KR880000960B1 - Multiple system am stereo reiiever and pilot signal detector - Google Patents

Abstract

The receiver for stereo AM transmissions, can receive five types of transmission. These types are the AM/FM system, the compatible quadrature system, the variable compatible phas multiplex system, the independent side band system and the phase modulation system. These use widely different frequency ranges, and the pilot signals are all detected by a detection stage connected to a logic circuit from which all five signals can be obtained. The frequency dependent recognition circuit forming the pilot signal detector produces signals from three frequency bands with two bands above and below a first band.

Description

Multisystem AM Stereo Receiver and Pilot Signal Detector

1 is a partial schematic and partial block diagram of an AM stereo receiver according to the present invention;

2 is a block diagram of a pilot signal detection apparatus according to the present invention.

3 is a block diagram of another embodiment of a pilot signal detection apparatus according to the present invention;

Figure 4 is a block diagram of another embodiment of a pilot signal detection apparatus according to the present invention.

5 is a schematic diagram of a logic circuit that can be used in the present invention.

6 is a schematic diagram of another logic circuit that may be used in the present invention.

7 is a partial schematic and partial block diagram of a control circuit and a pilot signal detector according to the present invention.

8 is a block diagram of a pilot signal detector using a microprocessor to provide digital filtering.

* Explanation of symbols for main parts of the drawings

10: multi-system AM stereo receiver 16: AM demodulator

20: phase shift circuit 30: matrix

52: limiter 54: discriminator

96, 96 ': logic circuit 66: tangent circuit

68: multiplier 72: carrier track circuit

74: nonlinear circuit 78: multiplier

94, 94 ': pilot signal detector 92: starting circuit

112, 114, 116: band pass filter 124, 126, 128: threshold circuit

130, 132, 134: flip-flop 280: amplitude detector

284 Digital to Analog Converter 286 Micro Processor

139: Stereo indicator lamp

The present invention relates to an amplitude modulation (AM) stereo receiver, and more particularly to an AM stereo receiver capable of receiving a broadcast stereo signal having respective modulation and composite amplitude applied on a carrier according to another synthesis modulation standard scheme.

At least five different methods have been proposed for the implementation of stereo phonic broadcasts related to current AM radios. See, for example, the IEEE "Spectrum" magazine, published in June 1978, page 24, "AM stereo: Five Competing Options."

Each of the five systems described herein uses different modulation techniques to provide add-on stereo capability to AM transmitters and suitably equipped receivers.

All five proposed systems provide a transmitted synthesized signal with a compatible signal format so that current monophonic AM receivers can detect monophonic audio signal components from the synthesized signal transmitted in each system. . In addition to the monophonic component, a receiver specially equipped for one of the proposed synthesis modulation standard schemes receives a stereophonic signal component, which differs between left (L) audio information and right (R) audio information. It can be decoded and synthesized with the detected monophonic signal components to provide stereophonic sound.

One of the proposed AM stereo systems uses amplitude and frequency modulation (AM / FM) to extract the composite signal for transmission. According to this proposed system, the carrier is frequency modulated with information corresponding to the difference (L-R) between the left stereo audio signal and the right stereo audio signal. The frequency modulated carrier is then amplitude modulated as a signal corresponding to the sum of the left stereo audio signal and the right stereo audio signal corresponding to standard monophonic amplitude modulation (AM) and the resulting composite signal is broadcast. As a result, conventional AM receivers using envelope detectors detect the AM or (L + R) components of the synthesized signal and provide monophonic reception. Specially equipped stereo receivers also detect the frequency modulation or (L-R) component of the composite signal. As a result, the (L-R) display audio signal can be combined with the (L + R) signal in an additive and subtractive mixture to produce separate (L) and (R) output audio signals for stereo listening.

Another of the proposed systems uses phase modulation instead of frequency modulation of carrier (AM / PM) to transmit stereo difference (L-R) information. In this system, the phase modulated carrier is amplitude modulated with (L + R) information to extract the next transmitted composite signal.

Another of the proposed systems uses a modulation technique known as compatible quadrature amplitude modulation (CQVAM) to provide modified phase modulation of a carrier with (L-R) information. The phase modulated carrier is then amplitude modulated with (L + R) information to extract the composite signal. This synthesized signal may also appear to consist of a pair of carriers at the same frequency, but the phases are separated by 90 ° (orthogonal carriers), where one carrier is amplitude modulated with left (L) stereo audio information and the other carrier is right ( R) Amplitude is modulated with stereo information.

Another one of the proposed systems is known as a variable compatible phase multiplier (V-CPM) system, which is a variation of the rectangular system. In this system, at the same frequency, the two carriers are phase separated by an amount that varies between 30 ° and 90 ° depending on the content of the transmitted audio signal. One of these carriers is amplitude modulated with left (L) stereo audio information, the other is amplitude with right (R) stereo information, and the two are linearly synthesized. As a result, the signal can be divided into an in-phase component representing the (L + R) information and a quadrature phase component representing the (L-R) information. (L-R) information below 200 Hz is removed to provide room for frequency modulated, low frequency (55-96 Hz) pilot signals that perform two functions.

It indicates the presence of a stereo broadcast, whose modulation is specifically equipped with the instantaneous phase angle between the two variable carriers so that such a receiver can track the resulting change in phase modulation in the transmitted signal. Communicate to the receiver. In a corresponding stereo receiver, the synthesized signal will provide a detected (L + R) audio signal and quadrature sync to derive a signal indicating that the (L-R) audio information is detected. The pilot signal is detected separately and its modulation can be used to vary the gain of the (L-R) signal channel to provide an equivalent variable angle receiver to track the broadcast signal. As a result, the (L + R) and gain controlled (L-R) signals are then synthesized in a conventional stereo matrix to induce the (L) and (R) signals. In addition, the developers of the system have proposed a simplified receiver that does not change the gain of the (L-R) channel. This corresponds to receiving a variable angle broadcast signal at an eclectic fixed angle instead of tracking each change.

