JP3036135B2 - Signal input selection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal input selection circuit provided with a plurality of signal input terminals and for selecting a plurality of input signals respectively supplied from signal supply devices connected thereto.

[0002]

2. Description of the Related Art In the field of audio equipment, audio signals from a plurality of audio signal supply devices such as an open-reel type tape recorder, a cassette tape recorder, and a disc player are transmitted to an amplifier having a plurality of external input terminals. In many cases, a system is provided in which the audio signal is supplied through a plurality of external input terminals, and the audio signal selected and amplified by the amplifying device is supplied to a speaker to obtain a reproduced sound. In such an audio system, an amplifier which is a core of the audio system has output terminals of a plurality of audio signal supply devices connected to a plurality of external input terminals provided therein, respectively. A desired one of the input audio signals supplied from the audio signal supply device through a plurality of external input terminals is selected, and the selected input audio signal is amplified.
Therefore, the amplification device is provided with a signal input selection circuit including a plurality of external input terminals.

Conventionally, such a signal input selection circuit is generally configured as shown in FIG. FIG.
Is provided with three signal input terminals 12, 13, and 14 in the amplifying device 11, and the signal input terminal 12 is provided with the signal electrode 12S and the ground electrode 12E. And the signal input terminal 13 is formed including the signal electrode 13S and the ground electrode 13E.
It is formed including S and the ground electrode 14E.

The ground electrodes 12E to 14E of the signal input terminals 12 to 14 are commonly connected to a chassis 15 which is built in the amplifier 11 and forms a reference potential point.
Further, the signal electrode 1 included in each of the signal input terminals 12 to 14 is provided.
2S to 14S are selection contacts 20 of the signal changeover switch 20.
a, 20b and 20c, respectively. In the signal changeover switch 20, the movable contact 20d is connected to the selection contact 2
0a to 20c.
The signal derived through d is supplied to a signal amplification processing unit 21 built in the amplification device 11. Under the circumstances, the signal input terminals 12 to 14 and the signal changeover switch 20 constitute a signal input selection circuit. Note that the chassis 15 is equivalently grounded via a predetermined capacitance C1.

The signal input terminals 12 to 14 are connected to external signal supply sources 25 and 2 which are, for example, audio signal supply devices.
Output terminals 26, 29 and 32 respectively provided by 8 and 31
Are connected respectively. An output terminal 26 of the external signal supply source 25 is formed to include a signal electrode 26S and a ground electrode 26E. The signal electrode 26S is connected to a signal supply unit 27 built in the external signal supply source 25. The electrode 26E is connected to the chassis 3 built in the external signal supply source 25.
4 is connected. The signal electrode 26S and the ground electrode 26E at the output terminal 26 of the external signal supply source 25
Are connected to the signal electrode 12S and the ground electrode 12E at the signal input terminal 12 of the amplifier 11 through the connection cable 35.
Connected to each other.

Similarly, the signal electrode 29S and the ground electrode 29 at the output terminal 29 of the external signal source 28 are
E is a signal supply unit 30 built in the external signal supply source 28 and a chassis 3 built in the external signal supply source 28, respectively.
8 and through the connection cable 36,
Signal electrode 13 at signal input terminal 13 of amplifying device 11
S and the ground electrode 13E, respectively.
Signal electrode 3 at output terminal 32 of external signal supply 31
2S and the ground electrode 32E are connected to the signal supply unit 33 and the chassis 39 incorporated in the external signal supply source 31, respectively.
Are connected respectively to the signal electrode 14S and the ground electrode 14E of the signal input terminal 14 of FIG.

Under these circumstances, in the signal input selection circuit provided in the amplifying device 11, the signal changeover switch 20
Is connected to the selection contact 20a, the signal input terminal 12 is selected, and the signal from the signal supply unit 27 built in the external signal supply source 25 is output to the output terminal of the external signal supply source 25. 26, the signal is taken in through the signal input terminal 12 of the amplifying device 11 and the switch 20 and supplied to the signal amplification processing unit 21, and the movable contact 20d of the signal changeover switch 20 is connected to the selection contact 20b. , The signal input terminal 13 is selected, and the signal from the signal supply unit 30 incorporated in the external signal supply source 28 is output to the output terminal 29 of the external signal supply source 28 and the amplification device 1.
1 through the signal input terminal 13 and the switch 20 to be supplied to the signal amplification processing unit 21. Further, the movable contact 20d of the signal changeover switch 20 is connected to the selection contact 20c, so that the signal input terminal 14 is selected, and the signal from the signal supply unit 33 built in the external signal supply source 31 is output to the output terminal 3 of the external signal supply source 31.
2. Signal input terminal 14 and switch 20 of amplifying device 11
And supplied to the signal amplification processing unit 21 via the

