JPH08316926A - Noise reduction device for stereo receiver - Google Patents

Abstract

PURPOSE: To control a separation in a larger number of multipath disturbance conditions for reduction of the noises by providing plural systems of filter circuits and AC detection circuits to detect the multipath disturbance. CONSTITUTION: When the multipath disturbance occurs, the AC voltage is outputted to a signal meter output circuit 6. Then the AC voltage undergoes the band limitation through a filter circuit 7 and is converted into the DC voltage by an AC detection circuit 8. In the same way, the AC voltage also undergoes the band limitation through a filter circuit 10 and is converted into the DC voltage by an AC detection circuit 11. A separation control circuit 9 controls a multiplexer 5 according to one of both DC voltage that has larger output and controls the separation to reduce the noises.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to noise for reducing multipath interference noise in a stereo receiver such as a portable or vehicle-mounted FM stereo receiver, AM stereo receiver, and stereo receiver capable of receiving television. Reducing device

[0002]

2. Description of the Related Art Multipath interference noise becomes significant in the high frequency region of a demodulated signal. Therefore, the sub signal in the composite signal is more greatly affected. Therefore, multipath noise is reduced by reducing the stereo separation.

FIG. 2 shows the configuration of a conventional noise reducing device of this type. In FIG. 2, 1 is an antenna, 2 is a front end connected to the antenna 1, 3 is an intermediate frequency amplifier circuit connected to the front end 2, 4 is an FM detection circuit connected to the intermediate frequency amplifier circuit 3, and 5 is Multiplex connected to the FM detection circuit 4, 6 is a signal meter output circuit connected to the intermediate frequency amplifier circuit 3, 7 is a filter circuit connected to the signal meter output circuit 6, and 8 is connected to the filter circuit 7. An AC detection circuit, 9 is a separation control circuit connected to the AC detection circuit 8, and is connected to the multiplex 5.

Next, the operation of the above conventional example will be described.
In FIG. 2, the signal meter output circuit 6 outputs a DC voltage corresponding to the input level of the antenna 1 as shown in FIG. When multipath interference occurs, the FM radio wave undergoes amplitude modulation, and therefore the AC voltage is also output to the signal meter output circuit 6. Since the amplitude modulation increases as the multipath interference increases, the AC voltage output from the signal meter also increases. This AC voltage is band-limited by the filter circuit 7, and is converted into a DC voltage as shown in FIG. 4 by the AC detection circuit 8. The output of the AC detection circuit 8 has a time constant as shown in FIG. The separation control circuit 9 receives the multiplex 5 according to this DC voltage.
Control to reduce the separation as shown in FIG.

As described above, the conventional noise reduction apparatus can reduce the stereo separation according to the strength of the multipath interference and reduce the multipath interference noise.

[0006]

However, in the above-mentioned conventional noise reduction device, the band of the filter circuit 7 and the gain and time constant of the AC detection circuit 8 are set by one kind of setting, so that depending on the condition of multipath interference. There was a problem that could not get a sufficient effect.

The present invention solves such a conventional problem, and an object of the present invention is to provide an excellent noise reduction device which can obtain an effect under more conditions.

[0008]

In order to achieve the above object, the present invention provides a plurality of systems of filter circuits and AC detection circuits to obtain a noise reduction effect under more multipath interference conditions. Is.

[0009]

Therefore, according to the present invention, the bands of the filter circuits of a plurality of systems, and the gain and the time constant of the AC detection circuit are set differently, so that the separation can be performed even when the conditions of the multipath interference greatly differ. Can be controlled.

[0010]

1 shows the structure of an embodiment of the present invention, in which the same elements as those shown in the conventional example of FIG. 2 are designated by the same reference numerals. In FIG. 1, 1 is an antenna, 2 is a front end connected to the antenna 1, 3 is an intermediate frequency amplification circuit connected to the front end 2, 4 is an FM detection circuit connected to the intermediate frequency amplification circuit 3, and 5 is Multiplex connected to the FM detection circuit 4, 6 is a signal meter output circuit connected to the intermediate frequency amplifier circuit 3, 7 is a filter circuit connected to the signal meter output circuit 6, and 8 is connected to the filter circuit 7. An AC detection circuit, 10 is a filter circuit connected to the signal meter output circuit 6, 11 is an AC detection circuit connected to the filter circuit 10, 9 is a separation control circuit connected to the AC detection circuits 8 and 11, and It is connected to plex 5.

Next, the operation of the above embodiment will be described.
In the above embodiment, when multipath interference occurs, an AC voltage is output to the signal meter output circuit 6. This AC voltage is band-limited by the filter circuit 7, and converted into a DC voltage by the AC detection circuit 8. Similarly, the band is also limited in the filter circuit 10, and converted into a DC voltage in the AC detection circuit 11. The separation control circuit 9 controls the multiplex 5 in accordance with the larger output of each DC voltage to reduce the separation.

As described above, according to the above-described embodiment, the bands of the two filter circuits 7 and 10 and the gains and the time constants of the AC detection circuits 8 and 11 are set differently to prevent multipath interference. Even if the conditions are greatly different, there is an advantage that the separation can be appropriately controlled.

In the above embodiment, two systems are provided for the filter circuit and the AC detection circuit, but more systems may be provided for more detailed setting of conditions.

[0014]

As is apparent from the above-described embodiment, the present invention is provided with a plurality of systems of filter circuits and AC detection circuits, and each circuit operates under different multipath interference conditions. It has an effect that noise can be reduced under many multipath interference conditions.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a noise reduction device according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram of a conventional noise reduction device.

FIG. 3 is a characteristic diagram showing a relationship between an antenna input level and a signal meter output.

FIG. 4 is a characteristic diagram showing a relationship between an AC voltage level and an AC detection output.

FIG. 5 is a characteristic diagram for explaining the operation of the AC detection circuit.

FIG. 6 is a characteristic diagram showing the relationship between the output of the AC detection circuit and separation.

[Explanation of symbols]

 1 Antenna 2 Front End 3 Intermediate Frequency Amplifier Circuit 4 FM Detection Circuit 5 Multiplex 6 Signal Meter Output Circuit 7, 10 Filter Circuit 8, 11 AC Detection Circuit 9 Separation Control Circuit

Claims (2)

[Claims] 1. A signal meter output circuit for outputting an amplitude modulation component of an antenna input as an AC voltage, a filter circuit for band limiting the frequency of the AC voltage, and an AC for converting the band limited AC voltage to a DC voltage. A detection circuit and a separation control circuit that changes the stereo separation by the converted DC voltage,
A noise reduction device in a stereo receiver, wherein a plurality of systems of the filter circuit and the AC detection circuit are provided. 2. The noise reduction device for a stereo receiver according to claim 1, wherein the system is provided with two systems of a filter circuit and an AC detection circuit.