JPS60171819A - Mute control system - Google Patents

Abstract

PURPOSE:To prevent excess or shortage of mute time by releasing a silence state on the condition that a preceding bias voltage of a demodulation circuit is a prescribed value or below and a bias voltage selected newly is a prescribed value or over at the designation of new selection. CONSTITUTION:When a microcompuer 9 is actuated, an AM/FM switch signal A/F given to bias voltage changeove switches 3, 4 is brought inot a low level and a bias voltage V is applied only to an AM demodulation circuit. Then a mute command M is set to the microcomputer 9, a mute switch 6 is closed and an input terminal of a power amplifier 7 is grounded. Thus, the state is brought into the mute state. After a prescribed time, the microcomputer 9 inverts the signal A/F to high level, a bias voltage V1 of the AM demodulation circuit 1 is dropped, while a bias voltage V2 of an FM demodulation circuit 2 is increased. In discriminating the relation of V1 < pescribed value P1 and V2 > prescribed value P2, the microcomputer 9 releases the mute command M to complete the mute state.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a mute control system used in AM/FM shared radios and the like.

Prior Art and Problems In general, AM/FM dual-purpose radios use dedicated FFI-tuned color circuits connected in parallel to supply each of the AM demodulation output and FM demodulation output to the speaker.The operation of one of these demodulation circuits is selected. The device is configured to include bias voltage switching means that supplies bias voltage only to the selected demodulation circuit based on a selection command to prevent abnormal noise generated when switching between AM and FM from being supplied to the speaker. Therefore, a mute means is provided to temporarily silence the demodulated output supplied to the common speaker every time the selection command is issued.

Conventionally, the signal that commands the silent state (hereinafter referred to as the "mute signal") is turned on immediately after the demodulation circuit selection command is issued, allowing for the time it takes to determine whether each demodulation circuit is in operation or not. It was automatically turned off after a predetermined amount of time had passed.

However, with the conventional mute method described above, it is difficult to accurately evaluate the operation/non-operation time of the demodulation circuit, so the mute time may be longer than necessary, or the mute time may be too short, causing abnormal noise from the speaker. There was a problem that

If the mute time is changed due to the addition of a mute time, etc., there is a problem that the set mute time may be too long or too short.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to eliminate the need for highly accurate evaluation of the operation/non-operation determination time of the demodulation circuit.

Moreover, it is an object of the present invention to provide a mute control system that does not cause any excess or deficiency in the mute time even if the determined time changes after manufacturing.

Structure of the Invention The present invention achieves the above object, and each time a new selection command is issued, the iM selected immediately before this selection command is
The present invention is configured to include means for canceling the bias voltage state of a newly selected fjt 81M circuit every month when the bias voltage of the tFM circuit is below a predetermined value.

Further details of the present invention will be explained below with reference to two examples.

Embodiment of the Invention FIG. 1 is a block diagram illustrating the main parts of an AM/FM radio to which a mute control system according to an embodiment of the present invention is applied. circuit,
4 is a bias voltage selection switch, 5 is an inverter, 6
is the mute switch.

7 is a power amplifier, 8 is a speaker, and 9 is a microcomputer.

The operation of the microcomputer of the AM/FM radio shown in FIG. 1 will be explained below with reference to the flowchart shown in FIG. 2 and the time chart shown in FIG.

When the microcomputer 9 starts operating.

AM/FM connected to bias voltage selector switches 3 and 4
By turning the switching signal A/F low to close switch 3 and open switch 4 at the same time.

A M fat i! Supply bias voltage V to only one circuit.

When this initial setting is completed, the microcomputer 9, in step 10, receives an AM message from the user of this radio.
It is determined whether or not the /FM switching command SC has been issued, and if one has been issued, the process proceeds to the next step II. Microcomputer 9.

By turning on the mute command M and closing the mute switch 6 in step 11, the power amplifier 70
Ground the input terminal. This will mute the radio.

Next, in step 12, the microcomputer 9 inverts the AM/FM switching signal A/F connected to the switch 3.4 from low to high after a predetermined time delay after the mute command M is turned on. At the same time as opening 3, bias voltage changeover switch 4 is closed. As a result, as illustrated in FIG. 3, the bias voltage V1 of the AM demodulation circuit 1 begins to fall from the bias voltage ■, while the bias voltage V2 of the FM demodulation circuit 2 begins to rise toward the bias voltage ■.

Next, the microcomputer 9 proceeds to step 14,
Here, the AM/FM switching signal A/F is high, the bias voltage ■1 of the AM demodulation circuit 1 is smaller than the predetermined voltage P1, and the bias voltage ■2 of the FM demodulation circuit 2 is larger than the predetermined voltage P2. Determine whether or not. Predetermined voltages P1 and P2 are applied to AM demodulation circuit 1 and FM demodulation circuit 2, respectively.
is the critical bias voltage value between the operating state and the non-operating state. If this judgment result is negative, the next step 15
, the AM/FM switching signal A/F is low and the AM
It is determined whether the bias voltage 1 of the demodulation circuit 1 is larger than a predetermined voltage P1 and the bias voltage V2 of the FM demodulation circuit 2 is smaller than a predetermined voltage P2. If the result of this determination is negative, the microcomputer 9 returns to step 14 and repeats the above determination.

After a while after switching from the AM reception state to the FM reception state, the determination result in the first determination step I4 becomes positive,
The microcomputer 9 proceeds to step 16, where it turns off the mute command M and ends the mute state.

After this, when the AM/FM switching command SC is turned on again, the judgment operations in steps 14 and 15 are repeated for a while in the same way as the above-mentioned operation, and then the judgment result in step 15 becomes positive, and step ]6, the mute command M is turned off.

In the above embodiment, the mute switch is installed before the power amplifier, but it may be installed after the power amplifier.

In addition, the case of an AM/FM dual-purpose radio was given as an example.

Kahn, Motorola, 'Harris et al.3
The mute method of the present invention can also be effectively applied to radios and the like that use a dedicated demodulation circuit to receive AM stereo broadcasts in which more than one different system is used in combination.

Effects of Defense As explained in detail above, the mute method of the present invention has two mute methods that each time a new selection command is issued, the bias voltage of the demodulation circuit selected immediately before this selection command is below a predetermined value, and a new selection command is issued. Since it is configured to include means for canceling the silent state on condition that the bias voltage of the selected demodulation circuit becomes equal to or higher than a predetermined value, it is possible to highly accurately evaluate the operation/non-operation determination time of the demodulation circuit. There is an advantage in that it is possible to realize a mute control system that does not require any of the above and does not cause any excess or deficiency in the mute time even if the determined time changes after manufacturing.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main parts of an AM/FM radio to which an embodiment of the present invention is applied, and FIGS. 2 and 3 are a flowchart and time chart for explaining the operation of the radio in FIG. 1, respectively. It is a chart. 1...AM demodulation circuit, 2...FM demodulation circuit, 3゜4...
Bias voltage selector switch, 5... Inverter, 6...
・Mute switch, 7. Power amplifier, 8. Speaker, 9. Microcomputer. Figure 2! 3 diagram

Claims (1)

[Claims] A plurality of parallel-connected demodulation circuits that supply demodulated output to a common speaker, and a bias voltage applied only to the selected demodulation circuit based on a selection command that selects the operation of any one of these demodulation circuits. and muting means for temporarily muting the demodulated output supplied to the common speaker each time the selection command is issued. means for canceling the silent state on condition that the bias voltage of the demodulation circuit selected immediately before the selection command is below a predetermined value and the bias voltage of the newly selected demodulation circuit becomes above a predetermined value; A mute control system characterized by: