Source Measurement Unit with Protected Drive Circuit

Abstract

A test and measurement device includes a source configured to output a source signal; a source output configured to output the source signal to a connected cable; a protection drive circuit electrically coupled to the source and configured to receive the source signal and generate a protection drive signal, the protection drive circuit having a gain less than one; and a protection drive circuit output configured to output the protection drive signal to a connected protection device.

Description

Technical Field

[0001] Embodiments of the disclosed technology relate generally to electrical test and measurement instruments, and more particularly to apparatus and methods for protecting electrical components from unwanted electrical currents. Background Art

[0002] Guarding is an important aspect of almost any low current measurement. Electrical instrument manufacturers typically employ any of a number of conventional techniques to isolate the impedance desired to be measured from all currents and impedances that are not part of the desired measurement. Guarding is essentially a special case of shielding to prevent noise or unwanted currents from becoming part of the measurement by preventing coupling into the measurement leads. In addition, guarding prevents direct current (DC) and ideally alternating current (AC) normal mode currents from electrically coupling into the measurement terminals.

[0003] In conventional electrical test and measurement systems, a guard is typically driven by the test and measurement equipment to exactly the same voltage as the measurement terminals. The guard should be present at all locations around the measurement terminals, except directly at the intended measurement. However, several problems arise in driving the guard to the same voltage as the measurement terminals. For example, there is a feedback path from the guard amplifier to the measurement terminals, which are the inputs to the guard amplifier. Because the amplifier has a feedback path, frequency stability needs to be maintained, but conventional attempts to do so undesirably change the circuit phase characteristics.

[0004] Conventional systems generally involve adding resistors in series with the guard amplifier of the guard drive circuit to provide frequency stability, but this severely reduces the usefulness of the guard device as a shield. In addition, such systems allow the guard voltage to deviate from the measurement node voltage under transient conditions, such as due to the series guard resistor, and are therefore insufficient for typical fast low current measurement systems. Low current measurements require some technique to manage or control which currents or impedances are measured and which currents are excluded.

[0005] Even if the protection amplifier of the protection drive circuit can be returned to stable operation, provided the resistance is large enough, this is at the expense of protection device bandwidth and a higher impedance protection device output, and the protection device will lag behind the measurement terminals, allowing the protected dielectric to charge and discharge during the transient. Also, longer cables, which generally have more dielectric to charge, will undesirably see slow protection response and settling times, which is unacceptable performance.

[0006] Therefore, there remains a need for improved techniques for protection driver circuits integrated with electrical test and measurement equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 An example of electrical test and measurement equipment implementing a protection drive circuit is illustrated.

[0008] Figure 2A A first example of an electrical test and measurement device in accordance with certain implementations of the disclosed technology is illustrated.

[0009] Figure 2B It is a diagram of Figure 2A An example of a Bode plot showing the frequency response of electrical test and measurement equipment.

[0010] Figure 3A A second example of an electrical test and measurement device in accordance with certain implementations of the disclosed technology is illustrated.

[0011] Figure 3B It is a diagram of Figure 3A An example of a Bode plot showing the frequency response of electrical test and measurement equipment.

[0012] Figure 4 Can be incorporated Figure 2A and Figure 3A An example of a test system that is either an electrical test and measurement device. DETAILED DESCRIPTION

[0013] Many emerging market applications such as the Internet of Things (IoT) require faster low current measurements. IoT products require careful attention to power consumption because there are more battery-operated, low-power, mission-critical devices than ever before. Protection technology enables low current measurements at the output of the cable.

[0014] Other applications, such as parametric testing in the semiconductor industry, have become more demanding when it comes to electrical test and measurement speed and throughput. The parametric test market generally requires increased throughput, which means that test time must be reduced for all measurements, especially for low current testing, which typically takes up the majority of device test time.

[0015] Embodiments of the disclosed technology are generally directed to electrical test and measurement equipment designed to address frequency instability issues in a manner that does not require lower bandwidth protection drive circuits such as used in conventional systems.

[0016] Unlike conventional systems that typically address coupling paths by controlling phase, embodiments of the disclosed technology generally include removing some coupling paths and providing a protection drive circuit gain of less than 1.00 (i.e., less than unity gain) to stabilize the remaining coupling paths. In such embodiments, the signal is in phase with the measurement. If the protection drive circuit has insufficient gain, it will never oscillate.

