PC-level constant charge source circuit with feedback

Abstract

The invention relates to a pC-level constant charge source circuit with feedback, and the circuit comprises a voltage source which is used for driving charge output; a charge output terminal; a feedback resistor; the adder circuit is used for enabling the voltage at the two ends of the feedback resistor to be consistent with the amplitude of the driving voltage provided by the voltage source; the voltage following circuit is used for taking the load voltage of the charge output end as the output voltage of the voltage following circuit; the voltage reversing circuit is used for reversing and outputting the output voltage of the voltage following circuit; the voltage monitoring end is used for monitoring the output state of the charge output end; the voltage source and the voltage monitoring end are connected with the input end of the adder circuit, the two ends of the feedback resistor are connected to the output end of the adder circuit and the charge output end respectively, and the two ends of the voltage follower circuit and the voltage reverse circuit are connected with the voltage monitoring end and the charge output end respectively after being connected in series. According to the pC-level constant charge source circuit, charges can be continuously output, the limitation on equipment using a charge source and a using mode is small, and the application range is wide.

Description

Technical Field

[0001] The invention relates to the technical field of charge sources, and in particular to a pC-level constant charge source circuit with feedback. Background Art

[0002] The charge is referred to as the amount of charge, which is the value of the charge carried by an object. The unit is coulomb (symbol C), referred to as coulomb. Charge is divided into positive charge and negative charge. The charge source provides standard charge output, which is used for the metrological verification of charge amplifiers and charge test equipment. It is an important standard equipment in the electrostatic protection system.

[0003] The capacitance value C of a capacitor is the ratio of the charge Q carried by the capacitor to the potential difference U between the two plates of the capacitor, that is, Once the capacitor is selected, the capacitance value is a fixed value. In addition to the established temperature coefficient, humidity coefficient and aging, the capacitance value of the capacitor can be conveniently and accurately measured in the laboratory using a bridge. According to the definition of capacitance, the charge Q in a capacitive charge source is proportional to the capacitance C and the voltage U across the capacitor. When the capacitance is determined, the capacitance C remains unchanged, and the charge Q is only related to the voltage value between the two plates of the capacitor.

[0004] Current refers to the directional flow of electric charge. The magnitude of current refers to the amount of charge passing through a certain cross section of a conductor per unit time. The amount of charge passing through one coulomb per second is called one ampere, that is, From this we can see that when the output current is constant, the output charge amount is only related to the output duration.

[0005] 1pC=1E-12C. When the current-time integration method is used to achieve 1pC charge output, the output time is usually set to 1s. The output current setting value is determined by the output target charge Q, I=Qt. Therefore, pC level charge corresponds to a steady output of A level current.

[0006] The standard sources of pC-level charge output available on the market include Kistler's 5393A and Kiethley's 263-type charge source. The 5393A is a capacitor voltage charge source that outputs standard charge by controlling the voltage value on the standard capacitor. The principle of the Kiethley 263-type charge source is current-time integral, which uses a constant current source and output duration control to achieve a pC-level charge source. The schematic diagram is shown below. Figure 2 As shown in the figure, when working, the voltage source driving the charge output floats at the output end of the op amp. The voltage source must be powered by a separate isolated power supply and cannot share the same ground with the electrostatic amplifier. This solution has complex power supply, and there is parasitic capacitance between the floating system and the ground, which causes the reference potential of the voltage source to change, increasing the inductive interference. A discharge circuit needs to be added to ensure the performance of the floating voltage source and the safety of the equipment.

[0007] The Chinese invention patent with publication number CN103178708A and name “Static Charge Source and Calibration Method Thereof” states that the static charge source is made based on the principle of capacitor voltage, and can achieve pC-level charge output. The controllable voltage source and capacitor are both in the feedback loop of the operational amplifier, and the controllable voltage source is designed to be floating. The voltage-capacitor charge source has a complex workflow, requiring the standard capacitor to be charged first and then outputting the charge. The discharge current is not a constant current, which limits the type of device that can be used to generate the charge. After the charge output is completed, the residual charge on the standard capacitor must be released to avoid equipment damage and personal injury.

[0008] If the current of the current time integral charge source is a differential constant current source, it is not suitable for pC level charge source output. Because the input impedance of the differential constant current source is low, in order to ensure the virtual disconnection of the operational amplifier, the resistance of the feedback resistor must be much smaller than the input impedance, which results in the resistance of the feedback resistor not being too large, thus limiting the output current from being too small, and the minimum current output can be μA level. The differential constant current source cannot be used as a current source for the output of the pC level charge source. Summary of the invention

[0009] In order to solve the technical problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a pC-level constant charge source circuit with feedback, in which the output charge is obtained by current time integration, the charge can be output continuously, the load effect can be ignored, there are few restrictions on the equipment and usage of the charge source, and the scope of application is wide; there is no energy storage device in the circuit, and there is no charging and discharging link in the output process, and there will be no residual charge in the energy storage element to cause equipment damage and personal injury, and the safety is higher.

