Shunt probe

Abstract

An isolated differential shunt probe measurement probe for a test and measurement system has an isolation barrier between an input side and an output side of the probe. The input side is configured to receive a voltage signal across a shunt connected to a device under test and to transmit the voltage signal across the isolation barrier. The output side is configured to receive the voltage signal across the isolation barrier and to output the voltage signal to a test and measurement instrument.

Description

[0001] priority This disclosure claims the benefit of U.S. Provisional Application No. 63 / 008,720, filed April 11, 2020, entitled “CURRENT SHUNT PROBE,” the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to systems and methods associated with test and measurement systems, and particularly to test and measurement instrument probes for measuring current in a device under test (DUT). Background Technology

[0003] The ability to measure current is crucial when developing and testing switching power supplies, motor drivers, battery chargers, wireless chargers, photovoltaic inverters, and other related power electronics. A common method for measuring current involves connecting a low-value resistor (often called a "current shunt") in series with the path of the current to be measured. The resulting voltage drop across the shunt can be measured to determine the current based on the shunt's known resistance. However, when this method is used to measure dynamic currents, at least two substantial obstacles exist.

[0004] First, the voltage drop across the shunt is intentionally kept small to minimize the impact on the DUT, but this small voltage must typically be measured in the presence of a much higher common-mode voltage. For example, the shunt voltage can be in the range of millivolts or tens of millivolts, while the common-mode voltage can be hundreds of volts. Measuring such a relatively small shunt voltage usually requires the use of differential measurement equipment (such as, for example, oscilloscope probes) with extremely high common-mode range and common-mode rejection ratio (CMRR).

[0005] Secondly, the shunt will exhibit both inductance and resistance R, so the voltage V generated from the current i across the shunt is V = i∙R + L∙di / dt. The effective inductance L of the shunt varies depending on the physical shape, size, and placement of the shunt in the circuit, as well as the placement of the interconnects from the shunt to the measurement device. For fixed layouts with permanently attached measurement circuitry (such as permanently connected measurement probes), the fixed inductance effect can be compensated using analog hardware or digital signal processing (DSP) that implements a "pole" in the frequency response of the measurement system at the same frequency as the shunt's L / R "zero". However, this compensation technique may not be practical for general probing of the circuit during the design phase.

[0006] The examples disclosed herein address these and other shortcomings of the prior art. Attached Figure Description

[0007] Referring to the accompanying drawings, aspects, features, and advantages of this disclosure will become apparent from the following description of the examples, in which: Figure 1 This is a block diagram of a test and measurement system based on some examples of this disclosure.

[0008] Figure 2 Based on some examples of this disclosure Figure 1 A schematic block diagram of an example probe.

[0009] Figure 3 This is based on other examples of this disclosure. Figure 1 Another example schematic block diagram of a probe.

[0010] Figure 4 yes Figure 2 A schematic example of the input of any one of the probes in option 3.

[0011] Figure 5 yes Figure 2 Another illustrative example of the input of any of the three probes. Detailed Implementation

[0012] This paper discloses an isolated shunt measurement probe for measuring the dynamic current of a DUT. Figure 1 This is an example block diagram of a test and measurement system according to some examples of this disclosure. In this test and measurement system, an isolated shunt measurement probe 102 connects a test and measurement instrument 104 to a DUT 106.

[0013] To measure the load R flowing through DUT 106 L A current I of 108 will cause a precision shunt resistor of 110 R to... S It is placed in series with load 108. To minimize the voltage divider effect and the resulting impact on the performance of the DUT, the shunt resistor 110 is typically much smaller than load 108 to minimize the voltage drop across shunt 110. The two input leads of probe 102 are coupled across shunt 110 to measure the resulting voltage drop.

[0014] Probe 102 may have differential or single-ended output. Test and measurement instrument 104 receives the measured voltage and determines the resulting flowing current. For example... Figure 1As seen in the diagram, probe 102 includes an isolation barrier 112 to maintain isolation between DUT 106 and test and measurement instrument 104. Isolation barrier 112 can be any structure that maintains isolation between the input side and the output side of probe 102. In some examples, the isolation barrier can be a current isolation barrier that maintains current isolation between test and measurement instrument 104 and DUT 106. That is, current isolation prevents current flow between test and measurement instrument 104 and DUT 106. This allows isolation barrier 112 in probe 102 to achieve high common-mode range and high CMRR.