[0008]

When a signal input selection circuit composed of the signal input terminals 12 to 14 and the signal changeover switch 20 configured as described above is used,
Chassis 15 and external signal supply source 2 in amplifying device 11
5, the potential difference between the chassis 34 in the external signal supply 28, the chassis 38 in the external signal supply 28, and the chassis 39 in the external signal supply 31 causes the amplifier 11 to be connected to each of the external signal supply 25, 28, and 31. There will be a noise source. For example, between the amplifying device 11 and the external signal supply source 25, a noise source Sn is equivalently connected to the chassis 34 of the external signal supply source 25 via a predetermined capacitor C2, and the noise current is thereby reduced. But,
Ground electrode 12 at signal input terminal 12 of amplifier 11
E flows through the ground-side conductor of the connection cable 35 that connects E to the ground electrode 26E of the output terminal 26 of the external signal supply source 25, and noise corresponding to the product of the noise current and the impedance Z1 of the ground-side conductor of the connection cable 35 Voltage is generated. Similarly, the amplification device 11
And the external signal supply source 28,
The noise current flowing through the ground-side conductor of the connection cable 36 connecting the ground electrode 13E at the signal input terminal 13 and the ground electrode 29E at the output terminal 29 of the external signal supply source 28, and the impedance Z2 at the ground-side conductor of the connection cable 36 A noise voltage corresponding to the product of the above is generated. Further, between the amplifying device 11 and the external signal supply source 31, the ground electrode 14E at the signal input terminal 14 of the amplifying device 11 and the output terminal 3 of the external signal supply source 31
Connection cable 3 for connecting to ground electrode 32E in 2
7 and the impedance Z3 in the grounding conductor of the connection cable 37.
A noise voltage corresponding to the product of

The noise voltage generated as described above is changed by the grounding electrodes 12E to 14E at the respective signal input terminals 12 to 14 of the amplifying device 11 which are commonly connected to the chassis 15 of the amplifying device 11. The signal input terminal 1 of the amplifier 11 selected by the switch 20
Signal amplification processing unit 21 through any one of 2 to 14
Is superimposed on the signal supplied to the signal amplification processing unit 21 so that the noise-to-signal ratio (S / N
Ratio) is reduced.

In view of the above, the present invention provides a plurality of signal input terminal portions each formed by a pair of a signal electrode and a ground electrode, and an external signal supply connected to each of the plurality of signal input terminal portions. And a switch section for selecting a signal supplied from the source through each of the plurality of signal input terminal sections and supplying the selected signal to a common signal processing section for the plurality of signal input terminal sections. It is possible to suppress an influence of a noise voltage generated between a ground electrode at each of the plurality of signal input terminal units and a ground electrode at an output terminal of an external signal supply source connected thereto with respect to a supplied signal. It is an object of the present invention to provide a signal input selection circuit that can be used.

[0011]

To achieve the above object, a signal input selection circuit according to the present invention comprises a plurality of signal input terminal portions each formed by a pair of a signal electrode and a ground electrode; A plurality of first switch units connected between the signal electrodes in each of the signal input terminal units and a signal processing unit common to the plurality of signal input terminal units; A plurality of second switch units connected between the ground electrode and the reference potential point, and a test power supply common to the ground electrode and the plurality of signal input terminal units in each of the plurality of signal input terminal units. A plurality of third switch units connected therebetween; and an impedance determination unit configured to determine whether the impedance state of each of the plurality of second switch units is good or not. Selected Both the second and third switch units connected to the ground electrode are turned on, and current from the inspection power supply flows through the turned on second and third switch units. A state in which the quality of the impedance state in the second switch unit is determined by the impedance determination unit based on a voltage obtained between both ends of the second switch unit that is turned on, and a result of the determination of the impedance state by the impedance determination unit Is good, the first and second terminals respectively connected to the signal electrode and the ground electrode in the selected signal input terminal portion.
Is turned on, the third switch connected to the ground electrode of the selected signal input terminal is turned off, and the input signal from the selected signal input terminal is The state supplied to the processing unit is assumed.

