JPS6374232A - Stereo receiver - Google Patents

Abstract

PURPOSE:To evade the sound quality from being too much deteriorated under the condition that multi-path interference is generated frequently by operating a pseudo stereo sound generating means if the electric field strength with decreased separation is a prescribed value or over. CONSTITUTION:A control voltage generating circuit 8 detects the amplitude fluctuation component due to multi-path interference included in a signal meter voltage to decrease its signal data voltage. When the multi-path interference takes place and a control output voltage reaches 0.2V or below regardless of the presence of some electric field strength (sufficient strength for stereo reception), a voltage controlling a voltage control attenuator 25 is generated. In order to bring the voltage gradually into the pseudo stereo state, the attenuation of the signal retarded by a delay circuit 24 is decreased gradually to increase the addition/subtraction in the pseudo stereo operation thereby enhancing the pseudo stereo effect.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a stereo receiving device, particularly a vehicle-mounted receiving device that controls the degree of separation and frequency gain of a stereo demodulation circuit using a signal meter output voltage.

B0 Summary of the Invention Utilizes a signal meter voltage that is proportional to the electric field strength of broadcast radio waves, and when the signal meter voltage exceeds a predetermined voltage (field strength sufficient for stereo reception), the degree of separation is degraded by 1, and the signal becomes monaural. In a system that improves the S/N ratio by using a signal meter, when the voltage that controls the degree of separation is determined to be in a monaural state and the signal meter voltage is determined to be higher than a predetermined voltage, a pseudo stereo sound generation circuit is activated. In order to turn on the changeover switch for the stereo operation and determine the amount of pseudo stereo operation, the amount of addition/subtraction is gradually increased to eliminate the sense of discomfort. To gradually increase the amount of addition/subtraction, a voltage-controlled attenuator is used, and a sawtooth wave voltage is used as the control voltage, and when the voltage is at a predetermined value, the voltage is held to keep the pseudo-stereo state constant.

C0 Conventional technology Automotive FM receivers are affected by multipath fading, which causes amplitude fluctuations according to the Rayleigh distribution side.When receiving FM broadcasts, strong noise occurs in the demodulated output, significantly deteriorating the reception quality. Resulting in. To reduce this noise, in-vehicle FM receivers attempt to improve the S/N ratio by automatically controlling frequency gain characteristics and separation characteristics against multipath fading.

Figure 3 is a block diagram showing the configuration of a stereo detection stage of an FM receiver including a conventional sound field control circuit.

In the figure, the part surrounded by the dashed line is the sound field control circuit 1, 2 is the intermediate frequency input, 3 is the intermediate frequency amplifier/detector IC, 4 is the stereo detector (multiplexer), and 5 is the intermediate frequency input.
6 represents a left channel audio output, 6 represents a right channel audio output, 7 represents a signal meter voltage terminal, and 8 represents a control voltage generation circuit.

That is, for sound field control, as shown in FIG. 3, the voltage appearing at the signal meter voltage terminal 7 included in the intermediate frequency amplifier/detector IC 2, that is, the broadcast radio wave, is level-detected and the radio wave is detected. It utilizes the signal meter voltage obtained from a circuit that converts it into a voltage proportional to the intensity.

When multipath fading accompanied by amplitude fluctuation occurs, the signal meter voltage is cursed with a steep voltage change accompanying the amplitude fluctuation. The sound field control circuit 1 detects this change and generates a voltage to control the degree of separation and frequency gain characteristics according to the amount of change.

FIG. 4 is a block diagram showing the detailed configuration of the control voltage generation circuit 8 of FIG. 3, in which 9 is a multipath detection circuit;
10 is a detection level setting circuit, 11 is a charge/discharge control circuit,
12 represents a charging/discharging circuit, and 13 represents a control output terminal.

The amplitude fluctuation component due to multipath interference contained in the signal meter voltage is converted into AC-DC voltage by the multipath detection circuit 9 . When the DC voltage thus obtained is higher than the level set by the detection level setting circuit 1o,
Depending on the level, the capacitor C discharges the stored charge, lowering the output voltage v0 appearing at the output terminal 13, and after the discharge is finished, the capacitor C is gradually charged.

