JPH07226721A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To provide an FM stereo receiver in which the correlation between a monaural signal component and a stereo signal component is utilized and also the S/N of a multiplexed stereo signal at a weak electric field is improved by using a narrow band filter group in an FM broadcasting receiver. CONSTITUTION:A stereo signal is divided into an upper side band and a lower side band by branching filters 18, 19, synchronization-detected at synchronization detectors 20,21 and the result is fed to narrow band pass filter BPF groups 24, 25 and a monaural signal is fed to a narrow band pass BPF group 23. Outputs of the narrow band pass filter groups 23-25 are fed to an AM processing section 26, the outputs are synthesized by a synthesis circuit 27 and the synthesized signal is fed to an electronic switch 30. The electronic switch 30 receives the stereo signal obtained from the sum of the outputs of the synchronization detectors 20, 21 and selects its contact (a) or (b) from an output level of an LPF 29 based on an output of a synchronization detection circuit 22. Thus, a signal of a channel having a component of a stereo signal ES and a noise and a signal of only a channel having a signal with correlation to the monaural signal in common to the narrow band pass filter BPF groups 24, 25 are extracted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM stereo receiver, and more particularly to a left and right sum signal and a difference signal obtained from an FM demodulation output, and amplitude-modulating these two signals by a subcarrier to obtain a left ear signal and a right ear signal. The present invention relates to an FM stereo receiver suitable for obtaining

[0002]

2. Description of the Related Art FIG. 6 shows a noise distribution OADE of a demodulated signal (baseband signal) of an FM reception signal, a difference signal ((monaural signal EM (0 to 15 KHz)) and a sum signal (stereo signal ES (= EScos2ωpt (38 KHz)). 6), the noise shown by the triangle OAB is added to the monaural signal EM in the FM demodulation, and the quadrangle CDE is added to the stereo signal ES in the FM demodulation.
A component coherently detected by the noise cos2ωpt component indicated by F is added.

FIG. 7 is a block diagram showing the principle configuration of a conventional FM receiver. 1 is an antenna output, 2 is a frequency converter, 3 is a local oscillator, 4 is a limiter, 5 is an FM discriminator, and 6 is Narrow band BPF (narrow band band pass filter), 7 is a subcarrier oscillator, 8 is an LPF (low pass filter), 9 is a BPF, 10 is a synchronous detector, 11
Is an LPF, 12 is a matrix circuit, 13 and 14 are de-emphasis circuits, 15 is a right ear signal output (ER), 16
Is the left ear signal output (EL).

In FIG. 7, the receiving antenna output 1 is applied to the frequency converter 2 and the difference frequency from the output signal of the local oscillator 3 is taken to be converted into an intermediate frequency (IF) of 10.7 MHz and the limiter 4 and the FM discriminator. The baseband signal is demodulated via 5. Here, in FIG. 6, a triangle O
The triangular noise indicated by EF is the noise of the output of the FM discriminator 5. FM discriminator 5
The output of is a narrowband BPF6 with a pilot signal (fp = 19
KHz) is taken out and the cos2ωpt component is generated by the subcarrier oscillator 7 of 2fp = 38KHz.

Further, the output of the FM discriminator 5 is added to the LPF 8 and the BPF 9, and the monaural signal EM shown in FIG. 6 and the stereo signal EScos2ωpt are separated.
Specifically, the monaural signal EM is obtained by the LPF 8 in the band 0 to 15 KHz, and the band 23 KHz to 53 KHz (38 KHz ± 15
The stereo signal EScos2ωpt is obtained by the BPF 9 of KHz).

Further, the output of the BPF 9 is added to the synchronous detector 10 to obtain the product of the output of the subcarrier oscillator 7 and the cos2ωpt component, and the output is passed through the LPF 11 to take out the stereo signal ES and the matrix circuit 12 The right ear signal (ER) 15 and the left ear signal (EL) are obtained by the following mathematical expression (1).

[0007]

ER = EM + ES; EL = EM-ES (1) Finally, the output of the matrix circuit 12 is lowered in the high frequency range by the de-emphasis circuits 13 and 14, and the right ear signal (ER) is obtained.
15. Get left ear signal (EL).

