Electrical circuit for determining the intensity of an electric current and method for determining the intensity of an electric current using the electrical circuit

Abstract

A circuit for determining the intensity of an electric current is specified, comprising: a transimpedance amplifier (TIA) which converts the current flowing on the input side of the TIA into a voltage indicative of the current to be determined, which is applied to an output node (P1) on the output side of the TIA, and a circuit arrangement electrically connected in series to P1 with one or more circuit elements connected in series, wherein each circuit element comprises a diode arrangement, a feedback resistor, and an operational amplifier, wherein the diode arrangement, the feedback resistor, and the operational amplifier are connected via an output node of the respective circuit element, and wherein the operational amplifier amplifies the voltage applied to the output node of the respective circuit element.The indicative voltage is detected and provided as an indicative circuit element output voltage for this voltage, such that the current can be determined from the output voltage of the TIA and the feedback resistor, and / or wherein the current can be determined from a sum of the output voltage of the TIA and at least one circuit element output voltage via the respective feedback resistor of the circuit element or a feedback resistor of the TIA. Furthermore, a method for determining the electric current is specified.

Description

[0001] The invention relates to an electrical circuit for determining an electrical current intensity of an electrical current and a method for determining an electrical current intensity of an electrical current using the electrical circuit.

[0002] Output signals from sensors, for example, for light, infrared radiation, or radioactivity, or as the cantilever signal of a scanning tunneling microscope, are often recorded using an electrical current proportional to the output signal. The magnitude of this current can often fluctuate by five or more orders of magnitude in a short period of time. The solution to this problem is the use of a current-to-voltage converter (transimpedance converter, TIA) with manual or automatic measuring range switching. However, each switching process is associated with latency due to transient responses or relay switching times, resulting in data loss during this time. Rapidly fluctuating current signals are therefore difficult or impossible to track.

[0003] To enable measurements without time gaps, logarithmic current-to-voltage converters based on the exponential characteristic of a pn junction are used. One example is the ADL5304 "High Speed, 200dB Range, Logarithmic Converter" from Analog Devices. This circuit can map input currents in the range of 1 pA to 10 mA to an output voltage with a swing of approximately 2 volts. A disadvantage is the enormous dependence of the bandwidth on the input current. If the input current is only a few pA and the sensor connected to the input side, e.g., a photodiode (PD), has a significant capacitance of, say, 10...100 pF, the processable bandwidth drops to below 1 Hz.

[0004] DE 41 40 112 A1 describes an arrangement of two current-to-voltage converters with very different gains. Low input currents are processed solely by the high-gain, slow converter, while with increasing current, an operating point shift occurs such that the current increasingly flows into the input of the low-gain converter. This continuous operating point shift occurs within a control loop involving two operational amplifiers and two diodes, which places a limit on the control speed.

[0005] In DE 10 2019 112 769 A1, the speed problem is solved by distributing the input current between two current-to-voltage converters with different gains using only a diode and a resistor, which enables a wide measurement dynamic range at high speed. A disadvantage, however, is the fact that the input voltage of the circuit is neither constant nor zero, so only currents from photomultiplier tubes, biased photodiodes, and other sensors with high source impedance can be correctly processed.

[0006] US Pat. No. 6,404,281 B1 discusses a circuit in which the gain is automatically adjusted depending on the signal intensity, preventing overload at high input currents. The application is broadband communications. The unadulterated reproduction of analog signals with any waveform is not possible.

[0007] The paper "A high dynamic range, linear response transimpedance amplifier" (Rev. Sci. Instr. 83, 026106

[2012] ) presents a circuit that requires only one current-to-voltage converter, but whose negative feedback circuit consists of three resistors in series, stepped at a ratio of 1:300:10,0000, which are bridged by JFETs depending on the level. The circuit has three simultaneously active outputs with correspondingly stepped gain, each of which delivers valid signals with easily measurable amplitudes. The oscillations caused by the JFETs are problematic; these were eliminated by parallel capacitances across the negative feedback resistors, but this comes at the expense of the achievable bandwidth, particularly at the most sensitive output.

[0008] US 2011 / 0 109 300 A1 discloses an ammeter for measuring load currents in the mA and ampere ranges with multiple measuring ranges or channels. The ammeter has sharp switching thresholds, below which one channel is controlled and above which a current exceeding the threshold passes into the next channel and generates a measuring signal there with correspondingly lower amplification. For control purposes, a quasi-logarithmic overall characteristic curve with several defined break points is provided, with the aim of being able to measure very wide current ranges. The circuit proposed for this purpose is complex and not very stable, which is attempted to be compensated for by counter-control that contributes to the complexity. On this basis, the present invention is based on the object of providing an electrical circuit and an associated method whichwhich makes it possible to process electrical currents in a wide range of several orders of magnitude, in particular more than ten orders of magnitude, at medium speed (down to the µs range) and to always ensure an impedance approaching zero at the input of the circuit, so that currents from sources with low source impedance such as photodiodes can also be measured in element mode, and signals with a constant bandwidth that is independent of the level of the input current can be processed.

