JPH0637658A - Multi-pass distortion reduction circuit for radio receiver - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a separation rate owing to the variation of the modulation degree of a stereo signal by erasing a stereo signal remaining component in a multi-pass reduction circuit. CONSTITUTION:When an S-meter output signal is impressed to a multi-pass distortion detection circuit 2, AC component obtained by superposing the S-meter signal (DC) is extracted and added to a stereo signal remaining component erasing circuit 3, which erases the stereo signal remaining component in the AC component to output it to a detection circuit 4. Consequently, a control signal corresponding to multi-pass distortion is added to the control terminal 5a of a stereo demodulator 5 from the detection circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a multipath distortion reduction circuit for a radio receiver.

[0002]

2. Description of the Related Art A method for reducing noise caused by multipath distortion in an FM stereo radio receiver is disclosed, for example, in Japanese Patent Publication No. 63-40379, Japanese Patent Publication No. 61-202537, and Japanese Utility Model Publication No. 63-131243. As
The AC component corresponding to the multipath distortion superimposed on the S meter output signal when the multipath is generated is detected, and the stereo separation degree of the stereo demodulator is controlled according to the control signal generated from the detection signal to determine the multipath distortion amount. When is greater than a predetermined value, stereo reception is forcibly switched to monaural reception.

[0003]

However, in recent car radios and the like, the band of the intermediate frequency circuit is narrowed due to the influence of adjacent interference. For this reason, a stereo signal component (a signal component suppressed at 38 kHz) is generated in the S meter output signal. Therefore, the higher the degree of modulation of the stereo signal, the greater the amplitude of the S meter output signal, and the greater the deterioration of the degree of separation. Moreover, this stereo signal component is always a residual component as the control signal even if the multipath distortion disappears.

FIG. 6 is a characteristic diagram showing the relationship between the antenna input and the degree of separation with respect to the degree of stereo modulation, and the hatched portion shows the region where the degree of separation changes with the degree of modulation. According to the conventional method for reducing multipath distortion, when a stereo signal with a high modulation degree is transmitted in the above region with a weak signal as shown in FIG. 6, the degree of separation is deteriorated or a monaural state occurs. This means that when a stereo broadcast is received with a weak electric field, the degree of separation changes depending on the strength of the stereo signal transmitted from the broadcasting station, which causes a sense of discomfort to the listener.

It is an object of the present invention to propose a multipath distortion mitigation circuit which eliminates a stereo signal residual component to prevent deterioration of separation degree due to change of modulation degree of stereo signal.

[0006]

To achieve the above object, the present invention provides a multipath distortion mitigation circuit for a radio receiver, which controls at least the stereo separation of a demodulator according to the output of an S meter terminal. Between the multipath distortion detection circuit that extracts an AC component when multipath distortion occurs from the output of the S meter terminal and between the multipath distortion detection circuit and the control terminal of the demodulator, a stereo signal residual component from the AC component It is characterized in that a stereo signal residual component erasing circuit for erasing is eliminated.

[0007]

The separation degree is controlled by the control signal generated by eliminating the stereo signal residual component from the AC component of the S meter output signal when multipath distortion occurs.

[0008]

Embodiments of the present invention shown in the drawings will be described below.
1 is an embodiment of the present invention, 1 is an input terminal connected to an S meter terminal of an intermediate frequency amplification stage of an FM stereo radio receiver, 2 is a multipath distortion detection circuit, and 3 is a stereo signal residual component elimination circuit. Reference numeral 4 is a detection circuit, and 5 is a stereo demodulator of the radio receiver, which has an automatic separation degree adjusting function (and an automatic sound quality adjusting function). Reference numeral 6 is a stereo composite signal input terminal, and reference numerals 7 and 8 are a stereo R component signal output terminal and a stereo L component signal output terminal.

FIG. 2 shows a configuration example of the multipath distortion detection circuit 2 and the stereo signal residual component elimination circuit. In the figure, C ₁ is a high frequency component bypass capacitor, C ₂ is a direct current cut capacitor, C ₃ is a direct current cut and frequency characteristic adjustment capacitor for multipath with R _5, and R ₂ and R ₃
Is a bias resistor, R ₄ is an emitter floor resistor, R ₅ is a frequency adjustment and control voltage adjustment resistor for multipath, Q
Reference numeral ₁ is a transistor for eliminating stereo signal residual components.

