JPS6059781B2 - Muting control signal generation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a muting control signal generation circuit for audio equipment, and particularly to a muting control signal generation circuit for audio equipment such as a multi-band receiver that allows listening by selecting one of multiple sources by switching the power supply. It is related to circuits.

In order to receive broadcast signals of multiple bands, for example, FM and AM bands, a radio receiver is generally equipped with a built-in FM and AM tuner section, and uses a common main amplifier to amplify the tuner output signal to drive a speaker. .

One method for selecting one of the FM and tuner outputs to be input to the main amplifier is to selectively switch the power supply to the FM and AM tuner sections using a power supply changeover switch. This configuration has the disadvantage that a so-called hop sound is generated during the switching operation of the changeover switch, which gives an unpleasant feeling to the user. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a muting control signal generation circuit having a simple configuration for eliminating noise, that is, hop sound, generated when a changeover switch is operated to select one of the signal sources. be. The present invention will be explained below with reference to the drawings.

FIG. 1 is a circuit block diagram showing an embodiment of the present invention.
Power supply +B is applied via a changeover switch 1 to each power supply line of an AM tuner 2 and an FM tuner 3, which are respectively signal generation sources.

The changeover switch 1 has its movable contact a connected to the power supply side,
Output contacts b and c as fixed contacts are connected to the power lines of the AM tuner 2 and FM tuner 3, respectively, and this switch 1 is configured such that output contacts b and c as fixed contacts are short-circuited to each other when switching. This is a so-called relay contact switch. The output signals of both tuners are sent to the main amplifier 5 which is an amplifier via a muting switch 4.
A predetermined load, for example, is input to drive a speaker (not shown).

Further, the output contacts B and c of the switch 1 are both input to an AND gate 6, and the output thereof is applied to a voltage holding circuit 7 consisting of a diode D1 and a capacitor C1, and the holding output controls the on/off of the muting switch 4. Becomes a miute ink control signal.

Therefore, the AND gate 6 and the holding circuit 7 constitute a control signal generating circuit. In such a configuration, when the output of the AM tuner 2 is selected as the input of the main amplifier 5, the movable contact a of the switch 1 is connected to the fixed contact b as shown in the figure, and therefore the output of the AM tuner 2 is connected to the fixed contact b as shown in the figure. Power supply +B is supplied to and activated.

The other FM tuner 3 is naturally inactive. At this time, the output of the AND gate 6 is at a low level (ground potential), so the output of the voltage holding circuit 7 is also at a low level, the muting switch 4 remains on, and the w tuner output is input to the main amplifier 5. Width is increased. In this state, when switch 1 is switched to select the FM tuner output, since switch 1 is a relay contact switch, both inputs of AND gate 6 become high level (power level) at the time of switching, and the The output also changes to a high level.

Follow. The output of the voltage holding circuit 7 also instantaneously becomes high level in response to the change in the output of the AND gate, and the muting switch 4 is opened. When the switching operation of the switch 1 is completed, the output contact c becomes a high level and the contact b becomes a low level, so that the four outputs of the gate 6 return to a low level.

The output of the voltage holding circuit 7 returns to zero level after a predetermined period of time due to the power storage action of the capacitor C1, and at that waiting point, the muting switch is closed and the switching operation is completed. Therefore, when the switch 1 is switched, the muting switch 4 is in the open state, and after a predetermined period of time, it is closed again, so that the noise generated by the switching operation of the power switch 1 is completely suppressed. Become.

Furthermore, it is clear that the muting effect is performed in exactly the same way when the AM tuner output is selected by switching the switch 1 from output contact c to b. In the above circuit, when the switch 1 is switched, both tuners 2 and 3 are switched.
At the same time, the power supply +B is applied to the power supply, and the capacitance on the power supply side may become a problem.

In order to avoid the simultaneous application of power supplies, FIG. 2 shows another circuit configuration diagram of the present invention. "Parts equivalent to those in FIG.
A PNP transistor Q1 is provided as a switch element. That is, the emitter is connected to the output contact b, the collector is connected to the power line A1 of the tuner 2, and the base is connected to the power line B of the FM tuner 3 via the resistor R1. On the other hand, the output contact C. of switch 1. A PNP transistor Q2 as a switching element is provided between the 15FM tuner 3 and the power supply line B.

That is, the emitter is connected to the output contact c, the collector is connected to the power line B, and the base is connected to the power line A via the resistor R2. Large resistors R3 and R4 are provided between both power supply lines A and B and ground.
The other circuit configurations are the same as in FIG. 1.

In the illustrated state, the power supply + is connected to output contact b of switch 1.
When B is supplied, +B is applied to the emitter of transistor Q1, and the base is grounded via R1 and R4. Therefore, the transistor Q1 is turned on and the AM tuner 2 is activated. Since the other transistor Q2 is off, the FM tuner 3 is inactivated, and therefore, the AM tuner output is applied to the main amplifier 5 via the muting switch 4, which is in a closed state. ), when switch 1 is switched at time t1 (see Figure 3), time ! Well, output contact b
and c become short-circuited.

