Measurement circuit and voltage generator

Abstract

To provide a measuring device that can output more accurate measurement values ​​even when the characteristics of the amplifier or AD converter change depending on the measurement environment. [Solution] The measurement circuit (20, 20A) receives the voltage applied to the object to be measured and updates the correction value obtained by performing calibration while the feedback operation is stopped at the first voltage selector switch unit (21) located in the feedback path until it outputs to the device (10) that performs the feedback operation, with the correction value obtained by performing calibration while the feedback operation is running at the second voltage selector switch unit (23) located in the measurement path branched from the feedback path.

Description

Technical Field

[0001] The present invention relates to a measurement circuit, and more particularly to a voltage measurement circuit that measures a voltage applied to a measurement target.

Background Art

[0002] Patent Document 1 describes a measuring device including a measuring unit that measures a measurement voltage that changes according to a measured quantity of a measurement target within a selected measurement range, and converts and outputs the measurement voltage as a measurement value. In this measuring unit, in order to cancel the influence of the offset voltage existing in the amplifier constituting the measuring unit and the gain of the amplifier, the measurement voltage is corrected by a correction value and then output as a measurement value. Further, by sequentially updating the correction value for each measurement range, even if the offset voltage existing in the amplifier constituting the measuring unit and the gain of the amplifier vary according to the measurement environment, it is possible to output a highly accurate measurement value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such a measuring device, the correction value is updated by performing calibration using a predetermined reference voltage generated within the measuring unit instead of the voltage applied to the measurement target.

[0005] Consider the case where such a measuring device is incorporated as a measurement circuit into a voltage generating device having a voltage generating unit that generates a voltage. In the voltage generating device, when generating a voltage while performing feedback using the voltage output from the measurement circuit, since the voltage applied to the measurement target is not output during calibration, feedback processing cannot be performed, and it is necessary to stop the generation of the voltage.

[0006] However, depending on the characteristics of the AD converter used in the measurement circuit, the measurement environment during feedback processing may affect the results. If calibration cannot be performed during feedback processing, the correction value may not be able to compensate for the effects of offset voltage and gain. If the effects of offset voltage and gain cannot be compensated for, the accuracy of the output measurement value will decrease.

[0007] The objective of the present invention is to provide a measuring device that can output more accurate measurement values ​​even when the characteristics of the amplifier or AD converter change depending on the measurement environment. [Means for solving the problem]

[0008] A typical embodiment of the present invention includes a measurement circuit provided in a feedback path that receives a voltage applied to a device to be measured and outputs it to a device that performs a feedback operation, and a first voltage switching switch unit that switches the voltage in the feedback path to at least two reference voltages; a second voltage switching switch unit provided in a measurement path branched from the feedback path downstream of the first voltage switching switch unit, and switches the voltage in the measurement path to at least two reference voltages; an AD conversion unit provided in the measurement path downstream of the second voltage switching switch unit, which AD converts the voltage in the measurement path to a digital voltage value; and a data processing control unit that switches the first voltage switching switch unit and the first voltage switching switch unit, and corrects the digital voltage value by a correction value and outputs it as a measurement voltage, wherein the data processing control unit, while the feedback operation is stopped, the first voltage switching switch unit The system includes a calibration execution unit that switches the second voltage switching switch unit and performs a first calibration to acquire the digital voltage value at the AD conversion unit at that time, a correction value calculation unit that calculates the correction value based on the result of the first calibration, a correction value storage unit that stores the calculated correction value, a correction unit that corrects the digital voltage value output from the AD conversion unit with the correction value stored in the correction value storage unit to obtain a measured voltage value, and a measured voltage value output unit that outputs the measured voltage value obtained by the correction unit. When the calibration execution unit switches the second voltage switching switch unit during the execution of the feedback operation and performs a second calibration to acquire the digital voltage value at the AD conversion unit at that time, the correction value calculation unit calculates the correction value again based on the result of the second calibration and updates the correction value stored in the correction value storage unit with the newly calculated correction value. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows a schematic configuration of a voltage generation device using a measurement circuit according to the first embodiment. [Figure 2] This figure shows an example of the configuration of a measurement circuit according to the first embodiment. [Figure 3]This figure shows an example of FPGA configuration in the measurement circuit of the first embodiment. [Figure 4] This figure shows a schematic configuration of a voltage generation device using a measurement circuit according to the second embodiment. [Figure 5] This figure shows an example of the configuration of a measurement circuit according to the second embodiment. [Figure 6] This figure shows an example of FPGA configuration in the measurement circuit of the second embodiment. [Modes for carrying out the invention]

[0010] 1. Overview of the Embodiment First, a general overview of a typical embodiment of the invention disclosed in this application will be provided. In the following description, as an example, the reference numerals on the drawing corresponding to the components of the invention in Figure 4 are indicated in parentheses.