[0017] Figure 1 An example of an electrical test and measurement system 100 implementing a protection drive circuit is illustrated. The measurement system 100 includes a source measurement unit (SMU) 110 and a device under test (DUT) 102, wherein the source measurement unit (SMU) 110 has a source, which may be a current source 115 and / or a voltage source 117, a resistor 118, and a ground 119 shielded by a chassis 120, an instrument shield 130, and a protection device 150.

[0018] The SMU 110 includes a protection amplifier 112, which is connected to the protection device 150 through a resistor 114. Depending on whether the protection device 150 has a coupling to the ground 119, the resistor behaves somewhat differently. However, in either case, the protection amplifier 112 returns to stable operation at the expense of the protection device 150 bandwidth and the higher impedance protection device 150. Thus, the protection device 150 now lags behind the measurement terminal 116, allowing the protected dielectric to charge and discharge during transients. In addition, the value of the resistor 114 is often selected for the expected maximum cable length. Longer cables will see the lowest protection response and the slowest settling time. That is, a test environment with the longest cables and switches in the path typically requires about 10 seconds (s) to stabilize to hundreds of femtoampere (fA) levels for low current measurements, which is unacceptable performance for many applications. Over time, the protection device 150 eventually returns to the correct voltage, and the actual measurement does reject all impedance and leakage currents as DC errors.

[0019] Figure 2A A first example of an electrical test and measurement device 200 is illustrated in accordance with certain embodiments of the disclosed technology, which is not Figure 1 The electrical test and measurement system 200 is limited in bandwidth. The electrical test and measurement device 200 may be, for example, a source measure unit (SMU). A source measure unit is a type of electrical test and measurement device that is capable of sourcing a voltage signal to a device under test (DUT) and measuring a resulting current signal from the DUT, and / or sourcing a current signal to a device under test (DUT) and measuring a resulting voltage signal from the DUT. As will be appreciated by those skilled in the art, the test and measurement device 200 may include a source measure unit (SMU). Figure 2A There are no add-ons pictured in the image.

[0020] As in Figure 2AAs illustrated in FIG. 2 , the electrical test and measurement device 200 may be connected to a DUT (not shown) via ports 204 and 206. Ports 204 and 206 may be configured to receive cables, such as coaxial or triaxial cables, to carry signals between the electrical test and measurement device 200 and the DUT. The electrical test and measurement device 200 may include a source (e.g., a current source 215 and / or a voltage source 217) configured to output a source signal to the DUT on a first signal line 208 via a cable connected to port 204. The source signal is sent to the DUT via the first signal line 208 and the connected cable. The source signal then propagates through the DUT, and a second cable is connected from the DUT to port 206 to a second signal line 209, which is connected to ground 219, so that the source signal flows through the DUT to allow the signal from the DUT to be measured by the electrical test and measurement device 200.

[0021] The electrical test and measurement device 200 may include a protection driver circuit 250, which may include a first operational amplifier (op-amp) 212, an attenuator circuit 211, and a second operational amplifier 221. The electrical test and measurement device 200 may also include a first resistor 214 electrically coupled between the source 215 and / or 217 and the first operational amplifier 212. The first resistor 214 is a sense resistor that may be used by the electrical test and measurement device 200 to measure current in the system when connected to the DUT.

[0022] The attenuator circuit 211 is electrically coupled between the first operational amplifier 212 and the second operational amplifier 221. For example, the attenuator circuit 211 can be a resistor divider including a second resistor 222 electrically coupled between the first operational amplifier 212 and the second operational amplifier 221, and a third resistor 223 electrically coupled between the second operational amplifier 221 and the ground 219. The values ​​of the resistors 222 and 223 can be selected so that the attenuator circuit 211 is configured to reduce the amplitude of the signal output from the first operational amplifier so that the ratio (also referred to herein as the gain) between the amplitude of the signal input of the second operational amplifier and the signal output of the first operational amplifier is less than 1.00, i.e., less than unity gain. The output of the second operational amplifier 221 is connected to the protection device of the cable connected through the port 204 via the protection signal line 210. The output of the protection drive circuit, which is the output of the second operational amplifier 221, can drive the protection device of the cable in phase with the first signal line 208 to protect the first signal line 208 from electrical interference. As will be appreciated by those skilled in the art, although the guard signal line 210 is shown as part of the port 204, the guard signal line 210 may be connected to the shield of the cable through another port (not shown).