[0010] To achieve the above-mentioned object of the invention, the present invention provides a pC-level constant charge source circuit with feedback, comprising:

[0011] A voltage source for driving the charge output;

[0012] Charge output terminal;

[0013] Feedback resistor;

[0014] an adder circuit, used to make the voltage across the feedback resistor consistent with the amplitude of the driving voltage provided by the voltage source;

[0015] A voltage follower circuit, used for using the load voltage at the charge output terminal as the output voltage of the voltage follower circuit;

[0016] A voltage inversion circuit, used for inverting and outputting the output voltage of the voltage follower circuit;

[0017] A voltage monitoring terminal, used for monitoring the output state of the charge output terminal according to the output of the voltage inversion circuit;

[0018] The voltage source, the voltage monitoring terminal and the input terminal of the adder circuit are connected, the two ends of the feedback resistor are respectively connected to the output terminal of the adder circuit and the charge output terminal, and the two ends of the voltage follower circuit and the voltage reverse circuit are respectively connected in series to the voltage monitoring terminal and the charge output terminal.

[0019] According to a technical solution of the present invention, the adder circuit includes a third operational amplifier, a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor. The non-inverting input terminal of the third operational amplifier is connected in series with the seventh resistor and then connected to a reference ground. The voltage monitoring terminal is connected in series with the fourth resistor and then connected to the inverting input terminal of the third operational amplifier. The voltage source is connected in series with the fifth resistor and then connected to the inverting input terminal of the third operational amplifier. The two ends of the sixth resistor are respectively connected to the output terminal and the inverting input terminal of the third operational amplifier.

[0020] According to a technical solution of the present invention, the resistance values ​​of the fourth resistor, the fifth resistor, and the sixth resistor are equal.

[0021] According to a technical solution of the present invention, two ends of the feedback resistor are respectively connected to the output end of the third operational amplifier and the charge output end.

[0022] According to a technical solution of the present invention, the voltage follower circuit includes a first operational amplifier and a first resistor, the two ends of the first resistor are respectively connected to the output terminal and the inverting input terminal of the first operational amplifier, and the non-inverting input terminal of the first operational amplifier is connected to the charge output terminal.

[0023] According to a technical solution of the present invention, the input impedance of the first operational amplifier is greater than 10 TΩ and the bias current is less than 100 fA.

[0024] According to a technical solution of the present invention, the voltage reversal circuit includes a second operational amplifier, a second resistor, and a third resistor, wherein the two ends of the second resistor are respectively connected to the output end of the first operational amplifier and the inverting input end of the second operational amplifier, the two ends of the third resistor are respectively connected to the inverting input end and the output end of the second operational amplifier, and the non-inverting input end of the second operational amplifier is connected to the reference ground.

[0025] According to a technical solution of the present invention, the resistance values ​​of the second resistor and the third resistor are equal.

[0026] According to a technical solution of the present invention, the voltage monitoring terminal is connected to the output terminal of the second operational amplifier, and the voltage monitoring terminal and the charge output terminal are both grounded.

[0027] According to a technical solution of the present invention, the charge amount output by the pC-level constant charge source circuit is controlled according to the following formula:

[0028] Q out =V in *t / R f

[0029] Among them, Q out is the output charge, V in is the driving voltage provided by the voltage source, t is the output time, R f is the feedback resistor.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The pC level charge source in the present invention is a constant current output with feedback. The first operational amplifier selected is an electrostatic amplifier with an input impedance of up to 1E+15Ω, so that the first operational amplifier will not affect the output of the charge output end. The resistance of the feedback resistor is on the order of 1E+12Ω, and a 1E-12A DC current can be stably output, thereby achieving a high-precision output of a minimum 1E-12C level, i.e., a pC level charge.

[0032] 2. In the present invention, the output charge is obtained by current time integration, and the charge can be output continuously, with few restrictions on the equipment and usage of the charge source, and a wide range of applications; there is no energy storage device in the circuit, and there is no charging and discharging link in the output process, so there will be no charge residue in the energy storage element, causing equipment damage and personal injury. Voltage value V in , feedback resistor R f and the output time t determine the output charge Q out Amplitude.