[0009] This object is achieved by an electrical circuit for determining an electrical current intensity of an electrical current having the features of claim 1 and a method for determining an electrical current intensity of an electrical current according to claim 8.

[0010] Advantageous embodiments of these aspects of the invention are specified in the corresponding subclaims and are described below.

[0011] A first aspect of the invention relates to an electrical circuit for determining an electrical current intensity, in particular over several orders of magnitude of the current intensity. The electrical circuit comprises: - a transimpedance amplifier which is designed to convert the electrical current flowing on the input side of the transimpedance amplifier into an electrical voltage indicative of the electrical current to be determined, which voltage is applied to the output side of the transimpedance amplifier as an output voltage at an output node, and - a circuit arrangement electrically connected or connectable in series to the output node, comprising one circuit element or several circuit elements connected in series, each circuit element comprising a diode arrangement with at least one diode, as well as a negative feedback resistor and an operational amplifier, the diode arrangement, the negative feedback resistor and the operational amplifier being electrically connected to one another via an output node of the respective circuit element.

[0012] The operational amplifier of each circuit element is designed to detect the voltage present at the output node, which is also indicative of the electrical current intensity to be determined, and to provide it as a circuit element output voltage indicative of this voltage, so that the current intensity of the electrical current can be determined from the output voltage of the transimpedance amplifier and the negative feedback resistor using Ohm's law, and / or wherein the current intensity of the electrical current can be determined from a sum of the output voltage of the transimpedance amplifier and at least one circuit element output voltage using Ohm's law via the respective negative feedback resistor of the circuit element or a negative feedback resistor of the transimpedance amplifier.

[0013] In particular, the electric current can be determined from the output voltage of the transimpedance amplifier and the negative feedback resistor using Ohm's law, as IE = UA1 / R1, where IE is the current, UA1 is the output voltage at the output node of the transimpedance amplifier, and R1 is the negative feedback resistor of the transimpedance amplifier. In other words, the output voltage of the transimpedance amplifier is indicative of the current to be determined, since, according to Ohm's law, there is a proportionality between the current and the output voltage at the output node.If the current becomes so large that the resulting increased output voltage at the transimpedance amplifier causes the diode array at the transimpedance amplifier's output node to conduct, a finite voltage is present at the output node of at least one circuit element, which is thus also indicative of the current to be determined. This voltage is detected by the operational amplifier of the respective circuit element and provided as a circuit element output voltage indicative of this voltage. The electrical current is thus determined via IE = UA1 / R1 + Σ. i=1 UA i+1 / R i+1can be determined, where i counts the circuit elements connected in series at the output node of the transimpedance amplifier with a measurable circuit element output voltage. In other words, the circuit element output voltage of each circuit element is indicative of the current to be determined in that each circuit element contributes a term to the current or current intensity according to Ohm's law, with the circuit element output voltage in the respective term being proportional to the current.

[0014] For each circuit element, the circuit element output voltage is in turn indicative of the voltage at the output node of the circuit element in question in that the operational amplifier converts the output voltage at the output node into the circuit element output voltage with a gain value or gain factor determined by the operational amplifier.

[0015] In particular, the diode arrangement of each circuit element is electrically connected to the output node of the series-connected circuit element or to the output node of the transimpedance amplifier. The latter applies in the case of a first circuit element adjacent to the output node. The first circuit element is thus the circuit element directly connected to the output node of the transimpedance amplifier, so that no further circuit element is present between this circuit element and the output node of the transimpedance amplifier.

[0016] In particular, it is provided that the negative feedback resistance of the circuit element is preferably smaller by a factor of between 5 and 50 than the negative feedback resistance of the transimpedance amplifier, to which the circuit element is electrically connected in parallel. Thus, the negative feedback resistances of the transimpedance amplifier and the circuit element are electrically connected to an input of the circuit, at which the electrical current to be measured flows. Corresponding negative feedback currents flow through the respective negative feedback resistances. Depending on the magnitude of the electrical current, a measurable voltage other than zero can be present either only at the output node of the transimpedance amplifier or, as soon as the diode begins to conduct, additionally at the output node of at least one circuit element.The smaller negative feedback resistance in relation to the negative feedback resistance of the transimpedance amplifier ensures that the voltage applied to the output node of the transimpedance amplifier and the circuit element output voltages are in a similar range, e.g. between 0 and 12 volts, which enables a uniform controllability of the electrical circuit.