Finally, there is a proposed system known as an independent sideband (ISB) system. The system modulates the carrier with a moderately modified (L-R) signal and then phase shifts the phase modulated carrier so that the (L + R) and (L-R) signals are in a quadrature phase relationship. As a result, the lower band of the result synthesis signal mainly contains left (L) stereo information while the upper band mainly contains right (R) stereo information (hence referred to as "ISB"). This system is also described in the inventors of US Pat. Nos. 3,218,393, 3,908,090 and 4,018,994.

The synthesized signal transmitted by each proposed system includes a low frequency pilot signal component for identifying the presence of stereo broadcast. Since the pilot signal frequency is different for each of the above mentioned systems (ie AM / FM-20HZ; AM / PM-5Hz; CQUAM-25Hz; V-CPM-55 to 96Hz and ISB-15Hz), this frequency It also uniquely identifies the modulation method used for each composite signal.

A more detailed description of these systems can be found in the aforementioned IEEE Spectrum paper and in the various patents granted to the initiators of these systems.

Although significant differences remain in the performance of the various proposed systems, it was difficult to select one of these systems as the basis for the national standard for AM stereo broadcasting. As a result, one or more of these systems may be used.

In this case, normal free competitiveness in the market will make it possible to determine whether one of the systems will eventually become a potent AM stereo system, or whether two or more systems will be able to dig.

It is therefore an object of the present invention to provide a receiver capable of receiving an AM stereo signal having a composite modulation in accordance with any one or more of several proposed modulation techniques.

Another object of the present invention is to provide an AM stereo receiver capable of detecting a pilot signal used in connection with one of several proposed AM stereo broadcasting techniques.

It is yet another object of the present invention to provide an AM stereo receiver which can be automatically distinguished as a pilot signal, some of which have been used for specially received AM stereo broadcast signals.

According to the present invention, an apparatus for determining the presence and absence of such a pilot signal is provided in a receiver for a stereophonic broadcast signal including a modulation component consisting of a pilot signal having a selected frequency characteristic.

Such an apparatus may be used for detecting a received signal component located within a first frequency band containing the pilot signal and for detecting a received signal component within another band of at least one of the frequencies located above or below the first band. Means are provided. In addition, means are provided for evaluating signals detected in these first and other bands to induce an output signal indicative of when the signal in the first band exceeds the first level and the other band signal exceeds the second level. have.

According to another aspect of the invention, a plurality of different types of AM stereos each including a modulation component having a pilot signal having a particular selected frequency characteristic for a plurality of different types of AM stereophonic broadcast signals An apparatus for indicating which type of stereophonic broadcast signal is being received by determining the presence of one of these pilot signals in the receiver for the phonic broadcast signal is provided. The apparatus includes means for detecting received signal components within a plurality of narrow frequency bands, each of which comprises only one of the pilot signals. It also evaluates the signals detected in each of these frequency bands, indicating when a signal in one band exceeds a predetermined level, and when a signal in all other bands does not exceed the level, and wherein such one band is a plurality of bands. Means for indicating which type of AM stereo broadcast signal will be received next by inducing the output signal indicative of which.

Finally, according to another aspect of the present invention, an amplitude modulation indicating stereo sum (L + R) information and a stereo difference (LR) information, which is applied to a carrier according to one of at least two synthesis modulation techniques, A receiver is provided for receiving and demodulating a composite amplitude modulated (AM) stereo broadcast signal consisting of a carrier having each modulation comprising a pilot signal component having a selected frequency characteristic indicating one such synthesis modulation technique. Such a receiver comprises means for receiving a synthesized AM stereo receiver and converting this signal into a corresponding intermediate frequency (IF) signal. It also includes means for amplitude modulating the IF signal to derive a signal representing (L + R) information therefrom.

The system is also subject to the requirements of the first and second composite modulation techniques to induce corresponding first and second audio frequency output signals indicative of (LR) information transmitted according to such first and second composite modulation techniques. Each demodulation means for demodulating the IF signal is included. Detects a received signal component that is within a first narrowband frequency that includes a pilot signal indicative of such a first synthesis modulation technique, and also detects a received signal component within a second narrowband frequency that includes a pilot signal indicative of such a second synthesis modulation technique. Means are provided for detecting received signal components that are present. The receiver also evaluates the detected signals in the first and second bands, and also indicates when a signal in only one of the frequency bands exceeds a predetermined level and in which of the two bands the signal lies in. Or means for inducing more output signals. In addition, the receiver has first and second audio output signals supplied thereto in response to the output of the evaluating means and only when the output of the evaluating means indicates that a corresponding pilot signal is present in the received signal. Means for processing the two signals.

Finally, the receiver comprises means for using the audio signal passed by the last mentioned means for deriving the (L R) indication signal and the left (L) and right (R) stereo output signals.

In addition to other and other objects of the present invention, in order to better understand the present invention, it will be described in detail with reference to the accompanying drawings. Claims will be pointed out in the appended claims.

1 illustrates an AM stereo receiver 10 of multiple systems embodying the present invention in one form. For example, the receiver 10 may receive an AM stereo signal incorporating three (ISB) stereo signals, an (AM / PM) stereo signal, and a (CQUAM) stereo signal among the proposed modulation methods.

The receiver 10 is also connected by dashed lines with additional circuitry for receiving (AM / FM) stereo signals and (V-CPM) stereo signals as will be explained later. The receiver of FIG. 1 includes a receiving antenna 12 coupled to a suitable RF frequency converter and an IF circuit 14, which may be of conventional design. The output of the demodulator 16 is coupled to the gate 18 and at the same time via the phase shift network 20 to the gate 22, which is about the audio frequency over a suitable broadband, such as 100-5000 Hz. It provides a 45 degree relative phase shift. The phase shift network 20 is required for ISB stereo signals that decode according to well known phase shift techniques. Gate 22 is actuated by an ISB control signal, denoted by (B), which is induced when an ISB pilot signal is detected by circuits 94 and 96, as will be explained in more detail. In the absence of a control signal B indicated here as a " zero " signal state, the inverter 28 provides a signal to keep the gate 18 open, which is the non-phase shift output of the AM demodulator 16. L + R) or stereo sum information) can be applied to the stereo matrix 30 via the lead 24.

When the ISB AM stereo signal is being received, the control signal B changes to the "1" signal state which opens the gate 22. The inverted control signal B closes the gate 18 and the phase shift output signal from the AM demodulator 16 is thus fed to the stereo matrix 30 via the lead 24.

