JPH10117136A - Analog signal input circuit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To safely control the influence of a leakage current of an off- controlled semiconductor switch of another channel on an analog signal inputted through a semiconductor switch by preventing a signal line potential level from exceeding a source voltage due to the leakage current using a protecting circuit. SOLUTION: When an analog signal supplied to input terminals 11a and 11b of a 1st channel is converted from analog to digital, semiconductor switches 12a and 12b are turned on and semiconductor switches of other channels are turned off. At this point, the off-controlled semiconductor switches other than the 1st channel have leakage currents generated corresponding to the voltage levels of analog signals supplied to input terminals. The leakage currents flow from signal lines to a plus-side power source or a minus-side power source to the signal lines by diodes of protecting circuits 23a and 23b interposed between the signal lines and plus-side power source to suppress rises in signal line potential, thereby suppress influence such as the breakage of buffer amplifiers 24a and 24b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog signal input circuit device for converting a required analog signal from a plurality of channels into a digital signal and taking in the digital signal. The present invention relates to an analog signal input circuit device with improved insulation.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a configuration of a conventional analog signal input circuit device in which analog signals are supplied in a differential input format. In the figure, 1 is a first channel input circuit, and 2 is a second channel input circuit. 1a and 1b are input terminals of the first channel input circuit 1. Reference numerals 1c and 1d denote switches for turning on / off the supply of analog signals input to the input terminals 1a and 1b of the first channel input circuit 1 to the A / D converter 3, and use a mercury relay.
2a and 2b are input terminals of the second channel input circuit 2. 2c and 2d are input terminals 2 of the second channel input circuit 2.
a switch for turning on / off the supply of the analog signal to the A / D converter 3 to the A / D converter 3;
A mercury relay is used as in c and 1d. The reason why a mercury relay is used for the switches 1c and 1d and the switches 2c and 2d is that the voltage level of an analog signal input to each channel input circuit is different. Because there are signals, the switches 1c and 1d and the switches 2c and 2
This is because it is necessary to use a switch having excellent insulating properties for d. 3 is switch 1c, 1d or switch 2c,
This is an A / D converter for converting an analog signal of a differential input format supplied via 2d into a digital signal.

Next, the operation will be described. Input terminal 1
a, 1b and the analog signals input to the input terminals 2a, 2b are the switches 1c, 1d or the switches 2c, 2b.
selected by d. When an analog signal to be input to the first channel input circuit 1 is required, the switches 1c and 1d of the first channel input circuit 1 are turned on and input to the A / D converter 3, where they are converted into digital signals. You. When an analog signal to be input to the second channel input circuit 2 is required, the switches 2c and 2d of the second channel input circuit 2 are turned on and input to the A / D converter 3 to be converted into a digital signal. Is done.

[0004]

Since the conventional analog signal input circuit device is configured as described above, it is difficult to use a mercury relay for the switches 1c and 1d and the switches 2c and 2d from the viewpoint of environmental problems. There is a problem that replacement with a semiconductor switch is desired. Therefore, if the switches 1c and 1d and the switches 2c and 2d in FIG. 4 are replaced with the semiconductor switches 1e and 1f and the semiconductor switches 2e and 2f as shown in FIG. Affects the analog signal input to the A / D converter 3 via the semiconductor switch of the other channel, and the A / D converter 3
There is a problem that D conversion cannot be performed normally.

The present invention has been made in order to solve the above-mentioned problem, and is intended to prevent an analog signal input to the A / D converter 3 via a semiconductor switch from leaking current of a semiconductor switch of another channel. It is an object of the present invention to obtain an analog signal input circuit device that can suppress the influence of the signal.

[0006]

An analog signal input circuit device according to the present invention selects a necessary analog signal from a plurality of analog signals via semiconductor switches respectively controlled by a plurality of channels. An impedance conversion circuit that suppresses the influence of the leakage current of the semiconductor switch of the channel that is controlled to be off when inputting on the analog signal that is selectively input via the semiconductor switch of another channel; A protection circuit disposed on the output side when a signal line potential level due to the leakage current exceeds a power supply voltage, and selecting to select a necessary analog signal from the plurality of analog signals via the semiconductor switch of each channel; Having an input circuit having a circuit, and an A / D conversion circuit for A / D converting an output of the input circuit A.

According to a second aspect of the present invention, there is provided an analog signal input circuit device comprising: an input terminal for each channel to which an analog signal is input; and a semiconductor switch for controlling the supply of the analog signal from each input terminal. An input circuit having a buffer amplifier that receives the analog signal supplied through the semiconductor switch, and a selection circuit that selects an output of the buffer amplifier that receives the analog signal supplied through the semiconductor switch. , An A / D conversion circuit for A / D converting the selected output of the selection circuit.