[0008]

In the above conventional FM stereo receiver, the monaural signal EM that is the output of the LPF 8 and the stereo signal EScos that is the output of the BPF 9 are provided.
2ωpt is a triangle OAB and a quadrangle CD as shown in FIG.
Since noise of EF is added, there is a problem that the stereo signal ES, which is the output of the LPF 11, is about 20 dBS / N lower than that of the monaural signal EM in a weak electric field. For this reason, when stereo is received in a weak electric field, noise is conspicuous, and the listener is forced to listen in monaural mode. As a technique for solving such a problem, there is an improvement method utilizing the correlation of stereo signal components disclosed in Japanese Utility Model Publication No. 4-19862 (FM stereo receiver).

FIG. 8 is a diagram for explaining the S / N improvement principle of the FM stereo receiver disclosed in Japanese Utility Model Publication No. 4-19862, and FIG. 9 is the FM stereo receiver disclosed in Japanese Utility Model Publication No. 4-19862. 11 is a block diagram showing a configuration, and FIG.
FIG. 10 is a detailed block diagram around the signal processing circuit of FIG.
The M demodulator 91 corresponds to the configuration of the frequency converter 2 to the FM discriminator 5 in the conventional FM stereo receiver shown in FIG. 7, and each of the components 6 to 10 corresponds to the components 6 to 10 of the device of FIG. It corresponds to the configuration.

In FIG. 9, the output EM (monaural signal) of the low-pass filter (LPF) 8 and the output ES (stereo signal) of the synchronous detection circuit 9 are applied to the demultiplexers 97 and 98 each including a plurality of narrow band filter groups. Add (frequency characteristics of the duplexers 97 and 98 are equal). Here, FIG. 8A shows the duplexer 97 for the monaural signal EM, and FIG. 8B shows the duplexer 98 for the stereo signal ES (each is an example of 8 channels). .

Generally, a monaural signal EM and a stereo signal E
Since the spectrum distribution of S often has a correlation, when the signal S1 is present in the channel # 6 of the demultiplexer 97, the signal S1 ′ (stereo signal) is present in # 6 ′ corresponding to the channel # 6. To do. Here, the channels # 1 to # 8 of the monaural signal EM are amplitude-detected for each channel, and the channel of the stereo signal ES (# 6 in the example) corresponding to the channel (for example, # 6) in which the signal S1 equal to or more than the threshold exists.
Take out only, do not output other channels. As a result, it is assumed that channel # 5 'in FIG.
Since noise is not output even if there is noise, the S / N of the stereo signal ES is improved.

In view of the above-mentioned technique, the present invention provides an improvement method utilizing the correlation between a monaural signal component and a stereo signal component, and in addition, in a weak electric field, the S / N ratio of a stereo signal multiplexed by an FM broadcast receiver is It is an object of the present invention to provide an FM stereo receiver which can be improved by using a narrow band filter group and can realize improved sensitivity. Specifically, in order to improve the S / N ratio of the stereo signal of the FM received signal, it is practically fair 4-19862.
In addition to the improvement method utilizing the correlation of the frequency components disclosed in No. 1, the symmetry of the upper sideband and the lower sideband of the stereo signal is used to achieve a significant improvement in S / N. Also, FM radio and dcc (digital compact case)
tte) and a device for compressing a signal processing system as a narrow band filter for an audio signal in a composite device.

[0013]

In order to achieve the above object, an FM stereo receiver of the present invention separates an output signal obtained by FM demodulation into a sum signal and a difference signal, and performs matrix processing on the both signals. FM to obtain left and right ear signals
In a stereo receiver, first and second demultiplexers for separating a sum signal into upper sidebands and lower sidebands, and upper sidebands and lower sidebands are divided into a plurality of different frequency domain channels and output. And a fifth demultiplexer that divides the difference signal according to the number of channels in the same frequency region as the third and fourth demultiplexers, and outputs the divided signal. ，
A signal synthesizer for controlling the output of each frequency domain channel based on the level of the sum and difference of the output components of the fourth and fifth demultiplexers and synthesizing the outputs to obtain a synthesized signal; And a signal processing unit that performs matrix processing by selecting either the combined signal or the sum signal based on the noise level of the output signal obtained by demodulation.

