JPH0433421A - Radio receiver - Google Patents

Abstract

PURPOSE:To eliminate the sense of incongruity due to sound volume difference at the time of switching by connecting a mute circuit to a post stage of a switching means and controlling the mute circuit with the S meter output of a detector connected to a broad filter. CONSTITUTION:When an electric field strength from a broadcast station listening at present is decreased, since an S meter output from a detector 3b1 is sent to a mute circuit 4, it is activated to decrease the transmission of a sound signal to a multiplexer 5. Moreover, since only one mute circuit is used, even when the gain of a broad filter 3a1 or a narrow filter 3a2 is different, the change in the mute quantity is not generated even at the changeover of the switching means 3f. Thus, the sense of incongruity is not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radio receiver, and particularly to an improvement in a radio receiver suitable for use in a vehicle.

[Conventional technology]

In a radio receiver, when the level of a signal received by an antenna decreases, noise increases and the S/N ratio decreases. Therefore, this S/N
In order to prevent a drop in the antenna reception signal, two filters, a wide frequency band filter (hereinafter referred to as wide filter) and a narrow frequency band filter (hereinafter referred to as narrow filter), are connected to the IF (intermediate frequency) stage. When the level of the antenna reception signal is high, the received signal is output through the wide filter, and when the level of the above-mentioned antenna reception signal decreases, it is automatically or manually switched to the narrow filter.
were trying to improve N (for example,
Publication No.).

Although not disclosed in the conventional example described above, a mute circuit is connected to the rear stage of the wide filter and the narrow filter through a wave detector, so that when the level of the antenna reception signal decreases, the signal from each wave detector is The mute circuit was configured to be controlled by the S meter output.

[Problem to be solved by the invention]

By the way, in the conventional example described above, although it is effective in improving the S/N when the level of the antenna reception signal decreases, it is difficult to use the in-vehicle radio receiver to receive a certain broadcast station while driving. When the electric field strength of a broadcasting station adjacent to the frequency of the broadcasting station becomes strong, it is input as an interference radio wave to the broadcast currently being received, causing interference. In addition, if the gain of the wide filter and the narrow filter are different, the amount of muting will change when switching, causing a difference in volume at the time of switching, causing a sense of discomfort. and a mute circuit are each incorporated into one integrated circuit (for example, an integrated circuit manufactured by Sanyo Electric Co., Ltd., model number LA1140), resulting in a problem that the circuit configuration becomes complicated and the cost increases.

[Purpose of the invention]

The present invention is intended to solve the above-mentioned problems, and its purpose is to automatically switch from a wide filter to a narrow filter when adjacent interference waves arrive to prevent interference caused by adjacent interference waves. and also,
The mute circuit is integrated into one, simplifying the circuit, and
It is an object of the present invention to provide a radio receiver in which a mute circuit is controlled by an S meter output from a wave detector connected to a wide filter.

[Summary of the invention]

The radio receiver of the present invention is intended to achieve the above-mentioned object, and its gist is to distribute the output from the front end to a wide filter and a narrow filter,
The output from each of the filters is demodulated by a detector, the difference between the demodulated outputs is subtracted by a subtracter, and if the subtracted result is larger than a predetermined value by a comparator, the signal from the adjacent broadcasting station is Assuming that interference radio waves exist, the switch means is configured to output the output from the narrow filter side to the multiplex at the subsequent stage, and a mute circuit is connected to the rear stage of the switch means, and this mute circuit is connected to the wide filter. It is designed to be controlled by the S meter output of the connected detector.

[Embodiments of the invention]

Embodiments of the radio receiver according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of the first embodiment, in which 1 is an antenna, 2 is a front end consisting of a high frequency amplification stage, a mixer, and a local oscillation stage, which selects and amplifies radio waves of a desired frequency, and It attenuates other signals and converts them to intermediate frequencies. Reference numeral 3 denotes an intermediate frequency amplification stage connected to the output of the front end 2, which is constructed as follows. That is, a wide filter 3al, a narrow filter 3a2, and detectors 3tz and 3b connected to the outputs of the wide filter 3at and narrow filter 3a2.
2, a subtracter 3C that detects the difference between the outputs from the detectors 3bt and 3b2, and a low-pass filter 3d (shown in FIG. 3) that removes noise and modulation signals contained in the output of the subtracter 3C. It is an active low pass filter such as 3
a comparator 3e that sends out an output when the output from the low-pass filter 3d is larger than a predetermined value; vessel 3tz or 3
It is comprised of a switch means 3f that selects the output from b2 and sends it to the subsequent mute circuit 4.

4 is a mute circuit for muting the output from the switch means 3f, and is configured to be controlled by the S meter output from the detector 3b1.

A multiplexer 5 converts the audio signal that has passed through the mute circuit 4 into a stereo signal.

Next, the operation will be described based on the above-described configuration. FM radio waves from a broadcasting station inputted from the antenna 1 are amplified and outputted after a radio wave of a desired frequency is selected in the front end 2.

Then, the FM signal of the selected broadcasting station is inputted to the detector 3bx via the wide filter 3al, or inputted to the detector 3b2 via the narrow filter 3a2.

