JPH04119139U - Softmeute device - Google Patents

Abstract

(57) [Summary] [Purpose] The purpose is to prevent the audio output from being attenuated by the soft mute circuit even if a strong signal is input in a band near the desired signal. [Structure] The detection output of the peak detection circuit 1 is sent to the audio amplifier 3 via the soft mute circuit 2. The S meter voltage from the S meter circuit 4 is applied to a mute control circuit 6 via an OR circuit 5, and a control signal corresponding to the S meter voltage set by a resistor 7 controls the amount of attenuation of the soft mute circuit 2. When a strong signal is input into a band near the desired signal at a predetermined level or higher,
The wideband AGC signal from the wideband AGC 10 becomes high level. At this time, since the second switch means 9 is turned off by the S meter voltage, the first switch means 8 is turned on and short-circuits the resistor 7. Therefore, the amount of attenuation of the soft mute circuit 2 is minimized, and the audio output is not attenuated.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention relates to a soft mute suitable for mobile FM receivers, etc. For details, when receiving the broadcast of a desired station with a relatively low reception level, A soft mute device that stops operating when there is a strong radio signal from the desired neighboring station. It is about improvement.

0002

[Conventional technology]

FM receivers have the advantage of improving the S/N ratio with wideband gain, but On the other hand, there is a threshold level and in a weak electric field below a certain value, the S/N The disadvantage is that the ratio deteriorates rapidly. The reception status is poor while tuning to a specific broadcast frequency. If the condition worsens or the electric field strength becomes low, the AGC circuit (automatic gain control circuit) will operate. It is configured to increase the gain of the amplifier, so that The noise becomes louder and it becomes very difficult to hear. Therefore, if the input signal is below a certain level, Then, the audio signal is passed through a circuit that attenuates it, increasing the transmission path of the audio signal. There is a mute control that temporarily lowers the gain of the width. especially moving With FM receivers for Soft muting is performed in which the sound is muted sequentially.

0003 To perform soft mute, the DC voltage component in the detection output signal is detected and Muting is performed in synchronization with the synchronized display (hereinafter referred to as S meter) circuit. There is something that turns on and off the programming circuit.

0004 Figure 3 is a block diagram showing the soft mute device of a conventional FM radio receiver. In the figure, 1 is a peak detection circuit, 2 is a soft mute circuit, and 3 is an audio booster circuit. 4 is an S meter circuit, and 6 is a mute control circuit. Peak detection time Route 1 detects the FM reception signal and includes a soft mute circuit 2 that controls the detection output. In addition to the audio amplifier 3, the audio output is taken out through the audio amplifier 3. At this time , the S meter voltage output from the S meter circuit 4 is sent to the mute control circuit 6. given, the mute control circuit 6 outputs a control signal according to the S meter voltage. The signal is sent to soft mute circuit 2, and the configuration is configured to perform soft mute operation. . Note that the resistor 7 has a degree of attenuation in the soft mute circuit 2 that is at the level of the S meter voltage. The value is set to a desired value corresponding to . In other words, the S meter voltage decreases. When this occurs, a control signal is output that greatly attenuates the detection output. Set resistance 7 to .

[0005]

[Problem that the idea aims to solve]

As is clear from the above, in the conventional device, only the S meter voltage The soft mute circuit is controlled by , for example, if an undesired neighboring station is located near the broadcast frequency of the desired station with relatively low reception level. When a strong radio signal is input, wideband AGC is activated and the received signal of the desired station is As the output voltage of the S meter circuit decreases, the soft mute circuit operates and the voltage decreases. This has the disadvantage that the amount of attenuation increases and the audio signal output is attenuated.

[0006] Therefore, the purpose of this invention is to use the soft mute circuit not only for the S meter circuit signal. , by controlling in conjunction with wideband AGC signals, the reception level ratio can be improved. If there is a strong radio signal from an undesired adjacent station near the relatively low broadcasting frequency of the desired station. Attenuates the audio signal output by preventing the soft mute circuit from operating even when the It's about trying to prevent it.

[0007]

[Means to solve the problem]

In order to achieve the above object, the present invention provides a detection signal output circuit for an FM radio receiver. The inserted soft mute circuit and the above soft mute circuit according to the S meter signal. a soft mute control circuit that outputs a control signal to control the A soft microphone equipped with a mute attenuation setting resistor for setting the above control signal. In the mute device, the above mute attenuation setting is performed according to the level of the broadband AGC signal. a first switch means for controlling a constant resistance; and a first switch means for controlling a constant resistance; and a second switch means for turning off the first switch means when the It is characterized by.

[0008]

[Effect]

There is a strong signal from an undesired neighboring station near the broadcast frequency of the desired station, which has a relatively low reception level. If there is a wave signal, the wideband AGC signal will be at a high level, and conversely, the D in the detection output signal will be high. Since the C voltage decreases, the first switch means operates and the mute attenuation setting resistor audio output is not attenuated. On the other hand, wideband AG When the C signal becomes less than the S meter voltage, the second switch means switches the first switch means. Since it is turned off, the mute attenuation amount setting resistor is activated.

