. The signal cosωt from the VCO 36 is shifted by ±45° by phase shifters 38 and 39 and supplied to multipliers 40 and 41, which receive the output of the collector circuit 37, respectively. Therefore, by multipliers 40 and 41, L
and outputs of the sum of R and the DC term, respectively.

FIG. 4 shows the deformation locus 4 of the phase vector of the transmitted signal in the communication system equipped with the receiver of the present invention shown in FIG.
5 is shown. Each point in the trajectory 45 corresponds to each point in the trajectory 24 multiplied by cosφ. By multiplying cosφ in this manner, it is possible to generate a minimum number of higher order sidebands corresponding to the transmission of a compatible monophonic signal with minimum distortion.

The receiver of the invention and the corresponding transmitter are shown in more detail in FIG. In a monaural transmitter, a modulator 32 is supplied with a carrier wave from an RF exciter 15' consisting of a crystal oscillator. In this case the desired processing circuit 4 converting the output of the oscillator according to the invention
9 is shown within the dotted line. The frequency of the carrier wave from the oscillator 15' is divided and one part is shifted by 90 degrees by a phase shifter 16'. The two divided orthogonal carrier waves are then supplied to modulators 12' and 14', and the outputs of these modulators are supplied to an adder 17'. A portion of the carrier that is not phase-shifted and modulated is also supplied to adder 17' via a carrier level controller 50 that determines the level of the unmodulated carrier. The output of adder 17' is amplitude limited by limiter 31 to remove amplitude modulated components, thereby allowing an unmodulated carrier wave having only phase or stereo information to be supplied to high level modulator 32. Program channel input terminals 52L and 53R each have program level limiters 54 and 55 and a monitoring instrument 5.
6 and 57, respectively. The L and R signals are also input to an adder 5 connected to the multiplier 12'.
8 to form a signal component (L+R). Further, the R signal is inverted by an inverter 60 and is then inverted by a multiplier 14'.
is supplied to an adder 61 connected to L.
It is combined with the signal to form a signal component (LR).
The second output of the (L+R) adder 58 is provided to the high level modulator 32 via a time delay circuit 62. A delay time equal to the delay time of the signal processing circuit 49 is obtained by the delay circuit 62. Therefore, the output of the modulator 32 becomes a signal amplitude-modulated with (L+R) information and phase-modulated with stereo information.

FIG. 6 shows the stereo receiver 3 of the present invention shown in FIG.
3 is shown in more detail. Received signal is RF mixed - IF
It is supplied to an amplification stage 65. Since this RF mixing-IF amplification stage 65 is a conventional one, a description of its operation will be omitted. The amplitude modulation component of the signal at the output terminal 66b of the mixing-amplification stage 65 is removed by the limiter 34. The output of this limiter 34 is expressed as cos(ωt+φ), and this output is expressed by a multiplier 35 which is an in-phase detector.
It is also supplied to one input side of a multiplier 70, which is a quadrature detector. This multiplier 70 constitutes an integrating stage of a phase locked loop 71. A low pass filter 72 also prevents sudden phase changes from reaching the VCO 36, but allows phase drifts to pass through. The output of the VCO 36 is thus very closely controlled and can be fed to a π/2 or 90° phase shifter 73 since it is orthogonal to the output of the transmitter oscillator 15'. The output cosωt of the phase shifter 73 is output from the multiplier 3
5 to the second input. The output I ₀ cosφ appearing at the output 74 of the multiplier 35 is fed to the collector circuit 37 . Collector circuit 3, which will be described later with reference to FIG.
7, the signal at the output terminal 66a of the mixing-amplification stage 65 is divided by the output of the multiplier 35 so that a quadrature signal can be reproduced. The remaining portions of the circuit of FIG. 6 are similar to those described with respect to FIG.

