JPH0530054A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To reproduce a signal with high fidelity by obtaining a difference between a signal meter output and a predetermined reference signal and outputting the difference component as a prescribed reference level. CONSTITUTION:This receiver is provided with a subtractor 31 employing an operational amplifier comprising resistors R1-R4 and a differential amplifier circuit A, and an S meter voltage VSM and an optional constant voltage VB being outputs of a limiter or a discriminator are applied to the input side and an output signal VO is used for a reference voltage er of a comparator circuit of a signal processing section. The subtractor 31 outputs a signal VO being a difference between the optional constant voltage VB and the S meter voltage VSM (V0=VB-VSM). Furthermore, the VB is obtained by dividing a power supply voltage. Thus, when the output VO is used for the reference voltage ER, the control of a desired reference voltage er as er=VB-VSM is attained.

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 an improvement in S / N or HiFi depending on the electric field strength.
The present invention relates to an FM stereo receiver which gives priority to reproduction.

[0002]

2. Description of the Related Art In an FM stereo receiver, as a method for improving S / N of a sub signal (LR) which is disadvantageous to a monaural signal (L + R) which is a main signal in terms of S / N, the sub signal is narrow band. There is a method in which band division is performed by a filter BPF group, the sub-signal frequency spectrum is instantaneously analyzed, the frequency band that is not transmitted is cut, and then the remaining frequency bands are combined.

FIG. 1 shows a conventional example of an FM stereo receiver of this kind, which is shown in detail in Japanese Patent Application No. 1-116942 filed and filed by the present applicant. ..

In the figure, 1 is a receiving antenna, 2 is a high frequency amplifier, 3 is a frequency converter (IF generator), 4 is a local oscillator, 5 is a limiter, 6 is a discriminator, 7 is a 19 kHz band pass filter, and 8 Is a 38 kHz (2 fp) generator, 9 is a low pass filter, 10 is a band pass filter, 11 is a synchronous detector, 12 is a signal processing unit, 13 is a matrix amplifier, and 14 and 15 are left and right stereo signals E.
The outputs of L and ER are shown.

In FIG. 1, the output of the receiving antenna 1 is high-frequency amplified by a high-frequency amplifier 2, a high-frequency converter 3 takes a difference from the frequency of a local oscillator 4, converts it to an intermediate frequency (IF), and a limiter 5 is used. After the amplitude is limited, FM demodulation is performed by the discriminator 6. A signal meter (hereinafter referred to as S meter) output is obtained from the limiter 5 and the discriminator 6.

FIG. 2 shows the frequency spectrum of the FM demodulation output. The monaural signal EM (L
+ R) is obtained from the low-pass filter 9, and Escos2wpt containing the stereo signal Es (LR) is obtained from the band-pass filter 10. This Escos2wpt is a synchronous detector 11
Add to. On the other hand, the narrow band pass filter 7 extracts the pilot signal Pcos wpt and the 2fp generator 8 extracts the subcarrier cos cos.
Generate 2 wpt.

The output cos2wpt of the 2fp generator 8 is added to the synchronous detector 11, and Escos2wpt is synchronously detected to obtain a stereo signal Es. The output EM of the low pass filter 9 and the output Es of the synchronous detector 11 are processed by the signal processing circuit 12 to obtain a stereo channel output Es', which is added to the matrix amplifier 13 together with the output EM of the low pass filter 9. In the matrix amplifier 13, ER = EM-Es',
The calculation of EL = EM + Es' is performed to generate stereo audio signals ER and EL. In the signal processing unit 12, FIG.
The stereo noise peculiar to the FM demodulation as shown in FIG. 4 is reduced, and its concrete configuration example is shown in FIG.

In FIG. 4, 16 and 17 are narrow band filters, 18 is an amplitude detector, 19 is a reference voltage, 20 is a comparison circuit, 21 is a gain control circuit, and 22 is a # 1 to #N channel combination circuit. Both the monaural signal EM and the stereo signal Es are added to the narrow band filter groups 16 and 17 (shown only for the #n channel in the figure). The output of the narrow band filter 16 is applied to the comparison circuit 20 through the amplitude detector 18, the comparison circuit 20 compares the output of the narrow band filter 16 with the reference voltage (er) 19, and the reference voltage 19 When the output is large, a control voltage with a gain of 1 is input to the gain control circuit 21. The output of the narrow band filter 16 is the reference voltage er.
When smaller, there is no control voltage.

On the other hand, the stereo signal Es passed through the narrow band filter 17 is applied to the gain control circuit 21. In the gain control circuit 21, if the control voltage is not input, the stereo signal Es is cut, and if the control voltage is input, it is added to the synthesis circuit 22 as it is. The synthesis circuit 22 includes # 1 to # 1.
The output of the gain control circuit of the #n channel is combined, and the combined output is sent to the matrix amplifier 13 with the stereo channel being Es'.

