JPS6046580B2 - Compatible amplitude modulation stereo receiver - Google Patents

Description

Detailed Description of the Invention This invention was previously applied to Japanese Patent Application No. 36-4778 (Japanese Patent Publication No. 45-9761) and Japanese Patent Application No. 83348-1988 (Japanese Patent Publication No. -51
The present invention relates to an AM stereo receiver designed for the reception of carrier waves having stereo-related information appearing in each of the upper and lower sidebands of a transmitted signal, such as that described in US Pat.

An AM stereo receiver according to the invention provides carrier enhancement to reduce signal distortion at low levels of received signal strength and/or inverse amplitude modulation of the carrier to obtain a stereo sum (L-R) signal. (or) perform quadrature demodulation of the received carrier and use in-phase detection (e.g. envelope detection or product demodulation) to obtain the stereo sum (L+R) signal information and relative shift in a manner known per se. Stereo-related (L and R) outputs are generated by a combination of phase, stereo sum, and stereo difference signals.

Modulation of the carrier wave by a sub-audible frequency (e.g. GoTian) indicates the presence of a stereo modulated signal at the receiver. conveniently used. Aspects of the invention also relate to specialized receiver circuitry with stereophonic and monophonic capabilities and automatic switching between them. Six-phase modulation of the carrier wave using the difference stereo signal (L-R) information and the sum stereo signal (L+R)
Compatible stereophonic AM transmission and reception involving the upper and lower sidebands associated with stereo, in which the carrier wave is envelope-modulated with information, is described in Japanese Patent Application No. 1983-4778. It is described with some type of receiver for stereophonic sound reception. A more detailed discussion of this compatible ΔM stereophonic sound modulation technique can be found in IEEE Transactions on Proud Cursing, BX.
-Volume 17, No. 2, June 1971 (IEEE Tran
sactiOnsOnBrOadcasting, VO
l. BX-17, NO. 2, June 97l) 50
~ 1 amplitude modulation stereophonic sound system for broadcasting stations on page 55 (
AstereOphOnicSystemFOrAmp
lltudeMOdulatedBrOdcastSt
atiOns) J. The contents of the aforementioned patents and articles are incorporated herein to the extent pertinent.
BartOn US Patent No. 7310
The so-called 1-compatible three-dimensional sound A described in No. 2167
The M-scheme is also known, but it utilizes a compromise quadrature modulation technique in practice. To reduce monophonic distortion, the Burton method takes advantage of the relative phase angle between the carrier and sidebands of ±25 to 30 degrees, and uses a phase-shifted enhanced carrier and product demodulation to reduce monophonic distortion. It generates signals, but does not combine the demodulated signals. There is also a stereophonic sound transmission/reception system related to the Nichanel FM-AM stereo system, such as the one described in U.S. Patent No. 3,009,151 by ShOaf. and AM band carrier waves are frequency modulated and amplitude modulated, respectively.

Avins US Patent No. 30684
No. 75 discloses a stereo transmission and reception system in which one stereo-related signal is amplitude modulated on one carrier and another stereo-related signal is frequency modulated on the same carrier, and U.S. Patent No. 3 to HOlt et al.
No. 167,614 discloses the use of subaudible tones to indicate the presence of a stereo signal in an AM/PM type transmission system, and US Pat. An AM stereo system is disclosed that involves amplitude modulating and linearly adding different carrier waves with respective stereo related signals. Features and advantages of the invention include various forms of AM stereo for the reception of a radiated energy carrier modulated with two stereo related signals (L and R).
This is achieved by the presentation of a rheo receiver, where each signal amplitude modulates the carrier with essentially stereo sum (L+R) information and the carrier with essentially stereo difference (L-
R) information appears in an independent first-order single sideband by phase modulating the received signal, and the receiver performs quadrature demodulation of the phase modulation representing the stereo difference (L-R) information of the received signal. Incorporating the use and incorporating one or more of the following techniques to optimize the quality of the output stereo signal. (1
) Use of inverse amplitude modulation of the carrier, i.e. envelope basics to additively and inversely modulate the received carrier so as to reduce the distortion of the stereo difference signal derived from the additively modulated carrier. the use of waves (and one or more harmonics of the chosen form). (2) the stereo difference signal derived from the boosted carrier so that essentially no phase modulation distortion occurs accompanying the carrier boost and even when the received carrier is fully (i.e., 100%) modulated; Carrier augmentation, ie, the use of an enhanced carrier, preferably with control such as a phase lock loop of the carrier boost input so that the carrier does not contain noise bursts.