FIG. 7 shows the multiplier 3 of the receiver 33 of the invention shown in FIG.
5 and collector circuit 37 are shown in more detail.
The multiplier 35, which is a phase detector, has its input terminal 8.
0 is supplied with the output of the limiter 34. Limituta 3
The output of 4 alternately switches the active pair of transistors 81 and 82 into conduction in synchronization with the incoming carrier. Further, a reference input signal at a terminal 84 taken out from the phase-locked loop 71 is supplied to a current source 83 constituted by a transistor via a phase shifter 73. This phase shifter 73 also acts as a low pass filter and supplies a substantially sinusoidal reference current to the transistor current source 83. Base location 85 of transistor 82
The DC reference voltage is supplied from the emitter follower 88. This emitter follower 88 is a differential amplifier pair 8
Connect to 1,82. The current mirror 87 also balances out any static current from the transistor current source 83 at the output side 74 of the differential amplifier pair so that the output current is proportional to the cosine of the angular difference between the input signals at input terminals 80 and 84. I come to do it. The current pulse from multiplier 35 is smoothed by integrating capacitor 86.

In order to bring the output of the output side 74 of the multiplier 35 sufficiently close to a cosine function, it is necessary to substantially eliminate high-order harmonics at one of the input terminals 80 or 84.
For this reason, the phase shift network 73 is a low pass filter so that odd harmonics can be removed from the oscillator square wave.

The collector circuit 37 is a pair of transistors 100
and 101 is preferable. transistors 100 and 1
The current for the emitter 01 is supplied from a current source 102. Also two transistors 103 and 104
The current in transistor 104 is equal to the current in transistor 100 because it forms a current mirror. When the currents of transistors 100 and 101 are equal, the current of transistor 104 is equal to the current of transistor 101, and the current I ₀ becomes zero.

The signal voltage taken out from the signal input section 66a is applied to two resistors 108 and 109 and two diodes 1.
10 and 111 and a reference voltage source 112 between the bases of transistors 100 and 101, respectively. The reference voltage source 112 comprises an emitter follower 113 coupled to a voltage divider consisting of three resistors 114, 115 and 116. The base of the transistor 113 is the resistor 11
4 and 115 to obtain a reference voltage. Transistor pair 1 forming a differential amplifier by the emitter of the emitter follower 113
Provides a low impedance reference voltage for 00 and 101.

The current I _r from the multiplier 35 flows through the diode 110
and 111, resistors 108 and 109, voltage source 112, and input signal source 66 to forward bias diodes 110 and 111.

The forward impedance of diodes 110 and 111 and resistors 108 and 109 form a voltage divider, so the voltage supplied between the base of transistor 100 and the base of transistor 101 is equal to the forward impedance of diodes 110 and 111 and the resistance. 108 and 109.

Next, the collector circuit 37 is connected to the current and the multiplier 35
This will be explained by the output I _r =I _nax cosφ. Express the output current as I ₀ = I ₁ I _s /I _r , and I ₁ is the current source 10
Let the current be supplied by 2. _Is is terminal 66
It is the input signal current of a and is expressed as e _s /2r. Here, 2r is made equal to the sum of two extremely large resistors 91. Also, e _s is e _c (1+L+R)cos(ω _c
t+φ) and let e _c be the amplitude of the unmodulated carrier. Furthermore, _Inax is the peak signal current of the transistor 83. Therefore, the following equation holds.

I _s = [Ie _c (1 + L + R) cos (ωct + φ)] / 2r
and I ₀ = [I ₁ e _c (1+L+R)cos(ωct+φ)]/2r
I _nax cosφ ₀ In this case cosφ=(1+L+R)/(1+L+
R) ² + (L-R) ² , so I ₀ = (I ₁ e _c /2r I
_nax )√(1++) ² +(-) ² cos(ωct
+φ), which is the desired orthogonal signal.

FIG. 8 shows another example of a receiver compatible with the desired operation according to the invention. In this example, collector circuit 3
7 in the audio part of the receiver and actually two identical collector circuits 37a and 37.
b. RF Mixer - The output 66 of the IF amplifier stage 65 is a single output which is connected to multipliers 40 and 41.
Connect to. The output Lcosφ of the multiplier 40 is supplied to the collector circuit 37a, where
Divide by cosφ to obtain L output.
The output of the multiplier 41 is set to Rcosφ and is supplied to the collector circuit 37b, where it is divided by cosφ to obtain an R output. For this purpose, the output current at the output 74 of the multiplier 35 is divided and supplied to both collector circuits 37a and 37b.

