JP2010093538A - Ad conversion device and method for detecting failure of ad conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AD conversion device and a failure detecting method of the AD conversion device which detects an open failure that occurs on a signal input side of an external capacitor. <P>SOLUTION: The AD conversion device 1 is provided with a failure determining part 6 for determining an open failure that occurs on a signal input side of the external capacitor 8 on the basis of an AD conversion value of an AD converter 5 when the voltage value of a first input terminal 2 is made to fluctuate to perform AD conversion of an input signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention belongs to the technical field of an AD converter for AD-converting a signal from an analog voltage source and a failure detection method for the AD converter.

Patent Document 1 discloses a technique in which a sensor element that is an analog voltage source is connected to an AD converter via a noise filter. The external capacitor constituting the noise filter has a first end connected between the AD converter and the sensor element, and a second end connected to a fixed potential.
JP 2006-345237 A

  However, in the above prior art, when an open fault occurs on the signal input side of the external capacitor, the voltage charged in the external capacitor is input to the AD converter, so the open fault can be detected. Therefore, an incorrect sensor value is output.

  An object of the present invention is to provide an AD converter that can detect an open fault occurring on the signal input side of an external capacitor and a fault detection method for the AD converter.

  In order to achieve the above object, the AD converter of the present invention AD-converts the signal from the first input terminal by changing the voltage value of the first input terminal connected via the analog voltage source and the external capacitor. An open fault is determined based on the output value of the AD converter.

  Therefore, the AD converter of the present invention can detect an open failure that has occurred on the signal input side of the external capacitor.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for realizing an AD conversion apparatus and an AD conversion apparatus failure detection method according to the present invention will be described below based on embodiments shown in the drawings.

First, the configuration will be described.
FIG. 1 is a configuration diagram of an AD conversion apparatus 1 according to the first embodiment.
The AD conversion apparatus 1 according to the first embodiment is provided, for example, in an ECU of a vehicle, and is used to AD-convert a signal from an analog sensor into a digital signal and output the digital signal to a CPU in the ECU. The CPU performs various controls based on the digital signal from the AD conversion apparatus 1. Further, the AD converter 1 itself may be a microcomputer.

  The AD conversion apparatus 1 includes n (n is a natural number) input / output ports, a power supply port 4, an AD converter 5, and a failure determination unit 6. As for the input / output ports, only the first input / output port 2 and the second input / output port 3 are shown for simplicity of explanation and illustration.

  The first input / output port 2 is connected to a sensor element 7 that is an analog voltage source. Since the first input / output port 2 is always used as an input terminal for analog signals, it will be referred to as a first input terminal in the following description.

  An external capacitor 8 is connected on the signal input line 10 between the first input terminal 2 and the sensor element 7. The external capacitor 8 is a noise filter that removes a noise component from the analog signal output from the sensor element 7. The first end 8 a of the external capacitor 8 is connected between the first input terminal 2 and the sensor element 7. The second end 8b of the external capacitor 8 is connected to the ground GND as a fixed potential. Hereinafter, the sensor element 7 side on the signal input line 10 from the connection position of the first end 8a of the external capacitor 8 is referred to as the signal input side of the external capacitor 8, and the connection position of the first end 8a. The first input terminal 2 side is referred to as the signal output side of the external capacitor 8.

  The second input / output port 3 is an empty terminal that is not connected to the analog voltage source. In the first embodiment, when the second input / output port is used when determining an open failure to be described later, the function of the second input / output port is switched to one of “input / output port” and “analog input terminal”. Then, it calls a 2nd input terminal.

  Here, the “input / output port” function refers to connecting the second input terminal 3 to a fixed potential (power supply voltage in the first embodiment) in order to input a predetermined voltage value to the second input terminal 3. The “analog input terminal” function means that the second input terminal 3 is connected to the AD converter 5 in order to AD convert the signal from the second input terminal 3.

The other input / output ports (fourth to nth input / output ports) are vacant terminals that are not connected to the analog voltage source for the sake of simplification of explanation, but the analog voltage source is the same as the first input terminal. It is good also as a structure connected with.
The power supply port 4 is connected to a power supply voltage 9 for driving the AD converter 5 and the failure determination unit 6.

  The AD converter 5 includes an input terminal changeover switch 11, a sampling switch 12, a sampling capacitor 13, and a comparator 14.

  The input terminal changeover switch 11 selects one of the input terminals in response to a command from the failure determination unit 6. In the first embodiment, since the input / output ports used as the input terminals are only the first input terminal 2 and the second input terminal 3, one of the two is selected. The “analog input terminal” function described above indicates that the input terminal changeover switch 11 selects the first input terminal 2 or the second input terminal 3 in accordance with a command from the failure determination unit 6.

The sampling switch 12 switches the connection destination of the sampling capacitor 13 between the input terminal changeover switch 11 side and the comparator 14 side according to a preset sampling time. Here, the sampling time refers to the time until the charge amount of the sampling capacitor 13 matches the voltage level of the analog signal output from the sensor element 7.
The sampling capacitor 13 is charged by a signal from the input terminal selected by the input terminal changeover switch 11.

  The comparator 14 performs AD conversion, that is, converts an analog signal into a digital signal by comparing the voltage value charged in the sampling capacitor 13 with a comparison voltage. Here, when the voltage value charged in the sampling capacitor 13 is Vin and the comparison voltage is Vout, Vout is an output obtained by converting a binary output of a counter (not shown) into an analog voltage. And Vin are compared, and if Vin <Vout, zero is output, and if Vin> Vout, 1 is output. Here, since the counter is configured to count up when 1 is output from the comparator 14, the comparator 14 repeats the comparison until Vin <Vout, and when Vin <Vout is satisfied. Binary output with Vout as Vin.

  The H / L selector switch 15 switches the connection destination of the second input terminal 3 between the power supply voltage 9 and the ground GND in response to a command from the failure determination unit 6. The “input / output port” function described above refers to the H / L changeover switch 15 that switches the connection destination of the second input terminal 3 to the power supply voltage 9 and the input terminal changeover switch 11 that receives a command from the failure determination unit 6. It means that the first input terminal 2 or the second input terminal 3 is selected according to the above.

  The failure determination unit 6 determines whether an open failure (disconnection) has occurred on the signal input side of the external capacitor 8 based on the output value (binary output) of the AD converter 5. Hereinafter, an open failure determination method will be described in detail.

[Open failure judgment processing]
FIG. 2 is a flowchart illustrating the flow of the open failure determination process executed by the AD conversion apparatus 1 according to the first embodiment. Each step will be described below. This process is repeatedly executed at a predetermined control cycle.

  In step S1, AD conversion of the analog signal input from the first input terminal 2 that is the inspection target terminal is performed, and an AD conversion initial value Va that is an AD converted digital signal is stored, and the initial value Va is stored. Copy to Vb and go to step S2.

  In step S2, the function of the second input terminal 3, which is an empty terminal, is switched from “analog input terminal” to “input / output port” to fix the voltage value of the second input terminal 3 to High, and the process proceeds to step S3.

  In step S3, the function of the second input terminal 3 is switched from “input / output port” to “analog input terminal” to perform AD conversion, and the process proceeds to step S4.

  In step S4, the first input terminal 2 is selected by the input terminal changeover switch 11, AD conversion is performed, the obtained AD conversion value Vc is stored, and the process proceeds to step S5.

  In step S5, the fluctuation amount 1 per control period of the AD conversion value is calculated from the difference between the AD conversion value Vc stored in step S4 and the AD conversion value Vb stored in step S1, and the process proceeds to step S6.

  In step S6, it is determined whether or not the fluctuation amount 1 calculated in step S5 is smaller than zero. If YES, the process moves to step S8, and if NO, the process moves to step S7.

  In step S7, it is determined whether or not the absolute value | variation 1 | of the variation 1 calculated in step S5 is larger than the planned variation (predicted variation). If YES, the process proceeds to step S8, and if NO, the process proceeds to step S9. Here, the “scheduled fluctuation amount” means the voltage fluctuation amount of the first input terminal 2 predicted by the processing from step S1 to step S4, assuming that an open failure has occurred in A of FIG. That is, it means an increase in the charge amount of the capacitor 8.

  In step S8, it is determined that there is no open failure (normal), and the process proceeds to return.

  In step S9, the amount of variation 2 of the AD conversion value from the AD conversion initial value Va is calculated from the difference between the AD conversion value Vc stored in step S4 and the AD conversion initial value Va stored in step S1, and the process proceeds to step S10. Transition.

  In step S10, it is determined whether or not the absolute value of fluctuation amount 2 | variation amount 2 | calculated in step S9 is equal to or greater than a failure determination threshold value. If YES, the process proceeds to step S11. If NO, the process proceeds to step S12. Here, the “failure determination threshold” is set by, for example, “scheduled fluctuation amount” × m (m is a natural number, for example, 4). m is set to a smaller value as the AD conversion initial value Va is smaller. That is, the failure determination threshold is set to a smaller value as the AD conversion initial value Va is smaller. The “failure determination threshold” is set to a voltage outside the output voltage range of the sensor element 7, for example.

In step S11, it is determined that there is an open failure, and the process proceeds to return. In the first embodiment, even when it is determined that an open failure has occurred in the present control, the present control is repeated, and an open failure is determined when the determination of an open failure continues multiple times. When it is determined that an open failure has occurred, control based on an erroneous input signal can be avoided by stopping AD conversion.
In step S12, Vb = Vc, and the process proceeds to step S2.

Next, the operation of the first embodiment will be described.
In an AD converter connected via an analog voltage source and an external capacitor, when an open failure occurs on the signal input side of the external capacitor, the voltage charged in the external capacitor is input to the AD converter. Therefore, open failure cannot be detected.

  On the other hand, in the AD conversion apparatus 1 according to the first embodiment, the failure determination unit 6 changes the voltage value of the first input terminal 2 and AD-converts the input signal based on the output value of the AD converter 5. Determine open failure. In the first embodiment, the voltage value of the first input terminal 2 is varied by charging the sampling capacitor 13 before AD conversion of the signal from the first input terminal 2.

  In the first embodiment, the second input terminal 3 that is an empty terminal is used as a method of charging the sampling capacitor 13. That is, as shown in FIG. 3, the sampling capacitor 13 can be charged with the power supply voltage by AD conversion of the signal from the second input terminal 3 with the second input terminal 3 that is an empty terminal as the power supply voltage. it can. Thereafter, the signal from the first input terminal 2 is AD-converted, so that the charge amount of the external capacitor 8, that is, the voltage value of the first input terminal 2 is affected by the power supply voltage charged in the sampling capacitor 13. Increase.

  That is, when the voltage value of the first input terminal 2 is increased without an open failure occurring on the signal input side of the external capacitor 8, the external capacitor 8 is affected by the signal from the sensor element 7. The amount of charge varies independently of the amount of increase in the voltage value of the first input terminal 2. On the other hand, when the voltage value of the first input terminal 2 is increased in a state where an open failure has occurred, the charge amount of the external capacitor 8 is affected only by the voltage value of the first input terminal 2, and the first It becomes a predetermined fluctuation amount corresponding to the fluctuation amount of the voltage value of the input terminal 2.

  That is, in the first embodiment, paying attention to the fluctuation characteristics of the charge amount of the external capacitor 8 when the open failure occurs, the AD conversion value when the input signal is AD converted by changing the voltage value of the first input terminal 2. From this, an open failure is to be detected.

(Normal)
If no open failure has occurred, in the flow church of FIG. 2, step S1, step S2, step S3, step S4, step S5, step S6, step S8, or step S1, step S2, step S3, step The flow proceeds from S4 to step S5 to step S6 to step S7 to step S8.

  That is, when an open failure has not occurred, the AD conversion value when the signal from the first input terminal 2 is AD converted fluctuates due to the influence of the signal from the sensor element 7. It will not be the amount of fluctuation.

  That is, in step S6, the fluctuation direction becomes a decreasing direction (variation amount 1 <0) or exceeds the planned fluctuation amount in step S7 (| variation amount 1 |> planned fluctuation amount). Therefore, when the variation amount 1 is not the planned variation amount, it is possible to accurately detect a state in which no open failure has occurred by determining that there is no open failure.

(When open failure occurs)
When an open failure occurs, repeat the flow from step S2 → step S3 → step S4 → step S5 → step S6 → step S7 → step S9 → step S10 → step S12 in the flowchart of FIG. After satisfying 2 | ≧ failure determination threshold, the process proceeds from step S10 to step S11, and the failure is determined.

  That is, when an open failure has occurred, the AD conversion value when the signal from the first input terminal 2 is AD converted increases by a predetermined amount of fluctuation as shown in FIG. 4, and the AD conversion initial value Va The fluctuation amount 2 from is greater than or equal to the failure determination threshold.

  Here, if the fluctuation amount of the AD conversion value increases continuously by a predetermined number of times (until fluctuation amount 2 becomes equal to or greater than the failure determination threshold), it is highly likely that an open failure has occurred. Therefore, it is possible to accurately detect the occurrence of an open failure by determining an open failure when the variation amount 1 is equal to or greater than the failure determination threshold while the variation amount 1 maintains the planned variation amount.

Next, the effect of Example 1 will be described.
In the first embodiment, an open failure occurred on the signal input side of the external capacitor 8 based on the AD conversion value of the AD converter 5 when the input signal is AD converted by changing the voltage value of the first input terminal 2. A failure determination unit 6 is provided. Thereby, an open failure occurring on the signal input side of the external capacitor 8 can be detected.

  The AD converter 5 charges the sampling capacitor 13 with the input signal, performs AD conversion based on the charged voltage value, and the failure determination unit 6 samples the signal from the first input terminal 2 before AD conversion. By charging the capacitor 13, the voltage value of the first input terminal 2 is changed. Thereby, since the structure which fluctuates the voltage value of the 1st input terminal 2 using the sampling capacitor 13 incorporated in the existing AD converter 5 is realizable, an additional structure can be suppressed and cost increase can be suppressed.

The AD converter 5 has a second input terminal 3 that is not connected to the analog voltage source, and the failure determination unit 6 supplies the power supply voltage (predetermined voltage value) to the second input terminal 3 and then the second input terminal 3. The sampling capacitor 13 is charged by subjecting the signal from 3 to AD conversion. Thereby, the sampling capacitor 13 can be charged by effectively using the second input terminal 3 which is an empty terminal.
Here, the supply of the predetermined voltage value may be 'High' output by using the second input terminal 3 as an output terminal, or the second input terminal 3 may be connected to a power source while being an analog input terminal.

  The failure determination unit 6 switches the function of the second input terminal 3 to “input / output port” and sets it to the power supply voltage 9 (fixed potential), and then returns the function to the “analog input terminal” from the second input terminal 3. The AD signal is converted. Therefore, the function of an existing AD converter that sequentially selects signals from a plurality of channels (a plurality of input terminals), charges the sampling capacitor 13 with the selected signals, and performs AD conversion based on the charged voltage value. Can be used. Thereby, an additional structure can be suppressed and cost increase can be suppressed.

  The failure determination unit 6 alternately AD converts the signal from the first input terminal 2 and the signal from the second input terminal 3 and AD converts the AD conversion value Vc when the signal from the first input terminal 2 is AD converted. When the fluctuation amount 2 from the conversion initial value Va is equal to or greater than the failure determination threshold value, it is determined as an open failure. Thereby, the occurrence of an open failure can be accurately detected.

  The failure determination unit 6 sets the failure determination threshold value to a smaller value as the AD conversion initial value Va is smaller. For example, when the failure determination threshold is constant, when an open failure occurs, it takes time until the fluctuation amount 2 becomes equal to or greater than the failure determination threshold, and the open failure determination is delayed. Therefore, when the AD conversion initial value Va is small, the failure determination time can be shortened by setting the failure determination threshold value to a smaller value.

  The failure determination unit 6 determines whether or not the variation 1 that is the difference between the AD conversion value Vc and the previous value Vb (Va for the first time) exceeds the planned variation (| variation 1 |> planned variation), or When the variation direction of the variation amount 1 is opposite to the variation direction of the planned variation amount (variation amount 1 <0), it is determined that there is no open failure. That is, when an open failure has not occurred, the fluctuation amount 1 is not a planned fluctuation amount. In this case, it is possible to accurately detect a state in which no open failure has occurred by determining that there is no open failure.

  When the failure determination unit 6 determines an open failure a plurality of times, the failure determination unit 6 determines the open failure, so that the detection accuracy of the open failure can be improved and erroneous determination can be prevented.

  In the first embodiment, the fluctuation amount of the AD conversion value of the AD converter 5 when the input signal is repeatedly AD converted while changing the voltage value of the first input terminal 2 at a constant rate is the voltage of the first input terminal 2. If the value corresponds to the amount of fluctuation, it is determined that an open failure has occurred on the signal input side of the external capacitor 8. Thereby, an open failure occurring on the signal input side of the external capacitor 8 can be detected.

In the second embodiment, the fixed potential connected to the second input terminal 3 is the ground GND.
That is, in the “input / output port” function of the second embodiment, the H / L switch 15 switches the connection destination of the second input terminal 3 to the ground GND, and the input terminal switch 11 selects the first input terminal 2. Refers to the state. Since other configurations are the same as those of the first embodiment, illustration and description thereof are omitted.

[Open failure judgment processing]
FIG. 5 is a flowchart showing the flow of the open failure determination process executed by the AD conversion apparatus 1 according to the second embodiment. Each step will be described below. In addition, the same number is attached | subjected to the step which performs the same process as Example 1, and description is abbreviate | omitted.

  In step S21, the function of the second input terminal 3, which is an empty terminal, is switched from “analog input terminal” to “input / output port” to fix the voltage value of the second input terminal 3 to Low, and the process proceeds to step S3.

  In step S22, it is determined whether or not the fluctuation amount 1 calculated in step S5 is larger than zero. If YES, the process moves to step S8, and if NO, the process moves to step S7.

Next, the operation of the second embodiment will be described.
(Normal)
If no open failure has occurred, in the flowchart of FIG. 5, step S1 → step S21 → step S3 → step S4 → step S5 → step S22 → step S8 or step S1 → step S21 → step S3 → step S4. → Step S5 → Step S22 → Step S7 → Step S8.

  That is, when an open failure has not occurred, the AD conversion value when the signal from the first input terminal 2 is AD converted fluctuates due to the influence of the signal from the sensor element 7. It will not be the amount of fluctuation.

  That is, in step S22, the variation direction becomes an increasing direction (variation amount 1> 0) or exceeds the planned variation amount in step S7 (| variation amount 1 |> planned variation amount). Therefore, when the variation amount 1 is not the planned variation amount, it is possible to accurately detect a state in which no open failure has occurred by determining that there is no open failure.

(When open failure occurs)
When an open failure occurs, repeat the flow from step S21 → step S3 → step S4 → step S5 → step S22 → step S7 → step S9 → step S10 → step S12 in the flowchart of FIG. After satisfying 2 | ≧ failure determination threshold, the process proceeds from step S10 to step S11, and the failure is determined.

  That is, when an open failure has occurred, the AD conversion value when the signal from the first input terminal 2 is AD-converted decreases by a predetermined amount of fluctuation as shown in FIG. 6, and the AD conversion initial value Va The fluctuation amount 2 from is greater than or equal to the failure determination threshold.

Here, if the fluctuation amount of the AD conversion value decreases continuously by a predetermined number of times (until fluctuation amount 2 becomes equal to or greater than the failure determination threshold), it is highly possible that an open failure has occurred. Therefore, it is possible to accurately detect the occurrence of an open failure by determining an open failure when the variation amount 1 is equal to or greater than the failure determination threshold while the variation amount 1 maintains the planned variation amount.
As described above, also in the second embodiment, the same function and effect as in the first embodiment are obtained.

  The third embodiment is an example in which an open failure is determined from the AD conversion value. Since other configurations are the same as those of the first embodiment, illustration and description thereof are omitted.

[Open failure judgment processing]
FIG. 7 is a flowchart showing the flow of open failure determination processing executed by the AD conversion apparatus 1 according to the third embodiment. Each step will be described below. In addition, the same number is attached | subjected to the step which performs the same process as Example 1, and description is abbreviate | omitted.

  In step S31, it is determined whether or not the absolute value | Vc | of the AD conversion value Vc stored in step S4 is equal to or greater than a failure determination threshold value. If YES, the process proceeds to step S11. If NO, the process proceeds to step S12. Here, the “failure determination threshold value” is a value that exceeds the maximum value of the output possible range of the sensor element 7 in a normal use state.

Next, the operation of the third embodiment will be described.
When an open failure occurs, in the flowchart of FIG. 7, the flow of steps S2 → Step S3 → Step S4 → Step S5 → Step S6 → Step S7 → Step S31 → Step S12 is repeated, and in step S31, Vc ≧ failure determination threshold value After the establishment, the process proceeds from step S31 to step S11, and a failure determination is made.

  That is, when an open failure has occurred, the AD conversion value when the signal from the first input terminal 2 is AD-converted increases by a predetermined amount of variation, and the AD conversion value Vc becomes equal to or greater than the failure determination threshold. Here, since the failure judgment threshold is a value that cannot be obtained by the actual output of the sensor element 7, the fluctuation amount 1 increases while maintaining the planned fluctuation amount, and the AD conversion value Vc becomes equal to or greater than the failure judgment threshold. In this case, it is possible to accurately detect the occurrence of the open failure by determining that the open failure occurs.

Next, the effect of Example 3 is demonstrated.
The failure determination unit 6 alternately AD converts the signal from the first input terminal 2 and the signal from the second input terminal, and AD conversion of the AD converter 5 when the signal from the first input terminal 2 is AD converted. Since the open failure is determined when the value Vc is equal to or greater than the failure determination threshold, the occurrence of the open failure can be accurately detected.

  The fourth embodiment is an example in which an open failure is determined from the AD conversion value. Since other configurations are the same as those of the second embodiment, illustration and description thereof are omitted.

[Open failure judgment processing]
FIG. 8 is a flowchart showing the flow of an open failure determination process executed by the AD conversion apparatus 1 according to the fourth embodiment. Each step will be described below. In addition, the same number is attached | subjected to the step which performs the same process as Example 2, and description is abbreviate | omitted.

  In step S41, it is determined whether or not the absolute value | Vc | of the AD conversion value Vc stored in step S4 is equal to or less than a failure determination threshold value. If YES, the process proceeds to step S11. If NO, the process proceeds to step S12. Here, the “failure determination threshold value” is set to a value lower than the minimum value of the output possible range of the sensor element 7 in a normal use state. Further, the failure determination threshold is set to a larger value as the AD conversion initial value Va is smaller.

Next, the operation of the fourth embodiment will be described.
When an open failure occurs, in the flow chart of FIG. 8, the process of step S2, step S3, step S4, step S5, step S6, step S7, step S41, and step S12 is repeated. In step S41, Vc ≦ failure determination threshold value After the establishment, the process proceeds from step S41 to step S11, and a failure determination is made.

  That is, when an open failure has occurred, the AD conversion value when the signal from the first input terminal 2 is AD converted decreases by a predetermined amount of fluctuation, and the absolute value | Vc | of the AD conversion value Vc is a failure. It becomes below the judgment threshold. Here, since the failure judgment threshold is a value that cannot be obtained by the actual output of the sensor element 7, the fluctuation amount 1 decreases while maintaining the planned fluctuation amount, and the AD conversion value Vc becomes equal to or less than the failure judgment threshold. In this case, it is possible to accurately detect the occurrence of an open fault by determining that the fault is an open fault.

Next, the effect of Example 4 is demonstrated.
The failure determination unit 6 alternately AD converts the signal from the first input terminal 2 and the signal from the second input terminal, and AD conversion of the AD converter 5 when the signal from the first input terminal 2 is AD converted. Since the open failure is determined when the value Vc is equal to or less than the failure determination threshold, the occurrence of the open failure can be accurately detected.

The fifth embodiment is an example in which the second input terminal 3 is always connected to a fixed potential.
FIG. 9 is a configuration diagram of the AD converter 20 according to the fifth embodiment. The second input terminal 3 is connected to the output terminal 21 a of the transistor switch 21. The transistor switch 21 can change the voltage value of the output terminal 21a, that is, the voltage value of the second input terminal 3 by changing a signal (voltage value) supplied to the input terminal 21b. That is, by adding a “1” signal to the input terminal 21b, the output voltage of the output terminal 21a is maintained at zero, and by applying a “0” signal to the input terminal 21b, the output voltage of the output terminal 21a is maintained at the power supply voltage. The
Since other configurations are the same as those of the first embodiment, illustration and description thereof are omitted.

  As described above, in the second embodiment, since the second input terminal 3 is always connected to the power supply voltage 9 or the ground GND which is a fixed potential, for example, a “0” signal is applied to the input terminal 21b of the transistor switch 21 to turn off the switch. In other words, the power supply voltage 9 is always supplied to the second input terminal 3. For this reason, when the signal from the second input terminal 3 is AD-converted, the function of the second input terminal 3 is switched from “analog input terminal” to “input / output port” and then changed to “analog input terminal” again. No switching process is required.

  Therefore, as shown in FIG. 10, the time for AD conversion of the signal from the second input terminal 3 is shortened, so that the time for AD conversion of the signal from the first input terminal 2 can be shortened. Thereby, compared with Examples 1-4, the judgment time of an open failure can be shortened, and an open failure can be detected earlier.

(Other examples)
The best mode for carrying out the present invention has been described based on each embodiment. However, the specific configuration of the present invention is not limited to the configuration shown in each embodiment. Design changes and the like within a range that does not depart from the gist are also included in the present invention.

  For example, when judging an open fault multiple times, after judging an open fault once, AD conversion of the signal from the first input terminal is performed only, without AD conversion of the signal from the second input terminal. The open failure may be determined by comparing the fluctuation amount 2 or the absolute value of the AD conversion value Vc with the failure determination threshold.

  Further, as a method of always connecting the second input terminal to a fixed potential, a configuration as shown in FIG. 11 can be used. In the AD converter 22 shown in FIG. 11, the empty terminal 3a is connected to the power supply voltage 9, and the empty terminal 3b is connected to the ground GND. By selecting the empty terminal 3a by the input terminal changeover switch 11, the empty terminal 3a can be used as the second input terminal. On the other hand, the empty terminal 3b can be used as the second input terminal by selecting the empty terminal 3b with the input terminal changeover switch 11.

  In the AD converter 22 in FIG. 11 as well, since the function of the second input terminal does not need to be switched as in the fifth embodiment, the open failure determination time can be shortened and the open failure can be detected earlier.

1 is a configuration diagram of an AD conversion apparatus 1 according to a first embodiment. 3 is a flowchart illustrating a flow of open failure determination processing executed by the AD conversion apparatus 1 according to the first embodiment. It is a time chart of the 1st terminal voltage and the 2nd terminal voltage which show the open failure judgment logic of Example 1. It is a time chart of the 1st terminal voltage and the 2nd terminal voltage which show the open failure judgment action of Example 1. 10 is a flowchart illustrating a flow of open failure determination processing executed by the AD conversion apparatus 1 according to the second embodiment. It is a time chart of the 1st terminal voltage and the 2nd terminal voltage which show the open failure judgment action of Example 2. 12 is a flowchart illustrating a flow of an open failure determination process executed by the AD conversion apparatus 1 according to the third embodiment. 10 is a flowchart illustrating a flow of an open failure determination process executed by the AD conversion apparatus 1 according to the fourth embodiment. It is a block diagram of AD converter 20 of Example 5. FIG. It is a time chart of the 1st terminal voltage and the 2nd terminal voltage which show the open failure judgment time shortening operation of Example 5. It is a block diagram of AD converter 22 of the other Example.