[0023] like Figure 2AAs illustrated in FIG. 1 , the source signal is received at a first operational amplifier 212, which includes a 100% negative feedback path to feed the output of the first operational amplifier 212 to the input of the first operational amplifier 212. The output of the first operational amplifier 212 is received at an attenuator circuit 211, which is also connected to a second operational amplifier 221. As mentioned above, the attenuator circuit 211 has a gain of less than 1.00, and the output of the attenuator circuit 211 is used as an input to the second operational amplifier 221 (which also includes a feedback loop) to stably drive the protection device of the cable connected to the signal line 210 in phase with the first signal line 208. This allows the protection device of the cable connected to the port 204 to be driven at almost the same voltage as the source 215 and / or 217 without limiting the bandwidth. As mentioned above, if the protection driving circuit has insufficient gain, it will never oscillate. The attenuator circuit 211 prevents the amplifiers 212 and 221 from oscillating by having a gain less than unity.

[0024] The electrical test and measurement device 200 may also include a first shielding structure 220, such as a chassis, for example, which is configured to protect the electrical test and measurement device 200 and the first and second signal lines (when connected to the DUT) from electrical interference. A second shielding structure 230, which may also be referred to herein as an instrument shield, is configured to further protect the electrical test and measurement device 200 and the DUT (when connected to the electrical test and measurement device 200) from electrical interference. For example, the second shielding structure 230 may be connected to a cable through the port 206. In other embodiments, the second shielding structure 230 may be connected to the cable through another port.

[0025] Figure 2B It is a diagram of Figure 2A An example of a Bode plot 280 of the frequency response of the electrical test and measurement device 200 when connected to a DUT is shown. The Bode plot 280 shows a range of stable operation for a gain of 0.999, ranging from very high capacitance shown via line 282 (e.g., closure starting at 0 Hz), to a minimum capacitance shown by line 284, such as Cg=1 / (Rh)(100 Hz)(2)(PI) (where Rh represents the resistance present at the high measurement terminal, e.g., the DUT and any impedance seen back to the SMU). The intersection 286 indicates a pole due to the impedance of the low current measurement being performed and the cable length. The intersection 288 is the point at which the protection drive circuit 250 becomes unstable, and the line 292 shown as a dotted line indicates where the instability region begins. As can be seen in the Bode plot 280, keeping the gain less than one prevents the line 284 from being in the unstable region. The intersection 290 indicates the gain bandwidth of the protection drive circuit 250.

[0026] exist Figure 2A In the electrical test and measurement device 200 illustrated in FIG. 1 , the gain of the protection circuit amplifiers 212 and 221 can be reduced to any gain less than 1.00 that makes the protection drive circuit stable. Although generally effective, the electrical test and measurement device 200 may not be ideal for certain or some high voltages. For example, for a high voltage system using a gain of 0.999, such as operating at 1000V, the protection error voltage will be: (1-0.999)*1000V=1V, which may be higher than desired.

[0027] Figure 3A Another example of an electrical test and measurement device 300 according to certain embodiments of the disclosed technology is illustrated. The electrical test and measurement device 300 includes some components similar to those discussed above with respect to the electrical test and measurement device 200, and therefore, similar components will be numbered with the same reference numerals plus 100. For example, the electrical test and measurement device 300 may include a first shield structure 320 and a second shield structure 330, which are similar to those discussed above with respect to the electrical test and measurement device 200. Figure 2A are similar to those discussed above, and therefore, no further discussion is given in this article. Figure 3A Further discussion.

[0028] The electrical test and measurement device 300 can be connected to a device under test (DUT) through ports 304 and 306. Ports 304 and 306 can be configured to receive cables, such as coaxial or triaxial cables, to carry signals between the electrical test and measurement device 300 and the DUT. As will be appreciated by those skilled in the art, the electrical test and measurement device 300 can include a source 315, which can be either a current source or a voltage source, depending on whether a voltage or a current is fed back to the source 315. The source can be configured to output a source signal to the DUT on a first signal line 308 through a cable connected to port 304. The source signal is sent to the DUT through the first signal line 308 and the connected cable. The source signal can propagate through the DUT, and a second cable is connected from the DUT to port 306 to connect the DUT to a second signal line 309, which is connected to ground 319. This allows the source signal to flow through the DUT so that the signal from the DUT can be measured by the electrical test and measurement device 300 based on the source signal.