[0017] Preferably, the negative feedback resistances of the circuit elements decrease with each circuit element along a series circuit. The "series circuit" here comprises the transimpedance amplifier and a circuit element, or possibly several circuit elements electrically connected in series with it. In particular, the negative feedback resistances can decrease with constant reduction factors, for example, with a reduction factor of 10 or 50 between two circuit elements adjacent along the series circuit or between the transimpedance amplifier and the circuit element adjacent to the transimpedance amplifier.Accordingly, depending on the magnitude of the electrical current, a non-zero voltage may be present either only at the output node of the transimpedance amplifier or, as soon as the respective diodes of the circuit elements arranged one after the other along the series circuit begin to conduct, also at the output nodes of the respective circuit elements. The negative feedback resistors, which decrease along the series circuit, ensure that the voltage applied to the output nodes of the respective circuit elements and, in particular, the respective circuit element output voltages are in a similar range, e.g., between 0 and 12 volts, which enables a uniform controllability of the electrical circuit.

[0018] In particular, it is provided that the operational amplifier of the circuit element adjacent to the output node of the transimpedance amplifier is connected as a voltage follower.

[0019] According to one embodiment of the invention, the electrical circuit comprises a plurality of circuit elements connected electrically in series, in particular four to eight circuit elements, so that a plurality of circuit element output voltages indicative of the electrical current to be determined can be provided. Along the series circuit, the individual circuit elements are preferably electrically connected to one another via the output points of the circuit elements immediately upstream of the series circuit.

[0020] In one embodiment of the invention, at least one circuit element comprises at least two diodes connected in parallel and polarized in opposite directions. Thus, both positive and negative polarities of the current to be measured can be processed equally.

[0021] According to a further embodiment of the invention, a circuit element, in particular the circuit element adjacent to the output node, comprises a plurality of series-connected diodes, wherein at a connection point between the series-connected diodes a capacitor is connected to the ground of the electrical circuit or another point equivalent to ground in terms of alternating voltage.

[0022] The number and threshold voltage of the diodes are preferably selected such that, when a negative feedback current is applied, which produces a voltage of, in particular, between 1 volt and 2 volts at an output node, the diode of the circuit element connected in series to the output node begins to conduct. This means that, with varying current levels, several output channels of the electrical circuit usually simultaneously deliver a voltage different from zero. The smooth transitions between the individual output channels, in conjunction with the junction capacitances of the diodes, ensure operation free of jumps and oscillations, even when the current level changes relatively rapidly in the range between 1 pA and 10 mA.

[0023] According to a further embodiment of the invention, a capacitor is electrically connected in parallel with at least one negative feedback resistor, so that the negative feedback resistor and the capacitor define a time constant of the respective circuit element.

[0024] In particular, it is provided that several circuit elements, with their respective negative feedback resistors, each have capacitors electrically connected in parallel, wherein the respective negative feedback resistors and capacitors are dimensioned such that the time constants of the circuit elements do not deviate from each other by more than 50%, specifically 25%, even more specifically 10%. This measure allows the respective bandwidths of the individual circuit elements to be matched to each other.

[0025] According to one embodiment of the invention, a gain value of the operational amplifier of the circuit element adjacent to the output node is equal to 1 and / or a gain value of at least one operational amplifier of one of the circuit elements electrically connected in series to the adjacent circuit element is greater than 1. In particular, it is provided that the gain values ​​of the operational amplifiers of the circuit elements connected in series increase along the series. For example, in the case of three circuit elements connected in series, the operational amplifier of the first circuit element can have a gain value of 1, the operational amplifier of the second circuit element has a gain value of 1.1, and the operational amplifier of the third circuit element has a gain value of 1.2.By this measure, the circuit element output voltages of the output channels can be adjusted in such a way that they have a substantially uniform controllability, for example in the range between 0 and 12 volts.

[0026] A second aspect of the invention relates to a method for determining an electrical current intensity of an electrical current using the electrical circuit according to the first aspect of the invention, wherein the output voltage at the transimpedance amplifier and the circuit element output voltages are added to a sum, whereby the electrical current intensity is determined. In particular, the current intensity of the electrical current is determined from the output voltage of the transimpedance amplifier and the negative feedback resistor using Ohm's law according to IE = UA1 / R1. If the current is so large that a measurable circuit element output voltage is applied to at least one circuit element, the electrical current intensity is determined in particular via IE = UA1 / R1 + Σ i=1 UA i+1 / R i+1 where i counts the circuit elements connected in series to the output node of the transimpedance amplifier with a measurable circuit element output voltage.

[0027] According to one embodiment of the invention, the output voltage and the circuit element output voltages are each added in a weighted manner to form a weighted sum, wherein respective weighting factors are reciprocal to the respective negative feedback resistances.

[0028] In a further embodiment of the invention, based on predefined output voltage thresholds - the weighting factor associated with at least one circuit element output voltage is set to zero if the at least one circuit element output voltage falls below a respective predetermined circuit element output voltage threshold, or - the weighting factor associated with a circuit element output voltage of a circuit element of the circuit elements electrically connected in series is set to zero if the circuit element output voltage of the circuit element immediately electrically connected upstream of the circuit element in the series or of the transimpedance amplifier falls below a predetermined output voltage threshold or circuit element output voltage threshold.

[0029] The weighted addition to a sum based on the output voltage threshold of the voltage at the transimpedance amplifier or the circuit element output voltage thresholds takes into account the fact that decreasing negative feedback resistances along the series circuit lead to a correspondingly increasing thermal noise current in the output channels. By introducing the output voltage threshold or the circuit element output voltage thresholds, correspondingly noisy output voltages or circuit element output voltages can be ignored for the current determination, which improves the accuracy of the current determination.

[0030] The output voltage threshold or the circuit element output voltage thresholds can be determined based on the diode characteristics of the diodes. The output voltage threshold or the circuit element output voltage threshold of an output channel preferably corresponds to the voltage at the output node of the respective output channel at which the diode connected there just begins to conduct, and thus the voltage present at the output node following along the series circuit is still zero within the measurement accuracy.

[0031] Since the method according to the second aspect of the invention is carried out using the electrical circuit according to the first aspect of the invention, the embodiments according to the first aspect of the invention also relate to the second aspect of the invention, and vice versa.

[0032] A third aspect of the invention relates to a computer program comprising instructions that, when executed by a computing unit, cause the computing unit to execute the method according to the second aspect of the invention. Accordingly, the embodiments according to the second aspect of the invention can also be related to the third aspect of the invention.

[0033] A fourth aspect of the invention relates to an ammeter comprising at least one electrical circuit according to the first aspect of the invention. The ammeter can further comprise a computing unit designed to carry out the method according to the second aspect of the invention. Furthermore, the ammeter can comprise a display device, in particular a digital display, which is controlled by the computing unit and is designed to display the amperage of the electrical current determined by the electrical circuit. Furthermore, it is provided that the ammeter can comprise a battery which supplies the electrical circuit and / or the computing unit and the display device with energy.

[0034] In the following, exemplary embodiments as well as further features and advantages of the invention will be explained with reference to the figures. They show: Fig. 1 shows an embodiment of the electrical circuit according to the first aspect of the invention, comprising four circuit elements; Fig. 2 schematically shows an embodiment of the method according to the second aspect of the invention using the electrical circuit of Fig. 1; Fig. 3 Example of the proportions of negative feedback currents in the electrical current, based on the electrical circuit from Fig. 1 over several orders of magnitude of the electric current; Fig. 4 schematically shows an embodiment of an ammeter according to the fourth aspect of the invention; Fig. 5 shows an embodiment of a current measuring device according to the fourth aspect of the invention, for measuring photocurrents; and Fig. 6 spectrally dependent measurements with the current meter from Fig. 5.

[0035] Fig. 1 shows an embodiment of the electrical circuit 10 according to the first aspect of the invention. The electrical circuit 10 shown here comprises a transimpedance amplifier TIA with an operational amplifier OA1 and a negative feedback resistor R1. The transimpedance amplifier TIA converts the electrical current IE flowing at the input E of the electrical circuit 10 at the transimpedance amplifier TIA, the electrical current intensity of which is to be determined by the electrical circuit 10, into an output voltage U1 proportional to this current IE, which is applied on the output side to an output node P1 of the transimpedance amplifier TIA and is made available directly as an output voltage UA1 via a first output channel K1.The electric current IE can, for example, be current from a photodiode PD, so that the electric current IE can fluctuate by several orders of magnitude within a short period of time as a result of changing illumination conditions.

[0036] At the output node P1, a first circuit element 100, 110 is electrically connected in series to the transimpedance amplifier T1A via a diode arrangement D1. The diode arrangement D1 comprises one or more first diodes D11 and one or more second diodes D12. At a connection point P between the first diode D11 and the second diode D12, a capacitor C1 is optionally present, which is connected to the ground of the electrical circuit 10 or another point equivalent to ground in terms of AC voltage. The bandwidth of the transimpedance amplifier is limited by a time constant corresponding to the product of its negative feedback resistance R1 and the junction capacitance of the diode arrangement D1 electrically connected in series. Fig. The design of the diode arrangement D1, as shown in Figure 1, as a series circuit comprising at least two individual diodes D11 and D12, from whose junction point P a capacitor C1 is connected to ground, forms a capacitive voltage divider from the junction capacitance of D11 and capacitor C1. This causes the negative feedback resistor R1 to be capacitively short-circuited to a much lesser extent via the negative feedback resistors R2, R3, R4 of the following circuit elements 100, 110, 120, 130, and thus the bandwidth of the transimpedance amplifier, as the highest-gain channel, is limited almost exclusively by the smaller time constant resulting from R1 and its design-related stray capacitance.