[0011] [1] A typical embodiment of the present invention includes a measurement circuit (20, 20A) provided in a feedback path that receives the voltage applied to the object to be measured (50) and outputs it to a device (10) that performs a feedback operation, and a first voltage switching switch unit (21) that switches the voltage in the feedback path to at least two reference voltages, a second voltage switching switch unit (23) provided in a measurement path branched from the feedback path downstream of the first voltage switching switch unit (21), and switches the voltage in the measurement path to at least two reference voltages, an AD conversion unit (25, 25A) provided in the measurement path downstream of the second voltage switching switch unit (23) that AD converts the voltage in the measurement path to a digital voltage value, and a data processing control unit (30) that switches the first voltage switching switch unit (21) and the first voltage switching switch unit (21), and corrects the digital voltage value by a correction value and outputs it as a measurement voltage, wherein the data processing control unit (30) switches the first voltage switching switch unit (21) while the feedback operation is stopped. A calibration execution unit (31) performs a first calibration to acquire the digital voltage value at the AD conversion unit (25, 25A) at that time; a correction value calculation unit (32) calculates the correction value based on the result of the first calibration; a correction value storage unit (33) stores the calculated correction value; a correction unit (34) corrects the digital voltage value output from the AD conversion unit (25, 25A) with the correction value stored in the correction value storage unit (33) to obtain a measured voltage value; and the correction unit (34) The system includes a measurement voltage value output unit (35) that outputs the obtained measurement voltage value. The calibration execution unit (31) performs a second calibration during the execution of the feedback operation by switching the second voltage switching switch unit (25B) to acquire the digital voltage value at the AD conversion unit (25, 25A) at that time. The correction value calculation unit (32) then recalculates the correction value based on the result of the second calibration and updates the correction value stored in the correction value storage unit (33) with the recalculated correction value.

[0012] [2] In the measurement circuit described in [1] above, the first voltage switching unit switches at least two reference voltages which are zero potential to the first reference voltage, and the second voltage switching unit switches at least two reference voltages which are zero potential to the second reference voltage, and the calibration execution unit, in the first calibration, obtains a first voltage value which is the digital voltage value in the AD conversion unit when the first voltage switching unit is switched to the first reference voltage, and a second voltage value which is the digital voltage value in the AD conversion unit when it is switched to zero potential, and the In the second calibration, the second voltage switching switch unit acquires a third voltage value, which is the digital voltage value at the AD conversion unit when the second voltage switching switch unit is switched to the second reference voltage, and a fourth voltage value, which is the digital voltage value at the AD conversion unit when the switch unit is switched to zero potential. The correction value calculation unit may then calculate the correction value based on the first reference voltage and the acquired first and second voltage values ​​as a result of the first calibration, and then calculate the correction value based on the acquired third and fourth voltage values ​​as a result of the second calibration.

[0013] [3] A voltage generating device (1, 1A) according to a typical embodiment of the present invention comprises a measurement circuit as described in either [1] or [2] above, and a voltage generation circuit that outputs a voltage based on the voltage in the feedback path and a voltage set to be applied to the object to be measured, as a device for performing the feedback operation.

[0014] 2. Specific Examples of Embodiments Specific examples of embodiments of the present invention will be described below with reference to the drawings. In the following description, components common to each embodiment will be denoted by the same reference numerals, and repeated explanations will be omitted. It should also be noted that the drawings are schematic, and the dimensional relationships and ratios of each element may differ from reality. There may also be parts where the dimensional relationships and ratios differ between drawings.

[0015] (First embodiment) Figure 1 is a diagram showing the schematic configuration of the main parts of a voltage generation device using a measurement circuit according to the first embodiment.

[0016] The voltage generator 1 shown in Figure 1 is connected to the device under test (DUT) 50 using a four-terminal method. The voltage generator 1 generates a constant voltage and applies it to the device under test 50, and can measure the voltage applied to the device under test 50 by detecting the potential difference across the device under test 50.

[0017] As shown in Figure 1, the voltage generation device 1 comprises a generation circuit 10 that generates a constant voltage and applies it to the object to be measured 50, and a measurement circuit 20 that measures the voltage applied to the object to be measured 50. The generation circuit 10 comprises a non-inverting amplifier 11, a digital-to-analog converter (DAC) 12, and an operational amplifier 13. The measurement circuit 20 comprises a first voltage switch unit 21, a differential amplifier 22, a second voltage switch unit 23, a differential amplifier 24, and an analog-to-digital converter (ADC) 25. The FPGA (an example of a data processing control unit) 30 has a configuration common to both the generation circuit 10 and the measurement circuit 20.