[0012]

In the signal input selection circuit according to the present invention, a signal from an external signal supply source through a selected one of the plurality of signal input terminals is supplied to the first switch. When supplied to the signal processing unit via one,
Only the ground electrode at the selected signal input terminal is connected to the reference potential point via the second switch connected thereto, and the connection of the ground electrode to the reference potential point at the unselected signal input terminal is , Are blocked by a second switch connected thereto. The state in which the signal from the external signal supply source through the selected signal input terminal is supplied to the signal processing unit via one of the first switch units is connected to the selected signal input terminal. The impedance state when the second switch section is turned on is determined when the impedance is determined to be good by the impedance determination section. Therefore, the signal state of the signal from the external signal supply source through the selected signal input terminal section is obtained. The supply to the processing unit is performed when the ground electrode at the selected signal input terminal is properly connected to the reference potential point. Therefore, for the signal supplied to the signal processing unit through the selected signal input terminal unit, the ground electrode at each of the plurality of signal input terminal units and the ground electrode at the output terminal of the external signal supply connected thereto. The effect of the noise voltage generated during the period is surely suppressed.

[0013]

FIG. 1 shows an example of a signal input selection circuit according to the present invention. In this example, an amplifier device 51 is provided with three signal input terminals 52, 53 and 54. I have.

The signal input terminal 52 is formed including a signal electrode 52S and a ground electrode 52E. The signal input terminal 53 is formed including a signal electrode 53S and a ground electrode 53E. 54 is a signal electrode 54S
And a ground electrode 54E. And
The signal electrodes 52S to which the signal input terminals 52 to 54 respectively have
54S is connected to a common connection point 58 via switches 55, 56 and 57, respectively. The common connection point 58 is
The buffer amplifier 60 is connected via a resistor 59, and the output terminal of the buffer amplifier 60 is connected via a switch 61 to a signal amplification processing unit 62.

The ground electrodes 52E to 54E of the signal input terminals 52 to 54 are connected to switches 63 and 6 respectively.
Via the reference numerals 4 and 65, it is connected to a reference potential point in the amplification device 51, for example, a chassis built in the amplification device 51. The ground electrodes 52E to 54E of the signal input terminals 52 to 54 are connected to a common connection point 69 via switches 66, 67 and 68, respectively. The common connection point 69 is connected via a resistor 70. It is connected to an inspection power supply 71. The inspection power supply 71 is configured by, for example, a battery. Further, the light emitting element 7 is connected to the common connection point 69.
2 is connected. An example of the signal input selection circuit according to the present invention is configured by the elements other than the signal amplification processing unit 62 among the various elements and components arranged in the amplification device 51 described above.
Among them, in particular, each of the switches 66, 67, and 68 ensures that a proper ON state and a proper OFF state are ensured.

The signal input terminals 52 to 54 are connected to external signal supply sources 75 and 7 which are, for example, audio signal supply devices.
8 and 81 have output terminals 76, 79 and 82, respectively.
Are connected respectively. An output terminal 76 of the external signal supply source 75 is formed to include a signal electrode 76S and a ground electrode 76E. The signal electrode 76S is connected to a signal supply unit 77 built in the external signal supply source 75. The electrode 76E is connected to a chassis 84 which is built in the external signal supply source 75 and forms a reference potential point. The signal electrode 76 at the output terminal 76 of the external signal supply source 75
S and the ground electrode 76E are connected through the connection cable 85,
Signal electrode 52 at signal input terminal 52 of amplifying device 51
S and the ground electrode 52E, respectively. Thereby, a signal from the signal supply unit 77 built in the external signal supply source 75 is transmitted from the signal electrode 76S at the output terminal 76 of the external signal supply source 75 to the signal input terminal 52 of the amplification device 51 through the connection cable 85. Signal electrode 52S
Is provided.