[0037] In this exemplary embodiment, the first circuit element 100, 110 comprises a diode arrangement D1 with a plurality of diodes electrically connected in series, including at least a first diode D11 and at least a second diode D12. The first circuit element 100, 110 also comprises an operational amplifier OA2 and a negative feedback resistor R2. A voltage U2 is applied to an output node P2 of the first circuit element 100, 110, which, in addition to the voltage U1 at the output node P1 or the output voltage UA1 of the transimpedance amplifier TIA, is also indicative of the electrical current to be determined. Based on the voltage U2 applied to the input side of the operational amplifier OA2, the operational amplifier OA2, which here is connected as a voltage follower with a gain value of 1, provides a circuit element output voltage UA2 on the output side at a second output channel K2.The circuit element output voltage UA2 therefore essentially corresponds to the voltage U2 and is thus, like the output voltage UA1, also indicative of the current intensity of the electric current IE.

[0038] As continues Fig. 1, a second circuit element 100,120 is electrically connected in series to the first circuit element 100,110 via its output node P2. The second circuit element 100,120 in turn comprises a diode arrangement D3, which can comprise one or more diodes, as well as a negative feedback resistor R3 and an operational amplifier OA3. Analogous to the first circuit element 100,110, a voltage U3, which is indicative of the current IE, is present at a third output node P3 of the second circuit element 100,120. The operational amplifier OA3 generates a circuit element output voltage UA3, which is made available at a third output channel K3 of the electrical circuit 10. The circuit element output voltage UA3 is determined by the gain value of the operational amplifier OA3 and is therefore indicative of the voltage U3 and consequently of the current to be determined.

[0039] In the same style, as in Fig. 1, a third circuit element 100, 130 is provided, which is connected in accordance with the second circuit element 100, 120. A fourth circuit element 100, 140 is only indicated to symbolize that more than three circuit elements can also be connected in series. The third circuit element 100, 130 provides a circuit element output voltage UA4 at a fourth output channel K4.

[0040] Via the negative feedback resistors R1, R2, R3, R4 of the transimpedance amplifier TIA or the circuit elements 100, 110, 120, 130, respectively, flows, as in Fig. As can be seen in Figure 1, a negative feedback current I1, I2, I3, I4 is generated. The sum of the negative feedback currents I1, I2, I3, I4 corresponds to the current IE to be determined, IE = I1 + I2 + I3 + I4.

[0041] For example, JFET or CMOS designs with bias currents below 1 pA are used for the operational amplifiers OA1, OA2, OA3, and OA4 of the electrical circuit 10 according to this embodiment. The negative feedback resistors R1, R2, R3, and R4 can be dimensioned as follows, for example: R1 = 100 MΩ, R2 = 2 MΩ, R3 = 40 kΩ, and R4 = 800 Ω. For the diode arrangement D1, a total of four low-capacitance, low-reverse-current Si diodes can be used. Diodes with a capacitance of less than 2 pF at 0 volts and a reverse current of less than 0.5 pA are suitable for this purpose. Without capacitor C1, a bandwidth of DC to 2.5 kHz (-3 dB) can be measured on the first output channel K1. With capacitor C1 installed, a capacitance of 10 pF even DC to 10 kHz is achievable. This corresponds to a stray capacitance of the feedback resistor R1 of 0.16 pF. "DC" here refers to the limiting case where the frequency of the current IE approaches zero.In the higher output channels K2, K3, K4, the decreasing negative feedback resistors R2, R3, R4 arranged along the series circuit elements 100, 120, 130 can be compensated by correspondingly increasing capacitances of parallel capacitors C2, C3, C4 such that the bandwidth of the individual circuit elements 100, 120, 130 essentially corresponds to the value of the bandwidth at the first output channel K1. Thus, the current is correctly determined even in dynamic operation, i.e., when the current IE changes over time, particularly over several orders of magnitude. In the case of alternating current (AC), currents IE with frequencies within the bandwidth defined by the circuit elements 100, 110, 120, 130 can be measured.

[0042] The diode arrangements D1, D2, and D3 are preferably dimensioned such that only approximately 1 volt difference can arise between the voltages U1, U2, and U3. Nevertheless, with a larger number of output channels K1, K2, K3, and K4, the drive capability toward the higher output channels K1, K2, K3, and K4 will be significantly lower than for the lowest output channel K1 with the operational amplifier OA1. To compensate for this reduction, it is further planned to provide the voltage followers OA2, OA3, and OA4 with small voltage gains in the range of 1.1 to 1.5 by means of appropriate resistor circuitry, with the goal of ensuring that all output voltages UA1, UA2, UA3, and UA4 have a uniform drive capability of, for example, between 0 and 10 volts. Conversely, the negative feedback resistors R2, R3, and R4 can be reciprocally reduced.