[0014]

In order to achieve the above object, the FM stereo receiver of the present invention takes out only the frequency domain channels having a certain value or more, which are contrasting with each other in the upper sideband and the lower sideband in the sum signal, and further subtracts them from the sum signal. Since only the frequency domain channel of the sum signal having the frequency component of the difference signal is selected and output using the correlation with the frequency component of the signal, the S /
N can be significantly improved, and sensitivity can be improved.

[0015]

4 and 5 are diagrams for explaining the S / N improvement principle of the FM stereo receiver according to the present invention. In FIG. 4, the stereo signal EScos2ωpt is divided into the upper sideband and the lower sideband with the subcarrier frequency 2fp as the boundary. Shows that the noise is present in fN here. Note that the units of frequency (horizontal axis) are different between FIG. 4 and FIG.

In the present invention, the stereo signal EScos of FIG.
The upper sideband and the lower sideband of 2ωpt are cos2ωp
Synchronous detection is performed at t and added to the filter group of FIGS. The monaural signal EM is also added to the filter group of FIG. Note that the configurations of the n channels of the three filter groups in FIGS. 5A, 5B, and 5C are the same, and here, the case of n = 8 is taken as an example.

In FIG. 5, the signal S1 is channel # 7 (#
7 ', # 7 ") and noise N1 is present in # 6', # 6".
However, it is assumed that the noise N2 exists in # 4 '. That is, the noise N2 is present only in the upper sideband of the stereo signal ES, and the noise N1 is present in the upper sideband and the lower sideband.

In comparison between FIG. 5 (a) and FIG. 5 (b) k, # 6 ', # 6 "with the stereo signal ES common to both filter groups.
And the noise signals # 7 'and # 7 "are output. Further, only the channel having the signal is output by taking the correlation with the monaural signal EM and the signal S1 is extracted. Is not output, the S / N of the stereo signal ES is significantly improved.

FIG. 1 is a block diagram showing the configuration of an embodiment of an FM stereo receiver according to the present invention.
The configurations of 9, 10 and 12 correspond to the configurations of the corresponding numbers of the FM receiver of FIG. Further, in FIG. 1, 17 is a 90 ° phase shifter, and 18 and 19 are demultiplexers, each of which is composed of a separation filter for an upper sideband and a lower sideband with ωc as a boundary. 20, 21, 22 are synchronous detectors, 23, 24, 25 are narrow band BPF filter groups corresponding to the fifth, third, and fourth demultiplexers, 26 is an AM processing unit, 27 Is a synthesizing circuit, 28 is a rectifying circuit, and 29 is an LP
F, 30 are electronic switches, 46 is an adder circuit, 47 is LP
It is F.

In FIG. 1, the antenna output 1 to the narrow band BPF are shown.
The outputs to 6, LPF8 and BPF9 are the same as those in the conventional system shown in FIGS. The output of the BPF 9 is the demultiplexer 18,
19 and the synchronous detector 22. The output of the BPF 9 includes a stereo modulated wave EScos2ωpt, and the demultiplexers 18 and 19 extract the upper sideband and the lower sideband at the boundary of 2fp shown in FIG. Of the narrow band BPF groups (demultiplexers) 24 and 25, respectively.
Add to.

Further, the synchronous detector 22 demodulates the output of the BPF 9 with the sin2ωpt component from the 90 ° phase shifter 17 (corresponding to FIGS. 5A and 5B). On the other hand, the monaural signal EM that is the output of the LPF 8 is also a narrow band BPF group (demultiplexer).
(Corresponding to FIG. 5 (c)).

Narrow band BPF groups 23, 24 and 25 have dcc
When using a filter for digital signal processing such as
8. It goes without saying that the outputs of the synchronous detectors 20 and 21 need to be A / D converted. In addition, in FIG.
The outputs of the F groups 23, 24, and 25 are indicated by thick arrows, indicating that there are a plurality of outputs (hereinafter, multi-output) from individual filters (channels) of the narrow band BPF group.