[0009]

【Example】

The present invention will be described below with reference to embodiments shown in the drawings. Figure 1 shows an embodiment of the soft mute device of the present invention, and the same symbols as in Figure 3 are the same or represents a similar circuit, furthermore, the first switch means 8 and the second switch means 9 is provided.

0010 The first switch means 8 has a mute attenuation amount depending on the output voltage of the wideband AGC 10. This short-circuits the setting resistor 7. Further, the second switch means 9 is connected to the S meter voltage. When the value falls below a predetermined level, the first switch means 8 is turned off.

[0011] The first switch means 8 includes, for example, transistors Q3, Q4 and a resistor R7, R8, the second switch means 9 consists of transistors Q1, Q2 and a resistor R 1 to R4, and transistor Q3 connects to broadband AGC via resistors R5 and R6. 10, and transistor Q2 is connected to the connection point of resistors R5 and R6. At the same time, the S meter voltage is applied to the transistor Q1 via the resistor R1. It has become.

0012 The broadcast frequency of the desired station has a certain level signal and is close to the desired station's broadcast frequency. Assume that there is no strong radio signal from an undesired neighboring station nearby. At that time, the S meter voltage is Since it is above a certain level, transistor Q1 is turned on and transistor Q2 is turned off. Therefore , the transistors Q3 and Q4 operate with a broadband AGC voltage. However, since the output of wideband AGC10 is at a low level, transistors Q3 and Q4 is turned off, and the mute attenuation amount setting resistor 7 that controls the soft mute circuit 2 is turned off. The soft mute characteristics are the same as the conventional soft mute characteristics.

[0013] If there is a strong radio signal from an undesired neighboring station near the broadcast frequency of the desired station, broadband A A high level is generated at GC and transistors Q3 and Q4 are turned on. On the other hand, S The motor voltage is at a low level, transistor Q1 is turned off, and Q2 is turned on, so this As a result, the mute attenuation amount setting resistor 7 is short-circuited, and the mute control effect is reduced. will disappear.

[0014] If the suppression of the signal of the station you wish to receive becomes large or weak, use wideband AGC. is at a low level, the S meter voltage is at a low level, transistor Q1 is turned off, and Q2 is at a low level. Turns on. Therefore, transistors Q3 and Q4 are turned off and the mute attenuation setting is Since the constant resistor 7 is in the operating state, the mute characteristics are the same as the conventional mute characteristics.

[0015] FIG. 2 is a two-signal suppression characteristic diagram showing the effect of the above-described embodiment. In the same figure, P, Q is the frequency of undesired adjacent stations near the broadcast frequency of the desired station with relatively low reception level. There is a strong radio signal, and the input signal of the strong radio signal is 100 dB and 120 dB, respectively. In this example, the vertical axis is the audio output response, and in the figure, S represents the noise component and N represents the received signal component. The horizontal axis represents the desired station signal input level, and the solid line represents the desired station signal input level. The signal suppression characteristics of the conventional FM radio receiver soft mute device, the dotted line is based on the present invention It shows the signal suppression characteristics of the related soft mute device.

[0016] Now, suppose there is a strong radio signal of 120 dB from an undesired neighboring station, and there is a 50 dB signal in the vicinity. If there is a radio signal from B's desired station, the conventional audio signal that corresponds to the difference of 70 dB The audio output response is at point a in the figure, and is achieved by the soft mute device of the present invention. If so, it becomes point b in the figure. Therefore, the desired station signal input level corresponding to A in the figure is suppressed. This means that Also, as shown in P, even if the strong radio signal of an undesired neighboring station is 100 dB, It has a similar effect.

[0017]

[Effect of the idea]

As explained above, there are strong signals from undesired neighboring stations near the broadcast frequency of the desired station. Even if there is a radio signal, the soft mute circuit will not attenuate the audio output Therefore, changes in volume caused by soft muting can be prevented.

[Brief explanation of drawings]

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

FIG. 2 is a two-signal suppression characteristic diagram showing the effects of the embodiment.

FIG. 3 is a block diagram showing a conventional soft mute device for an FM radio receiver.

[Explanation of symbols]

1 Peak detection circuit 2 Soft mute circuit 3 Audio amplifier 4 S meter circuit 6 Mute control circuit 7 Mute attenuation setting resistor 8 First switch means 9 Second switch means 10 Wideband AGC

Claims (1)

[Scope of utility model registration request] Claim 1: A wideband AGC circuit that controls the gain in a high frequency amplifier circuit, a soft mute circuit on the output side of the detection circuit, and software that outputs a control signal to control the soft mute circuit in accordance with an S meter signal. In an FM radio receiver equipped with a soft mute device including a mute control circuit and a mute attenuation setting resistor for setting the above control signal, a broadband A
A first setting means for turning off the mute attenuation amount according to the level of the GC signal, and a second switch means for turning off the first switch means when the S meter voltage falls below a predetermined level. Features a soft mute device.