[0043] Fig. Figure 2 shows an embodiment of the method for determining an electrical current intensity of an electrical current IE according to the second aspect of the invention. An electrical circuit 10 according to the first aspect of the invention is used here. By way of example, an electrical circuit 10 with four output channels K1, K2, K3, K4 is assumed, corresponding to the embodiment of Fig. 1. The electrical current IE to be determined flowing on the input side of the electrical circuit 10 leads to output voltages UA1, UA2, UA3, UA4 which are respectively made available on the output side at its output channels K1, K2, K3, K4.

[0044] For the first output channel K1, an output voltage threshold SW1 of the output voltage UA1 is predefined, for the second output channel K2, an output voltage threshold SW2 of the output voltage UA2 is predefined, and for the third output channel K3, a third output voltage threshold SW3 of the output voltage UA3 is predefined. According to this exemplary embodiment, the current IE is determined according to the equation IE = UA1 / R1 when the output voltage UA1 is less than or equal to the first output voltage threshold SW1.

[0045] If the output voltage UA1 is greater than or equal to the first output voltage threshold SW1, this indicates a current IE that is so large that the output voltage UA2 at the second output channel K2 should be included to correctly determine the current. Accordingly, the criterion applies here that the current IE is determined according to the equation IE = UA1 / R1 + UA2 / R2 if, at the same time, the output voltage UA2 is less than the second output voltage threshold SW2.

[0046] If the output voltage UA2 is greater than or equal to the output voltage threshold SW2, this indicates a current IE that is so large that the output voltage UA3 at the third output channel K3 should be included to correctly determine the current. Accordingly, the criterion applies here that the current IE is determined according to the equation IE = UA1 / R1 + UA2 / R2 + UA3 / R3 if, at the same time, the output voltage UA3 is less than the third output voltage threshold SW3.

[0047] If the output voltage UA3 is greater than or equal to the third output voltage threshold SW3, this indicates a current IE that is so large that the output voltage UA4 at the fourth output channel K4 should be included to correctly determine the current. Accordingly, the criterion here is that the current IE is determined according to the equation IE = UA1 / R1 + UA2 / R2 + UA3 / R3 + UA4 / R4.

[0048] In other words, in this exemplary embodiment, the weighting factor associated with an output voltage UA2, UA3, UA4 of a circuit element 100, 110, 120, 130 of the circuit elements 100, 110, 120, 130 connected electrically in series is set to zero when the output voltage UA1, UA2, UA3 of the circuit element 100, 110, 120 or of the transimpedance amplifier TIA that is electrically immediately upstream of the circuit element 100, 110, 120, 130 in the series falls below a predetermined output voltage threshold value SW1, SW2, SW3.

[0049] The output voltages UA1, UA2, UA3, UA4 applied to the output channels K1, K2, K3, K4 are weighted according to the magnitude of the electric current IE and added to a sum that is linked to the electric current IE, thereby determining the electric current. The weighting factors are reciprocal to the negative feedback resistors R1, R2, R3, R4 of the transimpedance amplifier TIA or the circuit elements 100, 110, 120, 130. This principle can be extended to additional circuit elements 140.

[0050] In an alternative embodiment, instead of the threshold-dependent assessment of the output voltage UA1, UA2, UA3 of the respective lower output channel K1, K2, K3, the output voltage UA2, UA3, UA4 of the respective channel K2, K3, K4 itself is used as a criterion for determining whether its signal should contribute to the weighted addition. The weighting factor associated with the corresponding output voltage UA2, UA3, UA4 is set to zero if the respective output voltage UA2, UA3, UA4 falls below a predetermined respective output voltage threshold SW2, SW3, SW4.

[0051] Fig. 3 shows the components of the negative feedback currents I1,I2,I3,I4 according to the electrical circuit 10 of Fig. 1 depending on the current intensity of the electrical current IE. The sum of the negative feedback currents I1, I2, I3, I4 is always equal to the input current IE to be measured. Over wide current intensity ranges, 3 of the 4 processing channels K1, K2, K3, K4 simultaneously contribute significant portions to the weighted sum signal.

[0052] Fig. Figure 4 shows a schematic embodiment of a current measuring device SMG according to the fourth aspect of the invention, which comprises an electrical circuit 10 according to the first aspect of the invention. For example, this may be the electrical circuit 10 according to the embodiment of Fig. 1. Accordingly, in Fig. 4 four output channels K1, K2, K3, K4 are shown. The current measuring device SMG further comprises a computing unit RE, which is designed to carry out the method according to the second aspect of the invention, for example as in the embodiment of Fig. 2. In other words, the computing unit RE can execute the computer program according to the third aspect of the invention. The determined electrical current intensity IE can be displayed via a display device D of the current measuring device SMG, which is controlled by the computing unit RE. Furthermore, the current measuring device SMG has a battery PS, which supplies the computing unit RE, the display device D, and the electrical circuit 10 with energy. Thus, the current measuring device SMG is galvanically isolated from the environment. A load current IL flowing into an input E of the current measuring device SMG or the electrical circuit 10 must therefore flow out again from a ground terminal M of the current measuring device SMG or the electrical circuit 10. The current measuring device SMG can thus be used similarly to a handheld multimeter, for currents over an extremely wide range of approximately 10 decades, without the need for a measuring range switch.The voltage drop UE between the input E and the ground terminal M is always zero.