Explanation of symbols

GND Ground (fixed potential)
1 AD converter 2 First input / output port (first input terminal)
3 Second input / output port (second input terminal)
4 Power supply port 5 AD converter 6 Failure judgment unit 7 Sensor element (analog voltage source)
8 External capacitor 9 Power supply voltage (fixed potential)
10 signal input line 11 input terminal switch 12 sampling switch 13 sampling capacitor 14 comparator 15 H / L switch

Claims (13)

A first input terminal connected to the analog voltage source via an external capacitor;
An AD converter for AD conversion of the input signal;
In an AD converter having
Failure determination for determining an open failure occurring on the signal input side of the external capacitor based on an output value of the AD converter when the input signal is AD converted by changing the voltage value of the first input terminal An AD converter characterized by comprising a unit. The AD converter according to claim 1,
The AD converter charges a sampling capacitor with an input signal, performs AD conversion based on the charged voltage value,
The fault determination unit varies the voltage value of the first input terminal by charging or discharging the sampling capacitor before AD converting the signal from the first input terminal. . The AD converter according to claim 2,
The AD converter has a second input terminal not connected to an analog voltage source,
The fault determination unit charges or discharges the sampling capacitor by AD-converting a signal from the second input terminal after supplying a predetermined voltage value to the second input terminal . The AD converter according to claim 3,
The failure determination unit switches the function of the second input terminal to an input / output port and connects it to a fixed potential, and then returns the function to the analog input terminal and AD-converts the signal from the second input terminal. A featured AD converter. The AD converter according to claim 3,
An AD converter characterized in that the second input terminal is always connected to a fixed potential. The AD conversion apparatus according to any one of claims 3 to 5,
The failure determination unit alternately AD-converts the signal from the first input terminal and the signal from the second input terminal, and outputs the AD converter when the signal from the first input terminal is AD-converted. An AD conversion apparatus, wherein an open failure is determined when a variation amount from an initial value of the value is equal to or greater than a failure determination threshold value. The AD converter according to claim 6, wherein
The AD converter according to claim 1, wherein the failure determination unit sets the failure determination threshold value to a smaller value when the initial value of the output value is small than when the output value is large. The AD conversion apparatus according to any one of claims 3 to 5,
The failure determination unit alternately AD-converts the signal from the first input terminal and the signal from the second input terminal, and outputs the AD converter when the signal from the first input terminal is AD-converted. An AD converter characterized by determining that the open fault occurs when a value deviates from the output voltage range of the analog voltage source. The AD converter according to claim 8, wherein
The AD converter according to claim 1, wherein the failure determination unit narrows the output voltage range when the initial value of the output value is small than when it is large. The AD converter according to any one of claims 6 to 9,
The failure determination unit, when the difference between the output value and the previous value exceeds a predicted fluctuation amount that is a voltage fluctuation amount of the first input terminal predicted when the open failure occurs, or a fluctuation direction of the voltage value Is the direction opposite to the fluctuation direction of the predicted fluctuation amount, it is determined that there is no open failure. The AD converter according to any one of claims 1 to 10, wherein
The AD converter according to claim 1, wherein the failure determination unit determines the open failure when the open failure is determined a plurality of times. In an AD converter that AD-converts a signal input to a first input terminal connected to an analog voltage source and an external capacitor by an AD converter,
The output value of the AD converter or the amount of fluctuation of the output value when the input signal is repeatedly AD converted while changing the voltage value of the first input terminal at a constant rate is the voltage value of the first input terminal. Alternatively, in the case of corresponding to the fluctuation amount of the voltage value, it is determined that an open failure has occurred on the signal input side of the external capacitor. In a fault detection method for an AD converter that AD-converts a signal input to a first input terminal connected to an analog voltage source via an external capacitor by an AD converter,
The AD signal is repeatedly AD converted while changing the voltage value of the first input terminal at a constant rate,
When the output value of the AD converter or the fluctuation amount of the output value corresponds to the voltage value of the first input terminal or the fluctuation amount of the voltage value, an open failure occurs on the signal input side of the external capacitor. A fault detection method for an AD converter, characterized in that it is determined that

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