Next, the outputs of the narrow band BPF groups 23, 24 and 25 are added to the AM processing unit 26. The multiple outputs of the AM processing unit 26 are combined by the combining circuit 27 and added to the electronic switch 30. The electronic switch 30 takes the output from the synthesizing circuit 27 as the a terminal input, takes the sum of the outputs of the synchronous detection circuits 20, 21 in the synthesizing circuit 46, and takes the stereo signal ES passing through the LPF 47 of 0 to 15 KHz as the b terminal input. . Narrow band BP
The output of F6 is given to the subcarrier oscillator 7, and its output (cos2ωpt component) is supplied to the synchronization circuit 2 as described above.
Enter 0, 21. The output c of the subcarrier oscillator 7
The os2ωpt component is -sin2 by the 90 ° phase shifter 17.
ωpt.

As described above, in the synchronous detector 22, the BPF is
The output of 9 is demodulated by the sin2ωpt component from the 90 ° phase shifter 17, and this demodulated output is EScos2ωpt · s.
Since in2ωpt = 0, the output of the synchronous detector 22 indicates the magnitude of noise. The output of the synchronous detector 22 is given to the electronic switch 30 as a control signal through the rectifier circuit 28 and the LPF 29. The electronic switch 30 takes the a contact when the output level of the LPF 29 is a certain value or more, and the b contact when the output level is less than the certain value.

Next, the output of the electronic switch 30 (stereo signal ES) and the output of the LPF 8 (monaural signal EM) are passed through the matrix circuit 12 and the de-emphasis circuits 13, 1 are provided.
A right ear signal (ER) and a left ear signal (EL) are sent to 4.
When the narrow band BPFs 23, 24, 25 are digital filters, the processes after the narrow band BPFs 23, 24, 25 are processed by digital signals, and the outputs ER, EL of the matrix circuit 12 are analog signals by a D / A converter. It goes without saying that there is a need to make this a reality.

FIG. 2 is a block diagram showing details of an embodiment of the AM processing unit 26, and the AM processing unit 26 is shown as a portion surrounded by a chain line in the drawing. In FIG. 2, 31 is an adding circuit, 32 is a subtracting circuit, 33 is a rectifying circuit, and 34 is an LP.
H, 35 are gate signal generating circuits, 36 are delay circuits, 3
7, 38, 39 are electronic switches, 40 is a rectifier circuit, 41
Is LPH, 42 is a gate signal generation circuit, 43 is LPH,
Reference numeral 45 is a gate signal generation circuit.

The adder circuit 31 to the gate signal generator circuit 45 are provided in correspondence with the number of channels of the narrow band filter (n sets if the number of channels is n), but in FIG. Narrow band filters 23, 2
Channels 4 and 25 are shown as one channel. Also, in the following description, only one channel is described for convenience of description, but the same applies to each of the other channels.

Channel 1 of narrow band filters 24 and 25
Are output to the adder circuit 31 and the subtractor circuit 32. The output (difference component) of the subtraction circuit 32 is generated by the gate signal generation circuit 35 via the rectification circuit 33 and the LPF 34. on the other hand,
The output of the adder circuit 31 (the sum signal of the output signals of channels # 1 ′ and # 1 ″) is given to the delay circuit 36 and the rectifier circuit 40.

The output signal of the adder circuit 31 input to the delay circuit 36 is added to the electronic switch 37, and when the output from the gate signal generating circuit 35 is a certain value or more, the electronic switch 37.
Turns off. On the other hand, the output of the adding circuit 31 input to the rectifying circuit 40 passes through the LPF 41 and the gate signal generating circuit 4
2 and the output of the electronic switch 37 is controlled by the electronic switch 38 as a control signal of the electronic switch 38. The electronic switch 38 is turned on when the output of the gate signal generating circuit 42 is a certain value (noise level) or more.

The output of the electronic switch 38 is further applied to the electronic switch 39. The electronic switch 39 is a narrow band BPF group 2
The signal of channel # 1 of the monaural signal EM (multi-output), which is the output of No. 3, is input to the gate signal generating circuit 45 via the rectifying circuit 43 and the LPF 44, and is controlled by the gate signal generated. At this time, the low-level signal component output from the LPF 44 is regarded as noise and removed. In other words, the electronic switch 39 is turned on when the channel # 1 of the monaural signal EM (multi-output) is above the noise level. Outputs of the electronic switches 39-1, 39-2, ..., 39-n corresponding to the channels # 1, # 2, ..., #n are combined by the combining circuit 27 and further added to the electronic switch 30.