[0033] 3. The working voltage on the load is reversed and superimposed with the standard voltage before being loaded onto the feedback resistor to form output negative feedback. In principle, this ensures that the voltage amplitude across the feedback resistor is equal to the voltage amplitude of the drive charge output, the output charge is linearly related to the working current, and the output time is set reasonably. The short-term stability of the current will not affect the output accuracy, and the output charge is stable and reliable.

[0034] 4. The output impedance of the charge source in the present invention is large enough and is a stable system with feedback. The output charge amount does not change with the change of the load at the charge output end, nor is it affected by the working principle and charge measurement method of the charge tester. The input impedance requirement for the load is low, and it can meet the working requirements of different types of charge testing equipment to achieve a stable output of the charge source.

[0035] 5. With feedback voltage monitoring terminal, it is convenient to detect the output state of the charge source output terminal.

[0036] 6. The charge output terminal shares a common ground with the driving voltage source. The voltage source will not float on the output charge signal, forming parasitic capacitance to generate potential charge storage and affect the output charge accuracy; nor will charge accumulation form on the parasitic capacitance to cause electrostatic discharge. The equipment has high safety and output accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 The schematic diagram schematically shows the principle of the pC-level constant charge source circuit with feedback of the present invention;

[0039] Figure 2 The schematic diagram of the principle of the 263 type charge source of Kiethley Company in the background technology is schematically shown. DETAILED DESCRIPTION

[0040] The description of the embodiments of this specification should be combined with the corresponding drawings, which should be considered as part of the complete specification. In the drawings, the shape or thickness of the embodiments may be enlarged and indicated for simplification or convenience. Furthermore, the parts of each structure in the drawings will be described separately. It is worth noting that the elements not shown in the drawings or not described in words are in a form known to ordinary technicians in the relevant technical field.

[0041] The description of the embodiments herein and any reference to directions and orientations are only for the convenience of description and are not to be construed as any limitation on the scope of protection of the present invention. The following description of the preferred embodiments may involve combinations of features, which may exist independently or in combination, and the present invention is not particularly limited to the preferred embodiments. The scope of the present invention is defined by the claims.

[0042] like Figure 1 As shown, the present invention proposes a pC level constant charge source circuit with feedback, comprising:

[0043] A voltage source for driving the charge output;

[0044] Charge output terminal;

[0045] Feedback resistor;

[0046] The adder circuit is used to make the feedback resistor R f The voltage at both ends is consistent with the driving voltage amplitude provided by the voltage source;

[0047] A voltage follower circuit is used to use the load voltage of the charge output terminal as the output voltage of the voltage follower circuit without affecting the output of the charge output terminal;

[0048] A voltage inversion circuit, used for inverting and outputting the output voltage of the voltage follower circuit;

[0049] A voltage monitoring terminal, used to monitor the output state of the charge output terminal according to the output of the voltage inversion circuit;

[0050] The voltage source, voltage monitoring terminal and input terminal of the adder circuit are connected, and the feedback resistor R f The two ends are connected to the output end of the adder circuit and the charge output end respectively. After the voltage follower circuit and the voltage reverse circuit are connected in series, the two ends are connected to the voltage monitoring end and the charge output end respectively.

[0051] The adder circuit includes a third operational amplifier U3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a seventh resistor R7. The non-inverting input terminal of the third operational amplifier U3 is connected in series with the seventh resistor R7 and then connected to the reference ground. The voltage monitoring terminal is connected in series with the fourth resistor R4 and then connected to the inverting input terminal of the third operational amplifier U3. The voltage source is connected in series with the fifth resistor R5 and then connected to the inverting input terminal of the third operational amplifier U3. The two ends of the sixth resistor R6 are respectively connected to the output terminal and the inverting input terminal of the third operational amplifier U3.

[0052] The fourth resistor R4 , the fifth resistor R5 , and the sixth resistor R6 have the same resistance.

[0053] Feedback resistor R f The two ends are respectively connected to the output end of the third operational amplifier U3 and the charge output end.

[0054] The voltage follower circuit includes a first operational amplifier U1 and a first resistor R1. Two ends of the first resistor R1 are respectively connected to the output terminal and the inverting input terminal of the first operational amplifier U1. The non-inverting input terminal of the first operational amplifier U1 is connected to the charge output terminal.

[0055] The input impedance of the first operational amplifier U1 is greater than 10 TΩ, and the bias current is less than 100 fA.

[0056] The voltage reversal circuit includes a second operational amplifier U2, a second resistor R2, and a third resistor R3. The two ends of the second resistor R2 are respectively connected to the output end of the first operational amplifier U1 and the inverting input end of the second operational amplifier U2. The two ends of the third resistor R3 are respectively connected to the inverting input end and the output end of the second operational amplifier U2. The non-inverting input end of the second operational amplifier U2 is connected to the reference ground.