The matrix 30 (LR) across the lead 32 is induced by demodulating the IF signal from the unit 14 according to the particular stereo modulation technique used for the next AM stereo signal received, as will be explained later. A stereo difference information signal is provided. Matrix 30 will be a conventional stereo matrix, such as currently used in FM stereo receivers.

The matrix 30 adds and subtracts audio (L + R) and (LR) signals and is thus separated (L) which is provided on output leads 34 and 36 and can be coupled to speakers 38 and 40, respectively. ) And (R) output signals.

The remaining circuit of receiver 10 includes circuitry 42 provided for phase demodulating a received signal having a stereo difference (L-R) modulation component in accordance with AM / PM or CQUAM modulation techniques. Circuitry 44 is provided to demodulate a received signal having a (L-R) modulation component in accordance with an ISB modulation technique.

Gates 46, 48, and 50 are provided with control signals A, C and B, respectively, in which the AM / PM, CQAM or ISB AM stereo signals are used to detect the corresponding pilot signals. Each gate opens when logic 96 determines that it is being received on the basis. For example, when the logic circuit 96 determines that an AM / PM stereo signal is being received, the control signal A is output to open the gate 46 so that the corresponding (LR) signal is transmitted to the matrix 30. Supplied. When logic 96 determines that an ISB AM stereo signal is being received, it provides control signal B to open gate 50 so that the corresponding LR signal is supplied to matrix 30. . As mentioned previously, the control signal B also changes the state of the gates 18 and 22 so that the phase shifted (L + R) signal from the network 20 is supplied to the matrix 30. do.

When the logic circuit 96 determines that a CQUAM stereo signal is being received, it provides a control signal C to open the gate 48 so that the corresponding L-R signal is supplied to the matrix 30. If none of the control signals (A), (B) and (C) is present, only the gate 18 is opened due to the inverter 26, so the receiver only applies the (L + R) signal to the matrix 30. Only monophonic performance is provided.

Receiver element 42 for phase demodulating an AM / PM stereo signal includes a limiter 52, which has an appropriate limiting effect (eg 400 db) on the received AM / PM and CQUAM composite signals. The limiter 52 effectively removes AM from the supplied IF signal and provides a limited signal (containing the PM component) to the discriminator 54, which discriminates the frequency of the limited signal. The output signal from the discriminator 54 is amplified in the amplifier 58 and corresponds to the frequency change of the limited signal. Capacitor 56 is selected to provide IF bypass for the output of discriminator 54. Resistor 60 and capacitor 62 form an integrated circuit that converts the frequency demodulated signal available at the output of amplifier 58 into a phase demodulated signal representing LR, which is then demodulated. The control signal A is supplied to the matrix 30 via the gate 46 when present to support that the received signal is an AM / PM type stereo signal.

This phase demodulated signal is also provided to a combination of tangent circuit 66 and multiplier 68 that modifies the phase demodulated signal as required for CQUAM stereo technology. Reasons for such modifications as well as alternative circuits for achieving the same results are described in the references cited earlier and in US Pat. No. 4,172,966. According to the contents of the patent, the multiplier 68 is provided with a (L + R) signal induced through the lead 70 from the output of the AM demodulator 16. The output of the multiplier 68 is supplied to the matrix 30 via the gate 48 when the control signal C is present to indicate that the received signal is a CQUAM stereo signal.

Circuitry 44 includes components used in conjunction with demodulation of the ISB stereo signal to produce a corresponding stereo difference (L-R) signal. These components include a carrier tracking circuit 72, which uses the one or more phase locked loops as described in more detail, for example, in US Pat. Nos. 3,973,203 and 4,081,994 to the inventors. Reproduce the carrier frequency signal.

The IF signal from unit 14 is coupled to carrier track circuit 72 and simultaneously to multiplier 76, where it is a demodulated stereo sum signal supplied from AM demodulator 16 via lead 23. Is synthesized with the nonlinear derivative of. The operation to be performed by the combination of the nonlinear circuit 74 and the multiplier 76 is known as amplitude modulation, or simply inverse modulation, and is fully described in the prior art US Pat. No. 4,018,994.

The output of the multiplier 76 is a carrier synthesized from another multiplier 78, the multiplier 78 acting as a synchronous quadrature detector and its output is a corresponding stereo difference (LR) signal, which is a stereo sum. Amplified in amplifier 80 to equalize for signal (L + R) channels. However, according to the phase shift technique for detecting the ISB stereo signal, the (L-R) signal present at the output of the detector 78 should be phase shifted by 45 degrees. This is accomplished in the phase shift network 86. This resulting phase shifted signal is supplied to the matrix 30 via a gate 50. Gate 50 is opened when a control signal B is provided from logic circuit 96 indicating that an ISB stereo signal is being received.

Additional circuitry is connected in dashed lines in FIG. 1 for the implementation of AM stereo reception capability. The lead 100 and the gate 102 provide a frequency demodulated (LR) signal to the matrix 30 corresponding to the case where an (AM / FM) stereo signal is being received, which means that the control signal D is a logic circuit. It will indicate when it is output from (96). The lead 104 and quadrature detector 106 are provided for simplified fixed angle modulation of the (L-R) component of the V-CPM stereo signal. The output of the quadrature detector 106 is supplied to an amplifier 108 providing increased amplification for the stereo sum signal (L + R) channel (in this case AM demodulator 16 and gate 18) for signal equalization. . The output of amplifier 108 is provided to matrix 30 via gate 110 when control signal E is provided by logic circuitry 96 instructing reception of a V-CPM stereo signal.

In the foregoing description, a reference is made to the presence of other pilot signal components in the received stereo signal, which indicates what type of stereo signal is being received (ie AM / PM, CQUAM or Used to determine if an ISB). As noted previously, the proposed modulation technique for each other AM stereo uses a low frequency pilot signal (frequency or phase modulated on the carrier) to indicate the presence of stereo broadcasts to the stereo receiver.