[0015] Figure 2 This is an example circuit of probe 102 according to some examples of this disclosure. Probe 102 includes an input 202 directly coupled to low-noise amplifier 204. Because the isolation barrier 112 prevents any common-mode current from flowing through probe 102 despite potentially high common-mode input voltage, low-noise amplifier 204 can have a low input impedance, such as approximately 50 ohms. For example, a suitable low-noise amplifier could be a Texas Instruments LMH5401 amplifier. However, the examples of this disclosure are not limited to this low-noise amplifier, but can be any amplifier with a suitably low effective input noise resistance. The Johnson voltage noise of the physical resistor is... Where k is the Boltzmann constant, T is the absolute temperature, R is the resistance, and B is the noise measurement bandwidth. The effective noise resistance of the amplifier includes any physical resistance in series with the input, as well as any other noise sources in the amplifier that will produce the same amount of noise, referred to as the effective input resistance. Compared to the input impedance of typical test and measurement instrument probes, the low input impedance of probe 102 can provide a lower thermal noise density or Johnson noise density, which allows for low-noise measurements of small voltage drops across shunts. Compared to conventional probes exhibiting noise densities greater than 10 nV / sqrt(Hz), the example probe 102 according to embodiments of this disclosure can achieve an input-referred noise density of around 2-3 nV / sqrt(Hz).

[0016] In contrast, conventional differential probes have much higher input impedance to avoid loading of the DUT 106 in the presence of high common-mode voltage. In the example disclosed, the low (differential) input impedance is acceptable when measuring the voltage drop across a shunt resistor typically measured in milliohms. Furthermore, the common-mode input impedance remains very high due to the current isolation barrier 112.

[0017] The differential output of the low-noise amplifier 204 can be fed to the differential variable gain amplifier 206. An example of a suitable differential variable gain amplifier is the Texas Instruments LMH6401 amplifier. However, the examples in this disclosure are not limited to this particular differential variable gain amplifier. The gain of the variable gain amplifier can be controlled by the user via the user interface (UI) of the test and measurement instrument 104 or probe 102 based on the expected voltage drop across the shunt 110.

[0018] The differential output of the differential variable gain amplifier 206 can be transmitted across the current isolation barrier 112 between the input side 208 and the output side 210 of probe 102. The input side 208 of probe 102 includes an upconverter 212 configured to upconvert the input signal from a baseband frequency to a microwave band. A microwave structure is provided to transmit microwave frequency signals across the isolation barrier 112. The microwave structure electromagnetically couples microwave frequency analog signals across the isolation barrier but does not couple signals outside the desired microwave band (e.g., submicrowave signals) across the isolation barrier.

[0019] The output side 210 of probe 102 includes a microwave structure for receiving microwave frequency signals and a downconverter 214 for downconverting the microwave frequency signals back to the baseband frequency. Upconverter 212 and downconverter 214 may share a common clock and / or oscillator 216. This common oscillator or clock signal can be transmitted across isolation barrier 112 via a suitable microwave structure.

[0020] Once the signal is received at downconverter 214 across isolation barrier 112 and has been downconverted to a baseband frequency signal, it can be transmitted to low-noise amplifier 218, depending on the implementation. In some examples of this disclosure, low-noise amplifier 218 is not required. The signal is then output 220 to test and measurement instrument 104. In some examples, the output 220 of probe 102 may include an optional balun, producing a single-ended output signal to be input to test and measurement instrument 104 instead of a differential output signal. Test and measurement instrument 104 receives the measured voltage signal and can then determine the current flowing through DUT 106 based on the known shunt resistance and the measured voltage.

[0021] However, examples of the present invention are not limited to those spanning isolation barriers (e.g., Figure 2 The microwave isolation barrier illustrated in the figure is used to transmit analog signals. Conversely, in some examples, an analog-to-digital converter 302 can be provided on the input side 208, such as... Figure 3 As shown in the diagram. Figure 3 Another example of probe 102 is illustrated, and compared with... Figure 2 The similar components discussed herein are given the same reference numerals and will not be discussed further herein.