[0053] Fig. Figure 5 shows an embodiment of a current measuring device SMG according to the fourth aspect of the invention that is switch-free over more than 10 orders of magnitude and is suitable for measuring photocurrents. The current measuring device SMG contains an electrical circuit 10 according to Fig. 1, a 4-channel analog-to-digital converter 30 with circuit board 50 for connections to the electrical circuit 10, and a computing unit RE (not shown) for executing the computer program according to the third aspect of the invention. The computing unit RE is connected to the analog-to-digital converter 30 via a cable connection 40. The current measuring device SMG can be used to measure, for example, light-induced current from a photodiode PD. Fig. 5, a photodiode PD is placed directly behind the exit slit of a monochromator 20.

[0054] Fig. 6 shows spectral dependent measurements, which were carried out with the Fig. 5 shown ammeter SMG. For this purpose, electromagnetic radiation from a source of electromagnetic radiation is measured via the Fig. 5 visible monochromator 20 and the light-induced current generated in the photodiode PD was investigated spectrally dependently with the ammeter SMG.

[0055] The upper measurement, referenced by (a), shows the output voltages UA1, UA2, UA3, UA4 at the four output channels K1, K2, K3, K4 of the electrical circuit 10. The middle measurement, referenced by (b), shows the respective negative feedback currents I1, I2, I3, I4, determined using the negative feedback resistors R1, R2, R3, R4, which flow from the transimpedance amplifier OA1 or the first, second, and third circuit elements 100, 110, 120, 130. The lower measurement, referenced by (c), shows the current IE determined from the sum of the negative feedback currents I1, I2, I3, I4. List of reference symbols 10 Electrical circuit 20 Monochromator 21 Exit slit 30 analog-to-digital converters 40 cable connection 50 boards 100 circuit elements 110 First circuit element 120 Second circuit element 130 Third circuit element 140 Fourth circuit element C1 capacitor C2 capacitor of the first circuit element C3 capacitor of the second circuit element C4 capacitor of the third circuit element D Display device D1 Diode arrangement of the first circuit element D2 diode arrangement of the second circuit element D3 Diode arrangement of the third circuit element D11 First diode D12 Second diode E Entrance IE Electric current IL load current K1 First output channel K2 Second output channel K3 Third output channel K4 Fourth output channel M ground terminal OA1 operational amplifier of the transimpedance amplifier OA2 operational amplifier of the first circuit element OA3 operational amplifier of the second circuit element OA4 operational amplifier of the third circuit element P connection point P1 output node P2 Output node of the first circuit element P3 Output node of the second circuit element P4 Output node of the third circuit element PD photodiode PS battery R1 negative feedback resistor of the transimpedance amplifier R2 negative feedback resistor of the first circuit element R3 negative feedback resistor of the second circuit element R4 negative feedback resistor of the third circuit element RE computing unit SMG current meter SW1 Output voltage threshold of the transimpedance amplifier SW2 Output voltage threshold of the first circuit element SW3 Output voltage threshold of the second circuit element SW4 Output voltage threshold of the third circuit element TIA transimpedance amplifier U1 Voltage at the output node of the transimpedance amplifier U2 voltage at the output node of the first circuit element U3 Voltage at the output node of the second circuit element U4 Voltage at the output node of the third circuit element UA1 Output voltage of the transimpedance amplifier UA2 Circuit element output voltage of the first circuit element UA3 circuit element - output voltage of the second circuit element UA4 Circuit element Output voltage of the third circuit element UE voltage drop