[0018] In the generation circuit 10, the DA converter 12 generates an analog voltage corresponding to the set voltage value received from the FPGA 30 and inputs it to the operational amplifier 13. The output of the non-inverting amplifier 11, which is input via the measurement circuit 20, is also input to the operational amplifier 13.

[0019] The input to the non-inverting amplifier 11 is branched from the measurement circuit 20, and the output is a voltage that is an amplified version of the potential difference between the two lines of the branched measurement circuit 20. When the input to the non-inverting amplifier 11 is connected to both ends of the object to be measured 50, the potential applied to the object to be measured 50 is generated at the output of the non-inverting amplifier 11.

[0020] The operational amplifier 13 receives the voltage generated at the output of the DA converter 12 and the voltage generated at the output of the non-inverting amplifier 11 as inputs. When the input of the non-inverting amplifier 11 is connected to both ends of the device to be measured 50, the potential applied to the device to be measured 50 is generated at the output of the non-inverting amplifier 11, so the operational amplifier 13 receives the analog voltage corresponding to the set voltage value and the potential applied to the device to be measured 50 as inputs. The output of the operational amplifier 13 is a voltage adjusted so that the current applied voltage approaches the set voltage. With this configuration, the generation circuit 10 performs a feedback operation.

[0021] The measurement circuit 20 has terminals T2 and T3 connected in parallel to both ends of the object to be measured 50. The voltage applied to the object to be measured 50 can be measured by detecting the voltages in the two lines connected to terminals T2 and T3, respectively, using the AD converter 25 and processing them with the FPGA 30.

[0022] The measurement circuit 20 has a feedback path that receives the voltage applied to the object to be measured and outputs it to the generation circuit 10, which is a device that performs feedback operation, and a measurement path that branches off from the feedback path and goes to the AD converter 25.

[0023] In the example shown in Figure 1, the feedback path in the measurement circuit 20 is provided with a first voltage switch unit 21 that switches the voltage of the feedback path, which is the voltage input from terminals T2 and T3, to a predetermined reference voltage, and a differential amplifier 22 that amplifies the voltage of the feedback path.

[0024] The measurement path in the downstream measurement circuit 20 of the feedback path is provided with a second voltage switch unit 23 that switches the voltage in the measurement path to another predetermined reference voltage, and a differential amplifier 24 that amplifies the voltage in the measurement path. At the end of the measurement path in the measurement circuit 20, an AD converter 25 is provided that performs AD conversion of the voltage in the measurement path into a digital voltage value and outputs it to the FPGA 30.

[0025] Here, the first voltage switch unit 21 and the second voltage switch unit 23 will be explained further.

[0026] Figure 2 shows an example of the configuration of a measurement circuit according to the first embodiment.

[0027] As shown in Figure 2, the measurement circuit 20 includes a first voltage switch unit 21, a differential amplifier 22, a second voltage switch unit 23, and a differential amplifier 24 in the path from the voltage generated between terminals T2 and T3, which are electrically connected to the object to be measured 50 (see Figure 1), to the input to the AD converter 25. In the measurement circuit 20 shown in Figure 2, an example is shown in which the differential amplifier 22 is composed of amplifiers 26, 27 and a differential amplifier 28. It is known that elements such as differential amplifiers 22, 24 and the AD converter 25, due to their characteristics, can impart an offset or gain to the measured voltage in relation to the voltage generated between terminals T2 and T3.

[0028] The measurement circuit 20 performs calibration at least twice to measure the effects of offset and gain caused by elements present in the path from terminals T2 and T3 to the AD converter 25. The first calibration, performed at the initial timing, is carried out with the feedback operation stopped. The second calibration, performed at the subsequent timing, is carried out with the feedback operation continuing.

[0029] In the measurement circuit 20, the first calibration is performed by switching the first voltage switch unit 21, and the second calibration is performed by switching the second voltage switch unit 23.

[0030] The first voltage switch unit 21 and the second voltage switch unit 23 are switches that switch the voltage generated between terminals T2 and T3 to a voltage output from a known reference voltage source, respectively. By inputting a predetermined reference voltage to the first voltage switch unit 21 and the second voltage switch unit 23, it is possible to detect the influence of elements provided downstream of each unit on the measured voltage.

[0031] The first voltage switch unit 21 is located in the feedback path from terminals T2 and T3 to the output to the generation circuit 10 (non-inverting amplifier 11), and is located in the measurement path branched off from the feedback path downstream of the second voltage switch unit 23 and the first voltage switching switch unit 21. Therefore, when the first voltage switch unit 21 switches to a predetermined reference voltage, the feedback operation cannot be continued, but when the second voltage switch unit 23 switches to a predetermined reference voltage, the feedback operation can be continued.