According to a third aspect of the present invention, there is provided an analog signal input circuit device, wherein an input terminal for each channel to which an analog signal is input in a differential input format, and the differential input format from each input terminal. A semiconductor switch for controlling the supply of analog signals, a buffer amplifier for receiving the analog signal of the differential input type supplied through the semiconductor switch, and a buffer amplifier of the differential input type supplied via the semiconductor switch; An input circuit having a selection circuit for selecting an output of the buffer amplifier for receiving an analog signal;
And an A / D conversion circuit for performing D / D conversion.

According to a fourth aspect of the present invention, there is provided an analog signal input circuit device comprising: an input terminal for each channel to which an analog signal is input; a semiconductor switch for controlling the supply of the analog signal from each input terminal; An input circuit having a selection circuit for selecting the analog signal supplied through the semiconductor switch, a buffer amplifier receiving an output of the selection circuit, and an output of the buffer amplifier
And an A / D conversion circuit for performing D / D conversion.

According to a fifth aspect of the present invention, there is provided an analog signal input circuit device, wherein an input terminal for each channel to which an analog signal is input in a non-differential input format, and the non-differential input format from each input terminal. A semiconductor switch for controlling the supply of the analog signal of each of the above, a selection circuit for selecting the analog signal of the non-differential input format supplied through the semiconductor switch, and the non-differential input selected by the selection circuit An input circuit having a buffer amplifier for receiving an analog signal of a type, and an A / D conversion circuit for receiving the output of the buffer amplifier by a non-differential input and performing A / D conversion.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a circuit block diagram showing a configuration of the analog signal input circuit device according to the first embodiment. In the figure, reference numerals 11a and 11b denote input terminals of a first channel to which analog signals are input in a differential input form, 12a denotes a high-voltage semiconductor switch for controlling on / off of the supply of analog signals from the input terminal 11a, and 12b denotes a switch. Input terminal 11b
A high-voltage semiconductor switch 13a for controlling on / off of the supply of the analog signal from the input terminal 11a is a protection circuit having a protection function when the analog signal level supplied from the input terminal 11a exceeds the power supply voltage. And a signal line and a diode inserted between the positive power supply and the signal line. Reference numeral 13b denotes a protection circuit having a protection function when the analog signal level supplied from the input terminal 11b exceeds the power supply voltage, and has the same configuration as the protection circuit 13b. A buffer amplifier (impedance conversion circuit) 14a receives the analog signal of the differential input type supplied via the semiconductor switch 12a, and constitutes a voltage follower circuit having a high input impedance and a low output impedance by an operational amplifier. A buffer amplifier (impedance conversion circuit) 14b receives the differential input analog signal supplied via the semiconductor switch 12b, and has the same configuration as the buffer amplifier 14a.

Reference numerals 21a and 21b denote input terminals of an n-th channel to which analog signals are inputted in a differential input form; 22a, a high-voltage semiconductor switch for controlling on / off of the supply of analog signals from the input terminal 21a; Input terminal 21
A semiconductor switch 23a having a high withstand voltage for turning on / off the supply of the analog signal from the terminal b. A protection circuit 23a having a protection function when the level of the analog signal supplied from the input terminal 21a exceeds the power supply voltage. It is composed of a diode inserted between the power supply and the signal line and a diode inserted between the positive power supply and the signal line. Reference numeral 23b denotes a protection circuit having a protection function when the level of the analog signal supplied from the input terminal 21b exceeds the power supply voltage, and has a configuration similar to that of the protection circuit 23b. Reference numeral 24a denotes a buffer amplifier (impedance conversion circuit) that receives the differential input type analog signal supplied via the semiconductor switch 22a, and constitutes a voltage follower circuit having a high input impedance and a low output impedance by an operational amplifier. Reference numeral 24b denotes a buffer amplifier (impedance conversion circuit) that receives the analog signal of the differential input format supplied via the semiconductor switch 22b, and is configured similarly to the buffer amplifier 24a.

Reference numeral 25 denotes an n-channel multiplexer (selection circuit) in which each channel is composed of two circuits so as to be compatible with a differential input format, and each channel circuit is switched by a channel selection signal. An A / D converter (A / D conversion circuit) that receives the converted analog signal in a differential input format and converts it into a digital signal. 100 denotes input terminals 11a, 11b, 21a, 21
b, semiconductor switches 12a, 12b, 22a, 22b,
The input circuit includes protection circuits 13a, 13b, 23a, 23b, buffer amplifiers 14a, 14b, 24a, 24b, a multiplexer 25, and the like.

Next, the operation will be described. The on / off control of the semiconductor switch for each channel and the switching control of the multiplexer 25 for each channel are switched at the same timing. Further, a short-circuit prevention period in which the semiconductor switch of each channel is always turned off is provided on the semiconductor switch side of each channel so that a period in which the channels are simultaneously turned on does not occur between different channels. When the analog signals supplied to the input terminals 11a and 11b of the first channel are A / D-converted, the semiconductor switches 12a and 12b are turned on, and the semiconductor switches of the other channels are turned off. The multiplexer 25 is switched by a channel selection signal, the outputs of the buffer amplifiers 14a and 14b are selected by the multiplexer 25, and the A / D converter 26 performs A / D conversion.

At this time, in the semiconductor switches other than the first channel which are controlled to be turned off, a leakage current occurs according to the voltage level of the analog signal supplied to the input terminal. FIG. 1 shows the presence of leakage current in the n-th channel. This leakage current is caused by the high input impedance of the buffer amplifiers 24a and 24b.
The potential of the signal lines on the input sides of the input terminals 4a and 24b is increased to exceed the power supply voltage of the buffer amplifiers 24a and 24b, but the leakage current is caused by the protection circuit 23a, The diode 23b flows from the signal line to the plus side power supply or from the minus side power supply to the signal line, thereby suppressing the rise of the signal line potential and suppressing the effects such as the destruction of the buffer amplifiers 24a and 24b. Is secured. The multiplexer 25
Since the outputs of the buffer amplifiers 14a and 14b on the first channel side are selected, the circuit of the n-th channel of the multiplexer 25 has a high impedance.
The leakage current of the n-th channel semiconductor switches 22a and 22b has almost no effect on the A / D conversion result of the analog signal supplied from the first channel input terminals 11a and 11b.

Embodiment 2 FIG. 2 shows the second embodiment.
2 is a circuit block diagram showing a configuration of the analog signal input circuit device of FIG. 1. The same or corresponding parts as those in FIG. This analog signal input circuit device corresponds to a non-differential input type analog signal, whereas the analog signal input circuit device of the first embodiment shown in FIG. 1 corresponds to a differential input type analog signal. It has a configuration. Therefore, the input terminal 1 of the first channel
1b is grounded via a semiconductor switch 12b,
The input terminal 21b of the n-th channel is also connected to the semiconductor switch 2
It is grounded via 2b. One input terminal of another channel is similarly configured. The multiplexer 25 also has one circuit for each channel corresponding to non-differential input type analog signals, and the input circuit configuration of the A / D converter 26 also supports non-differential input type analog signals. .

Also in this analog signal input circuit device, the on / off control of the semiconductor switch for each channel and the switching control of the multiplexer 25 for each channel are switched at the same timing. Further, a short-circuit prevention period in which the semiconductor switch of each channel is always turned off is provided on the semiconductor switch side of each channel so that a period in which the channels are simultaneously turned on does not occur between different channels. And the first
When the analog signals supplied to the input terminals 11a and 11b of the channels are A / D converted, the semiconductor switches 12
a and 12b are on-controlled, and the semiconductor switches of the other channels are off-controlled. The multiplexer 25
Are switched by the channel selection signal, and the output of the buffer amplifier 14a is selected by the multiplexer 25, and A
A / D conversion is performed by the / D converter 26.

At this time, a leakage current corresponding to the voltage level of the analog signal supplied to the input terminal occurs in the semiconductor switches other than the first channel which are controlled to be off, and this leakage current is supplied to the buffer amplifier 24a by the high input. Because of the impedance, the potential of the signal line on the input side of the buffer amplifier 24a is increased. When the potential of this signal line exceeds the power supply voltage of the buffer amplifier 24a, the leakage current flows from the signal line to the positive power supply by a diode inserted between the signal line of the protection circuit 23a and the positive and negative power supplies. Alternatively, the rise in the potential of the signal line flowing into the signal line from the negative side power supply is suppressed, so that the influence such as the destruction of the buffer amplifier 24a is suppressed, and safety is ensured. Further, since the multiplexer 25 selects the output of the buffer amplifier 14a on the first channel side, the circuit of the n-th channel has high impedance, and the semiconductor switch 2 of the n-th channel
2a, 22b is the input terminal 11 of the first channel.
The effect on the A / D conversion result of the analog signal supplied from a and 11b is almost eliminated.