Since the frequency of this pilot signal depends on each of the five AM stereo systems considered here, the pilot signal can be used in an AM stereo receiver to identify which stereo broadcast technology is being received. As mentioned above, the AM / PM stereo system uses a pilot signal of 5 Hz for the stereo differential channel. The ISB system uses a pilot signal of 15 Hz, the AM / FM system uses a 20 Hz pilot signal, and the CQUAM system uses a 25 Hz pilot signal. Finally, the V-CPM system uses a pilot signal that varies between 55 Hz and 96 Hz. Since the V-CPM pilot signal frequency is in the audible range, it is necessary to remove it from the stereo output signal of the (L-R) channel for V-CPM stereo signal reception. Thus, a high pass filter 109 is provided in the V-CPM (L-R) signal channel portion of the multi-system AM stereo receiver shown in FIG. 1, for example, to pass signals above 200 Hz.

The receiver 10 of FIG. 1 receives the AM stereo signal received to generate the control signals A, B and C (also (D) and (E) when an additional dashed circuit is coupled to the receiver). Multiple pilot signal components are used for The control signal generation circuit is based on the fact that different pilot signal frequencies are used for each different AM stereo system. The control signal generated in response to the reception of the other pilot signal indicates what kind of AM stereo signal is being received, if any, and according to the type of the stereo signal received, the gate 46, 48, 50, 102 or 110 may be changed. This activates the corresponding (LR) stereo difference signal to the matrix 30 accordingly. Gates 18 and 22 also provide control signals B to provide proper gating of the stereo sum signal L + R depending on whether an ISB stereo signal or other type of stereo signal, or a monophonic signal is being received. Is activated by

The detection of the other pilot signal is performed by a pilot signal detector 94 operating in conjunction with the logic circuit 96, which logic circuits control signals (A) to () on the corresponding separate output leads (98). C) or (A) to (E). The input signal for the pilot signal detector 94 is taken from the output of the frequency detection circuits 54, 56, 58, which are integrated by the resistor-capacitor combinations 62, 60 to provide a phase demodulated audio signal. Since all five proposed AM stereo systems use each modulation technique to transmit pilot signals, it is possible to detect all system pilot signals from this phase demodulated signal. However, the pilot signal component may be detected in any respective demodulation signal, such as the frequency demodulation signal present at the output of the discriminator 54 or at the output of the quadrature detectors 78 and 106. As used herein, each modulation includes both frequency modulation and phase modulation. Although all of the systems use each modulation for a slightly different type of stereo difference (LR) signal, the phase demodulation signal appearing between the resistor 60 and the capacitor 62 is applied to the stereo difference signal (LR) component as properly demodulated. It can be seen that it may vary in phase or amplitude, but will include pilot signal components for any of these systems.

The demodulated pilot signal is amplified by transistor 88, which is connected across low resistance load 90 and is provided to pilot signal detector 94 via lead 91. This demodulated signal is also provided to the starter circuit 92 for detecting a sudden change in the output of the phase demodulation circuit. This change indicates whether the receiver was initially turned on to start up to receive the station, or if the receiver returned to another frequency in the AM broadcast band and a new station started to be received by the receiver.

A sudden change in the phase demodulation circuit triggers an output signal from the circuit 92, thus starting the pilot signal detection process executed by the detector 94 and the logic circuit 96 as will be described later. . When the alternative to detection changes in phase demodulation output, the same result can be obtained by directly detecting the operation of the on / off and tuning control of the receiver.

The capacitor 82 consists of an IF bypass capacitor connected to the circuit portion 44 for receiving the ISB stereo signal. The switch 84 is used in one embodiment to provide a timing signal for the pilot signal detector 94. The skilled person can connect the capacitor 82 directly to the output of the quadrature detector 78, in which case the switch 84 is the timing of the capacitor 56 or pilot signal detector 94 as will be described later. It will be appreciated that it can be connected to a separate capacitor provided for use only in connection with it.

Referring to FIG. 2, there is shown in block form a pilot signal detection circuit 94 'that may be used for the multi-system AM stereo receiver of FIG. 1 as well as for a single system AM stereo receiver as will be described later.

The output of the amplifying transistor 88 of FIG. 1 is supplied to the band pass filters 112, 114, and 116 via the lead 91. In a single system receiver in which only a single pilot signal should be detected, the band pass filters 112, 114, and 116 are each arranged to pass a band of the same and above frequencies, each of which is below a predetermined pilot signal frequency. Narrowband filter. Thus, if the circuit 94 'of FIG. 2 is used to detect, for example, only an AM stereo pilot signal, the filter 114 would be a narrowband filter, for example passing 15 Hz ± 2.5 Hz. In this case, the filter 112 will be tuned below the nominal pilot signal frequency and will pass 10 Hz ± 2.5 Hz, for example, and the filter 116 will have a higher frequency than the expected pilot signal, for example 20 Hz ±. It will be tuned at 2.5Hz. Each filter 112, 114, 116 is coupled to a corresponding detection circuit 119, 120, 122 and then to one of the threshold circuits 124, 126, 128. If only the pilot signal, which is a nominal signal frequency of 15 Hz, appears on the lead 91 with sufficient amplitude, the detector 120 exceeds the threshold set in the threshold circuit 126 and thus sets the flip-flop 132. Will provide a signal.

Since it has been assumed that substantially no signal is present in the pass band of the filters 112 and 116, the flip-flops 130 and 134 will not be set by the corresponding threshold circuits 124 and 128.

Since substantial noise or other unwanted signals will be wide enough, the detectors 119, 120, 122 will all have enough output to trigger their corresponding threshold circuits 124, 126, 128 if they appear on the lead 91. Therefore, all flip-flops 130, 132, 134 will be set. For noise with a low noise level or other spectral form, only two of the flip-flops will be set, for example (130, 132) or (132, 134). After a time interval sufficient for the narrowband filters 12, 114, 116 and the detectors 119, 120, 122 to respond to the received pilot signal and / or noise, the logic circuit 96 ′ flips the flip-flop 130, Outputs on lead 142 indicating the presence of a predetermined 15 Hz pilot signal only when corresponding flip-flop 132 is set and other flip-flops 130, 134 are not set by evaluating the output of 132, 134. Provide signal B.

If more than one flip-flop is set, the logic circuit 96 'concludes that the flip-flop was triggered by noise or other unwanted signals and no output signal is generated.