Similarly, the signal electrode 79S and the ground electrode 79 at the output terminal 79 of the external signal supply source 78 are provided.
E is connected to a signal supply unit 80 built in the external signal supply source 78 and a chassis 88 built in the external signal supply source 78 to form a reference potential point, respectively. Signal input terminal 53
Are connected to a signal electrode 53S and a ground electrode 53E, respectively.
2, the signal electrode 82S and the ground electrode 82E are connected to and connected to a signal supply unit 83 built in the external signal supply source 81 and a chassis 89 built in the external signal supply source 81 to form a reference potential point, respectively. The signal electrode 54S and the ground electrode 54E of the signal input terminal 54 of the amplifier 51 are connected to each other through a cable 87.
As a result, a signal from the signal supply unit 80 incorporated in the external signal supply source 78 is output from the output terminal 7 of the external signal supply source 78.
9 and the signal electrode 53S at the signal input terminal 53 of the amplifying device 51 via the connection cable 86, and the external signal supply source 81
A signal from a signal supply unit 83 incorporated in the device is supplied from a signal electrode 82S at an output terminal 82 of an external signal supply source 81.
A state where the signal is supplied to the signal electrode 54S of the signal input terminal 54 of the amplifying device 51 through the connection cable 87 is established.

In such a configuration, a chassis 84 forming a reference potential point in the amplifier 51 and a reference potential point in the external signal supply source 75, and a chassis 88 forming a reference potential point in the external signal supply source 78. Due to the potential difference between the external signal supply source 81 and each of the chassis 89 forming a reference potential point, a noise source exists between the amplifying device 51 and each of the external signal supply sources 75, 78 and 81. Become. For example, between the amplifying device 51 and the external signal supply source 75, a noise source Si is equivalently connected to the chassis 84 of the external signal supply source 75 via a predetermined capacitance C3, and the noise current Flows through the ground-side conductor of the connection cable 85 that connects the ground electrode 52E at the signal input terminal 52 of the amplifying device 51 and the ground electrode 76E at the output terminal 76 of the external signal supply source 75. A noise voltage corresponding to the product of the impedance and the impedance Z4 at the ground side conductor is generated. Similarly, between the amplifying device 51 and the external signal supply source 78, the ground electrode 53E at the signal input terminal 53 of the amplifying device 51 and the ground electrode 79E at the output terminal 79 of the external signal supply source 78 are provided.
A noise voltage corresponding to the product of the noise current flowing through the ground-side conductor in the connection cable 86 and the impedance Z5 of the ground-side conductor in the connection cable 86 is generated, and the amplification device 51 and the external signal supply source 8 are connected.
1, the signal input terminal 54 of the amplification device 51
Is equivalent to the product of the noise current flowing through the ground-side conductor of the connection cable 87 connecting the ground electrode 54E at the output terminal 82 of the external signal supply source 81 and the impedance Z6 of the ground-side conductor of the connection cable 87. A noise voltage will be generated.

Under the circumstances described above, the amplification device 51
A signal from a signal supply unit 77 incorporated in an external signal supply source 75 connected to the signal input terminal 52 of the amplifier, and a signal supply unit incorporated in an external signal supply source 78 connected to the signal input terminal 53 of the amplifier 51 Signal from 80 and amplifying device 5
1 external signal supply source 81 connected to the signal input terminal 54
One of the signals from the signal supply unit 83 incorporated in the amplifying device 51 is selected and supplied to the signal amplification processing unit 62 incorporated in the amplifying device 51.

For example, the signal input terminal 52 of the amplifier 51
When the signal from the signal supply unit 77 incorporated in the external signal supply source 75 connected to the amplifying device 51 is selected and supplied to the signal amplification processing unit 62 incorporated in the amplification device 51, first, Switches 55-57, 61, 63-
Only the switches 63 and 66 out of 68 are turned on, and all others are turned off. As a result, the current from the test power supply 71 flows through the resistor 70, the switch 66, and the switch 63, and the level of the voltage Vx obtained at the common connection point 69 at that time is detected by the level comparison unit 73. Under such circumstances, the voltage Vx obtained at the common connection point 69 is equal to the switch 66 and the switch 6
3, the switch 66 is substantially turned on since the switch 66 has an extremely low impedance since a proper ON state is ensured.
3 is applied. Therefore, the voltage Vx assumes a level corresponding to the impedance of the switch 63 that is turned on. When the switch 63 is in a proper on state and has a very low impedance, the level of the voltage Vx is When the switch 63 is low and has a relatively high impedance without the switch 63 being properly turned on, the level of the voltage Vx is high.