[0029] Similar to the electrical test and measurement device 200, the electrical test and measurement device 300 may also include a protection drive circuit 350, which may include a first operational amplifier 312, an attenuator circuit 311, and a second operational amplifier 321. The electrical test and measurement device 300 may also include a sense resistor 314 electrically coupled between the source 315 and the first operational amplifier 312. The electrical test and measurement device 300 may also include a current measurement device 318 and a voltage measurement device 319 as part of a source measurement operation.

[0030] exist Figure 3A In the protection drive circuit of the present invention, the attenuator circuit 311 includes a resistor divider including a second resistor 322 electrically coupled between the first operational amplifier 312 and the third resistor 323. In this embodiment, the third resistor 323 is electrically connected to the source signal instead of the ground 319. The values ​​of the resistors 322 and 323 can be selected so that the attenuator 311 is configured to have an output ratio less than 1.00. The output of the second operational amplifier 321 is connected to the protection device of the cable connected through the port 304 via the shielded signal line 310. The output of the protection drive circuit, which is the output of the second operational amplifier 321, can drive the protection device of the cable in phase with the first signal line 308 to protect the first signal line 308 from electrical interference. As will be understood by those skilled in the art, although the shielded signal line 310 is shown as part of the port 304, the shielded signal line 310 can be connected to the shield of the cable through another port (not shown). In some embodiments, the voltage of the source signal and the voltage from the protection drive circuit may not be equal.

[0031] and Figure 2A Certain potential defects associated with the electrical test and measurement equipment 200 illustrated in FIG. Figure 3A The electrical test and measurement device 300 illustrated in FIG. 1 solves this problem, where some coupling paths can be eliminated by referencing the 0.999 attenuation to the output of the low impedance source 315 rather than to ground 319 .

[0032] As mentioned above, conventional systems drive the protection device precisely to the source voltage. The coupling of the protection device to the source voltage completes the coupling around the protection drive circuit, and attenuator 311 provides a ratio less than one for this coupling to prevent op amps 312 and 321 from oscillating.

[0033] With the ratio appropriately changed, the protection drive circuit may be less affected by the source signal output on signal line 308. With the output current of the electrical test and measurement instrument 300 at or near zero, which is the usual case when protection is important, the protection drive circuit can drive the protection device so that the protection device voltage can be nearly perfect. The ratio or gain of the attenuator circuit 311 can be changed during production to allow the protection device to be at the maximum acceptable error for the full-scale current value and for the expected resistance to be protected. As long as the ratio is less than one, the attenuator circuit 311 will prevent the operational amplifiers 312 and 321 from oscillating.

[0034] Figure 3B It is a diagram of Figure 3A An example of a Bode plot 380 of the frequency response of the electrical test and measurement device 300 is shown. The Bode plot 380 shows improvements, such as with Figure 2B 280 of FIG. 280. The range of stable operation for a gain of 0.99 ranges from very high capacitance shown by line 382 (e.g., starting at 0 Hz), to a minimum capacitance shown by line 384, such as Cg=1 / (Rh)(10 kHz)(2)(PI) (where Rh represents the resistance present at port 204). Intersection 386 indicates a pole due to the impedance of the low current measurement being performed and the cable length. Intersection 388 is the point at which the protection drive circuit 350 becomes unstable, and line 392, shown as a dotted line, indicates where the instability region begins. As can be seen in the Bode plot 380, maintaining a gain less than one prevents line 384 from being in the unstable region. Intersection 390 indicates the gain bandwidth of the protection drive circuit 350. As can be seen, using Figure 3A The stable operating range of the electrical test and measurement equipment 300 extends from 0 to 10KHz, compared to the use of Figure 2A The electrical test and measurement equipment 200 sees the 0 to 100 Hz range.

[0035] Figure 4 An example system is illustrated in which either electrical test and measurement device 200 or 300 may be used. The system includes an electrical test and measurement device 400, which may be either electrical test and measurement device 200 or 300, connected to a DUT 402 via a first cable 420 connected to a port 404 similar to either port 204 or 304 and a second cable 422 connected to a port 406 similar to either port 206 or 306.

[0036] The first cable 420 may include a protection device 450 that is driven by a protection driving circuit of the electrical test and measurement equipment 400 to prevent electrical interference with signals traveling through the first cable 420 .

[0037] Example

[0038] Illustrative examples of the technology disclosed herein are provided below. Embodiments of the technology may include any one or more of the examples described below and any combination thereof.

