CN201654137U - Charge transfer type capacitance measuring device - Google Patents

Abstract

The utility model discloses a charge transfer formula capacitance measuring device is providing a simple and easy, quick and accurate capacitance measuring device. The measuring method is that the object to be measured is discharged to 0V, then the electric charge of the object to be measured is transferred to the object to be measured successively by utilizing a capacitor smaller than the object to be measured, the electric potential of the object to be measured is changed continuously in the process of transferring the electric charge, and the capacitance value of the object to be measured can be calculated according to the variation of the electric potential and the number of times of transferring the electric charge.

Description

Charge-transfer capacitance measurement device

technical field

The utility model relates to a measuring device for measuring capacitance, in particular to a measuring device (for example, a digital electric meter) for measuring the capacitance to be measured by charge transfer. the

Background technique

The utility model is to provide a simple and fast capacitance measurement framework. The structure of general capacitance measurement often has complex control procedures, difficult design, and requires the use of analog/digital converters (A/D converters), which cost a lot of circuit costs. For example, US Patent Nos. It is disclosed that the capacitance value is measured using the method described above. In addition, for example, the capacitance measurement method disclosed in Taiwan Patent No. 453443, although the use of analog/digital converters can be avoided, so that the cost of its circuit design is low, but its measurement method requires multiple fully matched current sources ; However, the current source manufactured in the integrated circuit (IC) is difficult to be completely matched, and it is easy to cause measurement errors. For the above problems, the measuring device of the present invention can not only greatly reduce the circuit cost, but also can obtain an accurate capacitance measurement value through the adjustment of the variable resistor. the

Utility model content

In view of the above background of the utility model, in order to obtain an accurate capacitance measurement value, the utility model provides a digital electric meter or a multimeter equipped with a capacitance measuring device. Therefore, a main purpose of the present invention is to provide a capacitance measuring device, which can measure the capacitance to be measured by charge transfer, so as to obtain an accurate capacitance measurement value. the

Another main purpose of the present invention is to provide a capacitance measuring device, which can measure the circuit of the capacitance to be measured through charge transfer, and can simplify the structure of capacitance value measurement. the

Another main purpose of the present invention is to provide a capacitance measuring device, which can be integrated into an integrated circuit chip, which can reduce the cost and improve the reliability of the capacitance measuring device. the

According to the above purpose, the utility model provides a charge-transfer type capacitance measuring device, comprising: a reference voltage device, which is used to provide a first reference voltage, a second reference voltage and a third reference voltage; A voltage divider, one end of which is connected to the first reference voltage to provide a fourth reference voltage (V _stop ); a first comparison device, one of its input ends is connected to a capacitor to be measured (C _x ), and its other An input terminal is then connected with the fourth reference voltage; a second comparison device, one input terminal thereof is connected with a transfer capacitor (C _t ); a first switching device, one terminal thereof is connected with the capacitance to be measured (C _x ), and The other end is connected to the transfer capacitor (C _t ); a second switching device, one end of which is connected to the second reference voltage and the third reference voltage, and the other end is connected to the other input end of the second comparison device; A counting device, one end of which is connected to the output end of the first comparison device; and a control device, which is connected to the output ends of the first switching device, the second switching device, the counting device and the second comparison device; wherein, the transfer capacitor The capacitance value of C _t is smaller than the capacitance value of the capacitor C _x to be measured.

The beneficial effect that the utility model obtains is:

1) The capacitance measurement device provided by the utility model can not only greatly reduce the circuit cost, but also obtain an accurate capacitance measurement value through the adjustment of the variable resistor. the

2) The capacitance measuring device provided by the utility model can measure the capacitance to be measured through charge transfer, which can simplify the structure of capacitance value measurement. the

3) The capacitance measuring device provided by the utility model can be integrated into an integrated circuit chip, which can reduce the cost and improve the reliability of the capacitance measuring device. the

Description of drawings

Fig. 1 is the functional block diagram of the capacitance measuring device of the present utility model;

Fig. 2 is the schematic diagram of the embodiment of capacitance measuring device of the present utility model;

Fig. 3 is the flow chart of capacitance measuring device of the present utility model;

Fig. 4 is a schematic diagram of the switch configuration of the utility model in the charging stage and the charge transfer stage respectively;

Fig. 5 is the electric potential change schematic diagram of capacitance C _t of the present utility model and capacitance _C to be measured;

Fig. 6 is a schematic diagram of the measuring device of the present invention. the