(3) In connection with any of the foregoing techniques, an apparatus for detecting and utilizing a subaudible (e.g., 15 hertz) signal tone modulated on a received carrier as an indication of the presence of a stereo signal, such that the signal tone is (It is desirable to use it to automatically control the machine output method).

Another feature and advantage of the invention arises from the avoidance of the use of circuit components such as sideband filters in the receiver of the invention, thereby readily allowing the employment of integrated circuits.

Yet another advantage and feature of the stereophonic sound transmission and reception system of the present invention is the selective modulation of a carrier wave with a subaudible frequency signal to indicate the presence of a stereophonic signal at the receiver; It can be used to automatically switch between monophonic reception systems and to provide a carrier tuning indicator.

Other features and advantages of the invention will become apparent from the following description and discussion of certain representative embodiments of the invention.

FIG. 1 is a block diagram illustrating a typical compatible AM stereo receiver according to the present invention.

Antenna 10 is connected in line 12 to a conventional RF/IF superheterodyne circuit 14 which produces an intermediate frequency output 16, a portion of which is
A common mode detection device such as an envelope (envelope) detector 18 (for which a conventional diode detection circuit is suitable) is supplied. The lower output 16 also provides a carrier track to perform carrier selection without inducing phase distortion.
- A filter circuit 20, for example a phase locked loop device, is supplied, which circuit is, for example, an ICNO. The circuit may be conventional in itself, such as the circuit that can be obtained by using a 562. The output 22 of the carrier track circuit 20 represents the carrier portion of the received carrier wave and is output by the summing circuit 2.
4, where it is added to the (IF) received carrier, a portion of the output 16 from the RF/IF stage 14 also serves as an input to the summing circuit 24.

The combined output 26 from the summing circuit 24 is
Conveniently, as shown in the representative example of FIG. 4, the enhanced carrier is about half as large as the received carrier, i.e., compared to the relative carrier level at the received signal of 0.9415 volts in the particular case shown. The carrier wave is raised to have a relative voltage of 1.5 volts. This phase-modulated, enhanced carrier output means that the enhanced carrier has an instantaneous zero amplitude, i.e., negative unity
Since it cannot have 00% modulation, it is more suitable for demodulation to combat its phase modulation (after being reversely amplitude modulated in amplitude modulation 28, as discussed in more detail below). The carrier track circuit output 22 is also provided to a phase shift network 30 which shifts the carrier phase by +90 degrees, and the network 30 then provides the phase shifted carrier output 32 to a product demodulator 34.

Collectively, circuitry 30 and demodulator 34 collectively
6 constitutes what is known per se as a quadrature demodulator. The phase shift network 30 has two! Published by McGraw-Hill, New York, NY 1959, Edited by Keith Henney 1. Radio Engineer's Handbook 5th Edition, Chapter 12, pp. 16-52.
rHandb00k″,EditedbyKeithH
enny, 5thEd. McGraw-Hill COm
pany, NewYOrk, NewYOrk, l95
9, AtChapterl2, AndalsOatpa
gesl6-52) are suitable. Further, the product demodulator 34 is, for example, an ICN manufactured by Motorola (MOtOrOla).
O. MCl596l. Per se customary forms, such as those known in the art, are suitable.

The output 38 of the common mode detector 18 is the amplitude modulation envelope of the received carrier, and more particularly, as is known per se, the amplitude modulation or envelope in this type of AM stereo transmission is the sidewave of the received carrier. It is the fundamental wave of such an envelope, since it is an essentially undistorted reproduction of the stereo sum (L+R) information in the band.

This envelope fundamental output 38 is provided to an amplifier 40, the amplified output 42 is applied to a summing circuit 44, which in turn amplitude modulates the phase modulated and enhanced carrier (output 26) in an amplitude modulator 28. Audible modulation input 4 for
Give 6. The output 48 from amplitude modulator 28, which may be termed inverse amplitude modulation, phase modulation, and enhanced carrier, is utilized as a second input to product demodulator 34 in quadrature demodulation circuit 36. An important feature of the invention is that the additional amplitude modulation applied to the carrier wave in amplitude modulator 28 significantly reduces distortion that would otherwise be present at the output 5 of quadrature demodulator 36.
It will appear at 0.