Then, the FM signals from the respective filters 3a1t3a2 are demodulated by the detectors 3b1 and 3b2, and then sent to the subtracter 3c.
is input.

Here, if there is no adjacent broadcasting station whose broadcasting frequency is close to each other, the output signal level from the wide filter 3at and the narrow filter 3a2 is between -, so the output from the subtractor 3c is small, and therefore No output is sent out, the switch means 3f is switched to the detector 3b1 side, and the signal from the detector 3b1 is output to the multiplex 4.

On the other hand, if there is an adjacent broadcasting station whose broadcasting frequency is close to each other, the output from the detector 3bx that is outputted via the wide filter 3a1 has a signal from the adjacent broadcasting station as shown in (a) of FIG. Although the signals are superimposed, the narrow filter 3a
The output from the detector 3b1 which is output via the second
As shown in (b) in the figure (signals from adjacent broadcasting stations are not superimposed. Therefore, when the outputs from the detectors 3bs and 3bt are subtracted by the subtractor 3C, the output of the difference is sent out. The output is compared with a reference value in the comparator 3e, and if the output from the subtractor 3c is larger than the reference value, the output is compared with the reference value in the comparator 3e.
The output is sent out, and the switch means 3r is switched to the narrow filter 3a2 side. As a result, the signal output via the narrow filter 3a2 and the detector 3b2 is input to the multiplex 4, so radio waves from adjacent broadcasting stations are removed and only broadcasts from the desired broadcasting station can be received and listened to. It is something.

Next, when the electric field strength from the broadcast station currently being listened to decreases in the case where the above-mentioned adjacent broadcast station does not exist or exists, the S meter output from the detector 3b is sent to the mute circuit 4. Therefore, the mute circuit 4 operates to reduce the output of the audio signal to the multiplex 5.

This reduces the noise-containing audio signal and prevents it from becoming harsh to the ears.

Furthermore, since only one mute circuit is used, even if the gains of the wide filter 3a1 or the narrow filter 3a2 are different, the amount of mute does not change even when the switch means 3f is switched. will not occur.

Here, the mute circuit 4 is controlled by the S meter output from the detector 3b1 on the wide filter aal side.
Since the output from the narrow filter 3a2 has large distortion,
This is because the gain of the amplifier connected before the narrow filter 3a2 is increased, so the area in which the S meter output can be used becomes smaller.

In this embodiment, the low-pass filter 3d is connected after the subtracter 3c because the difference in characteristics between the wide filter 3a1 and the narrow filter 3a2 directly becomes the difference between the detector 3bx and the detector 3b. Even if there is no interfering radio waves from an adjacent broadcasting station, noise or modulated signals may cause a difference in the output between the detectors 3bl and 3b, leading to a risk of false detection. Noise and modulation signals are removed by passing the output through a low-pass filter 3d. Therefore, it can be determined whether or not there is a radio wave from an adjacent broadcasting station based on the output level of the low-pass filter 3d.In other words, if interference is received from an adjacent broadcasting station, the sound of the interfering station will be heard in the audio band. Broadcasting energy is generally IKH
z or less, and adjacent stations can be detected even after passing through the low-pass filter 3d. Further, the difference in characteristics between the wide filter 3a1 and the narrow filter 3a2 is 1, which is particularly noticeable in the high frequency range of the audio signal, and the influence thereof is very small (as a result, false detections are reduced).

〔Effect of the invention〕

As described above, the present invention distributes the output from the front end to a wide filter and a narrow filter, demodulates the output from each filter using a detector, and subtracts the difference between the demodulated outputs using a subtracter. When the subtraction result reaches a level set in advance by the comparator, it is determined that there is interference from an adjacent broadcasting station, and the switch means is configured to output the output from the narrow filter side to the subsequent multiplex. Therefore, as an in-vehicle radio receiver, it eliminates the difficulty of listening due to interference, and since the mute circuit is connected after the switch means, one mute circuit can cut noise even if the electric field strength becomes small. Since there is no difference in volume even when switching between the wide filter and the narrow filter, there is no possibility of causing a sense of discomfort.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the output of the detector shown above, and FIG. 3 is a circuit diagram of the low-pass filter shown above. 2...Front end, 3...Intermediate frequency amplification stage, 3
a1... Wide filter, 3a2... Narrow filter, 3 b i y 3 b2... Detector, 3c...
- Subtractor, 3d...Low pass filter, 3e...Comparator, 3f...Switch means, 4...Mute circuit, 5...Multiplex.

Claims (1)

[Claims] In the intermediate frequency amplification stage connected between the front end and the multiplex, there are a wide filter and a narrow filter into which the output from the front end is input, and an output from the filter connected to each filter. a subtracter that obtains the difference between the outputs from the detector, a comparator that sends out an output when the output from the subtracter exceeds a preset reference level, and the comparator. a switch means which is switched to output a signal from a detector connected to the narrow filter side by an output from the narrow filter side; and an output from the switch means by an S meter output from the detector connected to the wide filter side. a mute circuit that mutes and outputs the muted signal to the multiplex.