[0032] The first voltage switch unit 21 has a plurality of switches SW1 to SW6, and SW1 to SW3 selectively switch between inputting the voltage from terminal T2, the first reference voltage V1, and zero potential. In the first voltage switch unit 21, SW1 and SW4, SW2 and SW5, and SW3 and SW6 switch in synchronous operation.

[0033] The second voltage switch unit 23, like the first voltage switch unit 21, has multiple switches SW7 to SW12, and SW7 to SW9 selectively switch between inputting the voltage from terminal T2, the second reference voltage V2, and zero potential. In the second voltage switch unit 23, SW7 and SW10, SW8 and SW11, and SW9 and SW12 switch in synchronous operation.

[0034] The non-inverting amplifier 11 amplifies the voltage generated at the branching point of the two transmission lines in the measurement circuit 20 and outputs it to the operational amplifier 13, which performs feedback operation.

[0035] FPGA30 controls the switching between the first voltage switch unit 21 and the second voltage switch unit 23, and corrects the digital voltage value output from the AD converter 25 using a correction value to output the measurement voltage. FPGA30 also outputs the digital voltage value set to be applied to the object to be measured to the DA converter 12. FPGA30 will now be explained further.

[0036] Figure 3 shows an example of FPGA configuration in the measurement circuit of the first embodiment.

[0037] The FPGA 30 has the following functional units: a calibration execution unit 31, a correction value calculation unit 32, a correction value storage unit 33, a correction unit 34, a measured voltage value output unit 35, and a set voltage value output unit 36.

[0038] The calibration execution unit 31 controls the first voltage switch unit 21 and the second voltage switch unit 23 to acquire the voltage detected by the AD converter 25 when the voltage in the measurement circuit 20 is switched.

[0039] The calibration execution unit 31 controls the first voltage switch unit 21 to perform the first calibration at a time when the feedback operation in the generation circuit 10 is not being performed, and acquires the voltage detected by the AD converter 25 at that time. In the first calibration, the calibration execution unit 31 controls the first voltage switch unit 21 to selectively switch between the first reference voltage V1 and zero potential as input, and acquires the voltage detected by the AD converter 25.

[0040] During the timing of the execution of the feedback operation in the generation circuit 10, the calibration execution unit 31 controls the second voltage switch unit 23 to execute the second calibration, and acquires the voltage detected by the AD converter 25 at that time. In the second calibration, the calibration execution unit 31 controls the second voltage switch unit 23 to selectively switch and input the second reference voltage V2 and the zero potential, and acquires the voltage detected by the AD converter 25.

[0041] The correction value calculation unit 32 calculates a correction value based on the voltage acquired by the calibration execution unit 31. The correction value calculation unit 32 stores the reference voltage value V1 in the first calibration and the voltage value acquired by executing the first calibration in the correction value storage unit 33 as the first correction value, calculates the correction value again using the voltage value acquired by executing the second calibration, and updates the correction value stored in the correction value storage unit 33 with the recalculated correction value.

[0042] Here, taking the measurement circuit 20 shown in FIG. 2 as an example, the correction value in the correction value calculation unit 32 will be described. First, let the gain of the differential amplifier 22 in the measurement circuit 20 be G1 and the offset be V os1 and let the gain of the differential amplifier 24 and the AD converter 25 be G2 and the offset be V os2 and consider the voltage value detected by the AD converter 25 when the voltage of the measurement circuit 20 is changed.

[0043] Before the operation of the measurement circuit 20 starts, when the voltage (V1) of the first voltage value V ref1 is input in the first voltage switch unit 21, the detected voltage is V a and when the voltage value V ref01 of the zero potential is input, the detected voltage is V b . Similarly, before the operation of the measurement circuit 20 starts, when the voltage (V2) of the second voltage value V ref2 is input in the second voltage switch unit 23, the detected voltage is V c and when the voltage value V ref02When a voltage is input, the detected voltage is V d Let's assume that this is the case.

[0044] In this case, the detected voltage V a , V b , V c , V d Considering the gain and offset of the components in the measurement circuit, this can be expressed as follows: (Equation 1) to (Equation 4).

number

[0045] Assuming zero potential is common, V ref01 =V ref02 =V ref0 Since the above holds true, (Equation 2) and (Equation 4) can be expressed as (Equation 5) and (Equation 6) below.

