Amplification device for amplifying small currents

Abstract

An amplifier apparatus and method for amplifying small currents with improved switching to amplifying larger currents is provided. [Solution] An amplifier device for receiving a current includes a first current path for measuring a small current of less than 100 pA, an input amplifier device (50) included in the first current path, and a second current path for measuring a large current whose maximum current is at least 10 times the current received in the first current path. The input amplifier device (50) includes at least one first amplifier (1), an output section, an inverting input section (30), a first feedback path (41) connecting the output section to the inverting input section (30), and a feedback element (2) included in the first feedback path (41). The first amplifier (1) has at least one protection element (18, 19, 20, 21). At least one of the protection elements (18, 19, 20, 21) of the input amplifier device (50) is part of the second current path.

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for amplifying small currents. [Background technology]

[0002] In many measuring instruments, such as spectrometers, vacuum measuring instruments, measurements are made based on the current generated by the impact of positively or negatively charged particles on electrodes. The dynamic range of the intensity of the generated ionic or electronic current to be measured is very wide. This dynamic range often extends from several hundred attoamperes (aA) to several microamperes (μA), i.e. several decades.

[0003] Specifically, small currents are measured in low pressure regions or in vacuum measuring devices and leak detectors. Mass spectrometers are often used for this purpose. When trying to configure an amplifier that can simultaneously measure ultra-small currents of less than 10 femtoamperes (fA) and large currents, it is necessary to switch the range from measuring small currents to measuring large currents, which creates circuit difficulties. In a current amplifier using resistors, a high impedance resistor must be included for ultra-small currents because the higher the resistance value, the lower the current noise of the resistor. However, for currents exceeding, for example, 10 picoamperes (pA), the voltage drop across the resistor becomes excessive, so a high impedance resistor cannot be used. Even if a capacitor is used as a reference element, the same difficulties as with resistors arise. In conventional amplifiers, semiconductor switches or relays are used to switch resistors or current paths to enable switching from an operating state for measuring small currents to an operating state for measuring large currents. In either case, for the above purpose, an additional element must be connected to the detection input node to ensure that the current can be measured no matter how small the current flows.

[0004] To measure such particle currents, a measuring device is used that generates a measurable measurement potential from the particle current (i.e., ion current or electron current). For this purpose, the measuring device usually includes a current amplifier (typically a current amplifier using an operational amplifier). By using a measuring resistor (e.g., a measuring resistor arranged in the feedback path of the operational amplifier), a measurable potential is generated from the amplified current.

[0005] In order to cover the entire dynamic range of the generated particle current with the same measurement circuit, whether it is a conventional amplifier or the amplifier according to the present invention, a switch is made between precision operation for measuring small currents of less than 100 picoamperes (pA) (e.g., 1 picoampere (pA)) and operation for measuring large currents of 1 picoampere (pA) or more (e.g., 100 picoamperes (pA)). In conventional current amplifiers, for example in sector field mass spectrometers, the switch is made by means of a relay. For resistor-based current amplifiers covering a wide current range, range switching is essential, since only high impedance resistors are considered for small currents, while only low impedance elements can carry large currents. At small currents, the useful range is narrowed due to resistor noise.

[0006] EP 0 615 669 B1 describes an amplifier in which the current signal is propagated via a diode. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] European Patent No. 0615669 Summary of the Invention [Problem to be solved by the invention]

[0008] It is an object of the present invention to provide an amplifier device for amplifying small currents, which is improved with respect to said switchover to the amplification of larger currents, and a corresponding method. [Means for solving the problem]

[0009] An amplifier device according to the invention is defined in independent claim 1.

[0010] The amplifier device according to the present invention comprises a first current path for amplifying a small current. The first current path includes an input amplifier device having at least one first amplifier. The first amplifier includes at least one protection element such as a protection diode. A feedback path connecting an output of the input amplifier device to an inverting input includes a feedback element. A second current path at least partially different from the first current path is provided and formed for measuring a large current. At least one of the protection elements of the first amplifier is included in the second current path.