FIGS. 5A and 5B show a monaural signal E.
M and a stereo signal Es, both signals EM and E
Both s are composed of stereo audio signals ER and EL. That is, since EM = ER + EL and Es = EL-ER, the frequency components are highly correlated.

Therefore, assuming that the channel whose monaural signal EM is equal to or higher than the reference voltage er is as shown in FIG. 5A, the pass band of the corresponding stereo signal Es is shown in FIG. 5B.
Becomes Monaural signal E of channels other than that shown in FIG.
M is less than the reference voltage er, is regarded as noise, and the gain of the channel of the corresponding stereo signal Es is zero. Therefore, even in a noisy stereo signal channel, noise is output only from the narrowband channel group where the signal component exists,
Since the noise of other narrow band channels is cut, the S / N of the stereo channel is improved.

[0012]

In setting the reference voltage er in the above-mentioned method, if the reference voltage er is increased, the FM
The detection output can be expected to improve S / N when S / N deteriorates. FIG. 6 shows the states of the output Es ′ of the signal processing circuit 12 when the reference voltage er is high (er = VH) and low (er = VL) during S / N deterioration of the FM detection output (note that
S ₁ and S ₂ are signals, and N is noise).

[0013] (i) and the case of er = VH, it is assumed that the signals S ₁ and the signal S ₂ of frequency f ₂ of the frequency f ₁ signal EM, present in Es {FIG _{6 (a)}, S 1} > VH , S ₂ <VH, N <
Since it is VH, the frequency of the stereo channel Es' is f ₁
6 except the narrow band filter corresponding to
As shown in (b), a significant S / N improvement can be expected.

(Ii) When er = VL, S ₁ > VL, S ₂
> VL, N> VL, and for the stereo channel Es', all the narrow band filter outputs are combined, and the S / N is not improved [Fig. 6 (c)]. Next, when S / N is good,
When the reference voltage er is high (er = VH) and when it is low (e
r = VL) stereo channel E of the signal processing circuit 12
The state of s'is shown in FIG. Note that S ₁ and S ₂ are signals and N ′
Indicates noise.

[0015] (iii) In the case of a er = VH, it is assumed that the signals S ₁ and the signal S ₂ of frequency f ₂ of the frequency f ₁ is present in the signal EM, Es as shown in Figure 7 (a). In this case, S ₁ >
Since VH, S ₂ <VH, N ′ <VH, the stereo channel Es ′ is cut except for the narrow band filter corresponding to the frequency f ₁ and becomes as shown in FIG. 7B, which improves the S / N ratio. As can be expected, since the signal S ₂ for which S / N is secured is also cut, high-fidelity (Hi-Fi) signal reproduction cannot be performed.

When (iV) er = VL, S ₁ > VL, S ₂ >
VL, N '<VL, and the stereo channel Es' is cut as shown in FIG. 7C except for the narrow band filters corresponding to the frequencies f ₁ and f ₂ . In this case, since the noise included in the narrow band filter of the signal S ₂ is added, er =
Compared with the case of VH, it is somewhat disadvantageous in terms of S / N,
Since the original S / N of the FM detection output is good and the signal S ₂ is reproduced, the case of er = VL is superior in that the signal reproduction is high fidelity.

As described above, in order to improve the S / N ratio of the stereo channel Es' when the FM detection output is low S / N,
The reference voltage er must be set to a high value to some extent.
However, when the FM detection output is high S / N, there is a drawback that high-fidelity signal reproduction cannot be performed. Further, when the FM detection output is high S / N, if the reference voltage er is lowered so as to reproduce a high-fidelity signal, the S / N improvement of the stereo channel Es ′ is hardly performed when the FM detection output is low S / N. was there.

An object of the present invention is that the FM detection output has a low S / N.
In the case of, the S / N improvement of the stereo channel Es ′ is prioritized, and in the case of the high S / N, the high-fidelity signal reproduction of the stereo channel Es ′ can be prioritized.

[0019]

In order to achieve such an object, the present invention provides an FM demodulation means for FM demodulating a received signal to obtain an FM demodulation output and a signal meter output, and the FM demodulation output. Extraction means for extracting the monaural component signal and the stereo component signal, frequency division means for dividing the extracted monaural component signal and the stereo component signal into a plurality of different frequency bands to obtain a band-divided signal, and the monaural component signal A level control that compares the level of each band division signal with a reference level, outputs a level control signal based on the comparison result, and controls the level of each band division signal of the stereo component signal by the level control signal. Means and a plurality of signals whose levels are controlled, are combined, and a stereo signal is obtained based on the combined signal and the monaural component signal. In FM stereo receiver comprising the output means obtains a difference component of a predetermined reference signal with a predetermined and said signal meter output, outputs to the level control means difference component as the predetermined reference level,
According to the S / N of the FM demodulation output, the S / N of the stereo component signal is prioritized, and the reference level control means variably controls the reference level so that HiFi reproduction without signal loss can be performed. It is characterized by

[0020]

In the FM stereo receiver of the present invention, the monaural component signal and the stereo component signal are divided into a plurality of frequency bands, and the level control signal is output based on the comparison result between the band division signal of the monaural component signal and the reference level. The level of the band division signal of the stereo component signal is controlled by this signal. A stereo signal is synthesized from each level-controlled signal and the monaural component signal. The reference level consists of the signal meter output and the reference signal difference component.
The reference level is controlled according to / N.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 8 shows the correspondence between the FM detection output S / N and the S meter voltage VSM with respect to the antenna input voltage.