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[0046] Similarly, when the first voltage switch unit 21 and the second voltage switch unit 23 are switched to input the voltage between terminals T2 and T3, the voltage detected by the AD converter 25 is V in If this is the case, the value of the corrected measured voltage, the voltage Vm between terminals T2 and T3, can be expressed by the following (Equation 7).

number

[0047] Here, in the above (Equation 7), G1, V os1 G2, V os2 This value is determined by the characteristics of the differential amplifier 22, the differential amplifier 24, and the AD converter 25 of the measurement circuit 20, and is therefore an unknown value. Thus, it is necessary to express (Equation 7) without using these values. Therefore, by rearranging (Equation 3) and (Equation 6), we obtain the following (Equation 8) and (Equation 9).

number

[0048] Furthermore, by rearranging (Equation 5), (Equation 8), and (Equation 9), we obtain the following (Equation 10).

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[0049] Furthermore, from (Equation 1), (Equation 8), (Equation 9), and (Equation 10), the following (Equation 11) is obtained.

number

[0050] Substitute (Equation 8), (Equation 9), (Equation 10), and (Equation 11) into (Equation 7) and V ref0 If we set the voltage to 0V, then (Equation 7) can be expressed as (Equation 12) below.

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[0051] In other words, in the first calibration, the first voltage value V input to the first voltage switch unit 21 ref1 The detected voltage V a , V b By substituting these values ​​into (Equation 12) as correction values, the voltage V detected by the AD converter 25 during measurement (when the first voltage switch unit 21 and the second voltage switch unit 23 are switched to input voltage between terminals T2 and T3) can be calculated. in Measure voltage V m It can be corrected to this.

[0052] As is clear from (Equation 12), the correction value for the measured voltage is the first voltage value V input from the first voltage switch unit 21 in the first calibration. ref1 And the voltage V detected by the AD converter 25. a , V b Only the following is required. That is, the first voltage value V input to the second voltage switch unit 23ref2 Then, the voltage V, which is switched in the second voltage switch unit 23 and detected in the AD converter 25, is c , V d This is not necessary. Therefore, it can be seen that only the first calibration is needed to calculate the correction value immediately after the start of operation of the measurement circuit 20.

[0053] On the other hand, as is clear from (Equation 1) and (Equation 2), V a , V b G2, V os2 It is clear that the following coefficients are included as elements: G2, V os2 These coefficients include the gain and offset of the AD converter 25, which have characteristics that are easily affected by the measurement environment. In other words, while the measurement circuit 20 is operating, G2 and V change with changes in the measurement environment. os2 Therefore, if time has elapsed since the start of operation of the measurement circuit 20, G2 and V will change. os2 It is considered necessary to correct these coefficients. In the measurement circuit 20 of this embodiment, in order to correct these changing coefficients, the input voltage in the second voltage switch unit 23 is switched to perform a second calibration and update the correction value.

[0054] First, G2, V os2 Let's consider correcting these coefficients. Expanding (Equation 1) yields (Equation 13) below.

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[0055] (Equation 13) of which, (V ref1 +V os1 )·G1 can only be calibrated by switching in the first voltage switch section 21, so this term is obtained before the start of operation of the measurement circuit 20. a , V c , V d Calibrate using V. ref1 When = 0V, (Equation 8) and (Equation 9) can be expressed as (Equation 14) and (Equation 15) below, respectively.

number

[0056] Using (Equation 14) and (Equation 15), (V ref1 +V os1 )·G1 can be expressed as follows (Equation 16).

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[0057] Here, G2, V os2 Since it is composed only of Vc and Vd, as shown in (Equations 14) and (Equation 15), it can be said that it can be calibrated by switching in the second voltage switch section 23. The V acquired during the second calibration c , V d V c ',V d If we set it as ', then we get the following (Equation 17) and (Equation 18).

number

[0058] Expressing (Equation 13) in terms of (Equation 17), (Equation 18), and (Equation 16), we get (Equation 19) below.

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[0059] Similarly to the above, expanding (Equation 2) yields the following (Equation 20).

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[0060] (Equation 20) of which, (V ref1 +V os1 )·G1 can only be determined by calibration by switching in the first voltage switch unit 21, so this term is obtained during calibration in the first voltage switch unit 21.b , V c , V d It will be determined using [this method].

[0061] V a As in the previous case, we can derive the following (Equation 21) using (Equation 14) and (Equation 15).

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[0062] Thus, in the first calibration, the correction value calculation unit 32 calculates the first voltage value V input to the first voltage switch unit 21. ref1 The detected voltage V a , V b The correction value is stored in the correction value storage unit 33 along with (Equation 12) as a correction value. Furthermore, the correction value calculation unit 32, in the second calibration, stores the detected voltage V c , V d Substituting this into (Equation 19) and (Equation 22) yields V a 'and V b 'and the new correction value V a and V bThe correction value is calculated and the correction value stored in the correction value storage unit 33 is updated.