[0011] That is to say, in the amplifier device according to the invention, besides the elements for measuring the minimum current (i.e. the current input section, the measuring resistor in the form of the feedback element and the input amplifier device including at least the first amplifier), no additional elements for measuring the large current need to be provided at the input section. Conventionally used input amplifiers already have protection elements for the input range (e.g. protection diodes). The protection elements are necessary to protect the input circuit in the integrated circuit. In the present invention, the range is switched using the protection elements. This stabilizes the most precise range for measuring the minimum current of the circuit as if it were the only range for measuring the amount of current. When switching from the precision range to the range for measuring the large current, the input current flows through at least one of the protection elements. This results in a low impedance input range, even if the input current becomes much larger. Since a protection element must be present in the integrated circuit of the first amplifier, not all amplifier modules can be used. Any amplifier module can be used as long as it has a protection element for the power supply voltage (supply voltage) or has a protection element between the input lines.

[0012] The number of amplifiers n of the input amplifying device may be n ≥ 1. In the simplest case where n = 1, the input amplifying device includes only the first amplifier. In the case where n ≥ 2, the input amplifying device may be composed of two or more amplifiers forming an amplifier bank.

[0013] The input amplifier includes an inverting input and an output, the output being connected to the inverting input of the input amplifier via a feedback path, the feedback path including a feedback element.

[0014] The amplifier is an operational amplifier and / or the protection element is a protection diode.

[0015] Exemplary embodiments of the present invention will now be described in detail with reference to the drawings. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 illustrates a first operating state of the first exemplary embodiment. [Diagram 2] FIG. 2 is a detailed view of FIG. [Diagram 3] FIG. 2 illustrates the second operating state of the exemplary embodiment. [Figure 4] FIG. 4 shows a detail of FIG. 1 or FIG. 3 in a second exemplary embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The amplifier arrangement of the illustrated exemplary embodiment comprises a first operational amplifier 1 having an inverting input 30 , a non-inverting input 31 , an output 34 , a positive power supply connection 32 and a negative power supply connection 33 .

[0018] The operational amplifier has protective elements 18, 19, 20, 21 (diodes in this embodiment) arranged in the manner of a bridge rectifier between an inverting input 30 and a non-inverting input 31 and between two power supply connections 32, 33 and interconnecting them. The diodes 18, 19, 20, 21 are arranged so that they conduct from the negative power supply connection 33 to the positive power supply connection 32 but not in the opposite direction.

[0019] The expression "in the form of a bridge rectifier" means that a bridge branch includes the two inputs 30, 31 of an operational amplifier 1. This is based on the idea that in an ideal operational amplifier, there would be zero voltage drop between the two inputs 30, 31. One end of the bridge branch is connected to the inverting input 30 and the other end is connected to the non-inverting input 31. This means that the differential voltage that appears between these two inputs, which would be zero in an ideal operational amplifier, forms part of the bridge branch.

[0020] The output 34 of the first operational amplifier 1 is connected to the non-inverting input 35 of the second operational amplifier 3, the output of which is connected to the inverting input 30 of the first operational amplifier 1 via a feedback branch or first feedback path 41. The feedback path 41 includes two resistors 2 and 4. The feedback path 41 is connected by a third switch 12 to a reference voltage input 22 to which a diode forward voltage of, for example, about 0.5 volts, adjustable only by the forward voltage of the protection element 18, is applied between the resistors 2 and 4.

[0021] The output 16 of the second operational amplifier 3 is further connected to ground (GND) via a control element 5. The control element 5 is composed of a resistor 5a, a capacitor 5b and a further resistor 5c. The inverting input 36 of the second operational amplifier 3 is electrically feedback connected between the capacitor 5b and the further resistor 5c.

[0022] An output 34 of the first operational amplifier 1 is connected via a first resistor 6a to a positive power supply connection 32 of the first operational amplifier 1 and via a second resistor 6b to a negative power supply connection 33. The negative power supply connection 33 is alternatively connectable by a first switch 10 to a power supply voltage of -5 volts applied to a voltage source 14 or to ground.

[0023] The positive power supply connection 32 of the first operational amplifier 1 is electrically connected to the inverting input 38 of a third operational amplifier 7, whose output 17 provides feedback in a second feedback path 43 via a resistor 8. Diodes 9 are connected in parallel with the resistor 8 and are conductive in the direction from the output 17 of the third operational amplifier 7 to the positive power supply connection 32 of the first operational amplifier 1 but not in the opposite direction.

[0024] The first amplifier 1 and the further amplifier second amplifier 3 form an input amplifier arrangement 50. The amplifiers 1 and 3 together form an amplifier bank. A feedback path 41 connects the output of the input amplifier bank 50 to the inverting input 30 of the input amplifier bank 50.

[0025] The non-inverting input 37 of the third operational amplifier 7 is selectively connectable by a second electrical switch 11 to a voltage source 15 (in this embodiment, 5 volts) or to ground.

[0026] In the illustrated exemplary embodiment of the amplifier device according to the invention, a first operational amplifier 1 is used as an input amplifier. The protection elements 18, 19, 20, 21 of the first operational amplifier 1 are provided as input protection diodes to the supply voltage. When the amplifier device operates to measure small currents in the most precise range, for example less than 100 picoamperes (pA), an input current signal arrives at the input 13 to the first operational amplifier 1. The first operational amplifier 1 receives a negative supply voltage (in this embodiment, -5 volts) from a voltage source 14 via a first switch 10 in the switch position shown in FIG. 1. The operational amplifier 1 receives a positive supply voltage from a voltage source 15 (in this embodiment, amounting to +5 volts) via a second switch 11 in the switch position shown in FIG. 1 at the non-inverting input 37 of the third operational amplifier 7.

[0027] The output voltage at the output 17 of the third operational amplifier 7 is adjusted to a value increased by the diode forward voltage of the diode 9. As a result, the voltage reaching the first operational amplifier 1 is of the same order of magnitude as the voltage at the non-inverting input 37 of the third operational amplifier 7.

[0028] Amplifier 7 is not part of input amplifier 50. Amplifier 7 serves to receive the large current from input 13 of input amplifier 50. This input current flows directly from amplifier 1 to input 38 of amplifier 7 via diode 18. On the other hand, the small current from input 13 undergoes initial amplification in input amplifier 50.

[0029] For measuring small currents, the third electrical switch 12 is open as in this first operating state shown in figure 1. The feedback resistors 4, 2 together form the feedback element (in the present embodiment in the form of an electrical resistor).

[0030] At this time, the input 13 connected to the inverting input 30 of the first operational amplifier 1 is substantially at a zero point, which means that there is no voltage at the input 13.

[0031] An inverted voltage proportional to the input current of the first operational amplifier 1 is applied to the output 16 of the second operational amplifier 3. At this time, the protection diodes 18, 19, 20, and 21 of the input amplifiers are driven in the reverse direction and therefore do not carry any current.

[0032] An input amplifier 50 consisting of a first amplifier 1 and a second operational amplifier 3 forms a control circuit. The control element 5 must be dimensioned according to the cutoff frequencies of the elements 5a, 5b, and 5c used so that the circuit is maintained stable. For example, the resistance 5a is 120 kΩ, the capacitor 5b is 1 nF, and the resistance 5c is 10 kΩ.

[0033] FIG. 1 shows the entire amplifier device in a first operating state in which a small current is measured through a first current path, and FIG. 2 is a detailed diagram showing a first operational amplifier 1, protection elements 18, 19, 20, and 21 provided within the first operational amplifier 1, and the electrical interconnections between the protection elements 18, 19, 20, and 21 and each connection point of the first operational amplifier 1.

