JPS628973B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal reproducing device, and more particularly to a signal reproducing device having a plurality of signal reproducing sources.

A typical example of such a device is a radio receiver having multiple reception bands. Band switching in a receiver that has multiple receiving bands, such as AM broadcasts and FM broadcasts, is accomplished by selectively supplying power to the tuner section for each band using a selector switch to select one band. There is something to be done. In such a receiver, when the tuner power is switched, it takes a predetermined time for the capacitor that has been charged to the power supply voltage due to the existence of a decoupling capacitor etc. in the tuner whose power has been cut off to be discharged. Therefore, the tuner does not turn off immediately but remains active for a certain period of time. Therefore, the spark noise caused by the changeover switch jumps into the tuner and is generated as an unpleasant sound to the speaker.

In order to prevent such noise, a circuit as shown in FIG. 1 is used. Referring to FIG. 1, AM tuner 1 and FM tuner 2 are supplied with power +B via a band changeover switch _S1 . Further, power +B is applied to the noise prevention circuit ₃ via a leaf switch S2 which closes every time the switch _S1 is switched. The circuit 3 has a transistor Q ₁ that turns on when the leaf switch S ₂ is closed, and connects the output line of each tuner to an alternating current via a capacitor C ₁ and backflow prevention diodes D ₁ and D ₂ . It is in a grounded state to prevent noise from entering.

In this way, in the conventional circuit shown in Figure 1,
To prevent noise when switching bands, remove leaf switch _S2 , transistors, capacitors, resistors, etc.
It has the disadvantage that many circuit parts are required and the circuit becomes complicated.

Such a problem similarly occurs in the case of a signal reproducing device that uses a tape or record as a signal source and incorporates a preamplifier and the above-mentioned tuner section.

An object of the present invention is to provide a signal reproducing device such as a radio receiver that can prevent noise when switching signal sources with a simple circuit configuration.

The device of the present invention includes a plurality of signal sources, that is, signal generating means, whose gain can be controlled by a control voltage, for example, a plurality of tuners (such as an AM or FM tuner), and selectively switches and supplies power to one of these tuners. The target is a device that switches and selects one of the frequency bands using a switch, and amplifies the unselected tuner by applying the power of the tuner selectively supplied by the switch as the gain control voltage of the other unselected tuner. It is characterized by reducing the gain and preventing the generation of noise during switch switching.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a circuit diagram showing an embodiment of the present invention.
This example shows a 3-band radio receiver that can receive AM, FM, and SW (shortwave) broadcasting bands. The power +B is supplied to each power terminal (+) of the AM tuner 1, FM tuner 2, and SW tuner 4 via the band changeover switch _S1 . The positive power supply terminal of the AM tuner is connected to diode D ₃ and resistor R _4.
via the FM tuner 2 AGC circuit (not shown)
It is also connected to the control terminal of the AGC circuit (not shown) of the SW tuner 4 via a diode _D3 and a resistor _R5 .

The positive power supply terminal of FM tuner 2 is connected to the control terminal of the AGC circuit (not shown) of AM tuner 1 via diode _D4 and _R6 , and is further connected to the control terminal of the AGC circuit (not shown) of AM tuner 1 via diode _D4 and resistor _R7 . 4 AGC
Connected to the control terminal of the circuit. In addition, the positive power supply terminal of SW tuner 4 is connected to diode _D5 and resistor _R8.
is connected to the control terminal of the AGC circuit of AM tuner 1 via diode D5 and resistor _R9 , and to the AGC circuit control terminal of FM tuner 2 via diode _D5 and resistor R9. Diodes D ₃ to _{D 5} are connected in the direction in which the positive power supply +B is applied to the AGC control terminal of each tuner, and are so-called backflow prevention elements, and can be replaced with unidirectional switching elements. It is.

In such a configuration, to select the AM band
Let us consider the case where the band changeover switch _S1 is operated to supply power to the AM tuner 1. In this case, if the power supply is switched from a state in which positive power was applied to FM tuner 2 to AM tuner 1, the power to FM tuner 1 will be cut off when switch S ₁ is switched, but the internal device Still active due to coupling capacitor. However, since power is applied to the AM tuner 1, a positive voltage is applied to the AGC control terminal of the FM tuner 2 via the diode _D3 . Therefore, this voltage causes the FM tuner 2 to
By configuring the AGC circuit to reduce the gain of the amplifier, switching noise that has entered the FM tuner 2 will not be generated at its output even though the FM tuner is in an active state.

It is clear that noise prevention can be similarly achieved in other situations as well.

Although the case where the AGC control voltage is used as the positive power supply voltage is shown, the AGC control voltage can be used as the negative voltage by providing the band switching switch _S1 on the negative side of the power supply line. Furthermore, the present invention can be applied not only to a three-band receiver but also to a two-band, for example, AM and FM broadcast receiver, and it goes without saying that the present invention can also be applied to a receiver having a large number of bands.

Furthermore, the present invention is not limited to the tuner of a receiver, but is applicable to devices having various signal sources and configured to perform a selection operation by switching the power source to select the signal source.

In addition, in the above example, the non-selected tuner
Although the configuration is such that a voltage is always applied to the AGC terminal, it is sufficient to apply the AGC voltage only for a predetermined period of time after the switching operation of _the changeover switch _S1 , thereby reducing power consumption. For this purpose, a separate charging/discharging circuit having a predetermined time constant may be provided.

As described above in detail, the present invention has the advantage of eliminating noise during signal switching with an extremely simple circuit configuration.

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[Brief explanation of the drawing]

FIG. 1 is a diagram showing a band switching noise prevention circuit in a conventional receiver, and FIG. 2 is a diagram showing an embodiment of the present invention. Explanation of the symbols of the main parts, 1...AM Chuyuna,
2...FM Chuyuna, 3...SW Chiyuna, S ₁ ...
...Band selection switch, _D1 to _D5 ...Diode for backflow prevention. 〓〓〓〓

Claims (1)

[Claims] 1. A plurality of signal generating means whose gain can be controlled by a gain control voltage, and selectively supplying power to one of the signal generating means to selectively drive one of the signal generating means. 1. A signal reproducing device comprising: a switching drive means for controlling a signal generating means other than the signal generating means selected by the switching driving means; and an applying means for applying the power source as a gain control voltage to a signal generating means other than the signal generating means selected by the switching drive means. 2. Claim 1, wherein the signal generating means is a plurality of tuners for respectively receiving signals within a plurality of reception frequency bands.
The signal reproducing device described in Section 1. 3. The application means has a unidirectional switching element connected between the power supply line of the selected signal generation means and the control input terminal of the automatic gain control circuit of the non-selected signal generation means. The signal reproducing device according to item 1 or 2. 4. The signal reproducing device according to claim 3, wherein the switching element is a diode.