【Description of main component symbols】

10 Measuring device

20 Shell

22 Test Probes

24 Test Probes

26 Signal to be tested

28 Operation interface

30 Display

32 Knob

34 Voltage/frequency measurement switch

36 Frequency switch

100 Reference voltage generating device

200 Pressure divider

300 The first comparison device

400 Second comparison device

500 First switchgear

600 Second switch device

700 control device

800 Counting device

900 display device

Detailed ways

The direction of the utility model discussed here is a device for measuring capacitance value. In order to thoroughly understand the utility model, detailed steps and circuit components will be provided in the following description. Clearly, the practice of the invention is not limited to specific details familiar to those skilled in capacitance measuring devices. On the other hand, well-known capacitance measurement devices or measurement steps are not described in detail to avoid unnecessary limitations of the present invention. The preferred embodiments of the present utility model will be described in detail as follows, but in addition to these detailed descriptions, the present utility model can also be widely implemented in other embodiments, and the scope of the present utility model is not limited, and it is with the following rights The required range shall prevail. the

First, please refer to FIG. 1 , which is a functional block diagram of the capacitance measuring device of the present invention. As shown in Figure 1, the relevant circuit of the capacitance measuring device of the present invention includes the following main parts: one is used to provide the first reference voltage (Vr1), the second reference voltage (Vr2) and the third reference voltage (Vr3 ) reference voltage generator 100; a voltage divider 200 that is connected to the first reference voltage (Vr1) and adjusts another reference potential (V _stop ) by voltage division; the first switch device 500, one end of which is connected to the The capacitor C _x is connected; a transfer capacitor C _t used to transfer the charge to the capacitor C _x to be measured, one end of which is connected to the first switching device 500, wherein the capacitance of the transfer capacitor C _t is much smaller than the capacitor C _x to be measured ; The second switching device 600, its first input terminal and the second input terminal are respectively connected with the second reference voltage (Vr2) and the third reference voltage (Vr3); the first comparison device 300, its first input terminal and the second The input end is respectively connected with the capacitor _Cx to be measured and the voltage divider 200; the second comparator 400, its first input end and the second input end are respectively connected with the first switching device 500 and the second switching device 600; a counting device 800, connected to the output terminal of the first comparison device 300, for accumulating and calculating the value of the capacitance; a control device 700, connected with the first switching device 500, the second switching device 600 and the counting device 800, in order to control the first A switch device 500 , a second switch device 600 and a counting device 800 ; a display device 900 is connected with the counting device 800 for displaying the value of the counting device 800 .

Next, in order to further describe the detailed operation process of the capacitance measuring device of the present invention, please continue to refer to FIG. 2 . FIG. 2 is the actual circuit of the utility model corresponding to the voltage dividing device, switch device 1 and switch device 2 in FIG. 1 . As shown in FIG. 2, the voltage dividing device 200 includes resistors R1, R2 and a variable resistor R3. Obviously, according to the circuit voltage dividing principle, the magnitude of the reference voltage V _stop (also called the fourth reference voltage) can be determined by R1 And the ratio of R2 is determined, and can be fine-tuned by the variable resistor R3. Next, the first switching device 500 includes switches s1, s2 and resistors R4, R5, and Vs connected to the resistor R5 is a voltage source. As shown in FIG. 1 and FIG. 2 , the switches s1 and s2 are controlled by the control device 700 ; the second switch device 600 includes the switches s3 and s4 , and similarly, the switches s3 and s4 are controlled by the control device. In addition, the absolute value of each potential shown in FIG. 1 and FIG. 2 has the following relationship: |Vs|>|Vr3|>|Vr2|>|Vr1|>|V _stop |.

Then please refer to FIG. 3 , which is a flowchart of the capacitance measuring device of the present invention. As shown in Figure 3, when starting to measure, the measuring device will first enter the capacitor charging phase (ChargePhase), as shown in step 310, at this time the control device 700 will drive the switch s2 and the second switch in the first switching device 500 The switch s3 in the device 600 is in the conduction (ON) state, and simultaneously drives the switch s1 in the first switch device 500 and the switch s4 in the second switch device 600 to a non-conduction (OFF) state, the connection diagram of the circuit As shown in Figure 4(a). At this time, the voltage source Vs will charge the transfer capacitor C _t through the resistor R5; when the potential of the transfer capacitor C _t is charged to be greater than the third reference voltage Vr3 by the voltage source Vs during the capacitor charging stage, then according to the circuit diagram of FIG. 2 , the output state of the second comparator 400 will change, and the change of this state will be sent back to the control device 700. At this time, the control device 700 will drive the switch s2 to a non-conductive (OFF) state, so the voltage source Vs has an effect on the transfer capacitance The charging operation of C _t will stop, and the potential of the transfer capacitor C _t will be maintained at the level of the third reference voltage Vr3 at this time.