[0063] The correction unit 34 corrects the digital voltage value output from the AD conversion unit 25 using the correction value stored in the correction value storage unit 33 to obtain a measured voltage value. That is, the digital voltage value V output from the AD conversion unit 25 in and V stored as a correction value ref1 , V a , V b The measured voltage V obtained by substituting the following (Equation 12) is V. m The measured voltage value can be corrected accordingly.

number

[0064] Thus, with the measurement circuit 20 of this embodiment and the voltage generation device 1 equipped therewith, a second calibration can be performed during the execution of the feedback operation to update the correction value. Therefore, even if the characteristics of the amplifier or AD converter change depending on the measurement environment, more accurate measurement values ​​can be output.

[0065] (Second embodiment) Next, in the measurement circuit of the first embodiment, the timing of the second calibration in the calibration execution unit was set to be at an arbitrary timing. In the measurement circuit of the second embodiment, the timing of the second calibration is determined by monitoring the fluctuations in the measured values ​​from the AD converter, which are prone to fluctuations in offset voltage and gain depending on the measurement environment.

[0066] Figure 4 shows a schematic configuration of the main parts of a voltage generation device using a measurement circuit according to the second embodiment. Figure 5 shows an example of the configuration of the measurement circuit according to the second embodiment. Figure 6 shows an example of the configuration of the FPGA in the measurement circuit of the second embodiment. Components that are denoted by the same reference numerals as in the first embodiment have the same configuration, so their explanation is omitted. In the measurement circuit 20A shown in Figures 4 and 5, unlike the first embodiment, there is no differential amplifier 24, but the method for calculating the correction value is the same as in the first embodiment.

[0067] As shown in Figure 4, the measurement circuit 20A differs from the measurement circuit 20 of the first embodiment in that it includes two AD converters 25A and 25B. The measurement circuit 20A further includes a second voltage switch unit 23A that switches the voltages input to the two AD converters 25A and 25B, and an FPGA 30A that processes the voltage values ​​output from the AD converters 25A and 25B.

[0068] The second voltage switch unit 23A inputs the voltage generated between the two lines of the measurement circuit 20A to either the AD converter 25A or the AD converter 25B, and, if necessary, inputs a predetermined monitoring voltage Vp to either the AD converter 25A or the AD converter 25B. Furthermore, during the second calibration, the second voltage switch unit 23A inputs a second voltage value Vp instead of the voltage generated between the two lines of the measurement circuit 20A. ref2 Switch between and zero potential and input. Note that the second voltage value V ref2 The zero potential and the second voltage switch section 23 in Figure 2 have the same configuration, and are omitted from the illustration in Figure 5.

[0069] In this embodiment, of the two AD converters 25A and 25B, one detects the voltage generated between the two lines of the measurement circuit 20 as a digital voltage value, similar to the AD converter 25 of the first embodiment, while the other detects the monitoring voltage as a digital voltage value. In this specification, when distinguishing between the two AD converters, the AD converter that detects the voltage generated between the two lines of the measurement circuit 20 as a digital voltage value may be referred to as the first AD converter, and the AD converter that detects the monitoring voltage as a digital voltage value may be referred to as the second AD converter.

[0070] The process of determining whether to use each of the two AD converters 25A and 25B as the first AD converter or the second AD converter will be described below.

[0071] First, after assembling the measurement circuit 20A in production, it is warmed up, and the monitoring reference voltage Vp is simultaneously input to two AD converters 25A and 25B, and the voltage detected by each is stored (first step).

[0072] After turning off the product's fan and allowing the temperature inside the enclosure to rise, a monitoring reference voltage Vp is input to the two AD converters 25A and 25B again after a certain period of time, and the voltage detected by each is stored (second step).

[0073] In the second step, the value detected is subtracted from the value detected in the first step. The module with the larger subtracted value is determined to have a larger drift and is selected as the second AD converter for monitoring the reference voltage (third step).

[0074] Once the second AD converter for monitoring the reference voltage is determined through the above steps, during the measurement operation in the measurement circuit 20A, the second voltage switch unit 23A inputs the voltage generated between the two lines of the measurement circuit 20A to the first AD converter among the two AD converters 25A and 25B, and inputs a predetermined monitoring voltage Vp to the second AD converter. In this embodiment, it is assumed that the AD converter 25A is the first AD converter and the AD converter 25B is the second AD converter.