If the envelope fundamental (as at output 38) is used as the only input to amplitude modulator 28 (such mode of operation is achieved by opening manual switch 52), the demodulated The distortion at output 50 is reduced to about 4% in voltage ratio. Stereo difference (L-R
) If further reduction of harmonic distortion in the signal is desired or necessary, frequency doubler 54 can be brought into the circuit by closing switch 52. In this mode of operation, the second harmonic output 56 from the frequency doubler 54 is combined with the envelope fundamental (output 42) in a summing circuit 44 to the amplitude modulator 28. Fundamental and harmonic envelope components are provided to the audible input 46 resulting in further reduction of distortion. The approximate relative best level of amplitude modulation in amplitude modulator 28 is approximately 26% of the total modulation voltage in voltage ratio for fundamental modulation and approximately 8% for second harmonic modulation. These inverse amplitude modulation levels reduce the total second and higher order distortion appearing in the output from quadrature demodulator 36 to 0.8% in voltage ratio. A phase-shifting network arrangement known per se converts the stereo difference (L-R) signal output 50 into an envelope fundamental (L-R) signal output 50.
+R) output 38 to provide relatively undistorted stereo-related signals (L and R) in a manner known per se and explained in more detail below.

The receiver shown in FIG. 1 responds to the subaudible signal subtone modulation of the carrier wave to indicate the presence of a stereo signal, and preferably converts the receiver output into a stereo format when such a stereo presence signal is present. Automatically establish and maintain it.

Automatic switching of receiver output formats is accomplished by control of electronic switch 58, as will be explained in more detail below. When electronic switch 58 closes, demodulator output 50 is connected to θ-45 phase shift network 60 from which output 62 is applied to summing circuit 64 and subtracting circuit 66. The stereo sum (L+R) signal appearing as detector output 38 is similarly provided to its associated θ+45 sum phase shift network 68, and the output 70 therefrom is also provided to sum and difference circuits 64,66. As shown, phase shifting networks 60 and 68 are phase difference network pairs (θ-45 and θ+458), which are known per se in the art and which provide a relatively constant signal amplitude. While maintaining a relatively constant relative phase difference of 90 strands over the effective audio frequency range. Generally, in this type of output circuit, the summing circuit 64 favors the left or L channel stereo information so that the L speaker 68 is driven by the L stereo signal, and the subtracting circuit 66 similarly favors the left or L channel stereo information. channel. The R speaker 70 is driven by advantageously acting on stereo information. Also, of course, as is known per se, the stereophonically indistinguishable information (i.e. monophonic information) in the received signal sidebands appears simply as two primary sidebands in the received carrier, i.e. the normal dual sidebands. appears as an amplitude modulation and as part of the detection envelope to the L speaker 68.
and the R speaker 70 is driven monophonically. Electronic switch 58 is controlled by a sub-audible tone (eg, 15 hertz) that appears as a modulation on the carrier of the received signal.

Assuming that the subaudible signal is transmitted by amplitude modulation of a carrier wave (which is currently considered to be the preferred method of modulation), the switch 72 in FIG. Illustrated in the correct position to respond to the display, the subaudible envelope component appearing at detector output 38 is passed through switch 72 to bandpass filter 7.
4 and from which an isolated sub-audible signal tone output 76 is provided to an amplifier 78 whose output 80 illuminates a stereo presence indicator light 82. The sub-audible signal tone output 80 is also applied to a detector 84 and
4 produces a DC component at output 86 which acts to control electronic switch 58 by closing the switch when a stereo subaudible signal is present. Another method of operation available is in which the sub-audible signal tone indicating the presence of a stereo signal is phase modulated on the carrier wave (see Japanese Patent Application No. 50-83348). In this mode of operation, the quadrature demodulator 36 of the receiver shown in FIG. The demodulator output 50 is sent to a bandpass filter 74, and the filter output 76 controls a stereo display 82 and electronic switch 58 in a manner similar to that described above.

It should be noted that if phase modulation or the like (e.g. quadrature modulation) is used to modulate the subaudible signal tone on the carrier wave, the carrier track circuit 20 will It must be narrow enough at its output 22 so as not to maintain track. If such a track were to be maintained, the sub-audible signal tone would be significantly attenuated and the response circuitry (eg, electronic switch 58) would be inoperable. Also the first
A manual switch 88 is shown in the figure, which is closed when the receiver is to be used exclusively for stereo reception. In this mode of operation with switch 88 closed, switch 88 provides a direct interconnection between product demodulator output 50 and its associated phase shift network 60, so that switch 72, bandpass filter amplifier 78, and stereo - Lamp 82, detector 84 and electronic switch 58
is unnecessary. Figure 2 shows another type of AM according to this invention.
1 shows a portion of a stereo receiver in which the receiver is similar to that shown in FIG. 1 except for the portions shown in FIG. 2 and discussed below.

