JPH02172336A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To convert a reproduced sound with much noise or distortion into an audio signal comparatively easy to listen to by varying separation and a high frequency with an output from a level detection circuit detecting the level of an intermediate frequency signal or a detuning detection circuit. CONSTITUTION:A separation control circuit 8 and a frequency characteristic control circuit 9 operated when an antenna input level is lowered provided to the receiver. When an output by detuning detection circuits 14, 15 is changed, the separation of left/right audio signals is varied continuously in response to the change and when the output by the detuning detection circuits 14, 15 is changed, the frequency characteristic with respect the audio signal is varied continuously in response to the change. If an unpleasant reproduced sound with much distortion is about to be reproduced, the separation of the left/right audio signals is reduced in response to the detuning state and the audio signal with less noise is reproduced and the level of the high frequency component of the audio signal is reduced in response to the detuning state to cut off the noise component. Thus, the audio signal comparatively easy to listen to is reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an FM stereo receiver, and particularly when the antenna input level decreases or during manual tuning, a slight i! ! The present invention relates to an FM stereo receiver that does not give an unpleasant feeling when the playback sound is in a Li tone state.

[Conventional technology]

FM stereo broadcast waves are easily affected by the influence of topography, etc., and the electric field strength changes significantly. Therefore, especially in-vehicle FM
Stereo receivers have disadvantages in that so-called skip noise occurs and the S/N ratio is significantly lowered particularly at weak electric field strengths due to the influence of multipath.

In order to eliminate such drawbacks, when the antenna input drops to a predetermined level, the separation of the left and right channels is first changed continuously according to the amount of reduction in the antenna input, and when the antenna input further drops, FM that continuously changes the frequency characteristics for the reproduced signal, and further changes the level of the reproduced signal continuously (Soft Mu 1) when the antenna power decreases, thereby reducing the audible discomfort. A stereo receiver is provided.

On the other hand, when manually tuning an FM stereo receiver, the demodulated output with a lot of distortion is often reproduced in a slightly detuned state, resulting in a harsh reproduction sound, so the DC power level is detected from the output of the FM detection circuit. There is also an FM stereo receiver that is equipped with an out-of-tune detection circuit that also functions as a soft mute function, and operates the above-described soft mute function according to the output level from the out-of-tune detection circuit.

[Problem to be solved by the invention]

In such an FM stereo receiver, the soft mute function is controlled by a control output corresponding to a decrease in the antenna input level and a control output generated by detecting a detuning state. If the manual tuning operation results in a slight detuning state, there is a problem in that sufficient muting cannot be obtained, and a harsh, distorted sound is reproduced, resulting in an audible sense of discomfort.

The present invention has been made in view of the problems of the conventional FM stereo receiver as described above.
It is an object of the present invention to provide an FM stereo receiver that does not reproduce unpleasant signals even when muting is not activated.

[Means to solve the problem]

In order to solve the above problems, the FM stereo receiver made according to the present invention combines a separation control circuit that operates when the antenna input level decreases and a frequency characteristic control circuit, and when the output from the detuning detection circuit changes. The degree of separation between the left and right audio signals is continuously changed according to the amount of change, and when the output from the detuning detection circuit changes, the frequency characteristic for the audio signal is continuously changed according to the amount of change. It is characterized by the fact that it changes to

[For production]

According to the above configuration, for example, when the tuning is detuned from the tuned state by manual operation and a harsh reproduction sound with a lot of distortion is attempted to be reproduced, the degree of separation between the left and right audio signals decreases depending on the detuning state, It is possible to reproduce an audio signal with less noise, and since the level of the high frequency component of the audio signal is lowered according to the detuning state, noise components are further blocked.

Therefore, the audio signal is reproduced as a relatively easy-to-listen audio signal, and it is possible to create a reproduction state with less discomfort.

〔Example〕

EMBODIMENT OF THE INVENTION Hereinafter, the FM stereo receiver of this invention is demonstrated using drawing.