[0022] exist Figure 3 In the example, the voltage signal can be digitized by analog-to-digital converter 302 before being transmitted by transmitter 304. Transmitter 304 can be a microwave structure as discussed above. However, transmitter 304 can also be a light, such as when the isolation barrier is an optical isolation barrier and receiver 306 can be a photodiode for receiving information.

[0023] Output side 210 may include receiver 306 as mentioned above and digital-to-analog converter 308 for converting digital voltage signals back into analog signals. However, in some examples, as those skilled in the art will understand, digital signals may be sent directly to test and measurement instrument 104 instead of being converted back into analog signals before being transmitted through output 220.

[0024] Transmitter 304 and receiver 306 can also be any other type of wireless transmitter and receiver, such as, but not limited to, radio frequency or wireless fidelity (WiFi). That is, any type of isolation barrier 112 and transmitter 304 and receiver 306 can be used, as long as the input side 208 and output side 210 are isolated from each other in probe 102.

[0025] Additionally or alternatively, some examples of this disclosure can minimize the inductance of shunt 110. The input 202 of probe 102 can be designed to interface with shunt 110 placed in or connected to DUT 106 to minimize or eliminate the dynamic magnetic field encircled by the measurement loop. In other words, although shunt 110 still exhibits some inductance due to the magnetic field generated by and surrounding the current flow within the shunt itself, placing a lead at the input 202 of probe 102 will avoid or eliminate the same magnetic field. That is, the specific design of the measurement sensing loop will result in a measurement voltage across the shunt of: v = iR + Ldi / dt − Mdi / dt (1) Where L is the self-inductance of shunt 110, M is the mutual inductance of the sensing loop with shunt 110, and the size and placement of the sensing loop are arranged such that M = L.

[0026] like Figure 4As shown, in some examples, two parallel shunts 402 can be connected to the load 108 of the DUT 106. The probe 102 may include two measurement leads 406 and 408 in the input 202. The measurement lead 406 is symmetrically positioned between the two parallel shunts 402 until it reaches lead 408, and then both leads are routed together to the probe 102. The symmetrical measurement lead 406 will pick up equal but opposite magnetic fields in a first order from the equal currents flowing through the two parallel shunts 402, thereby eliminating the inductive effect in voltage measurement.

[0027] In some examples, two parallel shunts 402 may be provided within the input 202 of probe 102 and attached to the circuit board of DUT 106. In other examples, the shunts 402 may already be connected to the circuit board of DUT 106, and one of the leads 406 and 408 of input 202 may be symmetrically positioned between the parallel shunts 402.

[0028] Figure 5 Another example of eliminating or reducing the inductance generated by shunt 504 is illustrated. In some examples, at least one of the measurement leads 502 of the input 202 of probe 102 may include one or more twists or loops, etc. Positioning the measurement leads in such a way that the measurement leads surround some induced magnetic field from the current flowing through the shunt can induce an additional voltage in the leads that either bucks or enhances the transient voltage generated by the shunt. Careful positioning of at least one of the leads relative to the shunt, as well as careful routing and dressing of the leads, can be used to eliminate some or all of the inductive pickup of the input 202 of probe 102.

[0029] In some probes 102, input 202 may include a shunt 504 and a twisted and / or looped measurement lead 502. The probe 102 can then be attached to the circuit board of the DUT 106 such that the shunt is provided in a straight line with the load of the DUT 106. In other examples, a twisted measurement lead 502 may be provided in the input 202 of the probe 102 and connected to a shunt 110 already located on the circuit board of the DUT 106.

[0030] In some examples, a coaxial shunt can replace a wire or surface-mount shunt on the DUT 106. The coaxial shunt can be positioned by placing the return measurement lead at the center of the cylindrical resistive surface that forms the shunt. The magnetic field from the current flow in the shunt surrounds both the shunt and the coaxial measurement return lead, causing inductive pickup in the shunt to be eliminated by inductive pickup in the return measurement lead at the input 202 of probe 102.

[0031] As discussed above, examples of this disclosure may include at least three different types of replaceable probe tips or inputs 202. The first type of input 202 is a type of probe 102 tip that has different embedded shunts and / or inductance elimination loops directly built into the input 202 of the probe 102.

[0032] Another type of input 202 is a probe tip that can be located on top of a shunt on a customer's printed circuit board or the device under test 106, where contacts and loops are built into the input 202 to eliminate mutual inductance. In some of these examples, the input 202 can be spring-loaded on top of the shunt 110.

[0033] The third type of input 202 may include a differential voltage measurement tip, which is used in conjunction with a shunt on DUT 106, and the printed circuit board of DUT 106 includes traces to generate mutual inductance elimination under the shunt within DUT 106. This type of input can also be used with a coaxial shunt.

[0034] In the examples discussed above, shunt 110 (or any other shunt mentioned) can be made of a non-magnetic material. Shunts made of magnetic materials can be used, but they may exhibit a greater skin-loss effect compared to shunts made of non-magnetic materials. In some examples, the skin effect may limit the bandwidth of current measurement.

[0035] The aspects of this disclosure can operate on specially created hardware, firmware, digital signal processors, or on a specially programmed computer including a processor that operates according to programmed instructions. The terms controller or processor used herein are intended to include microprocessors, microcomputers, application-specific integrated circuits (ASICs), and special-purpose hardware controllers. One or more aspects of this disclosure can be embodied in computer-usable data and computer-executable instructions, such as in one or more program modules executed by one or more computers (including monitoring modules) or other devices. Typically, program modules include routines, programs, objects, components, data structures, etc., which perform specific tasks or implement specific abstract data types when executed by a processor in a computer or other device. Computer-executable instructions can be stored on a computer-readable storage medium such as a hard disk, optical disk, removable storage medium, solid-state memory, random access memory (RAM), etc. As those skilled in the art will appreciate, the functionality of a program module can be combined or distributed in various aspects as needed. Furthermore, functionality can be wholly or partially embodied in firmware or hardware equivalents such as integrated circuits, FPGAs, etc. A particular data structure may be used to more efficiently implement one or more aspects of this disclosure, and such data structure is considered to be within the scope of the computer-executable instructions and computer-available data described herein.

[0036] In some cases, the disclosed aspects may be implemented in hardware, firmware, software, or any combination thereof. The disclosed aspects may also be implemented as instructions carried on or stored thereon by one or more computer-readable storage media, which may be read and executed by one or more processors. Such instructions may be referred to as a computer program product. As discussed herein, a computer-readable medium means any medium that can be accessed by a computing device. By way of example and not limitation, a computer-readable medium may include computer storage media and communication media.

[0037] Computer storage media means any medium that can be used to store computer-readable information. By way of example and not limitation, computer storage media may include RAM, ROM, electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD-ROM), digital video disc (DVD) or other optical disc storage devices, cassette tape, magnetic tape, disk storage devices or other magnetic storage devices, and any other volatile or non-volatile, removable or non-removable media implemented in any technology. Computer storage media excludes signals themselves and the transient form of signal transmission.

[0038] Communication medium means any medium that can be used for communication of computer-readable information. By way of example and not limitation, communication medium may include coaxial cable, fiber optic cable, air, or any other medium suitable for communication of electrical, optical, radio frequency (RF), infrared, acoustic, or other types of signals.

[0039] Example Illustrative examples of the techniques disclosed herein are provided below. Configurations of the techniques may include any one or more of the examples described below, as well as any combination of these examples.

[0040] Example 1 is an isolated differential shunt measurement probe, including an isolation barrier; a differential input side having a low-noise, low-impedance input, the differential input side being configured to receive a voltage signal across a shunt connected to the device under test and to transmit the voltage signal across the isolation barrier; and an output side being configured to receive the voltage signal across the isolation barrier and to output the voltage signal to a test and measurement instrument.

[0041] Example 2 is an isolated differential shunt measurement probe of Example 1, wherein the input side includes a low-noise amplifier configured to amplify the voltage signal before it is transmitted.

[0042] Example 3 is an isolated differential shunt measurement probe of Example 2, wherein the input side further includes a variable amplifier coupled to a low-noise amplifier.

[0043] Example 4 is an isolated differential shunt measurement probe of any of Examples 1-3, wherein the input side includes an upconverter configured to convert the voltage signal from a baseband frequency signal to a microwave frequency signal for transmission, and wherein the output side includes a downconverter configured to convert the microwave frequency signal back into a baseband frequency signal after receiving it on the output side.