As shown in FIG. 2, this alternative circuit uses two amplitude modulators 28'' and 28'' in place of modulator 28 of FIG. Amplifier 40 has detector output 38 as its input.
and provides a fundamental component input 42 (as in FIG. 1) to the first amplitude modulator 2'. In this variant circuit, the output of the first amplitude modulator 2'' is the input 90 to the second amplitude modulator 28'', and
Another audible input 92 for the second amplitude modulator 2' is taken from the frequency doubler 54. The output 94 of the second amplitude modulator 2' is then used as an input to the product demodulator 34. 28'', but provides somewhat less distortion than the circuit configuration shown in FIG. FIG. 3 shows a further alternative inverse modulation circuit that reduces distortion in the demodulated stereo difference signal output to even less than that of the configuration shown in FIG.

In the circuit of FIG. 3, the output 42 from amplifier 40 is provided to a frequency doubler 54 (as in FIG. 1), which in turn feeds a summing circuit 44'' (also 1) provides a second harmonic output 56 (as in FIG. 1).As can be seen, the amplifier 40, the frequency doubler
The operation of the frequency doubler output 56 and combined with the fundamental output 42 in the summing circuit 44'' is similar to that in the circuit of FIG. 1 when the switch 52 is closed.
However, in FIG. 31, another envelope fundamental component 42 is further removed from amplifier 40 and applied to a frequency tripler 96, from which a third harmonic output 98 is also added. This is applied to the summation circuit 44'' and is combined therewith with the fundamental component 42 and the second harmonic, all of which provide an output 100 from the summation circuit 44'' to the amplitude modulator 28. The modulator is further freed from fourth-order sideband components, which would otherwise cause distortion in the stereo difference signal output (such as at 50 from quadrature demodulator 36 in FIG. 1). It will be. An addition circuit (
44 or 44'') will be apparent to those skilled in the art.In general, as can be seen from the foregoing discussion of various types of receiver circuits according to the present invention, The inventive concept involved in this type of w stereo receiver is to inversely modulate the entire wave (carrier-enhanced, etc.) using components derived from the envelope of the received carrier, and to create a stereo difference signal. Stereo signal distortion is reduced by canceling or attempting to cancel undesirable spectral components that would produce distortion when detected by a quadrature demodulator or the like.

FIG. 4 is a diagram showing the spectrum of a modulated carrier wave received by the receiver shown in FIG. 1 and augmented by a carrier track filter circuit; The stereo channel (L) is fully modulated and the other stereo channel R is unmodulated.

Logical analysis shows that the demodulation of this signal by a quadrature demodulator without any additional amplitude modulation (i.e., in FIG. if applied directly to the product demodulator 34), a second harmonic distortion level of about 13% (more precisely 13.05%) and about 2112% (more precisely 2 A stereo difference output signal is produced at output 50 characterized by a third harmonic distortion level of .33%).

Although these amounts of harmonic distortion are acceptable in some types of equipment, such distortion. It will be appreciated that the levels are excessive in terms of normal standards for commercial broadcasting purposes. However, it is important to this invention that such harmonic distortion levels can be readily reduced to commercially acceptable values by selective inverse modulation of a phase modulated carrier wave with a detected envelope wave. This is a unique feature and advantage. If it is desired to apply such inverse amplitude modulation to almost eliminate second-order distortion, theoretical considerations suggest that the inverse modulation input will reduce the rate of modulation of the phase modulated carrier by a factor of about 26%. It turns out. By means of inversely modulating the phase modulated carrier with the envelope fundamental (i.e., opening switch 52 in FIG. ), the second harmonic distortion level is reduced to about 0.30% and the third harmonic distortion level is about 4.1%. (
In a particular example, if the carrier modulation results in a 26.09% reduction by adding inverse modulation, the resulting second harmonic distortion is 0.30% in voltage ratio and the third harmonic The strain was 4.13%. ) Although such an amount of third harmonic distortion is acceptable, it is desirable to reduce this harmonic distortion as well, and this is accomplished by switching switch 52 in the receiver shown in FIG. This can be done by applying the frequency-doubled envelope component (ie, the second harmonic envelope component) to the inverse modulation input 46 to the amplitude modulator 28. In a typical specific example, a fundamental wave envelope input of about 26% (4
2) and a second harmonic envelope input of about 8% (at 56 from frequency doubler 54), the inverse amplitude modulated phase modulated enhanced carrier as appearing at output 48 from amplitude modulator 28 is It essentially has a spectral distribution as shown in FIG. (In the particular example where the out-of-phase amplitude modulation fundamental wave component is at a level of 26.09%, the second harmonic inverse amplitude modulation is at a level of 8.115% and the spectral distribution level shown in Figure 5 is ) By using such inverse amplitude modulation of the fundamental and second harmonic, the second harmonic distortion level is 0.295% in the specific example cited, and the third harmonic Strain level is 0.1
45%, and the fourth harmonic distortion level is 0.72.
It was 5%. As previously mentioned, another technique for inverse amplitude modulating a phase modulated and enhanced carrier with a fundamental envelope component and a second harmonic envelope component is shown in FIG.