[0075] In the measurement circuit 20A of the present embodiment, in addition to having the same configuration as the FPGA 30 of the first embodiment, the FPGA 30A is provided with a drift monitoring unit 37. During the measurement operation in the measurement circuit 20A, the drift monitoring unit 37 monitors the voltage detected by the ADC 25B, which is the second ADC. When it determines that there is a drift exceeding a certain value, it instructs the calibration execution unit 31 to execute the second calibration.

[0076] When the calibration execution unit 31 receives an instruction to execute the second calibration from the drift monitoring unit 37, similar to the first embodiment, in the second voltage switch unit 23A, the ADC 25A, which is the first ADC, is switched to input the second reference voltage V ref2 and the zero potential, and the voltage value detected at that time is acquired.

[0077] As described above, in the measurement circuit 20A of the present embodiment, when the drift monitoring unit 37 determines that there is a drift exceeding a certain value in the ADC 25B, which is the second ADC, the second calibration is executed. A drift exceeding a certain value in the ADC 25B, which is the second ADC, is considered to be caused by the gain and offset in the ADC 25B changing by more than a certain value. In the measurement circuit 20A, since the two ADCs 25A and 25B exist in the same measurement environment, it is considered that the gain and offset of the ADC 25A also change by more than a certain value. This is because if the gain and offset of the ADC 25A change by more than a certain value, there is a possibility that the correct value cannot be calculated even if the measured voltage is corrected by the correction value calculated by the correction value calculation unit 32 through the first calibration.

[0078] The correction value calculation unit 32 uses the voltage value obtained by executing the second calibration and substitutes it into V in (Equation 19) and (Equation 22) c 、V d to calculate V a ’ and V b ’ and calculates the obtained V a ’ and Vb 'and the new correction value V a and V b The correction value is calculated and the correction value stored in the correction value storage unit 33 is updated.

[0079] Thus, with the measurement circuit 20A and the voltage generator 1A equipped with it in this embodiment, a second calibration can be performed at an appropriate timing during the execution of the feedback operation, thereby updating the correction value and enabling the output of more accurate measurement values.

[0080] Furthermore, in the measurement circuits 20 and 20A of the above embodiments, the first voltage switching unit (first voltage switch unit 21) switches at least two reference voltages which are zero potential to the first reference voltage, and the second voltage switching unit (second voltage switch unit 23) switches at least two reference voltages which are zero potential to the second reference voltage, and the calibration execution unit 31, in the first calibration, switches the first voltage switching unit (first voltage switch unit 21) to the first reference voltage, and the first voltage value which is the digital voltage value in the AD conversion unit (AD converters 25, 25A, 25B) when it is switched to zero potential, and the first voltage switching unit (first voltage switch unit 21) switches to the first reference voltage, and the first voltage value which is the digital voltage value in the AD conversion unit (AD converters 25, 25A, 25B) when it is switched to zero potential. In the second calibration, the second voltage switching unit (second voltage switching unit 23) is switched to the second reference voltage, and the third voltage value, which is the digital voltage value at the AD conversion unit (AD converters 25, 25A, 25B) when the second voltage switching unit (second voltage switching unit 23) is switched to the second reference voltage, and the fourth voltage value, which is the digital voltage value at the AD conversion unit (AD converters 25, 25A, 25B) when it is switched to zero potential, is obtained. The correction value calculation unit 32 calculates the correction value based on the first reference voltage and the obtained first and second voltage values ​​as a result of the first calibration, and calculates the correction value based on the obtained third and fourth voltage values ​​as a result of the second calibration. With this configuration, even during feedback operation, an appropriate correction value can be calculated based on the voltage value obtained by performing the second calibration.

[0081] The AD conversion unit includes a first AD converter 25A that converts the voltage in the measurement path into a digital voltage value, and a second AD converter 25B that converts a monitoring reference voltage into a digital voltage value. The data processing control unit 30 further includes a drift monitoring unit 37 that monitors the digital voltage value output from the second AD converter 25B and instructs the calibration execution unit 31 to perform a second calibration when the fluctuation of the digital voltage value exceeds a threshold. This configuration allows the second calibration to be performed at an appropriate timing.

[0082] The second AD converter 25B may have a greater drift due to environmental changes than the first AD converter 25A. In this case, the drift due to environmental changes can be determined with greater accuracy, allowing the second calibration to be performed at a more appropriate timing.

[0083] <Modified examples of embodiments> Although specific examples of the measurement apparatus in the above embodiments have been described, the apparatus is not limited to these examples, and various modified forms can be adopted. For example, FPGA30 can be any computing memory capable of data processing control, and a CPU, GPU, or other device can be used instead of FPGA30.

[0084] In the embodiments described above, the measurement circuits 20 and 20A were explained using examples of their integration into the voltage generators 1 and 1A. However, they can also be integrated into configurations other than the voltage generators 1 and 1A that have a voltage feedback mechanism.