[0044] Example 5 is an isolated differential shunt measurement probe of any of Examples 1-4, wherein the input side includes a digitizer configured to digitize the voltage signal before it is transmitted across the isolation barrier.

[0045] Example 6 is an isolated differential shunt measurement probe of any of Examples 1-5, wherein the input includes a shunt, and the shunt is a coaxial shunt.

[0046] Example 7 is an isolated differential shunt measurement probe for any of Examples 1-6, where the shunt is a coaxial shunt.

[0047] Example 8 is an isolated differential shunt measurement probe of any of Examples 1-7, wherein the input includes two parallel shunts and at least one measurement lead placed symmetrically between the parallel shunts.

[0048] Example 9 is an isolated differential shunt measurement probe of any of Examples 1-5, wherein the input includes at least one measurement lead positioned relative to the shunt to form a mutual inductance that at least partially eliminates errors in the voltage signal due to the inductance of the shunt.

[0049] Example 10 is an isolated differential shunt measurement probe of Example 9, wherein the input further includes a shunt.

[0050] Example 11 is an isolated differential shunt measurement probe of any of Examples 1-10, wherein the isolation barrier is a microwave isolation barrier or an optical isolation barrier.

[0051] Example 12 is an isolated differential shunt measurement probe including an isolation barrier; an input side including a low-noise, low-impedance input configured to receive a voltage signal across the shunt, and a transmitter configured to transmit the voltage signal across the isolation barrier; and an output side separated from the input side by the isolation barrier, including a receiver configured to receive the voltage signal from the input side across the isolation barrier, and an output for transmitting the voltage signal to test and measurement instruments.

[0052] Example 13 is an isolated differential shunt measurement probe of Example 12, wherein the input side further includes a low-noise amplifier directly electrically coupled to the input to amplify the voltage signal before it is transmitted.

[0053] Example 14 is an isolated differential shunt measurement probe of Example 13, wherein the input side further includes a variable amplifier coupled to a low-noise amplifier and a transmitter.

[0054] Example 15 is an isolated differential shunt measurement probe of any of Examples 12-14, wherein the input side further includes an upconverter configured to convert the voltage signal from a baseband frequency signal to a microwave frequency signal, and the transmitter is a microwave structure for transmitting the microwave frequency signal, and wherein the output side further includes a downconverter configured to convert the microwave frequency signal back into a baseband frequency signal after the receiver receives the microwave frequency signal.

[0055] Example 16 is an isolated differential shunt measurement probe of any of Examples 12-15, wherein the input side further includes a digitizer configured to digitize the voltage signal before the transmitter transmits the voltage signal.

[0056] Example 17 is an isolated differential shunt measurement probe of Examples 12-16, wherein the input side includes a shunt.

[0057] Example 18 is an isolated differential shunt measurement probe of Examples 12-17, wherein the shunt is a coaxial shunt.

[0058] Example 19 is an isolated differential shunt measurement probe of any of Examples 12-18, wherein the input side includes two parallel shunts and at least one measurement lead symmetrically placed between the parallel shunts.

[0059] Example 20 is an isolated differential shunt measurement probe of any of Examples 12-19, wherein the input includes at least one measurement lead positioned relative to the shunt to form a mutual inductance, which at least partially eliminates errors in the voltage signal due to the inductance of the shunt.

[0060] Example 21 is an isolated differential shunt measurement probe of Example 20, wherein the input further includes a shunt.

[0061] Example 22 is an isolated differential shunt measurement probe of any of Examples 12-21, wherein the isolation barrier is a microwave isolation barrier or an optical isolation barrier.

[0062] The previously described versions of the disclosed subject matter have many advantages, which have either been described or will be obvious to a person skilled in the art. Even so, not all versions of the disclosed apparatus, system, or method require these advantages or features.

[0063] Additionally, this written description refers to specific features. It should be understood that the disclosure in this specification includes all possible combinations of these specific features. Where a specific feature is disclosed in the context of a particular aspect or example, that feature may also be used to the extent possible in the context of other aspects and examples.

[0064] Furthermore, when a method having two or more defined steps or operations is referenced in this application, the defined steps or operations may be performed in any order or simultaneously, unless the context precludes such possibilities.