In this example, modulation of the enhanced carrier by the fundamental wave takes place in the first amplitude modulator 2', and another modulation with the second harmonic of its envelope takes place in the second amplitude modulator 2'. Analysis shows that the use of separate amplitude modulation stages for inverse modulation with the fundamental and second harmonics reduces the cost compared to using a single amplitude modulation stage as shown in Figure 1. It can be seen that the strain decreases. As a further improvement to reducing distortion in the stereo difference signal output 50 of FIG. 1, FIG.
are shown providing harmonic envelope outputs 98 and 56, respectively, and these outputs are combined with the fundamental envelope output 42 in a summing circuit 44'' to provide an out-of-band output. This will further reduce the strain.

The distortion level of the higher-order sidebands can be further reduced by inputting the corresponding higher-order envelope components, but the fundamental and harmonic components of the received wave envelope cause the phase-modulated carrier to be phase-modulated at various relative levels. It will also be readily apparent to those skilled in the art to which this invention pertains that the technique of reducing distortion by inversely modulating the will be understood.

FIG. 6 illustrates in some detail a typical carrier track filter circuit of the type indicated generally at 20 in FIG.

In a typical receiver, the receiver adjusts ±
Assuming that it is to drift in the 800 Hz range, the carrier track circuit needs a bandwidth significantly less than ±800 Hz to perform good carrier tracking to achieve an enhanced carrier signal without substantial phase distortion. However, this is because in a passband of this size, many sideband signal components pass in addition to the desired carrier wave, and these sideband components are not necessarily symmetrical, especially in the case of a stereo system. This is because if the passband width of the circuit is too wide, the carrier wave tracking circuit will not only pass the carrier wave, but will track the phase modulation component of the stereo wave.
For this reason, the carrier track circuit shown in FIG. 6 applies the received carrier input 16 to a first phase locked loop circuit (PLLA) 100, which is manufactured by ICNO. Types known per se, such as those obtained from 562B, are suitable and have a passband of ±800 pressures.

The output from phase locked loop 100 is then applied to frequency divider circuit 104 where the carrier frequency is divided by a suitable integer such as sixteen. This frequency division also helps to divide the frequency error by a similar amount (but an interesting problem is that the sideband spacing is not changed by frequency division or frequency multiplication, so it is useful to make the sidebands closer together). ) If the carrier and any frequency error are divided by a selected integer, the frequency-reduced output 106 is a second phase-locked signal.
A loop circuit (PLLB) 108 (also compatible with Signetics IC NO. 562B) is added, which in the selected example has a passband of ±50 pressures. This circuit 108 effectively acts as a carrier tracking filter, but is sufficiently narrowband to pass little sideband modulation, so that the filtered output 110 consists essentially only of the passing carrier of reduced frequency. Become. The filtered output 110 is then applied to a frequency multiplier 112 to isolate the original carrier frequency.
It is then multiplied by a suitable integer (16 in the example chosen) to produce an output 22, which is the pass carrier at the receive carrier frequency and is connected to the summing circuit 24 and the phase shift circuit. added to the network 30 (FIG. 1). Generally speaking, the carrier track circuit 20 should have a bandwidth that allows it to track expected frequency drifts in the transmitter and receiver, but this idea may in some cases affect the phase of the subaudible signal. May be incompatible with the use of modulation.

For this reason, it may be desirable to amplitude modulate such tones on a carrier wave, thereby avoiding problems associated with circuit 20 for tracking sub-audible tones. As previously mentioned, and due to the frequency division that occurs in stage 104, the filter system output 22
It is necessary to compare the phase of the received carrier with the phase of the received carrier.

In FIG. 6, a part of the output 22 is connected to a phase detector 114 (ICN manufactured by Motorola).
O. MC4OO4P is suitable) and low pass filter (
This is done by providing a control voltage input 11-8 to the phase locked loop circuit 100 through an LPF 116 (typically having a time constant of 15 milliseconds).