[0034] 3 shows the amplifier device in a second operating state for measuring a high current in a second current path. For this purpose, the amplifier device operates in an extended current range with the first electrical switch 10 switched to earth or ground potential. A voltage of approximately 0 volts is thus applied to the negative power supply connection 33 of the input amplifier. The input protection elements 20, 21 remain non-conductive.

[0035] The second switch 11 is also switched to ground potential. The third operational amplifier 7 is adjusted by the feedback resistor 8 so that there is no differential voltage between the inverting input 38 and the non-inverting input 37 of the third operational amplifier 7, so that the positive supply of the first operational amplifier 1 at the positive supply connection 32 also approaches 0 volts. If an input current is now applied to the input connection 13, it will flow through the protection diode 18 to the positive supply connection 32.

[0036] In this operating condition, the third electrical switch 12 is conductive. As a result, the voltage applied to the connection 22 (0.5 volts in this embodiment) is applied to the feedback resistor 2, but the current flowing through the feedback resistor 2 is minimized according to the diode forward voltage of the protection diode 18.

[0037] In this case, the second current path in the case of a large current flowing through the input 13 is conductive through the protection diode 18 to the feedback resistor 8 of the third operational amplifier 7. An inverted voltage proportional to the input current is applied to the feedback resistor 8 and leads to the output 17 of the third operational amplifier 7. In this case, the diode 9 is non-conductive. Thus, the second current path for measuring large currents runs from the inverting input 30 of the first operational amplifier 1 through the protection diode 18 of the protection diodes 18, 19, 20, 21 to the positive power supply connection 32 of the first operational amplifier 1 and from there through the feedback resistor 8 of the third operational amplifier 7 to the output connection 17 of said third operational amplifier 7.

[0038] In the circuit arrangement of this embodiment, when operating in a current path for large current, the input voltage 13 increases by the forward voltage of the protection element 18. To avoid this characteristic, it is possible to lower the ground potential of the ground points of the switches 10 and 11 by the forward voltage of the protection element 18. In this case, no current flows through the feedback element 2 even if 220 volts is applied to the input section.

[0039] The second current path is further improved by splitting diode 9 as in FIG. 4. When the second current path is activated, a negative voltage is applied to output 17. The reverse current of the diodes causes errors in the measurement. By complementing the circuit as in FIG. 4, the negative voltage of diode 9b is reduced. This causes approximately 0 volts to be applied across diode 9a, which significantly reduces the reverse current.

