JP3221281B2 - Noise reduction device for stereo receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a noise reduction device that reduces your Keru multi-path interference noise in portable or FM stereo reception machine mounted on a vehicle.

[0002]

2. Description of the Related Art Multipath interference noise becomes significant in the high frequency range of a demodulated signal. Therefore, the sub-signal in the composite signal is more affected. Therefore, reducing the circle Chipasunoizu between this reducing the stereo separation is performed.

FIG. 2 shows the configuration of a conventional noise reduction device of this type. 2, reference numeral 1 denotes an antenna, 2 is full b Ntoendo connected to the antenna 1, an intermediate frequency amplifying circuit is connected to the front end 2 3, FM detector circuit connected to the intermediate frequency amplifier circuit 3 is 4, 5 Is a 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 a filter circuit 7. The 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.
2, the signal meter output circuit 6 outputs a DC voltage as shown in FIG. 3 corresponding to the input level of the antenna 1. When multipath interference occurs, the FM radio wave is subjected to amplitude modulation, so that an AC voltage is also output to the signal meter output circuit 6 together. Since the amplitude modulation increases as the multipath interference increases, the AC voltage of the signal meter output also increases. This AC voltage is band-limited by a filter circuit 7 and converted into a DC voltage as shown in FIG. The output of the AC detection circuit 8 has a time constant as shown in FIG. The separation control circuit 9 controls the multiplex 5 according to the DC voltage.
To reduce the separation as shown in FIG.

As described above, in the above-described conventional noise reduction device, it is possible to reduce the stereo separation in accordance with the strength of the multipath interference and reduce the multipath interference noise.

[0006]

However, in the above-described conventional noise reduction device, since the band of the filter circuit 7 and the gain and time constant of the AC detection circuit 8 are set by one type, the condition of multipath interference depends on the condition. Has a problem that a sufficient effect cannot be obtained.

An object of the present invention is to solve such a conventional problem, and an object of the present invention is to provide an excellent noise reduction device capable of obtaining an effect under more conditions.

[0008]

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

[0009]

Therefore, according to the present invention, by setting the bands of the filter circuits of a plurality of systems and the gain and time constant of the AC detection circuit to be respectively different from each other, the separation can be performed even when the conditions of the multipath interference greatly differ. Can be controlled.

[0010]

FIG. 1 shows the structure of an embodiment of the present invention. The same elements as those of the conventional example shown in FIG. 2 are denoted 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 amplifying circuit connected to the front end 2, 4 is an FM detection circuit connected to the intermediate frequency amplifying circuit 3, and 5 is A multiplex connected to the FM detection circuit 4, a signal meter output circuit 6 connected to the intermediate frequency amplifier circuit 3, a filter circuit 7 connected to the signal meter output circuit 6, and a filter circuit 7 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 Connected to plex 5.

Next, the operation of the above embodiment will be described.
In the above embodiment, an AC voltage is output to the signal meter output circuit 6 when multipath interference occurs. 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 filter circuit 10 also limits the band, and the AC detection circuit 11 converts the DC voltage into a DC voltage. The separation control circuit 9 controls the multiplex 5 according to the output of each DC voltage which is larger, and lowers the separation.

As described above, according to the above-described embodiment, the band of the two filter circuits 7 and 10 and the gain and the time constant of the AC detection circuits 8 and 11 are set to be different from each other, so that the multipath interference can be prevented. There is an advantage that the separation can be appropriately controlled even when the conditions are largely different.

In the above-described embodiment, two systems of the filter circuit and the AC detection circuit are provided. However, more systems may be provided to set more detailed conditions.

[0014]

According to the present invention, as is apparent from the above embodiment, a plurality of filter circuits and AC detection circuits are provided, and each of the circuits operates under different multipath interference conditions. This has the effect that noise can be reduced under many multipath interference conditions.

[Brief description of the 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 a relationship between an output of an AC detection circuit and separation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 Front end 3 Intermediate frequency amplification 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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04H 5/00 H04B 1/10

Claims (2)

(57) [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, comprising 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 the filter circuits and the AC detection circuit are provided. 2. The noise reduction device for a stereo receiver according to claim 1, further comprising two systems of a filter circuit and an AC detection circuit.