In the level comparing section 73, the level of the voltage Vx is compared with, for example, a comparatively low reference level. As a result, if the level of the voltage Vx is lower than the reference level, the switch 63 is switched. Of the light emitting element 72 is maintained in the non-light emitting state while the level of the voltage Vx is equal to or higher than the reference level. Has a relatively high impedance,
Therefore, it is determined that the switch 63 is not in the proper ON state, and the light emitting element 72 is set to emit light intermittently. Thus, the level comparison section 73 forms an impedance determination section that determines whether the impedance state of the switch 63 under the ON state is good.

When the level of voltage Vx is higher than the reference level and light emitting element 72 emits light intermittently, ground electrode 52 at signal input terminal 52
E and the reference potential point in the amplifier 51 are in a relatively high impedance state, and therefore, the ground electrode 52E at the signal input terminal 52, which is generated between the signal input terminal 52 and the external signal supply source 75, External signal source 75
The noise voltage corresponding to the product of the noise current flowing through the ground-side conductor of the connection cable 85 connecting the ground electrode 76E of the output terminal 76 and the impedance Z4 of the ground-side conductor of the connection cable 85 has a relatively large level. Is superimposed on the signal supplied to the signal electrode 52S at the signal input terminal 52, so that the external signal supply source 75 connected to the signal input terminal 52
The signal from the signal supply unit 77 incorporated in the
Is not supplied to the signal amplification processing unit 62 incorporated in the controller 63. Instead, for example, a measure is taken to set the switch 63 to an appropriate ON state.

On the other hand, when the level of voltage Vx is lower than the reference level and light emitting element 72 is maintained in a non-light emitting state, ground electrode 52 at signal input terminal 52 is
E and the reference potential point in the amplifying device 51 are in a very low impedance state, and therefore occur between the signal input terminal 52 and the external signal supply 75, the ground electrode 52E at the signal input terminal 52 and the external Signal source 75
The noise voltage corresponding to the product of the noise current flowing through the ground-side conductor of the connection cable 85 connecting the ground electrode 76E of the output terminal 76 and the impedance Z4 of the ground-side conductor of the connection cable 85 is the signal at the signal input terminal 52. Since the influence on the signal supplied to the electrode 52S is extremely small, the signal from the signal supply unit 77 incorporated in the external signal supply source 75 connected to the signal input terminal 52 is transmitted to the amplification device 51. Is supplied to the signal amplification processing unit 62 incorporated in the device. Therefore, the switch 66 is turned off, the switch 55 is turned on, and then the switch 61 is turned on. Thus, from the signal supply unit 77 built in the external signal supply source 75, the signal electrodes 52 S at the output terminal 76 of the external signal supply source 75 and the signal electrode 52
S is supplied to the switch 55, the common connection point 5
8, the signal is supplied to the signal amplification processing unit 62 through the resistor 59, the buffer amplifier 60, and the switch 61.

At this time, the ground electrode 53E at the signal input terminal 53 and the ground electrode 54 at the signal input terminal 54
The switches 64 and 65 respectively connected to E are turned off, and the ground electrode 53E at the signal input terminal 53 and the ground electrode 54E at the signal input terminal 54 are turned off.
Are not connected to the reference potential points in the amplifying device 51, respectively. Accordingly, the grounding occurs in the connection cable 86 connecting the ground electrode 53E of the signal input terminal 53 and the ground electrode 79E of the output terminal 79 of the external signal supply source 78, which is generated between the signal input terminal 53 and the external signal supply source 78. A noise voltage corresponding to the product of the noise current flowing through the side conductor and the impedance Z5 of the grounding conductor in the connection cable 86; and a noise voltage generated between the signal input terminal 54 and the external signal supply source 81 at the signal input terminal 54. Ground electrode 54E and output terminal 8 of external signal supply source 81
Connection cable 8 for connecting to ground electrode 82E in 2
7 and the impedance Z6 in the grounding conductor of the connection cable 87.
Is not affected by the signal supplied to the signal electrode 52S at the signal input terminal 52.