[0040] Here, we have described the circuit for a positive input current. In principle, a circuit for a negative current direction is also possible. Circuit examples with both current directions are also possible. The present invention includes the following embodiments. [Aspect 1] a first current path for measuring a small current of less than 100 pA; An input amplifier device (50) included in the first current path, at least one first amplifier (1); Output section, An inverting input (30), a first feedback path (41) connecting said output to said inverting input (30); and a feedback element (2) included in the first feedback path (41); an input amplifying device (50) including the first amplifier (1) having at least one protection element (18, 19, 20, 21); a second current path for measuring a large current whose maximum current is 10 times or more the current received by the first current path; 1. An amplifier device for receiving a current, comprising: At least one of the protection elements (18, 19, 20, 21) of the input amplifier device (50) is a part of the second current path. [Aspect 2] In the amplifying device according to aspect 1, a power supply voltage of the first amplifier (1) is applied to at least one of the protection elements (18, 19, 20, 21). [Aspect 3] In the amplifying device according to aspect 1 or 2, at least one of the protection elements (18, 19, 20, 21) is disposed between two input portions (30, 31) of the first amplifier (1) and connected to the two input portions (30, 31). [Aspect 4] The amplifier according to any one of aspects 1 to 3, wherein the feedback element (2) of the first feedback path (41) is an electric resistor. [Aspect 5] 4. The amplifier according to claim 1, wherein the feedback element (2) of the first feedback path (41) is a capacitor. [Aspect 6] 6. The amplifier arrangement according to any one of the preceding aspects, characterized in that the input amplifier arrangement (50) comprises at least one further amplifier (3) forming a control loop together with the first amplifier (1). [Aspect 7] In the amplification device according to any one of aspects 1 to 6, at least one of the two power supply connection parts (32, 33) of the first amplifier (1) is connected to the output part of the first amplifier (1) via an electrical resistor (6a, 6b). [Aspect 8] 8. The amplifier device according to any one of the first to seventh aspects, characterized in that the first feedback path (41) connects an output of a last amplifier of an input amplifier device (50) consisting of the first amplifier (1) and at least one further amplifier (3) to the inverting input (30) of the input amplifier device (50). [Aspect 9] 10. The amplifier device according to claim 1, wherein a negative power supply connection (33) of the first amplifier (1) is selectively connectable to a negative power supply voltage (14) or ground by a first switch (10), a positive power supply connection (32) of the first amplifier (1) is conductively connected to an inverting connection (38) of a third amplifier (7), and a non-inverting input (37) of the third amplifier (7) is selectively connectable to a positive power supply voltage (15) or ground by a second switch (11). [Aspect 10] 10. The amplifier device according to claim 1, wherein the third amplifier (7) has a second feedback path (43) including an electrical resistor (8) and an electrical diode (9) arranged in parallel with the resistor (8), the electrical diode (9) conducting in a direction from the output (17) of the third amplifier to the positive power supply connection (32) of the first amplifier (1) but not conducting in the opposite direction. [Aspect 11] An amplifier device according to any one of aspects 1 to 10, characterized in that the first feedback path (41) can be selectively connected by a third switch (12) to a voltage that prevents current from flowing through the feedback element (2) or a voltage that allows current to flow through the feedback element (2) depending on the position of the switch. [Aspect 12] 12. The amplifier according to any one of claims 1 to 11, wherein the ground potential and the reference voltage (22) of the switch (10, 11) are adjusted by a forward voltage of the protection element (18). [Aspect 13] An amplifier device as described in claim 10, characterized in that the second feedback path (43) includes two diodes (9a, 9b) having a resistor (39) therebetween that is conductive relative to the switch (11). [Aspect 14] a mass spectrometry sensor or a total pressure sensor; An amplification device according to any one of aspects 1 to 13; A gas detector comprising: [Aspect 15] 14. A method for measuring a current using an amplifier device according to any one of claims 1 to 13, characterized in that a negative power supply connection (33) of the first amplifier (1) is connected to ground, thereby switching from the first current path to the second current path. [Aspect 16] The method according to claim 15, characterized in that the non-inverting input of a third amplifier (7), whose inverting input is connected to the positive power supply connection (32) of the first amplifier (1), is also connected to ground for the switching of the current path.

Claims

1. a first current path for measuring a small current of less than 100 pA; An input amplifier device (50) included in the first current path, At least one first amplifier (1), Output section, An inverting input (30), a first feedback path (41) connecting said output to said inverting input (30); and A feedback element (2) included in the first feedback path (41); an input amplifying device (50) including the first amplifier (1) having at least one protection element (18, 19, 20, 21) on the first current path; a second current path for measuring a large current whose maximum current is 10 times or more the current received by the first current path; 1. An amplifier device for receiving a current, comprising: When the measurement range is changed from a range for measuring a small current in the first current path to a range for measuring a large current in the second current path, the input current flows through the at least one protection element. At least one of the protection elements (18, 19, 20, 21) of the input amplifier device (50) is part of the second current path.