In the configuration shown in FIG. 2, a pilot signal detector 94 'and logic 96' may also be used to detect three pilot signals corresponding to three of the five proposed stereo systems. In one embodiment, shown by the solid line of receiver 10 in FIG. 1, the receiver is employed to receive three types of AM stereotransmissions. The first type, represented by control signal A, is AM / PM technology with a pilot signal frequency of 5 Hz. The second type, denoted as control signal B, is an ISB technique with a pilot signal frequency of 15 Hz. The third type, denoted as control signal C, is CQUAM technology with a pilot signal frequency of 25 Hz. For the circuit 94 'shown in FIG. 2 to be used in connection with the detection of these three pilot signals, the filters 112, 114, and 116 will each be arranged to pass only one of the pilot signal frequencies. Thus, filter 112 would be arranged to pass 5 Hz ± 1 Hz, filter 114 would be arranged to pass 15 Hz ± 1 Hz, and filter 116 would be arranged to pass 25 Hz ± 1 Hz. Therefore, each of the flip-flops 130, 132, 134 will be set by the output of the threshold detectors 124, 126, 128 indicating the presence of the corresponding pilot signal. In addition, the logic circuit 96 'determines which of the flip-flops 130, 132, 134 is set so that the presence of one of the pilot signals is only present if its corresponding flip-flop is set and the other flip-flop is not set. A control signal output is provided on one of the indicating control leads 140, 142 and 144. When two or more flip-flops are set, no control signal is generated by the logic circuit 96 '. Only by such explicit indication of the received pilot signal is it possible for the receiver 10 to be placed in the stereo reception mode by the activation of the gate or gates corresponding to the stereo modulation technique indicated by the received pilot signal.

The logic circuit 96 'is reset by the output of the starter circuit 92 via the lead 93 as shown in FIG. 2 and this signal also turns the flip-flops 130, 132 and 134 at terminal C. Used to reset or clear it. The logic circuit 96 'is provided with a timing signal T ₃ indicating the time at which the output of the flip-flops 130, 132, 134 should be evaluated, as will be explained later. Output 136 from logic 96'indicates that no explicit determination of which of the pilot signals has been received and may therefore be provided to allow the receiver to operate in monophonic mode. The logic circuit 96 'also includes an output lead 138 connected to the stereo indicator lamp 139. The circuit 96 'provides a signal on the lead 138 whenever one of the control signals A, B and C is generated.

3 is a block diagram of another embodiment of a pilot signal detector and logic circuit according to the present invention. The pilot signal detection circuit embodiment 94 shown in FIG. 3 is used in connection with pilot signal detection as in all five cases of the AM stereo broadcast system described previously. Referring to FIG. 3, there is shown a control circuit 146 that receives a start signal from the starter circuit 92 via the lead 93. Controller 146 provides control signals to voltage controlled narrowband band pass filter 148, threshold circuit 150, flip-flops 152, 154, 156, 158, 160, and logic circuit 96. . The control voltage supplied to the filter 148 initially sets this filter to the frequency of the first pilot signal, for example the 5 Hz pilot signal of the AM / PM stereo system.

This filter is maintained at a frequency of 5 Hz for a sufficient time period, for example 300 milliseconds, to provide an output to threshold circuit 150. The circuit 150 detects the signal appearing at the output of the filter 148 and compares it with an adjustable threshold set by the detected signal and the control signal from the unit 146. Flip-flop 152 is adjusted to respond to the output of threshold detector 150 during this initial period, and if the output of filter 148 triggers threshold detector 150 during this initial first sampling period, flip The flop 152 will be set. Control logic 146 provides a control signal to flip-flop 152 to enable it only during this first period of time.

Subsequent to 5 Hz sampled by the filter 148 during the first period, the control signal 146 supplies another control signal voltage to the controllable band pass filter 148 and supplies it to a second frequency, for example an ISB stereo system. Reset to the 15 Hz pilot signal frequency used in the. The control circuit 146 may also supply the control signal to the threshold level 150 to adjust the threshold level corresponding to the expected intensity of the ISB pilot signal. Threshold detector 150 sets flip-flop 154 when it detects a 15 Hz signal during this second sampling period, which is set to be set only during this second sampling period by control circuit 146. It can be enabled or conditioned.

At the end of the second period, the control circuit 146 resets the band pass filter 148 to the next pilot signal frequency, for example the 20 Hz pilot signal of the AM / FM stereo system. The flip-flop 156 is set when a 20 Hz signal is detected by the threshold circuit 150 during the third sampling period. Similarly, flip-flops 150 and 160 are fourth when bandpass filter 148 is tuned to a 25 Hz pilot signal used in a CQUAM stereo system and then to a variable frequency of 55 to 96 Hz used in a V-CPM stereo system. And when the threshold detector 150 detects the signal only for the fifth period of time. Alternatively, because of the wider bandwidth required, it is necessary to gate in the separate filter to detect the pilot signal of the variable frequency used in the V-CPM system.

Flip-flops 152, 154, 156, 158, 160 depending on whether the signal is to be detected in each of the pilot signal pass bands by sequentially sampling different frequency bands for five different frequency bands for five consecutive periods. After setting, the logic circuit 96 is operated by the timing signal T ₃ to enable the logic circuit to evaluate the output of the flip-flops 152, 154, 156, 158, 160.

The logic circuit 96 operates in a similar manner to the logic circuit 96 'shown in FIG. 2 to operate the corresponding gate in the receiver of FIG. 1 only when the pilot signal is detected as present during the first five sample periods. Outputs (A), (B), (C), (D) and (E) on lead 98. In addition, a separate signal is provided on the lead 138 when the stereo indicator lamp 139 is to be operated. If more than one signal in the pilot signal band is detected, the results indicate the ambiguity that the AM stereo modulation technique is present in the received 1F signal, or that significant noise or other unwanted signals are present. Thus, this state logic 96 will provide any output for any of the leads 98, 138, and the stereo indicator lamp 139 will not turn on. Therefore, receiver 10 will operate in monophonic mode until such time as a single pilot signal has been detected during the full sampling period.