A signal from a signal supply unit 80 built in an external signal supply source 78 connected to a signal input terminal 53 of the amplifier 51 is selected, and a signal amplification processing unit 62 built in the amplifier 51 is selected. To be supplied to the switches 55 to 57, 61, 63 to 6
Only the switches 64 and 67 of 8 are turned on, and all others are turned off. As a result, the current from the test power supply 71 flows through the resistor 70, the switch 67, and the switch 64, and the voltage Vx obtained at the common connection point 69 at that time is supplied to the level comparison unit 73, and the level comparison unit 73 performs the level comparison. The unit 73 determines whether the level of the voltage Vx is lower than the reference level. As a result, when the level of the voltage Vx is lower than the reference level, the impedance of the switch 64 is extremely low, so that the switch 64 is determined to be in an appropriate ON state, and the light emitting element 7
2 is maintained in a non-light emitting state, while the level of the voltage Vx is equal to or higher than the reference level, the impedance of the switch 64 is relatively high, and therefore, it is determined that the switch 64 is not properly turned on and the light is emitted. The element 72 is set to emit light intermittently. Thus, the level comparison unit 73
Also forms an impedance determination unit that determines the quality of the impedance state of the switch 64 under the ON state.

When the voltage Vx is higher than the reference level and the light-emitting element 72 emits light intermittently, the ground electrode 53 at the signal input terminal 53
There is a relatively high impedance state between E and a reference potential point in the amplifier 51, and therefore, a ground electrode 53E at the signal input terminal 53, which is generated between the signal input terminal 53 and the external signal supply source 78, External signal source 78
The noise voltage corresponding to the product of the noise current flowing through the grounding conductor of the connection cable 86 connecting the grounding electrode 79E of the output terminal 79 and the impedance Z5 of the grounding conductor of the connection cable 86 has a relatively large level. Is superimposed on the signal supplied to the signal electrode 53S at the signal input terminal 53, so that the external signal supply source 78 connected to the signal input terminal 53
The signal from the signal supply unit 80 incorporated in the
Is not supplied to the signal amplification processing unit 62 incorporated in the device, and instead, for example, a measure is taken to make the switch 64 take an appropriate ON state.

On the other hand, when the level of voltage Vx is lower than the reference level and light emitting element 72 is maintained in a non-light emitting state, ground electrode 53 at signal input terminal 53
E and the reference potential point in the amplifying device 51 are in a very low impedance state. Therefore, the ground electrode 53E at the signal input terminal 53 and the external Signal source 78
The noise voltage corresponding to the product of the noise current flowing through the grounding conductor of the connection cable 86 connecting the ground electrode 79E of the output terminal 79 of the output cable 79 and the impedance Z5 of the grounding conductor of the connection cable 86 is the signal at the signal input terminal 53. Since the influence on the signal supplied to the electrode 53S is extremely small, the signal from the signal supply unit 80 incorporated in the external signal supply source 78 connected to the signal input terminal 53 is transmitted to the amplification device 51. Is supplied to the signal amplification processing unit 62 incorporated in the device. Therefore, the switch 67 is turned off, the switch 56 is turned on, and then the switch 61 is turned on. Thus, from the signal supply unit 80 built in the external signal supply source 78, the signal electrode 79S at the output terminal 79 of the external signal supply source 78 and the connection cable 86 connect the signal electrode 53 at the signal input terminal 53.
S is supplied to the switch 56, the common connection point 5
8, the signal is supplied to the signal amplification processing unit 62 through the resistor 59, the buffer amplifier 60, and the switch 61.

In this case, the switches 63 and 65 connected to the ground electrode 52E at the signal input terminal 52 and the ground electrode 54E at the signal input terminal 54, respectively.
Are off, and the ground electrode 52E at the signal input terminal 52 and the ground electrode 54E at the signal input terminal 54 are not connected to the reference potential points in the amplifier 51, respectively. Therefore, the grounding occurs in the connection cable 85 connecting the ground electrode 52E of the signal input terminal 52 and the ground electrode 76E of the output terminal 76 of the external signal supply source 75, which is generated between the signal input terminal 52 and the external signal supply source 75. Current flowing through the side conductor and impedance Z on the ground side conductor in the connection cable 85
4 and a signal input terminal 5
4 and an external signal supply source 81, noise flowing through a ground-side conductor in a connection cable 87 connecting the ground electrode 54E at the signal input terminal 54 and the ground electrode 82E at the output terminal 82 of the external signal supply source 81. The noise voltage corresponding to the product of the current and the impedance Z6 of the grounding conductor in the connection cable 87 does not affect the signal supplied to the signal electrode 53S at the signal input terminal 53.