The operation of the circuit shown in FIG. 3 is detailed in Japanese Patent Application No. 60-42822 filed by the present applicant on March 6, 1985, so it will not be described further here, but the circuit shown in FIG. In this circuit, when multipath interference occurs, the control output voltage v0 is lowered according to the magnitude of the multipath interference to deteriorate the degree of separation, and further high-cut operation is performed.
Aim to improve the S/N ratio. If multipath disturbances occur frequently and continuously, depending on the time constant of the charging/discharging circuit 11 (this time constant has a value of several seconds), this control voltage v0 may remain low (in extreme cases). OV), and the device will continue to operate for a while with the degree of separation considerably degraded. In other words, you will be listening in a monaural state rather than a stereo state. As a result, the S/N ratio improves, but the sound quality deteriorates.

D9 The problem that the invention aims to solve: In situations where multipath interference frequently occurs, as in the case above, the voltage that controls the degree of separation and frequency gain characteristics is always kept close to OV, and the monophonic Although the S/N ratio is improved, the sound quality is degraded.

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks, an object of the present invention is to provide a stereo receiving device that can convert a monaural state into a stereo state in a manner such that the sound quality does not deteriorate much. It is.

Means for Solving the E0 Problem In order to achieve the above object, the stereo receiving apparatus according to the present invention includes a first detection means for detecting that the degree of separation is lowered, and a first detection means for detecting that the degree of separation is lowered, and a first detection means for detecting that the degree of separation is lowered. a second detecting means for detecting a certain thing; a pseudo-stereo sound generating means; detecting that both the first detecting means and the second detecting means are in a detection state; The gist is to include a control means for operating the system.

In an advantageous embodiment of the invention, the control means comprises an AND circuit and a sawtooth wave generating circuit.

It consists of a level comparator, a voltage hold circuit, an attenuator, a changeover switch for operating the pseudo stereo sound generating means, and a switch control circuit.

20 Action The basic operation of the present invention is that the signal meter voltage is at a certain level (
For example, voltage V. ) In the above case, when the output voltage of the control voltage generation circuit becomes less than v2, the field strength is such that it would normally receive stereo reception, but due to multipath interference, the reception is monophonic. If so, use pseudo-stereo operation. Even in this pseudo-stereo operation,
Since changing to pseudo-stereo suddenly after switching to monaural would create a sense of discomfort, the system gradually changes to pseudo-stereo operation until it reaches a certain point, and then maintains that state.

G. EXAMPLES The present invention will be explained in more detail below using examples with reference to the drawings, but these are merely illustrative and various modifications and improvements can be made without going beyond the scope of the present invention. Of course it is possible.

FIG. 1 is a block diagram showing the configuration of a stereo receiver according to the present invention. In the figure, the reference numbers common to FIG. 3 represent the same or corresponding parts as in FIG. 3, and 14 is a composite. Signal input terminal, 15.16
is a comparator, 17 is a changeover switch, 18 is an AND
19 is a reset circuit, 2o is a sawtooth wave generation circuit, 21 is a level comparator, and 22 is a voltage hold circuit.

23 is a changeover switch control circuit, 24 is a delay circuit,
25 represents a voltage attenuator, and 26.27 represents a buffer amplifier.

The stereo receiver according to the present invention utilizes a signal meter voltage that is proportional to the intensity of broadcast waves.

This signal meter voltage is branched into two paths.

One of them is to detect an amplitude fluctuation component due to multipath interference contained in the signal meter voltage using a conventional control voltage generating circuit 8, and lower the signal meter voltage. Further, the control output voltage is connected to a terminal for controlling the degree of separation and frequency gain characteristics included in the stereo demodulation circuit, and further to one input terminal of a comparator 15 for comparison with a certain voltage level v2. Here, the reference voltage v of comparator 15
2 determines that below that voltage, it is in a monaural state. This reference voltage v2 is set to about 0.27. (When the control output voltage is less than about 0.2'V, the degree of separation becomes OdB.) When the control output voltage is less than voltage 2, the output of the comparator 15 is made to be at the 11 HIT level.

The signal meter voltage, on the other hand, is a low-pass filter composed of R-C, which ensures that even if the signal meter voltage momentarily drops, the voltage at the input of the comparator 16 is stabilized (averaged).

Then, this stabilized signal meter voltage and reference voltage V. (usually about 0.5 V), and when the voltage is higher than this reference voltage Vo, the output of the comparator 16 is set to the tt Htt level. The outputs of these two comparators 15 and 16 are both input to an AND circuit 18.

Only when both inputs are at the HPj level, the output of the AND circuit 18 is at the H level. occurs and the control output voltage becomes 0.2V or less, which means that monaural reception is being performed.