The circuit 94 of FIG. 3 operates by sequential sampling of different frequency bands, while the circuit 94 'of FIG. 2 operates to sample all frequency bands of interest simultaneously. The skilled person can use sequential or simultaneous sampling to detect one or more of the other pilot signals. According to the initial sampling by the logic circuit 96 of all the outputs of the flip-flop of FIG. 3, when no single pilot signal is determined to exist, the control circuit 146 is reset to reset the pilot signal once or several times. It would be desirable to repeat the detection process. Recycling may be stopped once only a single pilot signal has been detected during the sampling period. This function can be implemented, for example, by feedback from logic circuit 96 to control circuit 146.

4 illustrates another pilot signal detection and logic arrangement using a microprocessor programmed to perform the logic functions described with reference to FIGS. 2 and 3. The start-up circuit 92 provides an initial signal to the microprocessor 162, which then provides a variable band pass filter 148 to provide sequential sampling of several pilot signal frequency bands as described with reference to FIG. And control the threshold detector 15.

The output of the threshold detector 150 for each frequency band can be inspected by the microprocessor 162 and the result is later to determine whether one and only one pilot signal has been detected during the sampling period. It is remembered here for interpretation.

8 illustrates other pilot signal detectors and logic circuits that use microprocessors for narrowband filtering as well as logic functions. A lead 91 carrying a phase detection pilot signal is coupled to an amplitude detector 280, which may include a lowpass filter to remove high frequency audio modulation components. Detector 280 supplies the detected output to integrator 282, which also averages this signal over a suitable time period (e.g., 1-10 milliseconds) to remove high frequency components.

The integrator output is converted by the analog-to-digital converter 284 into a digital signal every hour and a digitized signal level is provided to the microprocessor 286 for analysis. The microprocessor takes a weighted sum over a digitized detection signal for several pilot signal frequencies and compares this weighted sum to a preselected threshold to determine the presence or absence of a particular pilot signal or signals of interest. Digital filtering can also be performed. An advantage of this embodiment of the present invention is that the analog to digital converter 284 needs to handle one signal polarity, thus simplifying the design of the block 284. However, a good arrangement removes the detector 180 and integrator 282 and directly converts the signal on the lead 191 in digital form in the analog-to-digital converter 284 and then digitally processes it in the microprocessor 286. Convert all signals. This procedure avoids the undesirable generation of nonlinearities caused by the action of the detector 280.

3 and 4 show control leads from control circuit 146 or microprocessor 162 to threshold detector 150. This control lead derives from the fact that different amounts of each modulation are used to extract the various AM stereo broadcast signals, and adjusts the threshold level of the threshold detector appropriately to compensate for differences in the expected signal strength among the pilot signals. Used. This will be apparent to the skilled person from examination of the broadcast signal specifications that have been published for each of the proposed AM stereo systems.

FIG. 5 is a circuit diagram of a logic circuit 96 'that can be used in connection with the pilot signal detection arrangement of FIG. 2 for the purpose of detecting the presence of a single pilot signal and the absence of the signal in adjacent frequency bands.

As previously described with reference to FIG. 2 for the detection of a single pilot signal, for example an ISB pilot signal, the flip-flops 130, 132, 134 are at or below the frequency of the pilot signal at which the signal is expected, It is set according to whether or not a frequency is detected at a frequency above that frequency. Assuming a predetermined pilot signal has been received and no signal has been detected in the frequency band above and below the pilot signal frequency, the flip-flop 132 will be in the set state, while the flip-flops 130 and 134 are in the set state. Will not be. The set state of flip-flop 132 raises the output level on lead 184 to represent a binary "1" if flip-flop 180 is in the set state and transistor 176 is conducting as described later. Reverse bias is generated on the diode 166. If there is a "1" output from flip-flop 130 or 134, the high output will be conducted through diodes 172 and 174, thereby conducting transistor 176.

This will lower the output on lead 184 to a "zero" signal state. This condition will occur if there is a signal detected in the frequency band below or above the frequency band of the pilot signal of interest and will support that the signal setting flip-flop 132 may be caused by noise. . The flip-flop 180 is cleared by the start signal on the lead 93 supplied from the circuit 92. While cleared, diode 178 is inverted and the output on lead 184 becomes " 0 ". Flip-flop 180 is set by timing signal T ₃ indicating that the time for sampling three frequency bands is complete. When flip-flop 180 is set, diode 178 is reverse biased, and a " 1 " output is supplied on lead 184 if " 1 " appears at the output of flip-flop 132. The amplifier 182 is connected to the lead 184 to drive the stereo indicator lamp 139. Therefore, circuit 164 operates to provide an " 1 " output on lead 184 when flip-flop 132 is set and flip-flops 130 and 134 are not set. The output on lead 184 is enabled after the difference signal T ₃ is provided to flip-flop 132.

6 is a more complex logic circuit arrangement for use in connection with the detection of one of three different pilot signals. For example, this logic circuit can be configured to receive AM / PM stereo signals with a pilot signal of 5 Hz, ISB stereo signals with a pilot signal of 15 Hz, or CQUAM stereo signals with a pilot signal of 25 Hz. It can be used in connection with the receiver. Flip-flops 130, 132, and 134 are simultaneous or sequential bandpass filters and threshold detection (as shown in Figures 2 and 3) tuned to 5, 15, and 25 Hz pilot signal frequencies. Controlled by a circuit.

"0" in which the flip-flop 130 is in a "1" state instructing reception of a pilot signal at 5 Hz and flip-flops 132 and 134 are indicative of no reception of a signal other than the pilot signal at 15 and 25 Hz. If it has an output, the output lead 140 corresponding to the control signal A is enabled. The positive output of flip-flop 130 reverse biases diode 186. If none of the transistors 198, 216 or 218 are conducting, the diode 202 is reverse biased. Each of these transistors will only conduct if two of the flip-flop outputs have a "1". For example, transistor 198 has a base connected to the outputs of flip-flops 130 and 132 through diodes 192 and 194. These diodes are also connected to a positive voltage source through a resistor 196.