[0039] Example 1 is a test and measurement device comprising a source configured to output a source signal; a source output configured to output the source signal to a connected cable; a protection drive circuit electrically coupled to the source and configured to receive the source signal and generate a protection drive signal, the protection drive circuit having a gain less than one; and a protection drive circuit output configured to output the protection drive signal to a connected protection device.

[0040] Example 2 is a test and measurement device according to Example 1, wherein the protection drive circuit includes a first operational amplifier, which is electrically coupled to a source and configured to receive a source signal and output a signal based on the source signal; an attenuator circuit, which is electrically coupled to the first operational amplifier and configured to receive a signal from the first operational amplifier and reduce the gain of the signal received from the first operational amplifier; and a second operational amplifier, which is electrically coupled to the attenuator circuit and configured to receive a signal from the attenuator circuit and output a protection drive signal.

[0041] Example 3 is a test and measurement device according to Example 2, wherein the attenuator circuit includes a resistive voltage divider.

[0042] Example 4 is a test and measurement device according to Example 3, wherein the resistor divider includes a first resistor electrically coupled between the first operational amplifier and the second operational amplifier; and a second resistor electrically coupled between the second operational amplifier and ground.

[0043] Example 5 is a test and measurement device according to Example 3, wherein the resistor divider includes a first resistor electrically coupled between the first operational amplifier and the second operational amplifier; and a second resistor electrically coupled between the second operational amplifier and the source.

[0044] Example 6 is a test and measurement device according to any one of Examples 1-5, wherein the guard drive signal is an output in phase with the source signal.

[0045] Example 7 is a test and measurement device according to any of Examples 1-6, wherein the source is a current source or a voltage source.

[0046] Example 8 is a test and measurement device according to any one of Examples 1-7, wherein the test and measurement device is a source measurement unit (SMU).

[0047] Example 9 is a test and measurement device according to Example 2, wherein the first operational amplifier and the second operational amplifier both have 100% negative feedback.

[0048] Example 10 is a method for driving a protection device of a cable connected to a test and measurement instrument, comprising generating a source signal; outputting the source signal to an output terminal configured to be connected to the cable; and generating a protection drive signal based on the source signal by attenuating the source signal using a protection drive circuit having a gain less than one.

[0049] Example 11 is the method according to Example 10, wherein the source signal is either a current source signal or a voltage source signal.

[0050] Example 12 is a method according to either of Examples 10 or 11, wherein the protection drive circuit includes a resistor divider circuit.

[0051] Example 13 is a test and measurement device, including a source configured to generate a source signal; a port configured to be electrically coupled to a cable and a protection device of the cable; and a protection drive circuit configured to output a protection drive signal to the protection device of the cable through the port. The protection drive circuit includes a first operational amplifier configured to receive the source signal and output a signal based on the source signal; an attenuator circuit electrically coupled to the first operational amplifier and configured to receive a signal from the first operational amplifier and reduce the amplitude of the signal received from the first operational amplifier; and a second operational amplifier electrically coupled to the attenuator circuit and configured to receive a signal from the attenuator circuit and output a protection drive signal.

[0052] Example 14 is a test and measurement device according to Example 13, wherein the attenuator circuit is a resistor divider, the resistor divider including a first resistor electrically coupled between the first operational amplifier and the second operational amplifier; and a second resistor electrically coupled between the second operational amplifier and ground.

[0053] Example 15 is a test and measurement device according to Example 13, wherein the attenuator circuit is a resistor divider, the resistor divider including a first resistor electrically coupled between the first operational amplifier and the second operational amplifier; and a second resistor electrically coupled between the second operational amplifier and the source.

[0054] Example 16 is a test and measurement device according to any one of Examples 13-15, wherein the guard drive signal is an output in phase with the source signal.

[0055] Example 17 is a test and measurement device according to any one of Examples 13-16, wherein the source is a current source or a voltage source.

[0056] Example 18 is a test and measurement device according to any one of Examples 13-17, wherein the test and measurement device is a source measurement unit (SMU).

[0057] Example 19 is a test and measurement device according to any one of Examples 13-18, wherein the first operational amplifier and the second operational amplifier each have 100% negative feedback.

[0058] Example 20 is a test and measurement device according to any one of Examples 13-19, wherein the attenuator circuit has a gain less than unity.