[0065] While specific examples of this disclosure have been illustrated and described for purposes of explanation, it will be understood that various modifications may be made without departing from the spirit and scope of this disclosure. Therefore, this disclosure should not be limited except as defined by the appended claims.

Claims

1. An isolated differential shunt measurement probe, comprising: Isolation barrier; The differential input side has a low noise, low impedance input and is configured to receive a voltage signal across a shunt connected to the device under test and to transmit the voltage signal across an isolation barrier. as well as On the output side, it is configured to receive the voltage signal across an isolation barrier and output the voltage signal to test and measurement instruments. The isolation barrier is coupled between the differential input side and the output side, and maintains current isolation between the differential input side and the output side. The isolation barrier is either a microwave isolation barrier or an optical isolation barrier.

2. The isolated differential shunt measurement probe of claim 1, wherein the input side includes a low-noise amplifier configured to amplify the voltage signal before it is transmitted.

3. The isolated differential shunt measurement probe of claim 2, wherein the input side further includes a variable amplifier coupled to a low-noise amplifier.

4. The isolated differential shunt measurement probe of claim 1, wherein the input side includes an upconverter configured to convert the voltage signal from a baseband frequency signal to a microwave frequency signal for transmission, and wherein the output side includes a downconverter configured to convert the microwave frequency signal back into a baseband frequency signal after receiving the microwave frequency signal on the output side.

5. The isolated differential shunt measurement probe of claim 1, wherein the input side includes a digitizer configured to digitize the voltage signal before it is transmitted across the isolation barrier.

6. The isolated differential shunt measurement probe of claim 1, wherein the input includes a shunt.

7. The isolated differential shunt measuring probe according to claim 6, wherein the shunt is a coaxial shunt.

8. The isolated differential shunt measurement probe of claim 1, wherein the input comprises two parallel shunts and at least one measurement lead symmetrically placed between the parallel shunts.

9. The isolated differential shunt measurement probe of claim 1, wherein the input includes at least one measurement lead positioned relative to the shunt to form a mutual inductance, the mutual inductance at least partially eliminating errors in the voltage signal due to the inductance of the shunt.

10. The isolated differential shunt measurement probe of claim 9, wherein the input further comprises a shunt.

11. An isolated differential shunt measurement probe, comprising: Isolation barrier; The input side includes: Low-noise, low-impedance input, configured to receive voltage signals across the shunt, and A transmitter configured to transmit the voltage signal across an isolation barrier; and The output side, separated from the input side by an isolation barrier, includes: A receiver configured to receive the voltage signal from the input side across an isolation barrier, and The output is used to transmit the voltage signal to test and measurement instruments. The isolation barrier is coupled between the input and output sides and maintains current isolation between them. The isolation barrier is either a microwave isolation barrier or an optical isolation barrier.

12. The isolated differential shunt measurement probe of claim 11, wherein the input side further includes a low-noise amplifier directly electrically coupled to the input to amplify the voltage signal before it is transmitted.

13. The isolated differential shunt measurement probe of claim 12, wherein the input side further includes a variable amplifier coupled to a low-noise amplifier and a transmitter.

14. The isolated differential shunt measurement probe of claim 11, wherein the input side further includes an upconverter configured to convert the voltage signal from a baseband frequency signal to a microwave frequency signal, and the transmitter is a microwave structure for transmitting the microwave frequency signal, and wherein the output side further includes a downconverter configured to convert the microwave frequency signal into a baseband frequency signal after the receiver receives the microwave frequency signal.

15. The isolated differential shunt measurement probe of claim 11, wherein the input side further includes a digitizer configured to digitize the voltage signal before the transmitter transmits the voltage signal.

16. The isolated differential shunt measurement probe of claim 11, wherein the input includes a shunt.

17. The isolated differential shunt measurement probe according to claim 16, wherein the shunt is a coaxial shunt.

18. The isolated differential shunt measurement probe of claim 11, wherein the input comprises two parallel shunts and at least one measurement lead symmetrically placed between the parallel shunts.

19. The isolated differential shunt measurement probe of claim 11, wherein the input includes at least one measurement lead positioned relative to the shunt to form a mutual inductance, the mutual inductance at least partially eliminating errors in the voltage signal due to the inductance of the shunt.

20. The isolated differential shunt measurement probe of claim 19, wherein the input further comprises a shunt.

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