FIG. 1 is a block diagram showing an embodiment of the present invention, in which an input RF (high frequency) signal from an antenna 1 is amplified in a front I/end section 2 and converted into a TF (intermediate frequency) signal.

After that, it is input to a TF amplifier 3 having a limiter function, and is then input to an FM detection circuit 4 having a Ford Lacher detection configuration, for example.
is applied to

The audio signal demodulated in this detection circuit 4 is transmitted to an amplifier 5.
After amplification, the signal is applied to an MPX (multiplex) demodulation circuit 7 which obtains left and right channel audio signals via a variable attenuator 6 having an electronic volume configuration. The left and right channel audio signals are applied to a separation control circuit 8 for controlling separation (degree of separation), further passed through a frequency characteristic control circuit 9 for attenuating high frequency levels, and output to left and right channel output terminals 10.

On the other hand, in order to detect a level proportional to the electric field strength, the level detection circuit 1 has an IP signal level AM detection configuration of the IF amplifier 3.
1 is detected, and a detection signal corresponding to the level is applied to the level setting circuit 12 at the next stage. Level setting circuit 1
The output of 2 becomes a control signal corresponding to the IF level, and is applied to one input terminal of the OR circuit 13.

On the other hand, the output of the FM detection circuit 4 is passed through the amplifier 5 with reference numeral 14.
and 15, which is applied to the detuning detection circuit.

This detuning detection circuit is extracted from an amplifier 5 that amplifies the output of the FM detection circuit 4, detects the DC output level in the FM detection circuit 4, and rectifies it.

The DC output in the FM detection circuit has a so-called three-character characteristic as shown in FIG. 2(A). In other words, the horizontal axis in the figure is centered on 10.7 MHz (f o), which is the intermediate frequency of FM, and the left and right sides indicate the detuning direction, and the vertical axis indicates positive and negative values with the center as the reference potential (0■). indicates the DC output level.

Therefore, by rectifying the DC output obtained by the low-pass filter 14 in the rectifier circuit 15, the output becomes f as shown in FIG. 2 (b). Detuning the frequency in either direction around OV at will result in a V-shaped output that obtains a negative voltage.

The output of this detuning detection circuit is applied to the level setting circuit 16 at the next stage, and the output of this level setting circuit 16 becomes a control signal B corresponding to the detection output by the detuning detection circuit, which is connected to the other input terminal of the OR circuit 13. is applied to

The outputs of the OR circuits 13 and 13 are respectively output from the level setting circuit 1.
7 to 19, and the output of each level setting circuit 17 to 19 becomes a control signal C-E corresponding to the detection level of the level detection circuit 11 or the detuning detection circuit.

The control signal C is applied to the attenuator 6 as a muting control signal, and the signal C is applied to the separation control circuit 8 as a separation degree control signal.

Further, the signal E is added to the frequency characteristic control circuit 9 and becomes an f-characteristic control control signal.

When the output of the OR circuit 13 reaches the first level according to the settings of the level setting circuits 17 to 19, the separation control circuit 8 operates first, and when the level further increases, the separation degree is adjusted according to the level. is configured to continuously lower the output voltage, for example, to control up to monaural mode,
Further, the output of the OR circuit 13 is at a second level higher than the first level.
When the level reaches , the f-characteristic control circuit operates, and when the level increases further, the amount of high-frequency attenuation is increased in accordance with the level.

Furthermore, when the output of the OR circuit 13 reaches a third level, which is higher than the second level, the variable attenuator 6 operates, and when the level further increases, the amount of attenuation is increased according to the level. It works to make it happen.

FIG. 2(b) shows the relationship between the output of the detuning detection circuit and the above-mentioned effects, and x and y in the figure.

The level of Z is the same as the above-mentioned 1. Second. The third level is shown.

Further, the output from the level detection circuit 11 that detects the level of the intermediate frequency signal is adjusted by the level setting circuit 12, and the level of the signal X is adjusted according to the antenna input level.

If you bring about the same level of output as Y and Z,
Separation control, f-special control, and soft mute control are sequentially performed in accordance with the antenna input and detuning detection output.