Please continue to refer to FIG. 3, when the capacitor charging phase (Charge Phase) ends, then enters the charge conversion phase (Transfer Phase), as shown in step 320, at this time the control device 700 will drive the switches s1 and s4 to be turned on ( ON) state, and drive switches s2 and s3 to non-conducting (OFF) state, the connection diagram of the circuit is shown in Figure 4(b). At this time, the charge of the transfer capacitor C _t will be transferred to the capacitor C _x to be measured through the resistor R4. During the potential transfer process, the potential of the transfer capacitor C _t will form a gradually decreasing discharge curve according to the resistance value of the resistor R4. Correspondingly, the potential of the capacitor _Cx to be measured will be charged and rise slowly until the potential of the transfer capacitor C _t drops below the second reference voltage Vr2, then the output state of the second comparison device 400 will change again, And the change of this state is sent back to the control device 700. At this time, the control device 700 will drive the switch s1 to a non-conductive (OFF) state, so the charge transfer action in the transfer capacitor C _t will stop, and the transfer capacitor C _t The potential of the second reference voltage Vr2 will be maintained at the value of the second reference voltage Vr2, and the value of the counting device 800 will be automatically counted once (or incremented by 1) after a charge transfer is completed, as shown in step 330 .

As shown in FIG. 3 again, if the electric potential of the capacitor Cx to be measured is determined to be lower than the fourth reference voltage V _stop when the capacitance measuring device judges that the electric potential of the capacitor _Cx to be measured is lower than the fourth reference voltage V stop, as shown in step 340, the capacitance measuring device will repeat the capacitor charging phase (Charge Phase ) and the charge conversion stage (Transfer Phase), while the counting device 800 is also continuously accumulating until the potential of the capacitor C _x to be measured is higher than the fourth reference voltage V _stop , at this time the value of the counting device 800 is the value to be measured Capacitance value of capacitor _Cx . The above step 340 is executed by the first comparing device 300 in FIG. 1 and FIG. 2 . For example, when the potential of the capacitor C _x to be measured is lower than the fourth reference voltage V _stop , the state of the first comparing device 300 will not change, so the value of the counting device 800 will automatically count.

In addition, it should be emphasized that during the process of Figure 3, the object under test must be discharged to 0V first, so that the capacitance value of the capacitor under test can be accurately measured. the

Please refer to FIG. 5 , which is a schematic diagram of the potential variation with time of the transfer capacitor C _t and the measured capacitor C _x in the capacitor charging stage and the charge conversion stage of the present invention. As shown in Figure 5, T1 in the figure is the length of the capacitor charging phase (Charge Phase), and T2 is the length of the charge conversion phase (Transfer Phase). It can be seen from FIG. 5 that the potential of the transfer capacitor C _t is constantly changing between the second reference voltage Vr2 and the third reference voltage Vr3 , while the potential of the capacitor C _x to be measured is slowly rising from 0V. If after N cycles of the transfer phase, the potential of the capacitor C _x to be measured increases gradually to V _stop , then the law of conservation of charge has the following mathematical relationship:

C _x ×V _stop ＝C _t ×(Vr3-Vr2)×N-----(1)

＝＝＞C _x ＝C _t ×(Vr3-Vr2)/Vstop×N ----(2)

In equation (2), since the transfer capacitance C _t , the second reference voltage Vr3 and the third reference voltage Vr2 are all fixed values, the fourth reference voltage V _stop needs to be adjusted through the variable resistor R3 except for calibration. Fine-tuning, otherwise it is a fixed value, so C _t × (Vr3-Vr2)/V _stop in equation (2) is a constant, it can be deduced that the capacitance C _x to be measured is proportional to N, and is a linear relationship. Therefore, the capacitance of the capacitance C _x to be measured can be obtained by performing N times of charge conversion stages to obtain the capacitance value of the capacitance C _x to be measured, so as to achieve the purpose of measuring the capacitance of the capacitance C _x to be measured.

After the circuit construction of the present invention is completed, it needs to go through a calibration and comparison, so that the value N obtained by the final counting device can be consistent with the actual capacitance value. The purpose of the calibration is to make equation (2) valid by adjusting the magnitude of the fourth reference voltage V _stop . After we select the appropriate transfer capacitance C _t , the second reference voltage Vr2 and the third reference voltage Vr3, since they all have certain errors, the offset between the first comparison device and the second comparison device (i.e. offset) will also cause certain errors. The above errors can be corrected by adjusting the magnitude of the fourth reference voltage V _stop . The correction method can send a known capacitance value through another correction device (for example: calibrator, Calibrator), and input the signal of this known capacitance value to the position of the capacitance C _x to be measured, and then adjust the variable Resistor R3 to adjust the size of the fourth reference voltage V _stop ; when the size of the fourth reference voltage V _stop changes, the value N accumulated by the counting device will also change, and finally adjust until N is consistent with the known capacitance value . For example, if the capacitance value of the transfer capacitor C _t is 1uF, the third reference voltage Vr3 is 2.3V, and the second reference voltage Vr2 is 1.5V, when the calibrator sends a capacitance value of 10000uF for calibration, if If N=10000, it can be known from the equation (2), and the fourth reference voltage V _stop must be adjusted to 0.8V when performing calibration. After the fourth reference voltage V _stop is adjusted and fixed at 0.8V, a 5000uF capacitance _Cx to be tested is input next time, and the capacitance value N=5000 can be obtained from equation (2).