FIG. 3 is a block diagram of a simplified example of the switch circuit of the AM processing section. In the configuration example of the AM processing unit 26 shown in FIG. 2, the electronic switches 37, 38, 39 are arranged in series and controlled, respectively. However, in FIG. 3, the electronic switches 37, 38, 39 are arranged in order to simplify the switch circuit. Instead, A
The ND circuit 48 and the electronic switch 49 are provided, and the control signals from the gate signal generation circuits 35, 42, and 45 are ANDed, and the electronic switch 49 is controlled by one control signal.

The gate signal generation circuits 35, 42, 4
A signal inverting circuit is provided for each control signal from 5 if necessary in order to make their polarities coincide with each other. In the example of FIG. 2, the control signal from the gate signal generation circuit 35 is phase-inverted and added to the AND circuit 48.

From the above description, the correlation between the frequency components of the stereo signal and the monaural signal is used to improve the S / N ratio of the stereo signal of the FM reception signal, and the symmetry of the upper sideband and the lower sideband of the stereo signal is used. By doing so, a significant improvement in S / N can be realized. Further, as a result, it is possible to realize the compression of the signal processing system as a narrow band filter for the audio signal in the combined device of the FM radio and the dcc.

[0034]

As described above, according to the present invention, F
When the M broadcast wave is received in a weak electric field, only the sub-channels with a certain value or more that are symmetrical with respect to the upper side band and the lower side wave of the stereo signal are extracted, and the correlation between the stereo signal and the frequency component of the monaural signal is used. Since only the sub-channel of the stereo signal having the frequency component of the monaural signal is selected and output, the S / N of the stereo signal can be significantly improved and the sensitivity can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an FM stereo receiver according to the present invention.

FIG. 2 is a block diagram showing details of an AM processing unit.

FIG. 3 is a block diagram of a simplified example of a switch circuit of an AM processing unit.

FIG. 4 is an explanatory diagram of an S / N improvement principle of the FM stereo receiver of the present invention.

FIG. 5 is an explanatory diagram of the S / N improvement principle of the FM stereo receiver of the present invention.

FIG. 6 is a diagram showing a noise distribution of a demodulated signal of an FM reception signal and a frequency distribution of a monaural signal and a stereo signal.

FIG. 7 is a block diagram showing a principle configuration of a conventional FM receiver.

8 is an explanatory diagram of an S / N improvement principle of the FM stereo receiver of FIG.

FIG. 9 is a block diagram showing a configuration of an FM stereo receiver.

10 is a detailed block diagram of the periphery of the signal processing circuit of FIG.

[Explanation of symbols]

17 90 ° phase shifter 18, 19 Demultiplexer (first and second demultiplexer) 20, 21, 22 Synchronous detector 23, 24, 25 Narrow band BPF filter group (5th, 3rd, 4th) Demultiplexer) 26 AM processing unit (signal combining unit) 27 combining circuit (signal combining unit) 28 rectifier circuit 29 LPF 30 electronic switch 46 adder circuit 47 LPF

Claims (1)

[Claims] 1. An FM stereo receiver for separating an output signal obtained by FM demodulation into a sum signal and a difference signal, and matrix-processing the both signals to obtain a left ear signal and a right ear signal. First and second demultiplexers for separating the upper sideband and the lower sideband, and third and fourth demultiplexers for dividing the upper sideband and the lower sideband into a plurality of different frequency domain channels and outputting the divided frequency domain channels. A demultiplexer; a fifth demultiplexer that divides the difference signal according to the number of channels in the same frequency region as the third and fourth demultiplexers and outputs; And a signal combiner for controlling the output of each frequency domain channel based on the level of the sum and difference of the output components of the respective channels of the fifth demultiplexer and combining the outputs to obtain a combined signal, and an FM demodulator Based on the noise level of the output signal FM stereo receiver and having a signal processing unit for matrix processing by selecting one of the signal or the sum signal.