[0085] In the embodiments described above, the measurement circuit 20 is equipped with differential amplifiers 22 and 24, and the measurement circuit 20A is equipped with differential amplifier 22 as an example, but the invention is not limited to this configuration. Amplifiers and differential amplifiers can be provided wherever necessary as needed. In this case as well, the correction value can be calculated in the same manner as in the embodiments described above.

[0086] In the embodiments described above, the first voltage switch unit 21 selectively switches between the voltage between terminals T2 and T3, a first reference voltage V1, and zero potential, and the second voltage switch unit 23 selectively switches between the voltage between terminals T2 and T3, a second reference voltage V2, and zero potential. However, the embodiments are not limited to this. The first voltage switch unit 21 and the second voltage switch unit 23 only need to be able to selectively switch between the voltage between terminals T2 and T3 and at least two reference voltages, and the two reference voltages do not necessarily have to include zero potential.

[0087] Furthermore, while the configuration of the generation circuit 10 was described using a non-inverting amplifier 11, a DA converter 12, and an operational amplifier 13 to perform feedback operation as an example, the circuit is not limited to this configuration. [Explanation of Symbols]

[0088] 10 Generation circuit (example of voltage generation circuit), 11 Non-inverting amplifier, 12 DA converter, 13 Operational amplifier, 20 Measurement circuit, 21 First voltage switch section (example of first voltage switching switch section), 22 Differential amplifier, 23-23A Second voltage switch section (example of second voltage switching switch section), 24 Differential amplifier, 25-25A-25B AD converter (example of AD conversion section), 26-27 Amplifier, 28 Differential amplifier, 30 FPGA (example of data processing control section), 31 Calibration execution section, 32 Correction value calculation section, 33 Correction value storage section, 34 Correction section, 35 Measured voltage value output section, 36 Set voltage value output section, T1-T2-T3-T4 terminals

Claims

1. A first voltage switching switch unit is provided in the feedback path from which the applied voltage to the object to be measured is output to a device that performs a feedback operation, and switches the voltage in the feedback path to at least two reference voltages, A second voltage selector switch unit is provided in a measurement path branched from the feedback path downstream of the first voltage selector switch unit, and switches the voltage of the measurement path to at least two reference voltages, An AD conversion unit is provided in the measurement path downstream of the second voltage switching switch unit, which performs AD conversion of the voltage in the measurement path into a digital voltage value, The system includes a data processing control unit that switches the first voltage selector switch unit and corrects the digital voltage value by a correction value and outputs it as a measured voltage, The data processing control unit, A calibration execution unit performs a first calibration by switching the first voltage selector switch unit while the feedback operation is stopped, and acquiring the digital voltage value in the AD conversion unit at that time. A correction value calculation unit that calculates the correction value based on the result of the first calibration, A correction value storage unit that stores the calculated correction value, A correction unit that corrects the digital voltage value output from the AD conversion unit with the correction value stored in the correction value storage unit to obtain a measurement voltage value, The system includes a measurement voltage value output unit that outputs the measurement voltage value obtained by the correction unit, When the calibration execution unit performs a second calibration by switching the second voltage switching switch unit during the execution of the feedback operation and acquiring the digital voltage value at the AD conversion unit at that time, the correction value calculation unit calculates the correction value again based on the result of the second calibration and updates the correction value stored in the correction value storage unit with the newly calculated correction value. Measurement circuit.

2. A measurement circuit according to claim 1, The at least two reference voltages switched by the first voltage selector switch are at zero potential from the first reference voltage. The two reference voltages switched by the second voltage selector switch are at zero potential from the second reference voltage. In the first calibration, the calibration execution unit obtains a first voltage value, which is the digital voltage value in the AD conversion unit when the first voltage switching switch unit is switched to the first reference voltage, and a second voltage value, which is the digital voltage value in the AD conversion unit when it is switched to zero potential. In the second calibration, the calibration execution unit obtains a third voltage value, which is the digital voltage value in the AD conversion unit when the second voltage switching switch unit is switched to the second reference voltage, and a fourth voltage value, which is the digital voltage value in the AD conversion unit when it is switched to zero potential. The correction value calculation unit calculates the correction value based on the first reference voltage and the acquired first and second voltage values ​​as a result of the first calibration, and calculates the correction value based on the acquired third and fourth voltage values ​​as a result of the second calibration. Measurement circuit.

3. A measurement circuit according to claim 1 or 2, The device that performs the aforementioned feedback operation includes a voltage generation circuit that outputs a voltage based on the voltage in the feedback path and a voltage set to be applied to the object to be measured. Voltage generator.

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