FIG. 9 shows yet another example of the receiver of FIGS. 7 and 8. In this example, 2 of the collector circuit 37c
Two inputs 83 and 74 are connected to phase shifter 73 and multiplier 35, respectively. Collector circuit 37
The output side 95 of c is connected to the input side of phase shifters 38 and 39 and is taken as a reference voltage divided by cosφ. Therefore, the outputs of multipliers 40 and 41 become L and R signals, respectively.

FIG. 10 shows an example of a left-right SSB communication system, or an orthogonal communication system varying with cosφ, having a transmitter similar to that of FIG. In this example, the L and R input signals are added by an adder 58 and subtracted by an adder 61. The output of the adder 61 is transferred to the phase shifter 95.
The phase is shifted by 90 degrees at , and the signal is supplied to the transmitter in the same way as described above. Further, in a required stereo receiver, the decoding angle is changed so that (L+R) output 96 and (L-R)<π/2 output 97 can be extracted. This output 97 is phase-shifted by -π/2 by a phase shifter 98, and the output is supplied to a matrix circuit 99 of the receiver in the same manner as the output 96. Therefore, the output of matrix circuit 99 becomes L and R signals.

FIG. 11 shows the receiver of FIG. 10 in more detail. That is, the input side of the collector circuit 37 is connected to the output side 66 of the RF mixer-IF amplifier stage 65 of the receiver, the output side of the collector circuit 37 is connected to the multipliers 40 and 41, and the phase-locked loop and phase-shift circuit are connected. The network is connected in the same manner as described with respect to FIG. In this example, one output 97 of the multiplier is phase-shifted in the same way as described with reference to FIG. 10, and the outputs of both multipliers are fed to a matrix circuit 99 so that L and R outputs can be generated.

Figure 12 shows that the L signal among the transmitted signals is 1.
The signal spectrum is shown when the R signal is included in one set of sideband waves and the R signal is included in another set of sideband waves. Of course, this transmitted signal also includes higher-order corrected sidebands that are transmitted with double the sidebands.

FIG. 13 shows an example of another single sideband communication system similar to the communication system with the receiver of FIG. In this example, one of the program input signals, for example, the R signal, is phase-shifted by 90 degrees by a phase shifter 95. The phase-shifted signal is then supplied to an adder 58 and also to an adder 61 via an inverter 60. A second program signal, such as the L signal, is provided directly to adders 58 and 61. The outputs of these adders 58 and 61 are (L+R<π/2) and (L−R<π/2) signals, respectively.
2) Use it as a signal. These signals are modulated with a carrier wave as in a transmitter with cosine correction. When receiving with an orthogonal receiver that performs cosine correction, the corrected signals L and R are <π/2 signals, and this ratio R
The signal is delayed in phase by 90° in a phase shifter 98.

FIG. 14 shows the spectrum of the transmitted signal when the sum and difference signals are transmitted in a single sideband. In this case, the correction information is transmitted with twice as many sidebands.