Further, the signal input terminal 54 of the amplifying device 51
When a state is selected in which a signal from the signal supply unit 83 incorporated in the external signal supply source 81 connected to is selected and supplied to the signal amplification processing unit 62 incorporated in the amplification device 51, first, Switches 55-57, 61, 63-
Only the switches 65 and 68 out of 68 are turned on, and all others are turned off. As a result, a state is established in which the current from the inspection power supply 71 flows through the resistor 70, the switch 68, and the switch 65.
And the level comparing section 73 determines whether or not the level of the voltage Vx is lower than the reference level. as a result,
When the level of the voltage Vx is lower than the reference level, the impedance of the switch 65 is extremely low, and therefore, the switch 65 is considered to be in a proper ON state, and the light emitting element 72 is maintained in a non-light emitting state, while When the level of the voltage Vx is equal to or higher than the reference level, the impedance of the switch 65 is relatively high. Therefore, the switch 65 is not in an appropriate ON state, and the light emitting element 72 is set to emit light intermittently. You. Thus, the level comparison unit 73
Also forms an impedance determination unit that determines the quality of the impedance state of the switch 65 under the ON state.

When the level of the voltage Vx is equal to or higher than the reference level and the light emitting element 72 emits light intermittently, the ground electrode 54 at the signal input terminal 54
E and a reference potential point in the amplifier 51 are in a relatively high impedance state. Therefore, a ground electrode 54E at the signal input terminal 54, which is generated between the signal input terminal 54 and the external signal supply source 81, External signal source 81
The noise voltage corresponding to the product of the noise current flowing through the ground-side conductor of the connection cable 87 connecting the ground electrode 82E of the output terminal 82 to the impedance Z6 of the ground-side conductor of the connection cable 87 has a relatively large level. Is superimposed on the signal supplied to the signal electrode 54S at the signal input terminal 54, so that the external signal supply source 81 connected to the signal input terminal 54
The signal from the signal supply unit 83 incorporated in the
Is not supplied to the signal amplification processing unit 62 incorporated in the switch, and instead, for example, a measure is taken to make the switch 65 take an appropriate ON state.

On the other hand, when the level of voltage Vx is lower than the reference level and light emitting element 72 is maintained in a non-light emitting state, ground electrode 54 at signal input terminal 54
E and the reference potential point in the amplifying device 51 are in a very low impedance state, and therefore occur between the signal input terminal 54 and the external signal supply source 81, the ground electrode 54E at the signal input terminal 54 and the external Signal source 81
The noise voltage corresponding to the product of the noise current flowing through the ground-side conductor of the connection cable 87 connecting the ground electrode 82E of the output terminal 82 to the impedance Z6 of the ground-side conductor of the connection cable 87 is the signal at the signal input terminal 54. Since the influence on the signal supplied to the electrode 54S is extremely small, the signal from the signal supply unit 83 incorporated in the external signal supply source 81 connected to the signal input terminal 54 is transmitted to the amplifying device 51. Is supplied to the signal amplification processing unit 62 incorporated in the device. Therefore, the switch 68 is turned off, the switch 57 is turned on, and subsequently, the switch 61 is turned on. Thus, from the signal supply unit 83 incorporated in the external signal supply source 81, the signal electrode 82 S at the output terminal 82 of the external signal supply source 81 and the signal electrode 54 at the signal input terminal 54 through the connection cable 87.
S is supplied to the switch 57, the common connection point 5
8, the signal is supplied to the signal amplification processing unit 62 through the resistor 59, the buffer amplifier 60, and the switch 61.