2. A first current path for measuring a small current of less than 100 pA; An input amplifier device (50) included in the first current path, At least one first amplifier (1), Output section, An inverting input (30), a first feedback path (41) connecting said output to said inverting input (30); and A feedback element (2) included in the first feedback path (41); an input amplifying device (50) including the first amplifier (1) having at least one protection element (18, 19, 20, 21); a second current path for measuring a large current whose maximum current is 10 times or more the current received by the first current path; 1. An amplifier device for receiving a current, comprising: When the measurement range is changed from a range for measuring a small current in the first current path to a range for measuring a large current in the second current path, the input current flows through the at least one protection element. At least one of the protection elements (18, 19, 20, 21) of the input amplifier device (50) is a part of the second current path, An amplifier device, characterized in that a power supply voltage of the first amplifier (1) is applied to at least one of the protection elements (18, 19, 20, 21).

3. 3. The amplifier device according to claim 1, wherein at least one of the protection elements (18, 19, 20, 21) is arranged between two inputs (30, 31) of the first amplifier (1) and connected to the two inputs (30, 31).

4. 3. An amplifier arrangement according to claim 1 or 2, characterized in that the feedback element (2) of the first feedback path (41) is an electrical resistor.

5. 3. An amplifier arrangement according to claim 1 or 2, characterized in that the feedback element (2) of the first feedback path (41) is a capacitor.

6. 3. Amplification arrangement according to claim 1 or 2, characterized in that the input amplifier arrangement (50) comprises at least one further amplifier (3) forming a control loop with the first amplifier (1).

7. 3. An amplifier arrangement according to claim 1 or 2, characterized in that at least one of the two power supply connections (32, 33) of the first amplifier (1) is connected to the output of the first amplifier (1) via an electrical resistor (6a, 6b).

8. 3. The amplifier arrangement according to claim 1 or 2, characterized in that the first feedback path (41) connects the output of a last amplifier of an input amplifier arrangement (50) consisting of the first amplifier (1) and at least one further amplifier (3) to the inverting input (30) of the input amplifier arrangement (50).

9. 3. An amplifier arrangement according to claim 1 or 2, characterized in that the negative power supply connection (33) of the first amplifier (1) is selectively connectable by a first switch (10) to a negative power supply voltage (14) or to ground, the positive power supply connection (32) of the first amplifier (1) is conductively connected to an inverting connection (38) of a third amplifier (7), and the non-inverting input (37) of the third amplifier (7) is selectively connectable by a second switch (11) to a positive power supply voltage (15) or to ground.

10. 10. The amplifier arrangement according to claim 9, characterized in that the third amplifier (7) has a second feedback path (43) including an electrical resistor (8) and an electrical diode (9) arranged in parallel with the resistor (8), the electrical diode (9) conducting in a direction from the output (17) of the third amplifier to the positive power supply connection (32) of the first amplifier (1) but not in the opposite direction.

11. 10. The amplifier device according to claim 9, characterized in that the first feedback path (41) can be selectively connected by a third switch (12) to a voltage that prevents current from flowing through the feedback element (2) or a voltage that allows current to flow through the feedback element (2) depending on the position of the third switch.

12. 10. An amplifier device according to claim 9, characterized in that the ground potential and the reference voltage (22) of the switches (10, 11) are adjusted by the forward voltage of the protection element (18).

13. 11. An amplifier arrangement according to claim 10, characterized in that the second feedback path (43) includes two diodes (9a, 9b) with a resistor (39) therebetween that is conductive relative to the switch (11).

14. A gas detector comprising a mass spectrometry sensor or a total pressure sensor and an amplification device according to claim 1 or 2.

15. 14. A method for measuring a current with an amplifier arrangement according to any one of claims 1 to 13, characterized in that switching from the first current path to the second current path is performed by connecting a negative power supply connection (33) of the first amplifier (1) to ground.

16. 16. The method according to claim 15, characterized in that the non-inverting input of a third amplifier (7), the inverting input of which is connected to the positive power supply connection (32) of the first amplifier (1), is also connected to ground for said switching of current paths.

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