[0057] The resistance values ​​of the second resistor R2 and the third resistor R3 are equal.

[0058] The voltage monitoring terminal is connected to the output terminal of the second operational amplifier U2, and both the voltage monitoring terminal and the charge output terminal are grounded.

[0059] The output charge of the pC level constant charge source circuit is controlled according to the following formula:

[0060] Q out =V in *t / R f

[0061] Where t is the output time, Q out is the amount of charge output from the charge output terminal within the corresponding output time t, V in is the driving voltage of the voltage source.

[0062] The first operational amplifier U1 is an electrostatic amplifier with high input impedance; the second operational amplifier U2 and the third operational amplifier U3 are auto-zero operational amplifiers. The first resistor R1 and the seventh resistor R7 are ordinary resistors, the second resistor R2, the third resistor R3, the fourth resistor R4, the fifth resistor R5, and the sixth resistor R6 are precision resistors, the second resistor R2 and the third resistor R3 have the same resistance value, the fourth resistor R4, the fifth resistor R5, and the sixth resistor R6 have the same resistance value, and the feedback resistor R f It is a precision high value resistor that directly affects the output charge value.

[0063] The first operational amplifier U1 is used for load voltage following. According to the virtual short principle, the voltages of the positive and negative input terminals of the first operational amplifier U1 are equal, that is, the output voltage of the first operational amplifier U1 is equal to the load voltage of the charge output terminal.

[0064] The second resistor R2, the third resistor R3 and the second operational amplifier U2 form a voltage reversal circuit to reverse the output voltage of the first operational amplifier U1. The amplitudes of the two resistors, the second resistor R2 and the third resistor R3, that realize the reversal function are equal, so that the voltage at the voltage monitoring terminal is equal to the voltage amplitude on the load, but have opposite signs.

[0065] The third operational amplifier U3 acts as an adder, V in is the voltage source for driving the charge output; the negative value of the driving voltage and the load voltage are added so that the feedback resistor R f The voltage amplitude at both ends is consistent with the driving voltage amplitude, and the output current amplitude can be controlled by controlling the voltage amplitude.

[0066] The pC level constant charge source of the present invention works as follows:

[0067] According to the virtual short principle, the positive input current I + is 0, that is, the following formula (1):

[0068] I + =0=I f -I out

[0069] in:

[0070] I f is the feedback resistor R f The current flowing through

[0071] I out is the current output from the charge output terminal.

[0072] The output voltage of the third operational amplifier U3 is V f , the voltage on the charge output load is V out According to formula (1), the output current I + and flows through the feedback resistor R f The current amplitude is equal, that is, the following formula (2).

[0073]

[0074] According to the adding circuit formed by the third operational amplifier U3 in the attached figure, the output voltage amplitude V f It is shown by the following formula (3).

[0075]

[0076] in:

[0077] V in is the output voltage of the voltage source.

[0078] Since R4=R5=R6, formula (3) can be simplified to the following formula (4):

[0079] V f =-V in +V out

[0080] Substituting formula (4) into formula (2), we get the following formula:

[0081]

[0082] According to the current-time basic principle of charge output, the value of the output charge is

[0083]

[0084] In determining the feedback resistor R f In the case of resistance value, control the driving voltage V inBy adjusting the amplitude and output time t, the output charge can be precisely controlled.

[0085] The pC level charge source in the present invention is a constant current output with feedback. The first operational amplifier U1 selected is an electrostatic amplifier with an input impedance as high as 1E+15Ω, so that the first operational amplifier U1 will not affect the output of the charge output terminal. The feedback resistor R f The resistance value is on the order of 1E+12Ω, and it can stably output 1E-12A DC current, thus achieving a high-precision output of a minimum 1E-12C level, i.e., pC level charge.

[0086] The output charge is obtained by integrating the current over time. The charge can be output continuously, which has few restrictions on the equipment and usage of the charge source and has a wide range of applications. There is no energy storage device in the circuit, and there is no charging and discharging link during the output process. There will be no residual charge in the energy storage element, which will cause equipment damage and personal injury, and it is safer. Voltage value V in , feedback resistor R f The output charge amplitude is determined by the output time t. The working voltage on the load is reversed and superimposed with the standard voltage and then loaded onto the feedback resistor to form output negative feedback. In principle, it ensures that the voltage amplitude across the feedback resistor is equal to the voltage amplitude of the driving charge output. The output charge and working current are linearly related, and the output time is set reasonably. The short-term stability of the current will not affect the output accuracy, and the output charge is stable and reliable.