If both flip-flops 130 and 132 are of " 1 " output, these diodes will both be reverse biased, and transistor 198 conducts diode 202 to conduct and conducts the output on lead 140 to " 0 " "State. Similarly, trap resistor 216 having a base connected to a constant voltage source by resistor 212 and connected to the outputs of flip-flops 130 and 134 by diodes 204 and 206 is provided with flip-flops 130 and 134. Both will conduct if they have a constant voltage or "1" output. Flip-flops 132 and 134 through transistor 218 which are also connected to the constant voltage source through its base by resistor 214 and to the output of flip-flops 132 and 134 through diodes 208 and 210. Transistor 218 connected to the output of will conduct if the outputs of both flip-flops 132 and 134 have a positive " 1 " signal. Thus, the combination of transistors 198, 216 and 218 will draw the voltage through the diode 202 when any pair of two flip-flops has a "1" output. This provides an “0” output to the output lead when any pair of flip-flops has a “1.” The output control signal on leads 142 and 144 is likewise connected to these transistors by diodes 220 and 222. And connected to each flip-flop through diodes 188, 190. Thus, each output lead 140, 142, 144 has its corresponding flip-flops 130, 132, 134 having an " 1 " Only if this and all other flip-flops have a "0" output will be enabled.

The circuit diagram of FIG. 6 also includes circuitry for providing a stereo indicator output. The output of all three flip-flops is connected to transistor 234 through resistor 238 via diodes 224, 226, 228. Any of the flip-flops 130, 132, 134 has an "1" output, and as previously described, the base of the transistor 234 is pulled down by the operation of the flip-flop 180 through the diode 230. If not, transistor 234 is conducting.

This applies a low voltage input to transistor 232 which would otherwise be in a conductive state because of the voltage provided from the constant voltage source through resistor 236. Therefore, transistor 232 is turned off to bring the voltage on lead 241 to a high level.

This voltage will be at a high level if none of the transistors 198, 216, 218, as described above, will be low. An output signal is provided on 241. The output on the lead 241 is provided to the stereo indicator lamp 139 via the driver 242. Inverting circuit 244 may also be provided on lead 136 to output an output signal indicative of monophonic reception. As discussed above, the flip-flop 180 is associated with the diode 230 to hold the input to the transistor 234 in low state until the completion of the pilot signal detection cycle time as indicated by the timing signal T ₃ . It works.

As previously mentioned in connection with FIG. 1, the capacitor 82 used as the IF bypass capacitor for the stereo channel also switches 84 to provide timing signals for operation of the pilot signal detector 94 and logic circuit 96. Can be used in connection with 7 is a diagram illustrating the operation of this type of timing circuit. Switch 84 has one pole connected to the output of right angle detector 78 and the other pole connected to a constant voltage source via resistor 240. The output of the switch 84 is connected to the bypass capacitor 82. During normal stereo reception, switch 84 is in the left position and connects bypass capacitor 84 to the output of quadrature detector 78 for IF bypass. When the start-up circuit 92 indicates a sudden change in output from the discriminator 54 and the integrators 60 and 62, a start signal is provided to the switch 84 on the lead 93, which is a resistor. 246 and the switch is operated to couple the capacitor 82 to a constant voltage source. This connection to the resistor 246 applies the ramp voltage supplied to the threshold circuits 250, 252, 254 to the lead 248.

The start signal is also applied to a tunable band pass filter 256 at the input denoted f ₁ to reset the band pass filter to the sampled first frequency band. When the ramp voltage on the lead 248 reaches the first threshold state indicated by (e ₁ ), the threshold circuit 250 changes the filter center frequency to (f ₂ ) corresponding to the second pilot signal frequency. Trigger on providing output T ₁ to band pass filter 256. This signal is also provided across lead 258 to gate 260 connecting resistor 270 into threshold circuit 268 to lower its threshold. For example, in systems for detecting 5 Hz, 15 Hz and 25 Hz pilot signals, it is appropriate to lower the threshold to increase the sensitivity of the threshold circuit in order to receive weaker pilot signals. After a while, the ramp voltage on the lead 248 triggers a threshold circuit 252 that provides an output T ₂ that changes the band pass filter 265 to a third frequency, denoted by (f ₃ ), thereby providing a second threshold value. (e ₂ ) is reached. After some more time, the voltage on the lead 248 reaches a value e ₃ that triggers the circuit 254 providing the output T ₃ , which causes the switch 84 to be stereo in the ISB channel. It switches to the IF bypass state to detect the difference signal and provides a reset for the starter circuit 92. The appropriate timing value determined by the ramp voltage on the lead 248 is about 300 milliseconds when the start signal is generated with the output of the (T ₁ ) signal and 300 milliseconds when the output of the (T ₂ ) signal is (T ₃ ) Another 300 milliseconds for signal output.

This signal period should provide the phase splitter 262, diode detectors 264 and 266 and the threshold circuit 268 with a suitable time for passing the signal through the band pass filter 256.

As described above, following the output of the (T ₃ ) signal, when a single stereo pilot signal is correctly identified, the stereo indicator signal will reset the operation of the start-up circuit 92. However, if the stereo pilot signal is not correctly identified, the startup circuit 92 may be used to restart the search cycle for the stereo pilot signal.

Alternatively, one or a selected number of search cycles may be created to operate in monophonic mode when no pilot signal is detected. The receiver will be on the left side of the monophonic mode until it returns to another AM station or shuts off, or after some selected time period that can begin another search cycle. This is simply a matter of choice for a particular receiver designer, which will be apparent to the skilled artisan, given what is described later here.

In the various examples described above, specific embodiments have been described for practicing the present invention by using both analog ramp voltages and digital timing signals. Those skilled in the art will recognize that this signal format can be used by varying embodiments of the present invention and these are not limited to the above examples only. Similarly, the skilled person may be replaced by an integrated circuit or other logic element that performs the same function, although specific logic circuits as described in FIGS. 5 and 6 are given by way of example only.

The skilled artisan can employ any of the five other proposed AM stereo signals described herein in which the bonded embodiment of the receiver shown in solid lines in FIG. 1 is capable of receiving AM / PM stereo signals, CQUAM stereo signals and ISB stereo signals. It may be arranged to receive two or more signals and such modifications and variations are considered to fall within the scope of the invention as described in the claims.