Embodiment 3 FIG. 3 shows the third embodiment.
3 is a circuit block diagram showing a configuration of the analog signal input circuit device of FIG. 2. The same or corresponding parts as those in FIG. This analog signal input circuit device corresponds to a differential input type analog signal similarly to the analog signal input circuit device of the second embodiment shown in FIG. 2, but a buffer amplifier (impedance conversion) is provided on the output side of the multiplexer 25. By arranging the circuit) 31,
In contrast to the analog signal input circuit device shown in FIG. 2 in which a buffer amplifier is provided for each channel, only one buffer amplifier 31 can be used, so that the circuit configuration is simplified and the manufacturing cost is reduced.

Also in this analog signal input circuit device, on / off control of the semiconductor switch for each channel and switching control of the multiplexer 25 for each channel are switched at the same timing. Further, a short-circuit prevention period in which the semiconductor switch of each channel is always turned off is provided on the semiconductor switch side of each channel so that a period in which the channels are simultaneously turned on does not occur between different channels. And the first
When the analog signals supplied to the input terminals 11a and 11b of the channels are A / D converted, the semiconductor switches 12
a and 12b are on-controlled, and the semiconductor switches of the other channels are off-controlled. The multiplexer 25
Is switched by a channel selection signal, the output of the semiconductor switch 12a is selected by the multiplexer 25, and the buffer amplifier 31 impedance-converts the output of the semiconductor switch 12a selected by the multiplexer 25 and outputs it to the A / D converter 26. A / D conversion is performed by the A / D converter 26.

At this time, a leakage current corresponding to the voltage level of the analog signal supplied to the input terminal occurs in the semiconductor switches other than the first channel which are controlled to be turned off. Is high impedance, the signal line potential on the input side of the n-th channel of the multiplexer 25 is raised. When the potential of the signal line exceeds the power supply voltage of the multiplexer 25, the leakage current flows from the signal line to the positive power supply through the diode of the protection circuit 23a, thereby suppressing the rise of the potential of the signal line and affecting the multiplexer 25 and its output. Do not give.

[0022]

As described above, according to the first aspect of the present invention, it is possible to selectively input a necessary analog signal from a plurality of analog signals through semiconductor switches controlled respectively for a plurality of channels. An impedance conversion circuit that suppresses the influence of the leakage current of the semiconductor switch of the channel that is controlled to be turned off on the analog signal that is selectively input via the semiconductor switch of another channel, disposed on the output side of each of the semiconductor switches; A protection circuit for when a signal line potential level due to the leakage current exceeds a power supply voltage, and a selection circuit for selecting a necessary analog signal from the plurality of analog signals through the semiconductor switches of the respective channels. Since the input circuit and the A / D conversion circuit for A / D converting the output of the input circuit are provided, the off control It is that the signal line potential level exceeds the supply voltage by the leakage current when said inhibit the adverse leakage current of the semiconductor switches provide is protected by the protection circuit, the through the semiconductor switch A /
There is an effect that it is possible to safely suppress the influence of the leakage current of the semiconductor switch whose other channel is controlled to be off on the analog signal input to the D conversion circuit.

According to the second aspect of the present invention, an input terminal for each channel to which an analog signal is input, a semiconductor switch for controlling the supply of the analog signal from each input terminal, and the semiconductor switch A buffer amplifier that receives the analog signal supplied through the semiconductor switch, a selection circuit that selects an output of the buffer amplifier that receives the analog signal supplied through the semiconductor switch, and an output side of each of the semiconductor switches. The buffer amplifier, the protection circuit, and the selection circuit have an effect of safely and effectively suppressing an adverse effect due to leakage current.

According to the third aspect of the present invention, a semiconductor switch for controlling the supply of a differential input type analog signal from each input terminal, and the differential input type analog signal supplied via the semiconductor switch. A buffer amplifier that receives an analog signal; a selection circuit that selects an output of the buffer amplifier that receives the analog signal of the differential input format supplied via the semiconductor switch; and a selection circuit that is disposed on an output side of each of the semiconductor switches. An input circuit having a protection circuit;
With the configuration including the A / D conversion circuit for performing the conversion, an adverse effect due to a leakage current due to an analog signal given in a differential input form can be safely and effectively suppressed by the buffer amplifier, the protection circuit, and the selection circuit. effective.

According to the fourth aspect of the present invention, an input terminal for each channel to which an analog signal is input, a semiconductor switch for controlling the supply of the analog signal from each input terminal, and the semiconductor switch A selection circuit for selecting the supplied analog signal, a buffer amplifier receiving an output of the selection circuit, and an input circuit having a protection circuit disposed on an output side of each of the semiconductor switches;
An A / D conversion circuit for A / D converting the output of the buffer amplifier is provided, so that the selection circuit, the buffer amplifier, and the protection circuit can safely and effectively suppress adverse effects due to leakage current. Since the number of buffer amplifiers can be reduced, the circuit configuration is simplified and the manufacturing cost is reduced.