The phase of the passed carrier wave output 22 is compared to the phase of the input wave in a phase detector 114, and a control voltage output 118 from the phase detector corrects for such large phase errors between input and output (16 frequency divisions). Therefore, there are 16 different phase stability points, and if phase control is not applied to the phase lock loop 100 by the phase detector 114, the phase lock loop circuit 108 will be locked at the phase stability point. It should be noted that the control exerted on the phase locked loop 100 by the phase detector 114 is made relatively slow operating by the action of the low pass filter circuit 116. It primarily serves to correct large phase errors, such as may occur when the device is turned on or if there is severe carrier attenuation that causes the frequency division circuit 104 to malfunction. FIG. 7 is a block diagram showing still another type of circuit that is somewhat simplified from the carrier track circuit shown in FIG. 6.

In short, the phase lock of the circuit shown in Figure 6
Loop 108 and frequency multiplication stage 112 can be replaced by the circuit shown in FIG. 7 (known per se). Generally, this type of circuit applies a frequency-divided carrier output 106 to a phase detector 120, and
The output 122 from this detector is a voltage controlled oscillator (■C
O) 124, which generates a passing carrier output 22 at the desired frequency. VCOl24 is input 106
The output 22 is also fed to a frequency divider 126 where the frequency is downsized to exactly one fraction. Output 128 from frequency divider 126 is applied to phase detector 120 where the phase of frequency divided output 128 is -
An output 122 is generated by a phase detector 120, which output 122 is
24 to maintain the phase of the output 22 in phase with the phase of the input signal. From another point of view, the circuit shown in Figure 7 is an ordinary circuit. It acts as a used locked loop, but with a divide-by-16 frequency circuit in the return path, and the VCO operates at 16 times the input frequency to provide accurate in-phase frequency multiplication. FIG. 8 shows yet another type of AM system according to the present invention. 8 shows a portion of a tele-receiver whose circuit is similar to that shown in FIG. 1 (or FIG. 2 or 3) except as shown in FIG. 8 and as described below. be.

In place of the envelope detector 18 of the circuit of FIG. 1, this alternative utilizes a product demodulator 1' as the in-phase detection device for extracting the L+R signal output 38, which also has a pass carrier input 22. Supplied. Although the product demodulation circuit 1' is somewhat more complex than the envelope detector 18, it is advantageous from the standpoint of improving signal-to-noise characteristics;
This is currently desirable especially under noisy reception conditions. From the foregoing, further modifications, adaptations and applications of the stereo receiver according to the invention and its components will occur to those skilled in the art to which the invention pertains.

[Brief explanation of drawings]

l FIG. 1 is a block diagram of a typical compatible ΔM stereo receiver according to the present invention. FIG. 2 is a block diagram showing a portion of another type of AM stereo receiver according to the present invention; the other portions of this receiver are similar to those shown in FIG. Figure 3 is based on this invention.
2 is a block diagram showing a portion of yet another type of AM stereo receiver, the other portions of which are similar to those shown in FIG. 1; FIG. FIG. 4 is a diagram illustrating the spectrum of a modulated carrier (such as at 26 in FIG. 1) received and carrier multiplied by the receiver shown in FIG. FIG. 5 shows the spectrum of the amplitude modulator output (such as at 48 in FIG. 1) corresponding to the received signal spectrum shown in FIG. FIG. 6 is a more detailed block diagram of the typical carrier track circuit used in FIG. FIG. 7 is a block diagram showing a modified portion of the circuit shown in FIG. 6. FIG. 8 is a block diagram showing modified parts of the receiver shown in FIG. 1. 14: superheterodyne circuit, 18: envelope detector, 20: carrier track filter circuit, 24: summing circuit, 28: amplitude modulator, 30: +90 phase shift network, 34: product demodulator, 36: Quadrature demodulator, 40: amplifier, 44: summation circuit,
54: Frequency doubler, 58: Electronic switch, 60: -4
5-wave phase shift circuit network, 64: addition circuit, 66: subtraction circuit, 6
8: +45, phase shift network, 74: 15 cycle bandpass filter, 78: amplifier, 84: detector, 96: frequency tripler, 100: phase locked loop AllO4:
Division circuit, 108: Phase locked loop Bll
12: Multiplier circuit, 114゛: Phase detector, 120: Phase detector, 124: Voltage controlled oscillator, 126: Division circuit.