When a multipath occurs, an S meter output signal is applied to the input terminal 1, and as shown in FIG. 3, the DC component DC corresponding to the original S meter signal is applied to the point A at the AC corresponding to the multipath. A voltage is produced on which the component AC is superimposed. The high frequency component is bypassed by the capacitor C ₁ . This DC component is blocked by the capacitor C ₂ , and only the AC component is at the base of the transistor Q ₁ (point B).
Join in.

As described above, even when there is no multipath at the S meter terminal, a stereo signal component suppressed at 38 kHz appears at the time of reception of a stereo broadcast, so that it is included in the AC component at the point B.

On the other hand, as the transistor Q ₁ , for example,
When a silicon transistor is used, the relationship between its base-emitter voltage V _BE and collector current Ic is as shown in FIG. 4, and the voltage between the base and emitter is about 0.6 V.
The collector current will not flow unless the above conditions are met.

Therefore, if the stereo signal component is 0.
If was 2V (P-P), is set by R ₂ and R ₃ a V _BE to be 0.5V, as shown in FIG. 5 Q ₁
It can be erased without appearing at the emitter (point C). The signal generated at the point C is detected by the detection circuit 4 via the capacitor C ₃ and the resistor R _5.
In addition, a control signal for reducing multipath distortion is output to the control terminal 5a of the demodulator 5.

When the S meter output signal is in a saturated region, the AC component AC corresponding to the multipath is generated.
(Amplitude modulation component) decreases. For this reason, the relationship between the antenna input and the degree of isolation becomes as shown in FIG. 7 in the above area, so that the effect of the multipath countermeasure cannot be obtained when the antenna input is above a certain level.

FIG. 8 shows another embodiment of the present invention adapted to cope with such a case, in which a wideband AGC output terminal 11 of the front end 10 is connected to a multipath distortion detecting circuit via a resistor R ₁ and a diode D _1. It is connected to the output of 2. Reference numeral 12 is an intermediate frequency circuit. For example, normally, in an FM radio receiver, when the antenna input input to the front end 10 exceeds 60 dB, a wide band AGC voltage of 8 V is output to the terminal 11.

With the above arrangement, even if the AC component is reduced in the saturation region of the S meter output signal, the wide band AGC voltage is transmitted through the resistor R ₁ and the diode D ₁ to the transistor Q ₁
Since the relationship between the antenna input and the degree of separation is as shown in FIG. 9, the effect of reducing multipath can be sufficiently obtained.

[0017]

As described above, according to the present invention, since the stereo signal residual component is eliminated, the multipath distortion can be reduced without deteriorating the separation degree due to the change of the modulation degree of the stereo broadcast. .

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration example of a multipath distortion detection circuit and a stereo signal residual component elimination circuit of the above embodiment.

FIG. 3 is a waveform diagram for explaining the operation of the circuit of FIG.

FIG. 4 is a characteristic diagram of a silicon transistor.

5 is an explanatory diagram of the operation of the circuit of FIG.

FIG. 6 is a diagram showing a relationship between an antenna input and a degree of separation with respect to a degree of modulation of a radio receiver.

FIG. 7 is a diagram showing a relationship between an antenna input and a degree of separation in an S meter output signal saturation region.

FIG. 8 is a block diagram showing another embodiment of the present invention.

FIG. 9 is a diagram showing an effect of the embodiment of FIG.

[Explanation of symbols]

 1 Input terminal 2 Multipath distortion detection circuit 3 Stereo residual component elimination circuit 4 Detection circuit 5 Stereo demodulator

Claims (3)

[Claims] 1. A multipath distortion mitigation circuit for a radio receiver that controls at least the stereo separation of a demodulator according to the output of the S meter terminal, wherein an AC component at the time of occurrence of multipath distortion is output from the output of the S meter terminal. A multi-path distortion detection circuit for extracting, and a stereo signal residual component elimination circuit for eliminating a stereo signal residual component from the AC component is provided between the multi-path distortion detection circuit and the control terminal of the demodulator. Multipath distortion reduction circuit for radio receiver. 2. The multipath for a radio receiver according to claim 1, further comprising: a wideband AGC signal supply means for supplying a wideband AGC signal output from the front end of the radio receiver to an output of the multipath distortion detection circuit. Distortion reduction circuit. 3. The multipath distortion mitigation circuit for a radio receiver according to claim 2, wherein said wideband AGC signal supply means comprises a series circuit of a diode and a resistor.