As shown in FIG. 8, the FM detection output S / N and the S meter voltage VSM indicating the antenna input voltage are low when the FM detection output S / N is low and the S meter voltage VSM is high. , S meter voltage VSM also increases. On the other hand, the reference voltage er is the FM detection output S / N as shown in FIG.
It is desirable to lower the value when the S is low and to lower the value when the S / N is high. Therefore, if the relation of er = VB-VSM is provided, the desired reference voltage er can be controlled by the FM detection output S / N.
It is possible to correspond to the above (VB represents an arbitrary constant voltage).

FIG. 9 shows a structure of a main part for realizing an FM stereo receiver according to the present invention, which includes resistors R1 to R1.
A subtracter 31 using an operational amplifier composed of R4 and a differential amplifier A is provided, and an S meter voltage VSM output from the limiter 5 or the discriminator 6 in FIG. 1 and an arbitrary constant voltage are provided on the input side thereof. VB is applied, and the signal Vo on the output side is applied to the comparison circuit 20 of the signal processing unit 12 shown in FIG.
Used as the reference voltage er of.

The subtractor 31 outputs a signal Vo (= VB-VSM) which is the difference between the arbitrary constant voltage VB and the S meter voltage VSM. Note that VB is obtained, for example, by dividing the power supply voltage. Therefore, if this output Vo is used as the reference voltage er, the above-mentioned desired reference voltage er of er = VB-VSM
Can be controlled.

FIG. 10 shows the relationship between the S meter voltage VSM and the output Vo of the subtractor 31 with respect to the input voltage of the circuit of FIG. In the circuit of FIG. 9, the resistance values R1 to R4 may be the same, but the characteristic of Vo = aVB−bVSM (a and b are arbitrary constants) is realized by changing the resistance values. It goes without saying that you can do it.

[0026]

As described above, in the FM stereo receiver of the present invention, when the FM detection output S / N is low, the signal processing circuit operates so as to give priority to the improvement of the S / N of the stereo channel Es'. In addition, when the FM detection output S / N is high, the signal processing circuit can be operated so as to give priority to the high-fidelity signal reproduction of the stereo channel Es ′.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a conventional FM stereo receiver.

FIG. 2 is a diagram showing an FM detection output frequency spectrum of FM stereo broadcasting.

FIG. 3 is a diagram showing an FM demodulation noise frequency spectrum of an FM stereo receiver.

4 is a configuration diagram of an example of a signal processing unit in FIG.

FIG. 5 is an explanatory diagram of control of stereo channel frequency characteristics.

FIG. 6 is a diagram showing an input / output frequency spectrum of the signal processing circuit when the FM detection output S / N is deteriorated.

FIG. 7 is a diagram showing an input / output frequency spectrum of the signal processing circuit when the FM detection output S / N is good.

FIG. 8: FM detection output S / N with respect to antenna input voltage
It is a figure which shows the relationship of S meter voltage VSM.

FIG. 9 is a configuration diagram of an example of a main part of an FM stereo receiver according to the present invention.

10 is an output voltage characteristic diagram of the circuit of FIG.

[Explanation of symbols]

 3 frequency converter 5 limiter 6 discriminator 9 low pass filter 10 band pass filter 12 signal processing unit 13 matrix amplifier EM monaural component signal Es stereo component signal Es' stereo channel 19 reference voltage er 20 comparator Vs S meter voltage 31 Subtractor

Claims (1)

Claim: What is claimed is: 1. An FM demodulating means for FM demodulating a received signal to obtain an FM demodulated output and a signal meter output, and an extracting means for extracting a monaural component signal and a stereo component signal from the FM demodulated output. A frequency dividing means for dividing the extracted monaural component signal and stereo component signal into a plurality of different frequency bands to obtain a band-divided signal, and comparing the level of each band-divided signal of the monaural component signal with a reference level. Then, a level control signal is output based on the comparison result, and the level control signal controls the level of each band-divided signal of the stereo component signal, and the plurality of level-controlled signals are combined. And obtain a stereo signal based on the combined signal and the monaural component signal F
In the M stereo receiver, a difference component between the signal meter output and a predetermined reference signal determined in advance is obtained, and the difference component is output to the level control means as the predetermined reference level to output the S of the FM demodulation output. / N, priority is given to S / N of the stereo component signal, and FM is provided with reference level control means for variably controlling the reference level so as to enable HiFi reproduction without signal loss. Stereo receiver.