Claims (1)

[Scope of Claims] 1. A compatible amplitude modulation type stereo receiver that receives a carrier wave that is amplitude modulated with stereo sum (L+R) signal information and phase modulated with stereo difference (L-R) signal information, , (a) represents the envelope of the received carrier, thus representing the stereo sum (L+R) signal information, and (L+1
) a detection device that extracts a component called an audible signal, and (b
)(L-R) a quadrature demodulator for extracting an audible signal; and (c
) a device for combining (L+R) and (L-R) signals based on the components representing said envelope so as to provide L and R stereo signal output; and (d) generating a component resulting from the components representing said envelope. (e) inverting the phase modulated carrier with the components obtained from said means prior to quadrature demodulation of the carrier to reduce distortion in the demodulated (L-R) output signal induced by said quadrature demodulator; A compatible amplitude modulation type stereo receiver comprising an amplitude modulation device. 2. A compatible amplitude modulation stereo receiver according to claim 1, wherein the detection device is an envelope detection device. 3. A compatible amplitude modulation stereo receiver according to claim 1, wherein the obtained signal represents at least an envelope fundamental wave. 4. A compatible amplitude modulation stereo receiver according to claim 1, wherein the obtained components represent at least an envelope fundamental wave and a second harmonic. 5. Claim 1, wherein the obtained components represent at least an envelope fundamental wave, a second harmonic, and a third harmonic.
Compatible amplitude modulation stereo receiver as described in . 6. A compatible amplitude modulation type stereo receiver that receives a carrier wave that is amplitude modulated with stereo sum (L+R) signal information and phase modulated with stereo difference (L-R) signal information, comprising: (a) receiving carrier wave; , thus representing the stereo sum (L+R) signal information, and (L+R
) a detection device that extracts a component called an audible signal, and (b
)(L-R) a quadrature demodulator for extracting an audible signal; and (c
) an apparatus for combining (L+R) and (L-R) signals based on said envelope-representing components to provide L and R stereo signal output; and (d) generating components derived from said envelope-representing components. (e) inverse amplitude modulating the phase modulated carrier with the component obtained from said means prior to quadrature demodulation of the carrier to reduce distortion in the demodulated (L-R) output signal induced by quadrature demodulation; and (f) a device for enhancing a carrier wave of a received carrier wave before performing inverse amplitude modulation with the inverse amplitude modulation device. 7. A compatible amplitude modulation stereo receiver according to claim 6, wherein the detection device is an envelope detection device. 8. A compatible amplitude modulation stereo receiver according to claim 6, wherein the obtained component represents at least an envelope fundamental wave. 9. A compatible amplitude modulated stereo receiver according to claim 6, wherein the obtained components represent at least an envelope fundamental wave and a second harmonic. 10. A compatible amplitude modulated stereo receiver according to claim 6, wherein the obtained components represent at least an envelope fundamental wave, a second harmonic, and a third harmonic. 11. The device for enhancing the carrier of the received carrier comprises a carrier track circuit for separating the carrier frequency from the received carrier, and a device for combining a portion of the received carrier with the output of the carrier track circuit. A compatible amplitude modulation stereo receiver according to claim 6. 12 The carrier track circuit includes a first phase-locked loop circuit, a frequency division circuit, a second phase-locked loop circuit having a passband smaller than a passband of the first phase-locked loop circuit, and the first phase-locked loop circuit. a frequency multiplier circuit for restoring the frequency of the output of the second phase-locked loop circuit to the same wave number as the input carrier wave to the phase-locked loop circuit;
The frequency of the carrier wave input to the phase-locked loop circuit is compared with the carrier wave output of the second phase-locked loop circuit, and the frequency of the carrier wave input to the phase-locked loop circuit is compared with the carrier wave output of the second phase-locked loop circuit. 12. The compatible amplitude modulation type stereo receiver according to claim 11, further comprising a circuit for controlling the phase of the output from the loop circuit. 13 A compatible amplitude modulation type stereo receiver of a type that receives a carrier wave that is amplitude modulated with stereo sum (L+R) signal information and phase modulated with stereo difference (L-R) signal information, comprising: (a) receiving carrier wave; , thus representing the stereo sum (L+R) signal information, and (L+
R) a detection device that extracts a component called an audible signal;
b) (LR) a quadrature demodulator for extracting an audible signal;
c) (L+R) and (L-R) signals based on the components representing the above envelopes to give L and R stereo signal outputs;
