JPH028497B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a mute circuit used in a receiver.

[Prior Art] As shown in FIG. 4, in a conventional mute circuit of this type, a signal level detection circuit 28 compares an input signal with a predetermined threshold level, and determines whether the input signal exceeds the threshold level. When the input signal is above the threshold level, a signal as shown in Fig. 5 is generated which becomes "L" level, and when this signal is "H" level (that is, when the input signal is below the threshold level), mute is executed. The circuit 26 muted the output signal to remove unnecessary noise.

[Problems to be Solved by the Invention] However, although these conventional methods are effective in a receiving environment where a stable and strong electric field can be obtained, for example, in a mobile radio station, the input signal may be affected by fading, etc. If the signal exceeds the threshold level and fluctuates above and below it, the received signal itself becomes very difficult to hear. Therefore, there were problems such as the inconvenience of having to perform operations such as lowering the threshold level or stopping the mute.

An object of the present invention is to solve the problems of the above-mentioned conventional circuits and to provide a mute circuit that allows a received signal to be heard well even if the input signal exceeds the threshold level and fluctuates above and below the threshold level. That is.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a mute execution circuit that mutes an output signal when the input signal is below a predetermined level, and a mute execution circuit that mutes the output signal when the input signal is below a predetermined level. and a circuit for canceling the mute of the mute execution circuit when the mute level fluctuates above and below the level more than the frequency.

[Function] By employing the above means, the present invention allows the input signal to fluctuate above and below a predetermined level (threshold level), for example, when the receiving environment changes from a weak electric field to a strong electric field, or vice versa. When this happens, muting is automatically interrupted until the input signal stabilizes.

[Example] Hereinafter, an example of the present invention shown in the drawings will be described.

FIG. 1 shows an embodiment of the present invention, where 1 is an antenna, 2 is a mixing circuit, 3 is a local oscillation circuit, and 4 is a local oscillation circuit.
IF circuit, 5 is a detection circuit, 6 is a mute execution circuit,
7 is a speaker, 8 is an input signal that has passed through the mixing circuit 2 and IF circuit 4 from the antenna 1 and is compared with a predetermined threshold level, and when the input signal exceeds the threshold level, the signal goes to "L" level. 9 is a mute control circuit which generates a signal that changes to "L" level when the state of the signal changes more than a predetermined frequency (for example, the number of changes within a certain period of time). A signal level change judgment circuit 10 that generates a signal (mute cancellation signal), and a signal
It is composed of an AND circuit 11 that generates a MUTE signal at the "H" level when both the OPEN signals are at the "H" level.
The mute execution circuit 6 is configured to mute the output signal to remove unnecessary noise when the MUTE signal is at the "H" level.

When the receiving environment changes from a weak electric field to a strong electric field, the above-mentioned miute circuit, as shown in Fig. 2,
The MUTE signal remains at the "H" level for a short period of time until the state change of the CD signal exceeds a predetermined frequency.
It is linked to the CD signal, but if the frequency exceeds the above
Since the OPEN signal goes to the "L" level, the MUTE signal goes to the "L" level regardless of the subsequent state change of the signal, and the mute is canceled and interrupted. After that, if the signal remains stable for a certain period of time, the signal goes to the "L" level. Became “H” level
The CD signal and MUTE signal will be linked.

Further, when the receiving environment changes from a strong electric field to a weak electric field, the operation is as shown in FIG. 3, and since this case is also the same as the case of FIG. 2, the explanation will be omitted.

Although the signal level detection circuit 8 is used in the above embodiment, a squelch circuit may be used in place of this, and the signal level change judgment circuit 10 can be easily implemented by hardware logic using a timer, counter, and latch. Alternatively, the entire mute control circuit 9 including the AND circuit 11 may be configured by a microcomputer.

[Effects of the Invention] Since the present invention is configured as described above, the received signal can be heard well even if the input signal fluctuates above and below a predetermined level, and is therefore ideal for mobile radio stations that experience severe fading. In addition, it has excellent effects such as being applicable to general wireless systems or wired communication systems in poor environments.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 3 are timing charts showing the operation of the device shown in FIG. 1, FIG. 4 is a block diagram showing an example of the conventional device, and FIG. 4 is a timing chart showing the operation of the device shown in FIG. 4. 1, 21... Antenna, 2, 22... Mixing circuit, 3, 23... Local oscillation circuit, 4, 24...
IF circuit, 5, 25...Detection circuit, 6, 26...
Mute execution circuit, 7, 27... speaker, 8,
28...Signal level detection circuit, 9...Mute control circuit, 10...Signal level change judgment circuit, 11
...AND circuit.

Claims (1)

[Claims] 1. A mute execution circuit that mutes an output signal when the input signal is below a predetermined level, and a mute execution circuit that mutes the output signal when the input signal fluctuates above and below the level more than a predetermined frequency. A miute circuit characterized by comprising a circuit for releasing the .