Claims

[1] Electrical circuit (10) for determining an electrical current intensity of an electrical current (IE), comprising: - a transimpedance amplifier (TIA) which is designed to convert the electrical current (IE) flowing on the input side of the transimpedance amplifier (TIA) into an electrical voltage indicative of the electrical current to be determined, which voltage is applied on the output side of the transimpedance amplifier (TIA) as an output voltage (UA1) at an output node (P1), and - a circuit arrangement electrically connected or connectable in series to the output node (P1) with a circuit element (100, 110) or several circuit elements (100, 110, 120, 130) connected in series, each circuit element comprising a diode arrangement (D1, D2, D3) with at least one diode (D11, D12), as well as a negative feedback resistor (R2, R3, R4) and an operational amplifier (OA2, OA3, OA4), the diode arrangement (D1, D2, D3), the negative feedback resistor (R2, R3, R4) and the operational amplifier (OA2, OA3, OA4) being electrically connected to one another via an output node (P2, P3, P4) of the respective circuit element (100, 110, 120, 130), wherein the operational amplifier (OA2, OA3, OA4) of each circuit element is designed to detect the voltage present at the output node (P2, P3, P4) of the respective circuit element, which is also indicative of the electrical current intensity to be determined, and to provide it as a circuit element output voltage (UA2, UA3, UA4) indicative of this voltage, so that the current intensity of the electrical current (IE) can be determined from the output voltage (UA1) of the transimpedance amplifier (TIA) and the negative feedback resistor (R1) using Ohm's law, and / or wherein the current intensity of the electrical current (IE) is determined from a sum of the output voltage (UA1) of the transimpedance amplifier (TIA) and at least one circuit element output voltage (UA2, UA3, UA4) using Ohm's law via the respective negative feedback resistor (R2, R3, R4) of the circuit element (100,110,120,130) or a negative feedback resistor (R1) of the transimpedance amplifier (TIA) can be determined. [2] The electrical circuit (10) according to claim 1, wherein at least one circuit element (100,110,120,130,140) comprises at least two electrically parallel-connected, oppositely polarized diodes (D11,D12). [3] The electrical circuit (10) according to one of the preceding claims, wherein a first circuit element (100, 110, 120, 130, 140) of the circuit arrangement, in particular the circuit element (100, 110) adjacent to the output node (P1), comprises a plurality of series-connected diodes (D11, D12), wherein at a connection point (P) between the series-connected diodes (D11, D12) a capacitor (C1) is connected to ground of the electrical circuit (10) or another point equivalent to ground in terms of AC voltage. [4] The electrical circuit (10) according to one of the preceding claims, wherein a capacitor (C2,C3,C4) is electrically connected in parallel with at least one negative feedback resistor (R2,R3,R4), so that the negative feedback resistor (R2,R3,R4) and the capacitor (C2,C3,C4) define a time constant of the respective circuit element (100,110,120,130,140). [5] The electrical circuit (10) according to claim 4, wherein a plurality of circuit elements (100, 110, 120, 130) with their respective negative feedback resistors (R2, R3, R4) each have capacitors (C2, C3, C4) electrically connected in parallel, and wherein the respective negative feedback resistors (R2, R3, R4) and capacitors (C2, C3, C4) are dimensioned such that the time constants of the circuit elements (100, 110, 120, 130) do not deviate from each other by more than 50%, especially 25%, even more especially 10%. [6] The electrical circuit (10) according to one of the preceding claims, wherein a gain value of the operational amplifier (OA2) of the circuit element (100, 110) adjacent to the output node (P1) is equal to 1 and / or wherein a gain value of at least one operational amplifier (OA3, OA4) of one of the circuit elements (100, 120, 130, 140) electrically connected in series to the adjacent circuit element (100, 110) is greater than 1, in particular wherein the gain values ​​of the operational amplifiers (OA1, OA2, OA3, OA4) of the circuit elements (100, 110, 120, 130, 140) connected in series increase along the series. [7] Method for determining an electrical current intensity of an electrical current (IE) using the electrical circuit (10) according to one of claims 1 to 6, wherein an electrical current intensity of the electrical current (IE) is determined from the output voltage (UA1) of the transimpedance amplifier (TIA) and a negative feedback resistor (R1) using Ohm's law and / or wherein the current intensity of the electrical current (IE) is determined from a sum of the output voltage (UA1) of the transimpedance amplifier (TIA) and at least one circuit element output voltage (UA2, UA3, UA4), using Ohm's law via the respective negative feedback resistor (R2, R3, R4) of the circuit element (100, 110, 120, 130). [8] The method according to claim 7, wherein the output voltage (UA1) and the circuit element output voltage (UA2, UA3, UA4) of at least one circuit element (100, 110, 120, 130) are added in a weighted manner to form a weighted sum, wherein respective weighting factors are reciprocal to the respective negative feedback resistors (R1, R2, R3, R4). [9] The method according to claim 8, wherein based on predefined output voltage thresholds (SW1,SW2,SW3,SW4) - the weighting factor associated with at least one circuit element output voltage (UA2, UA3, UA4) is set to zero if the at least one further output voltage (UA2, UA3, UA4) falls below a respective predetermined further output voltage threshold value (SW2, SW3, SW4), or - the weighting factor of a circuit element (100,110,120,130) of the circuit elements (100,110,120,130) electrically connected in series, associated with a circuit element output voltage (UA2,UA3,UA4), is set to zero if the circuit element output voltage (UA2,UA3) of the circuit element (100,110,120) or of the transimpedance amplifier (TIA) electrically connected immediately upstream of the circuit element (100,110,120,130) in the series falls below a predetermined output voltage threshold value (SW1,SW2,SW3). [10] A current measuring device (SMG) comprising at least one electrical circuit (10) according to one of claims 1 to 6.

Images