According to the fifth aspect of the present invention, a semiconductor switch for controlling the supply of a non-differential input type analog signal from an input terminal of each channel, and the semiconductor switch supplied via the semiconductor switch. A selection circuit that selects a differential input type analog signal, a buffer amplifier that receives the non-differential input type analog signal selected by the selection circuit, and a protection circuit disposed on the output side of each of the semiconductor switches. And an A / D conversion circuit for receiving the output of the buffer amplifier at a non-differential input and performing A / D conversion, so that an analog signal provided in a non-differential input format is used. Adverse effects due to leakage current can be safely and effectively suppressed by the selection circuit, the buffer amplifier, and the protection circuit, and the number of buffer amplifiers can be reduced. Because the circuit configuration is effective in manufacturing cost is simplified is reduced.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a configuration of an analog signal input circuit device according to a first embodiment of the present invention.

FIG. 2 is a circuit block diagram showing a configuration of an analog signal input circuit device according to a second embodiment of the present invention.

FIG. 3 is a circuit block diagram showing a configuration of an analog signal input circuit device according to a third embodiment of the present invention.

FIG. 4 is a circuit block diagram showing a configuration of a conventional analog signal input circuit device.

FIG. 5 is a circuit block diagram showing a configuration when a semiconductor switch is used in a conventional analog signal input circuit device.

[Explanation of symbols]

11a, 11b, 21a, 21b Input terminals 12a, 12b, 22a, 22b Semiconductor switches 14a, 14b, 24a, 24b, 31 Buffer amplifiers (impedance conversion circuits) 13a, 13b, 23a, 23b Protection circuits 25 Multiplexers (selection circuits) 26 A / D converter (A / D conversion circuit) 100 Input circuit

Claims (5)

[Claims] When a required analog signal is selected and input from a plurality of analog signals through a semiconductor switch that is controlled in each of a plurality of channels, a leakage current of the semiconductor switch in a channel that is controlled to be turned off is: An impedance conversion circuit that suppresses the influence on the selected and inputted analog signal through the semiconductor switch of another channel; and a signal line potential level disposed on the output side of each semiconductor switch due to the leakage current exceeds a power supply voltage. And an input circuit having a selection circuit for selecting a required analog signal from the plurality of analog signals via the semiconductor switch of each channel, and performing an A / D conversion of an output of the input circuit. An analog signal input circuit device including an A / D conversion circuit. 2. The impedance conversion circuit includes a buffer amplifier. The input circuit includes an input terminal for each channel to which an analog signal is input, and a semiconductor switch that controls supply of the analog signal from each input terminal. A buffer amplifier that receives the analog signal supplied through the semiconductor switch; and a selection circuit that selects an output of the buffer amplifier that receives the analog signal supplied through the semiconductor switch. A / D conversion circuit outputs the selected output of the selection circuit to A / D
2. The analog signal input circuit device according to claim 1, wherein the conversion is performed. 3. An input terminal for each channel to which an analog signal is input in a differential input format, and a semiconductor switch controls the supply of the analog signal in the differential input format from each of the input terminals. A buffer amplifier receiving the differential input type analog signal supplied through the semiconductor switch, and a selection circuit receiving the differential input type analog signal supplied through the semiconductor switch. Output, and the A / D conversion circuit receives the selected output of the selection circuit at the differential input and
3. The analog signal input circuit device according to claim 2, wherein the conversion is performed. 4. An impedance conversion circuit comprising a buffer amplifier, an input circuit comprising: an input terminal for each channel to which an analog signal is input; and a semiconductor switch for controlling the supply of the analog signal from each input terminal. A selection circuit for selecting the analog signal supplied via the semiconductor switch, and the buffer amplifier receiving an output of the selection circuit, wherein the A / D conversion circuit converts the output of the buffer amplifier to A / D conversion The analog signal input circuit device according to claim 1, wherein 5. An input terminal for each channel to which an analog signal is input in a non-differential input format, and a semiconductor switch controls supply of the non-differential input type analog signal from each of the input terminals. Controlling, the selection circuit selects the non-differential input type analog signal supplied through the semiconductor switch, the buffer amplifier receives the non-differential input type analog signal selected by the selection circuit, 5. The analog signal input circuit device according to claim 4, wherein the A / D conversion circuit receives the output of the buffer amplifier at a non-differential input and performs A / D conversion.