(d) means for generating a component derived from the components representing said envelope; and (e) for reducing distortion in the demodulated (L-R) output signal induced by quadrature demodulation. (f) the received carrier wave is additionally modulated with a subaudible frequency tone indicating the presence of a stereo signal; a device for demodulating the output subaudible tones; and a device for demodulating the output subaudible tones;
A compatible amplitude modulated stereo receiver including means for providing a stereo signal output and controlling an audible output channel of the receiver to provide a monophonic output in the absence of such subaudible frequency sounds. 14. A compatible amplitude modulation stereo receiver according to claim 13, wherein the detection device is an envelope detection device. 15. A compatible amplitude modulation stereo receiver according to claim 13, wherein the obtained component represents at least an envelope fundamental wave. 16. A compatible amplitude modulated stereo receiver according to claim 13, wherein the obtained components represent at least an envelope fundamental wave and a second harmonic. 17. A compatible amplitude modulated stereo receiver according to claim 13, wherein the resulting components represent at least an envelope fundamental wave, a second harmonic, and a third harmonic. 18. A compatible amplitude modulated stereo receiver as claimed in claim 13, wherein said subaudible frequency sound is at a frequency of about 15 Hz. 19. A compatible amplitude modulated stereo receiver according to claim 13, wherein the received carrier wave is phase or frequency modulated with subaudible frequency sound. 20. A compatible amplitude modulated stereo receiver according to claim 13, wherein the received carrier wave is amplitude modulated with subaudible frequency sound. 21 A compatible amplitude modulation type stereo receiver that receives a carrier wave that is amplitude modulated with stereo sum (L+R) signal information and phase modulated with stereo difference (L-R) signal information, comprising: (a) receiving carrier wave; , thus representing the stereo sum (L+R) signal information, and (L+
R) a detection device that extracts a component called an audible signal;
b) (LR) a quadrature demodulator for extracting an audible signal;
c) (L+R) and (L-R) signals based on the components representing the above envelopes to give L and R stereo signal outputs;
a device for combining signals; and (e) means for generating.
(f) apparatus for inverse amplitude modulating a phase modulated carrier wave with a component obtained from said means prior to quadrature demodulation of the carrier wave in order to reduce distortions in the demodulated (L-R) output signal induced by quadrature demodulation; (g) the received carrier wave is additionally modulated with a subaudible frequency tone indicating the presence of a stereo signal; , an apparatus for demodulating output subaudible tones, and a device for demodulating output subaudible tones;
A compatible amplitude modulated stereo receiver including means for providing a stereo signal output and controlling an audible output channel of the receiver to provide a monophonic output in the absence of such subaudible frequency sounds. 22. A compatible amplitude modulation stereo receiver according to claim 21, wherein the detection device is an envelope detection device. 23. A compatible amplitude modulation stereo receiver according to claim 21, wherein the obtained component exhibits at least an envelope fundamental wave. 24. A compatible amplitude modulated stereo receiver according to claim 21, wherein the obtained components represent at least an envelope fundamental wave and a second harmonic. 25. A compatible amplitude modulated stereo receiver according to claim 21, wherein the resulting components represent at least an envelope fundamental wave and second and third harmonics. 26. The device for enhancing the carrier of the received carrier includes a carrier track circuit for separating a carrier frequency from the received carrier, and a device for combining a portion of the received carrier with the output of the carrier track circuit. A compatible amplitude modulation stereo receiver according to claim 21. 27 The carrier track circuit includes a first phase-locked loop circuit, a frequency division circuit, a second phase-locked loop circuit having a passband smaller than a passband of the first phase-locked loop circuit, and the first phase-locked loop circuit. a frequency multiplier circuit for restoring the frequency of the output of the second phase-locked loop circuit to the same wave number as the input carrier wave to the phase-locked loop circuit;
The frequency of the carrier wave input to the phase-locked loop circuit is compared with the carrier wave output of the second phase-locked loop circuit, and the upper first phase-lock circuit is set to maintain the input and the output of the carrier-wave track circuit in the same phase. 27. The compatible amplitude modulation stereo receiver according to claim 26, further comprising a circuit for controlling the phase of the output from the loop circuit. 28. A compatible amplitude modulated stereo receiver as claimed in claim 21, wherein said subaudible frequency tone is at a frequency of about 15 Hz. 29. A compatible amplitude modulated stereo receiver according to claim 21, wherein the received carrier wave is phase or frequency modulated with subaudible frequency sound. 30. A compatible amplitude modulated stereo receiver according to claim 21, wherein the received carrier wave is amplitude modulated with subaudible frequency sound.