[0087] The output impedance of the charge source is large enough and it is a stable system with feedback. The output charge amount does not change with the change of the load at the charge output end, nor is it affected by the working principle and charge measurement method of the charge tester. It has low requirements on the input impedance of the load and can meet the working requirements of different types of charge testing equipment to achieve stable output of the charge source.

[0088] It is equipped with a feedback voltage monitoring terminal to facilitate the detection of the output state of the charge source output terminal.

[0089] The charge output terminal shares a common ground with the driving voltage source. The voltage source will not float on the output charge signal to form parasitic capacitance to generate potential charge storage, affecting the output charge accuracy; nor will charge accumulation form on the parasitic capacitance to cause electrostatic discharge. The equipment has high safety and output accuracy.

[0090] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A pC level constant charge source circuit with feedback, characterized in that: include: A voltage source for driving the charge output; Charge output terminal; Feedback resistor (R f ); The adder circuit is used to make the feedback resistor (R f ) The voltage at both ends is consistent with the driving voltage amplitude provided by the voltage source; A voltage follower circuit, used for using the load voltage at the charge output terminal as the output voltage of the voltage follower circuit; A voltage inversion circuit, used for inverting and outputting the output voltage of the voltage follower circuit; A voltage monitoring terminal, used for monitoring the output state of the charge output terminal according to the output of the voltage inversion circuit; The voltage source, the voltage monitoring terminal and the input terminal of the adder circuit are connected, and the feedback resistor (R f ) are respectively connected to the output end of the adder circuit and the charge output end, and the two ends of the voltage follower circuit and the voltage reverse circuit are respectively connected to the voltage monitoring end and the charge output end after being connected in series.

2. The pC level constant charge source circuit according to claim 1, characterized in that: The adder circuit comprises a third operational amplifier (U3), a fourth resistor (R4), a fifth resistor (R5), a sixth resistor (R6), and a seventh resistor (R7); the non-inverting input terminal of the third operational amplifier (U3) is connected in series with the seventh resistor R7 and then connected to a reference ground; the voltage monitoring terminal is connected in series with the fourth resistor (R4) and then connected to the inverting input terminal of the third operational amplifier (U3); The voltage source is connected in series with the fifth resistor (R5) and then connected to the inverting input terminal of the third operational amplifier (U3), and the two ends of the sixth resistor (R6) are respectively connected to the output terminal and the inverting input terminal of the third operational amplifier (U3).

3. The pC level constant charge source circuit according to claim 2, characterized in that: The fourth resistor (R4), the fifth resistor (R5), and the sixth resistor (R6) have equal resistance values.

4. The pC level constant charge source circuit according to claim 2, characterized in that: The feedback resistor (R f ) are respectively connected to the output end of the third operational amplifier (U3) and the charge output end.

5. The pC level constant charge source circuit according to claim 1, characterized in that: The voltage follower circuit comprises a first operational amplifier (U1) and a first resistor (R1), wherein two ends of the first resistor (R1) are respectively connected to an output end and an inverting input end of the first operational amplifier (U1), and a non-inverting input end of the first operational amplifier (U1) is connected to the charge output end.

6. The pC level constant charge source circuit according to claim 5, characterized in that: The input impedance of the first operational amplifier (U1) is greater than 10TΩ and the bias current is less than 100fA.

7. The pC level constant charge source circuit according to claim 5, characterized in that: The voltage inversion circuit comprises a second operational amplifier (U2), a second resistor (R2), and a third resistor (R3), wherein two ends of the second resistor (R2) are respectively connected to the output end of the first operational amplifier (U1) and the inverting input end of the second operational amplifier (U2), two ends of the third resistor (R3) are respectively connected to the inverting input end and the output end of the second operational amplifier (U2), and the non-inverting input end of the second operational amplifier (U2) is connected to a reference ground.

8. The pC level constant charge source circuit according to claim 7, characterized in that: The resistance values ​​of the second resistor (R2) and the third resistor (R3) are equal.

9. The pC level constant charge source circuit according to claim 7, characterized in that: The voltage monitoring terminal is connected to the output terminal of the second operational amplifier (U2), and the voltage monitoring terminal and the charge output terminal are both grounded.

10. The pC level constant charge source circuit according to claim 1, characterized in that: The charge amount output by the pC-level constant charge source circuit is controlled according to the following formula: Q out =V in *t / R f Among them, Q out is the output charge, V in is the driving voltage provided by the voltage source, t is the output time, R f is the feedback resistor.

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