Therefore, during that period (t1 to T2), the control output C of the control voltage generation circuit consisting of the gate 6 and the voltage holding circuit 7 becomes high level, and the opening of the muting switch 4 is the first.
It is similar to the figure. In this case, positive power supply +B is applied to both the emitters of transistors Q1 and Q2, but transistor Q
Since the positive power supply (approximately equal to +B) of the power supply line A of the AM tuner 2 is applied to the base of the transistor Q2 via the resistor R2, the transistor Q2 is turned off. Therefore, during this period (t1 to T2), power is applied to the AM tuner 2, but power is not applied to the FM tuner 3. When the switching operation of the switch 1 is completed at the timing, no voltage is applied to the emitter of the transistor Q1 and it is turned off, and the AM tuner 2 becomes inactive, and at the same time, the base potential of the transistor Q2 becomes zero. FM tuner 3 is activated.

Then, until the output C of the voltage holding circuit 7 becomes approximately zero V (
T3) It can be seen that the muting switch 4 is opened and the switching noise is completely suppressed. After time T3, the muting switch is closed and the output of the FM tuner 3 is selected. Therefore, as shown in the timing waveform in FIG. 3, power is not applied to both tuners at the same time.

FIG. 4 is a circuit diagram showing another embodiment of the present invention, and shows the case of a three-band receiver.

That is, in addition to AM and FM tuners 2 and 3, the switch 1 is equipped with a shortwave SW tuner 8, and correspondingly, the switch 1 has fixed contacts B and c as well as d, and the contacts c and d are short-circuited when switching. This is the configuration that will be used. An AND gate 6b for detecting a short circuit between the contacts C and d is provided in addition to the gate 6a, and the outputs of both gates are input to the hold capacitor C1 via diodes Dla and Dlb. Further, a PNP transistor Q3 is provided as a switch element between the output contact d (power line D of the 5SW tuner 8).

Resistors Rl, R3 to R
6, R2l, R22 and diodes D2 to D4 are connected as shown in the figure, and a high resistance R is connected between the power line D and the ground.
5 is provided. Even in such a configuration, a high level is output by the AND gates 6a and 6b, respectively, when Bec and ced of the switch 1 are switched, and the muting switch 4 is opened by the control output C, thereby suppressing the hop sound. It's obvious.

Furthermore, simultaneous power supply to the two tuners when the switch 1 is switched is prevented by the transistors Q1 to Q3, resistors, and diode circuit network. Note that when the switch 1 is in the illustrated state, power +B is supplied to the power line A of the AM tuner 2, but at the same time the diode D2
A positive voltage is also applied to the power supply line D via the resistor R22.

However, there was no response. . By increasing , the positive voltage applied to the power supply line D can be made to a substantially negligible value. Similarly, the resistor R2l can be made large so that when power is supplied to the power line D, the voltage applied to the power line A can be ignored. As described above, according to the present invention, a relay contact switch is used as a power supply changeover switch, detects the short-circuit state of the contact and generates a muting control signal, and furthermore, each of the contacts and each power line of the signal source circuit. By installing a switch element between each contact and controlling the switch element to turn on and off appropriately according to the potential difference between each contact and each power line, simultaneous power supply to both signal source circuits is prevented when switching the switch. This makes it possible to perform extremely effective muting control. In the above example, AM, FM, and SW tuners are used as signal generation sources, but it is needless to say that the present invention is not limited to this and that various modifications and applications can be made.

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[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing another example of the present invention, FIG. 3 is a timing waveform diagram explaining the operation of FIG. 2, and FIG. 4 is a block diagram showing another example of the present invention. FIG. 3 is a block diagram showing still another example of the invention. Explanation of the symbols of the main parts, 1... Relay switch, 2... AM tuner, 3...
FM tuner, 4... Muting switch, 5... Main amplifier, 6... AND gate, Q1-Q3h... Transistor.

Claims (1)

[Claims] 1 first and second signal generating means, an amplifier for amplifying the output signal of the signal generating means, and a switching means for selectively switching and supplying power to one of the first and second signal generating means; A muting control signal generation circuit for an audio equipment configured to input an output signal of the signal generation means to which power is selectively supplied by the switching means to the amplifier, the switching means comprising: a power supply selector switch having first and second output contacts that are short-circuited to each other during a switching operation; and a power supply selector switch that is connected between the first output contact and a power line of the first signal generating means; a switching element connected between the second output contact and the power line of the second signal generating means, the switching element being turned on and off by a potential difference between the contact and the power line of the second signal generating means; a switching element that is controlled on and off by a potential difference between a second output contact and a power line of the first signal generating means, and the first and second output contacts are short-circuited to have the same potential. What is claimed is: 1. A muting control signal generation circuit comprising control signal generation means for generating a muting control signal by detecting that a mutating control signal has occurred.