Therefore, by multiplying orthogonal signals by the cosine of the angle π before transmission and dividing by the same cosine at the receiver, the communication system can be completely compatible with monophonic receivers and easily compatible with stereophonic receivers. A signal can be generated to be decoded. In this case, φ is the angle formed by the vector sum of the first orthogonal carrier waves and the bisector of the angle between the two orthogonal carrier waves. Advantageously, all transmitted signals can be quadrature modulated within the envelope detector without distortion. Therefore, the monophonic signal component that disappears due to the sky waves can be minimized and optimal stereo characteristics can be obtained. Therefore, the communication system of the present invention can be made compatible with monophonic receivers by using both envelope detection and synchronous detection. In order to optimize the characteristics of a synchronous detector, a collector (correction) circuit is required, but satisfactory characteristics can also be obtained with an unmodified synchronous receiver.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional communication method that transmits and receives two types of signals that are orthogonally amplitude modulated using a single carrier wave, and Figure 2 is a phase diagram showing the carrier wave and sideband waves transmitted using the communication method shown in Figure 1. 3 is a block diagram showing an AM stereo communication system equipped with the receiver and transmitter of the present invention, FIG. 4 is a phase vector diagram showing signals transmitted by the communication system of FIG. 3, and FIG. 5 is a vector diagram. 6 is a block diagram showing an example of a transmitter that corresponds to the receiver of the present invention and is compatible with the desired operation; FIG. 6 is a block diagram showing an example of a receiver that is compatible with the desired operation of the present invention; FIG. 6 is a circuit diagram showing a part of the receiver in detail, FIG. 8 is a block diagram showing another example of a receiver compatible with the communication system according to the present invention, and FIG. 9 is a still further example of the receiver. 10 is a block diagram showing a left-right SSB communication system comprising a receiver and a transmitter of the present invention, and FIG. 11 is a block diagram showing a receiver of the present invention in the communication system of FIG. FIG. 12 is a spectrum diagram of a signal transmitted using the communication system shown in FIG. FIG. 3 is a signal spectrum diagram transmitted using the communication method shown in the figure. 10...Orthogonal transmitter, 11, 11'...First input terminal, 12,12'...First modulator, 13,1
3'... Second input terminal, 14, 14'... Second modulator, 15, 15'... RF exciter, 16, 16'...
...90° phase shifter, 17, 17'...signal adder, 1
8... Stereo receiver, 20, 21... Product detector (multiplier), 22, 22'... Envelope detector, 2
3, 23'... monaural receiver, 24, 45...
Locus of phase vector, 25, 26, 27... Phase vector, 28... Combined phase vector, 30...
Transmitter, 31, 34... Limiter, 32... High level modulator (multiplier), 33... Stereo receiver, 35... Multiplier (in-phase detector), 36...
VCO, 37... Collector circuit, 38, 39...
45° phase shifter, 40, 41... multiplier, 49... signal processing circuit, 50... carrier wave level controller, 5
2, 53...Program channel input terminal, 5
4,55...Program level limiter, 56,
57... Monitoring instrument, 58... Adder, 60... Inverter, 61... Adder, 62... Time delay circuit,
65...RF mixing-IF amplification stage, 66a, 66b...
... Output terminal (65), 70 ... Multiplier (quadrature detector), 71 ... Phase lock loop, 72
...Low pass filter, 73...π/2 (90°)
Phase shifter, 95... Phase shifter, 98... Phase shifter.

Claims (1)

[Claims] 1. Amplitude modulated by signal information proportional to the sum of the first and second information signals A and B, and φ=tan ^-1 {C ₁ (A-B)/(C ₂ +A+B)}
In a receiver for receiving a broadcast carrier signal phase modulated by a signal proportional to an angle φ (where C ₁ and C ₂ are constants), an input device for receiving and amplifying the broadcast carrier signal a mixing device for converting into an intermediate frequency carrier signal, an intermediate frequency amplifying device for amplifying the intermediate frequency carrier signal of sufficient bandwidth to carry amplitude and phase modulation information, and demodulation means for extracting a signal proportional to the amplitude and phase of the carrier wave. and a correction signal generating means for generating a correction signal proportional to the phase of the carrier wave from the received signal;
A receiver comprising: reproducing means coupled to the demodulating means and the correction signal generating means for generating an output signal substantially equal to the first and second information signals. 2. A receiver according to claim 1, characterized in that the correction signal generating means comprises a device for dividing the output of the amplifier device by a signal proportional to the angle φ. 3. The receiver according to claim 2, wherein the signal proportional to the angle φ is made to be proportional to the cosine of the angle φ. 4. The receiver further includes an oscillation device and a limiter device that limits a signal proportional to the output of the amplification device, and the demodulation means receives the outputs of the oscillation device and the limiter device and supplies the output to the regeneration means. 2. A receiver according to claim 1, further comprising a first multiplication device that performs the following steps. 5. The reproduction means includes a first phase shifter that shifts the phase of the output of the oscillation device by 45 degrees, a second multiplication device that receives and multiplies the outputs of the first phase shifter and the correction signal generation means, and the oscillation device. A patent characterized in that it comprises a second phase shifter that shifts the phase of the output of the device by -45°, and a third multiplier that receives and multiplies the output of the second phase shifter and the correction signal generating means. A receiver according to claim 1.