As a result, even if the antenna becomes out of tune due to a decrease in the antenna power level or, for example, due to a manual tuning operation, the separation control circuit operates first according to the antenna input level and the degree of detuning, and continuously performs separation from stereo to monaural. Because of the control I roll, it is possible to obtain playback sound with less noise even if the distortion worsens due to the increase in noise due to a decrease in the antenna power level or detuning. In this case, the f-characteristic control circuit operates and attenuates the high-frequency components of the demodulated output in sequence according to the degree of
/N is operated to prevent deterioration. When the input level decreases or the signal to noise ratio is not improved by the effects of the separation control circuit and the f-characteristic control circuit, or the input level becomes disordered, the variable attenuator operates to gradually reduce the output level. However, the output is controlled so that the overall output does not feel strange.

In the embodiment shown in FIG. 1, the variable attenuation circuit 6 is operated by the output from the detuning detection circuit to reduce the output level, but the variable attenuation circuit 6 is not operated and the separation A sufficient S/N ratio improvement effect can be obtained by operating only the control circuit 8 and the f-characteristic control circuit 9.

〔effect〕

As is clear from the above description, the FM stereo receiver of the present invention is configured to change the separation and high frequency based on the output from the level detection circuit or detuning detection circuit that detects the level of the intermediate frequency signal. Therefore, reproduced sound with a lot of noise or distortion caused by a decrease in the antenna power level or a state of disordered tuning can be produced as an audio signal that is relatively easy to open.

Moreover, since the separation and high frequencies gradually change according to the decrease in the antenna input level or the detuning state, it is possible to create a reproduction state with less discomfort.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2(a) and 2(b) are characteristic diagrams for explaining the operation of the detuning detection circuit. 1...Antenna, 2...Front end section, 3...
Bow F amplifier, 4... FM detection circuit, 5... amplifier,
6... Variable attenuator, 7... MPX demodulation circuit, 8...
- Separation control circuit, 9... Frequency characteristic control circuit, 10... Output end, 11... Level detection circuit, 12... Level setting circuit, 13...
OR circuit, 14... low pass filter, 15... rectifier circuit, 16-19... level setting circuit.

Claims (3)

[Claims] (1) An FM detection circuit that receives an intermediate frequency signal and obtains a demodulated audio signal from this intermediate frequency signal, and a multiplex circuit that receives the demodulated audio signal from this FM detection circuit and separates it into left and right audio signals. An FM stereo receiver comprising: a level detection circuit that detects the level of the intermediate frequency signal; a detuning detection circuit that detects a DC output level from the output of the FM detection circuit; and a detection value of the level detection circuit or a separation control circuit that operates when the detection value of the detuning detection circuit changes and continuously changes the separation degree of the left and right audio signals according to the amount of change; and It is characterized by further comprising a frequency characteristic control circuit that operates when the detection value of the detuning detection circuit changes and continuously changes the frequency characteristics of the left and right audio signals according to the amount of change. FM stereo receiver. (2) The separation control circuit is configured to continuously reduce the degree of separation between the left and right audio signals in accordance with the amount of change when the detected value by the level detection circuit or the detuning detection circuit changes, The frequency characteristic control circuit is configured to continuously reduce the level of high frequencies in the left and right audio signals in accordance with the amount of change when the detected value by the level detection circuit or the detuning detection circuit changes. An FM stereo receiver according to claim 1, characterized in that the FM stereo receiver is made of: (3) The separation control circuit operates when the detected value by the level detection circuit or the detuning detection circuit changes to a first level, and continuously adjusts the degree of separation of the left and right audio signals according to the amount of change. The frequency characteristic control circuit operates when the detected value by the level detection circuit or the detuning detection circuit changes to a second level larger than the first level, and the frequency characteristic control circuit operates to change the amount of change. 2. The FM stereo receiver according to claim 1, wherein the FM stereo receiver is configured to continuously change the frequency characteristics of the left and right audio signals depending on the frequency of the left and right audio signals.