While what is believed to be a suitable embodiment of the present invention has been described, the skilled artisan can understand that other modifications can be made without departing from the spirit of the invention and claim all such changes and modifications that fall within the true scope of the invention. I was trying to.

Claims (14)

A stereo phone broadcasting signal receiver comprising a modulation component consisting of a pilot signal having a selected frequency characteristic, comprising: a stereo phone broadcasting receiver having a device for determining the presence or absence of the pilot signal. Band pass, which is a frequency detection device for determining a received signal component that lies within a first frequency band comprising, and for detecting a received signal component that lies within at least one other frequency band located above or below the first frequency band. The filters 112, 114, and 116 and the signals detected in the first and other frequency bands are evaluated, and the signal in the first frequency band exceeds the first level and the signal in the other frequency band is the second level. A pilot signal detector (9), which is a signal evaluation device for generating an output signal indicating when not exceeding 4, 94 ', 94 "). 2. The band pass filter (112, 114, 116) according to claim 1, characterized in that it detects received signal components lying in second and third different frequency bands above and below the first frequency band, respectively. Stereo phone broadcast signal receiver. 3. The receiver of claim 2, wherein the pilot signal has a narrow band frequency characteristic, and the first, second and third frequency bands are narrowed accordingly. 4. The receiver of claim 3, wherein the pilot signal may be slightly different and is substantially a single frequency tone. 5. The pilot signal detector of claim 4, wherein said pilot signal detectors 94, 94 ', 94 " are detected in said first band having a characteristic of said pilot signal and exceed a first threshold value for a selected evaluation period. And generating an output signal only when no signal is detected in any of the second and third other adjacent bands exceeding a second threshold value during the selected evaluation period. 6. The receiver of claim 5, wherein the band pass filter simultaneously detects signals of the first, second and third frequency bands. 6. The receiver of claim 5, wherein the band pass filter sequentially detects the signals of the first, second and third frequency bands in a predetermined order. A receiver according to claim 1 for receiving a plurality of different types of AM stereophone broadcast signals each comprising a modulation component comprising a pilot signal having a selected frequency characteristic that is specific for the type of AM stereophone broadcast signal. The pilot signal detector indicates when a signal of one of the bands exceeds a predetermined level and a signal of all other bands does not exceed the level, and which one of the plurality of bands is the one band. And an output signal for indicating which type of stereophone broadcast signal is to be received next. 9. The pilot signal detector according to claim 4 or 8, wherein the pilot signal detector has a plurality of outputs each representing a corresponding one of the same number of AM stereophone broadcast signal types, and the output signal of the pilot signal detector is a plurality of outputs. A receiver for a stereophone broadcast signal, supplied from one of the outputs, thereby indicating which type of AM stereophone broadcast signal is received next. 10. The method according to claim 9, wherein the band pass filter and the pilot signal detector are operated periodically so that a new evaluation of signal contents of the plurality of frequency bands is performed during each period when the band pass filter and the pilot signal detector are operated. Receiver for a stereo phone broadcast signal comprising a device to. A composite amplitude modulation technique having a carrier with an amplitude modulation indicating stereo sum (L + R) information and a carrier for each modulation indicating stereo difference (LR) information applied to a carrier according to one of at least two synthesis modulation techniques. A receiver for receiving and demodulating an (AM) stereophone broadcast signal, the receiver further comprising: a pilot signal having a selected frequency characteristic in which each modulation represents the one synthesis modulation technique, the receiver receiving an AM stereo signal; And frequency demodulating the IF signal with the antenna 12 and the IF circuit 14, which are devices for converting the corresponding intermediate frequency (IF) signal to the (L + R) information. A receiver according to any one of the first, second, third, fourth, fifth, sixth, seventh or eighth parts having a demodulator 16 for extracting a signal, according to the requirements of the first and second synthesis modulation techniques. Each demodulation device 20:52 to 68 for demodulating an IF signal to generate corresponding first and second audio frequency output signals representing (LR) information transmitted according to the first and second synthesis modulation techniques, respectively. : 72 to 86), the receiver for a stereo phone broadcast signal. Synthetic Amplitude Modulation (AM) Stereo with an Amplitude Modulation Representing Stereo Sum (L + R) Information Applied to a Carrier and Each Modulation Representing Stereo Difference Information According to at least Two Different Synthesis Modulation Techniques A receiver for receiving and demodulating a phone broadcast signal, wherein each modulation further comprises a pilot signal component having the selected frequency characteristic, wherein said modulation represents a particular one of said composite modulation techniques used to generate a broadcast signal. A receiver according to claim 1 for use in a multisystem AM stereo system, comprising: receiving a synthetic AM stereo radio frequency (RF) signal and converting the RF signal into a corresponding intermediate frequency (IF) signal; An antenna 12 and an IF circuit 14 and detecting the presence of an AM stereo pilot signal component in the received signal A discriminator 54 for determining a frequency characteristic of the pilot signal and for generating at least one control signal indicative of the specific composite modulation indicated by the pilot signal when the presence of the pilot signal is detected. A signal detector 94 and a logic circuit 96 and a different mode suitable for amplitude modulation and each modulation of an IF signal according to at least two of the different synthesis modulation techniques, wherein the control signal is any of the synthesis modulation techniques. In order to properly demodulate the IF signal to generate a pair of output signals representing (L + R) and (LR) information, respectively, when indicating reception of an AM stereo signal according to one technique, it may be selected in response to the control signal. To generate the left (L) and right (R) stereo audio output signals and circuit sections 42 and 44 which are decoding devices capable of operating in different modes Group (L + R) and (L-R) stereo phone broadcasting signal receiver comprising the matrix 30 and the output lead (34, 36) responsive to the display signal. 13. A circuit according to claim 12, wherein the circuit parts (42) and (44) generate only (L + R) output signals when the control signal appears that the AM stereo signal is not present in the received signal. Stereo phone broadcast signal receiver. 13. The circuit of claim 12, wherein the circuitry (42), (44) is of a first mode suitable for decoding an IF signal in accordance with an ISB composite modulation technique and a second mode suitable for decoding an IF signal in accordance with a CQUAM modulation technique. Receiver for stereophone broadcast signal, characterized in that it can operate as.

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