[0059] Aspects of the present disclosure are susceptible to various modifications and alternative forms. Specific aspects have been shown by way of example in the accompanying drawings and described in detail above in this document. However, it should be noted that, unless expressly limited, the examples disclosed herein are presented for the purpose of clear discussion and are not intended to limit the scope of the general concepts disclosed to the specific aspects described herein. Thus, the present disclosure is intended to cover all modifications, equivalents, and alternatives of the aspects described according to the accompanying drawings.

[0060] References to aspects, examples, etc. in the specification indicate that the items described may include a particular feature, structure, or characteristic. However, each disclosed aspect may or may not necessarily include the particular feature, structure, or characteristic. Furthermore, unless otherwise specified, such phrases do not necessarily refer to the same aspect. Additionally, when a particular feature, structure, or characteristic is described in conjunction with a particular aspect, such feature, structure, or characteristic may be employed in conjunction with another disclosed aspect, regardless of whether such feature is explicitly described in conjunction with such other disclosed aspect.

[0061] Communication media means any medium that can be used for communication of computer-readable information. By way of example, and not limitation, communication media may include coaxial cables, fiber optic cables, air, or any other medium suitable for communication of electrical, optical, radio frequency (RF), infrared, acoustic, or other types of signals.

[0062] The principles of the invention have been described and illustrated with reference to the illustrated embodiments, it will be appreciated that the illustrated embodiments may be modified in arrangement and detail without departing from such principles, and may be combined in any desired manner. And although the foregoing discussion has focused on specific embodiments, other configurations are also contemplated.

[0063] In particular, even though expressions such as "according to an embodiment of the present invention" are used herein, these phrases generally mean reference to the possibility of embodiments and are not intended to limit the present invention to a specific embodiment configuration. As used herein, these terms may refer to the same or different embodiments that may be combined into other embodiments.

[0064] Therefore, in view of the various permutations of the embodiments described herein, this detailed description and the accompanying materials are intended to be illustrative only and should not be taken as limiting the scope of the invention. Therefore, what is claimed as the present invention is all such modifications as may fall within the scope and spirit of the following claims and their equivalents.

Claims

1. A method for driving a protection device of a cable connected to a test and measurement instrument, comprising: generating a source signal; outputting the source signal to an output terminal configured to be connected to the cable; and generating a protection drive signal based on the source signal by attenuating the source signal using a protection drive circuit having a gain less than one; wherein the protection drive circuit includes: a first operational amplifier configured to receive the source signal and output a signal based on the source signal; an attenuator circuit electrically coupled to the first operational amplifier and configured to receive a signal from the first operational amplifier and reduce the gain of the signal received from the first operational amplifier; and a second operational amplifier electrically coupled to the attenuator circuit and configured to receive a signal from the attenuator circuit and output the protection drive signal.

2. The method according to claim 1, wherein the source signal is either a current source signal or a voltage source signal.

3. The method according to claim 1, wherein the protection drive circuit includes a resistive voltage divider circuit.

4. A test and measurement device, comprising: a source configured to generate a source signal; a port configured to be electrically coupled to a cable and a protection device of the cable; and a protection drive circuit configured to output a protection drive signal to the protection device of the cable through the port, the protection drive circuit including: a first operational amplifier configured to receive the source signal and output a signal based on the source signal; an attenuator circuit electrically coupled to the first operational amplifier and configured to receive the signal from the first operational amplifier and reduce the amplitude of the signal received from the first operational amplifier; and a second operational amplifier electrically coupled to the attenuator circuit and configured to receive a signal from the attenuator circuit and output the protection drive signal.

5. The test and measurement device according to claim 4, wherein the attenuator circuit is a resistive voltage divider, and the resistive voltage divider includes: a first resistor electrically coupled between the first operational amplifier and the second operational amplifier; and a second resistor electrically coupled between the second operational amplifier and ground.

6. The test and measurement device according to claim 4, wherein the attenuator circuit is a resistive voltage divider, and the resistive voltage divider includes: a first resistor electrically coupled between the first operational amplifier and the second operational amplifier; and a second resistor electrically coupled between the second operational amplifier and the source.

7. The test and measurement device according to claim 4, wherein the protection drive signal is output in phase with the source signal.

8. The test and measurement device according to claim 4, wherein the source is a current source or a voltage source.

9. The test and measurement device according to claim 4, wherein the test and measurement device is a source measurement unit, SMU.

10. The test and measurement device according to claim 4, wherein both the first operational amplifier and the second operational amplifier have 100% negative feedback.

11. The test and measurement device according to claim 4, wherein the attenuator circuit has a gain less than unity.

Images