Next, please refer to FIG. 6 , which is a schematic diagram of the measuring device of the present invention. The measuring device 10 is an ammeter, digital or multimeter, and has a casing 20 , and a pair of test probes 22 / 24 are arranged at the bottom of the casing 20 to measure a signal 26 to be tested. In addition, the casing 20 has an operation interface 28 and a display 30. The operation interface 28 is provided with a knob 32, which can be rotated to select different measurement functions or modes, such as: measuring voltage value, measuring current value, measuring The resistance value or capacitance value is measured, and the measurement result is displayed on the display 30 . In addition, the operation interface 28 also has a voltage/frequency measurement switching switch 34 and a frequency switching switch 36. The voltage/frequency measurement switching switch 34 is for the user to switch between voltage measurement and frequency measurement, and the frequency switching switch 36 can also be used for The user selects or switches to different frequencies, so that the measuring device 10 provides filtering functions of different frequencies. Therefore, when the circuit of the capacitance measuring device in the measuring device 10 is replaced by Fig. 1, the measuring device 10 can use a transfer capacitance C _t smaller than the capacitance C _x to be measured, and successively pass through the charging stage and the charge transfer stage Transfer the charge of the transfer capacitor C _t to the capacitor under test C _x , during the process of charge transfer, the potential of the capacitor C _x under test will change continuously, when the potential of the capacitor C _x under test is equal to a set voltage ( For example, when the fourth reference voltage V _stop ) is the same, the capacitance value of the capacitor C _x to be measured can be obtained through the number of charging phases and charge transfer phases. Because, the capacitance value of transfer capacitance C _t is less than the capacitance value of the capacitance C _x to be measured, and the capacitance C _x to be measured shown by equation (2) is linearly related to N simultaneously, so the measuring device of the present invention is performing the capacitance to be measured When measuring the capacitance _Cx , an accurate measurement capacitance value can be obtained. Furthermore, since all circuit elements in the capacitance measuring device of the present invention can be integrated in a chip formed by an integrated circuit, the cost and the volume of the measuring device can be reduced and the reliability of the measuring device can be increased. . At the same time, when the measuring device has been integrated into a chip formed by an integrated circuit, the capacitance measuring device of the present invention can be completely configured in the chip of the measuring device.

Apparently, according to the descriptions in the above embodiments, the present utility model may have many modifications and differences. It is therefore to be understood within the scope of the appended claims that the invention may be practiced broadly in other embodiments than those detailed above. The above is only a preferred embodiment of the utility model, and is not intended to limit the scope of claims of the utility model; all other equivalent changes or modifications that do not deviate from the spirit disclosed in the utility model should be included in the following within the scope of the preceding claims. the

Claims (3)

1. A charge-transfer type capacitance measuring device, characterized in that, comprising: A reference voltage device is used to provide a first reference voltage, a second reference voltage and a third reference voltage; a voltage divider, one end of which is connected to the first reference voltage, for providing a fourth reference voltage V _stop ; A first comparison device, one input end of which is connected to a capacitance _Cx to be measured, and the other input end thereof is connected to the fourth reference voltage; A second comparator, one of its input terminals is connected with a transfer capacitor C _t ; A first switch device, one end of which is connected to the capacitance _Cx to be measured, and the other end thereof is connected to the transfer capacitance _Ct ; a second switching device, one terminal of which is connected to the second reference voltage and the third reference voltage, and the other terminal of which is connected to the other input terminal of the second comparison device; a counting device, one end of which is connected to the output of the first comparison device; and a control device connected to the output terminals of the first switching device, the second switching device, the counting device and the second comparing device; Wherein, the capacitance value of the transfer capacitor C _t is smaller than the capacitance value of the capacitor C _x to be measured. 2. The charge transfer capacitance measuring device according to claim 1, wherein the voltage dividing device comprises a variable resistor. 3. The charge-transfer capacitance measuring device according to claim 1, wherein the measuring device is an integrated circuit chip. the

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