In this case, the switches 63 and 64 connected to the ground electrode 52E at the signal input terminal 52 and the ground electrode 53E at the signal input terminal 53, respectively.
Are both in the OFF state, and the ground electrode 52E at the signal input terminal 52 and the ground electrode 53E at the signal input terminal 53 are not connected to the reference potential points in the amplifier 51, respectively. Therefore, the grounding occurs in the connection cable 85 connecting the ground electrode 52E of the signal input terminal 52 and the ground electrode 76E of the output terminal 76 of the external signal supply source 75, which is generated between the signal input terminal 52 and the external signal supply source 75. Current flowing through the side conductor and impedance Z on the ground side conductor in the connection cable 85
4 and a signal input terminal 5
3 and the external signal supply source 78, the noise flowing through the ground-side conductor in the connection cable 86 connecting the ground electrode 53 </ b> E at the signal input terminal 53 and the ground electrode 79 </ b> E at the output terminal 79 of the external signal supply source 78. The noise voltage corresponding to the product of the current and the impedance Z5 of the grounding conductor of the connection cable 86 does not affect the signal supplied to the signal electrode 54S at the signal input terminal 54.

Switches 55 to 57, 6 in the above example
It is desirable that the on / off control for each of 1, 63 to 68 be provided, for example, by a control unit configured by using a microcomputer and automatically performed by such a control unit. .

In the above-described example, three signal input terminals are provided. However, the number of signal input terminals is not limited to three, and may be two or four or more. .

[0035]

As is apparent from the above description, according to the signal input selection circuit of the present invention, a plurality of pairs each formed by a pair of a signal electrode and a ground electrode and connected to an external signal supply source are provided. When a signal from an external signal supply source is supplied to the signal processing unit through a selected one of the signal input terminals, only the ground electrode at the selected signal input terminal is connected to the reference potential point through the switch. hand,
The connection of the ground electrode to the reference potential point at the signal input terminal that is not selected is prevented by the switch, and the signal from the external signal source through the selected signal input terminal is sent to the signal processing unit. Is supplied to the selected signal input terminal unit, the impedance state under the ON state of the switch connected between the ground electrode and the reference potential point is determined to be good, that is,
Since the ground electrode at the selected signal input terminal is properly connected to the reference potential point, a plurality of signal inputs to the signal supplied to the signal processing unit through the selected signal input terminal are taken. The effect of the noise voltage generated between the ground electrode at each of the terminal portions and the ground electrode at the output terminal of the external signal supply connected thereto is reliably suppressed.

[Brief description of the drawings]

FIG. 1 is a circuit connection diagram showing an example of a signal input selection circuit according to the present invention.

FIG. 2 is a circuit connection diagram showing a conventional signal input selection circuit.

[Explanation of symbols]

 52, 53, 54 Signal input terminal 52S, 53S, 54S Signal electrode 52E, 53E 54E Ground electrode 55, 56, 57 Switch 61 Switch 62 Signal amplification processing unit 63, 64, 65 Switch 66, 67, 68 Switch 71 Test power supply 73 Level comparison unit 75, 78, 81 External signal supply source 85, 86, 87 Connection cable

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-245612 (JP, A) JP-A-57-161903 (JP, A) JP-A-3-60213 (JP, A) 180365 (JP, U) JP-A 1-142223 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03K 17/00-17/693

Claims (1)

(57) [Claims] A plurality of signal input terminal portions each formed by a pair of a signal electrode and a ground electrode; and a signal electrode and a plurality of signal input terminal portions in each of the plurality of signal input terminal portions. A plurality of first switches connected to a common signal processing unit; and a plurality of second switches connected between a ground electrode and a reference potential point in each of the plurality of signal input terminals. A plurality of third switch sections connected between a ground electrode in each of the plurality of signal input terminal sections and a power supply for inspection common to the plurality of signal input terminal sections; An impedance determination unit that determines whether the impedance state of each of the second switch units is good or bad, wherein the second and the second signal units are connected to a ground electrode forming a selected one of the plurality of signal input terminal units. Third switch Are turned on, the current from the inspection power supply is passed through the on and off second and third switches, and the impedance determination unit turns on the second on. Based on the state where the quality of the impedance state in the second switch section is determined based on the voltage obtained between both ends of the switch section, and the result of the determination of the impedance state by the impedance determination section being good, First and second terminals respectively connected to a signal electrode and a ground electrode forming the selected signal input terminal portion.
Is turned on, the third switch connected to the ground electrode forming the selected signal input terminal is turned off, and the signal from the selected signal input terminal is turned off. A signal input selection circuit that takes a state in which an input signal is supplied to the signal processing unit.