FIG. 2 shows a timing chart for explaining the operation of the circuit shown in FIG. The output of the AND circuit 18 is “
, H'' level tl+j2 is a period in which monaural reception is being received due to multipath interference, even though the field strength is sufficient for stereo reception.During this period, the voltage controlled attenuator 25 Generates a voltage to control the

This voltage gradually reduces the amount of attenuation of the signal delayed by the delay circuit 24 to gradually create a pseudo-stereo state, and increases the amount of addition/subtraction in the pseudo-stereo operation to further enhance the pseudo-stereo effect.

However, if it is set too high, the phases of the right and left outputs will be reversed, creating an unnatural feeling, so it must be set appropriately. This setting is.

This is done using the voltage v1 of the level comparator, and when this voltage reaches vl, the AND circuit 18 outputs “L”
Hold until it reaches 7 levels. As a result, the pseudo stereo effect is maintained at its voltage V. When the output of AND circuit 18 reaches rr L” level,
The voltage held by the reset circuit 19 is reset to O level, and the amount of attenuation becomes the maximum again, so that the pseudo stereo effect is no longer produced.

Further, when the output of the AND circuit 18 is "HP Loubel", the selector switch 17 is turned on to transmit the signal to the route for performing the pseudo stereo operation.

Pseudo-stereo operation is performed in blocks surrounded by broken lines. This behavior works when the signal is mono.

The same signal is output for both left and right sides. The left and right signals added by the changeover switch 17 are delayed by several milliseconds in the delay circuit 24, and then added/subtracted after adjusting the level with an attenuator. The sound is diffused at this level of addition/subtraction. When the level increases, the left and right outputs become out of phase,
The sound will now be located right next to you. Therefore, when a monaural state occurs due to multipath interference, instead of instantaneously changing to a pseudo-stereo state, the amount of attenuation of the attenuator is reduced as the control voltage increases, and the amount of addition/subtraction is increased to a certain level. to hold the addition/subtraction amount. That is,
A pseudo-stereo state is set that does not cause discomfort with appropriate addition/subtraction. Addition takes place via resistors R1y R2, and subtraction takes place in buffer amplifiers 26, 27 consisting of operational amplifiers.

As explained in detail in the H0 invention, when multipath interference occurs, monaural reception occurs even though the electric field strength is sufficiently large, resulting in deterioration of sound quality, but according to the present invention, such deterioration of sound quality is prevented.

Furthermore, since the transition to pseudo-stereo is gradual, there is an advantage that the sense of discomfort that occurs when switching from monaural to pseudo-stereo is eliminated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a stereo receiver according to the present invention, FIG. 2 is a timing chart for explaining the operation of the circuit shown in FIG. 1, and FIG. 3 is a diagram showing the configuration of a conventional sound field control circuit. FIG. 4 is a block diagram showing the configuration of the control voltage generation circuit. 4...Stereo detector (multiplexer), 5...Left channel audio output, 6...Right channel audio output,
7... Signal meter voltage terminal, 14.
......Composite signal input terminal, 15.1
6・・・・・・Comparator, 17・・・・・・・・・
Selector switch, 18...AND circuit, 19...Reset circuit, 20...
...Sawtooth wave generation circuit, 21...
Level comparator, 22... Voltage hold circuit, 23... Changeover switch control circuit,
24...Delay circuit, 25...
...Voltage attenuator, 26.27...Buffer amplifier. Patent Applicant Clarion Co., Ltd.'s FM Ukuro Stereo 2nd Pinch Ichigo 7 "Mouth Gyri 7 No. 3"
Diagram nf galake circuit Confucian XA Do A

Claims (2)

[Claims] (1) In a receiving device that uses a signal meter output voltage to control the degree of separation and frequency gain of a stereo demodulation circuit, (a) a first device that detects that the degree of separation is lowered;
(b) a second detection means for detecting that the electric field strength is greater than or equal to a predetermined value;
(c) a pseudo-stereo sound generating means; and (d) detecting that both the first detecting means and the second detecting means are in a detection state, and operating the pseudo-stereo sound generating means. A stereo reception device comprising control means. (2) The control means is characterized by comprising an AND circuit, a sawtooth wave generation circuit, a level comparator, a voltage hold circuit, an attenuator, a changeover switch for operating the pseudo-stereo sound generation means, and a switch control circuit. , a stereo reception device according to claim 1.