GB2583058A

GB2583058A - A test probe and use of a test probe for measuring a waveform applied to a device under test

Info

Publication number: GB2583058A
Application number: GB1901274.9A
Authority: GB
Inventors: Negri Antoni; Pearson Jonathan
Original assignee: Owlstone Ltd; Owlstone Medical Ltd
Current assignee: Owlstone Ltd; Owlstone Medical Ltd
Priority date: 2019-01-30
Filing date: 2019-01-30
Publication date: 2020-10-21
Anticipated expiration: 2039-01-30
Also published as: GB201901274D0; GB2583058B; GB2583058B8

Abstract

A test probe 100 for measuring a waveform applied to a device under test. The device may be a Field Asymmetric Ion Mobility Spectrometer (FAIMS). The probe comprises a probe body 101, optionally made of conductive metal, first and second signal lines 131, 133, and an electrically insulating spacer 135, 137. A first and second pin 103, 105 are supported, in electrical isolation from each other, by the spacer, and connected electrically to the first and second signal lines respectively. The spacer maintains the two pins at a fixed spatial separation relative to each other and in electrical isolation from the probe body. A further third ground pin 107 may be electrically connected to the body and isolated from the first and second pins. The signal lines may include attenuation resistors and/or variable capacitors (figure 3).

Description

A TEST PROBE AND USE OF A TEST PROBE FOR MEASURING A WAVEFORM APPLIED TO A DEVICE UNDER TEST

[0001] The present invention is directed towards a test probe and use of a test probe, and in particular a test probe and use of a test probe for measuring a waveform applied to a device under test (DUT).

[0002] An example DUT is an ion filter device. A particular example of an ion filter device is a Field Asymmetric Ion Mobility Spectrometer (FAIMS). FAIMS may be used to distinguish charged gaseous molecules according to differences in the speed that the molecules move through a buffer gas under the influence of an oscillating electric field. FAIMS circuits comprise two electrodes in the form of parallel plates which are spaced apart so as to define a channel.

A waveform generator applies radio frequency waveforms across the parallel plates which results in an alternating electric field being applied across the channel. It is desirable to measure the waveform applied across the parallel plates in order to monitor the operation of the FAIMS and perform diagnostic operations, for example. To this end, test probes are provided to create temporary electrical connections the parallel plates of the FAIMS. The test probes are electrically conductively coupled to a measurement device such as an oscilloscope.

[0003] A problem with FAIMS and other similar DUT in terms of monitoring these circuits using test probes is that they act as a capacitive load. This means that any additional capacitance added to the circuit may alter the shape of the waveform to be measured, the peak voltage of the waveform, and the power consumption. The test probe is therefore required to have a low capacitance loading on the DUT. Moreover, the waveforms generally have a high voltage. The waveform voltage may be at least 300 V and even more than 500 V. The test probe is therefore required to be suitable for use with a high voltage. The waveforms may also have a high frequency, e.g. 25 MHz. In addition existing test probes are fragile devices that are susceptible to breaking after repeated use. The probe pins are, in particular, susceptible to twisting and breakage. Moreover, existing test probes can require careful positioning of two separate probe pins on to the two terminals of the DUT which the waveform is going to be measured across.

[0004] It is an object of the present invention to provide a probe for measuring a waveform applied to a test device.

[0005] It is a particular object of the present invention to provide a probe that is able to measure a high frequency, high voltage waveform without altering the DUT. In other words, the waveform is unchanged by coupling the probe to the DUT.

[0006] It is a particular object of the present invention to prove a probe that is more robust and less susceptible to damage.

[0007] It is a particular object of the present invention to prove a probe that facilitates repeated use of the probe for testing the DUT.

[0008] According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

[0009] According to a first aspect of the present invention, there is provided a test probe for measuring a waveform applied to a device under test (DUT). The test probe comprises a probe body containing a first signal line and a second signal line. A spacer is provided in the probe body. The spacer is constructed from an electrically insulating material. A first pin is supported by the spacer and projects from the probe body. The first pin is electrically conductively connected to the first signal line. A second pin is supported by the spacer and projects from the probe body. The second pin is electrically conductively connected to the second signal line. The spacer maintains the first pin and the second pin at a fixed spatial separation relative to one another. The spacer electrically insulates the first pin and the second pin from the probe body.

[0010] The test probe is therefore able to be used as a differential probe. The first pin is able to be connected to a first contact point of the DUT, and the second pin is able to be simultaneously connected to a second contact point of the DUT. In this way, the test probe can measure a waveform applied between the first and second contact points. The first and second pins are supported by the spacer. Importantly, the spacer maintains the first pin and the second pin at a fixed spatial separation relative to one another. Beneficially, the spacer therefore holds the first pin and the second pin at fixed position relative to one another, and prevents the first pin from moving relative to the second pin or vice versa. This facilitates repeated use of the probe for testing the DUT. Moreover, the probe body houses and protects the first and second signal lines and reduces the risk of damage or interference. In addition, the first and second pins are electrically insulated from the probe body (and one another) by the spacer which is constructed from an electrically insulating (low dielectric) material. The spacer may be supported by the probe body and beneficially helps hold the first pin in fixed position spaced apart from the probe body. This reduces the effect of or prevents the probe body for introducing a stray capacitance load on the DUT. In this way, the capacitive influence of the test probe on the DUT is minimised allowing the test probe to be used for measuring a high frequency, high voltage waveform without altering the waveform. The spacer helps maximise the separation between the first and second pins and the probe body, and therefore reduces stray capacitance effects on the DUT by the probe body.

[0011] A ground pin may be supported by the probe body and may project from the probe body. The ground pin may be electrically conductively connected to the probe body, and electrically insulated from the first pin and the second pin by the spacer.

[0012] The first and second pins may be spaced apart from one another by a distance corresponding to the spacing between two test points on the DUT that the probe is intended to measure the waveform across.

[0013] The spacer may comprise a first electrically conductive path by which the first pin is electrically conductively connected to the first signal line. The spacer may comprise a second electrically conductive path by which the second pin is electrically conductively connected to the second signal line.

[0014] The spacer may comprise a first spacer which supports the first pin, and a second spacer which supports the second pin. That is, two separate spacers may be provided for the first pin and the second pin. The spacer for the first pin and the second pin may also be provided as a single, unitary structure. The spacer or spacers may have a planar structure.

The spacer or spacers may extend across the width of the probe body. The spacer or spacers may be positioned towards a lower end of the probe body. The spacer or spacers may be fixed to the probe body by a fixed or removable connection. The spacer or spacers may be completely contained within the probe body. The spacer or spacers may be circuit boards, and in particular printed circuit boards.

[0015] The first pin and/or second pin and/or ground pin may be pogo pins. Pogo pins are beneficial for establishing a temporary connection with the DUT. Typically, a pogo pin is in the form of a cylindrical receptacle containing a spring-loaded pin which, when pressed onto the DUT, establishes a secure contact with the DUT.

[0016] The first signal line provides a path for signals to be transmitted from the first pin to a measurement device such as an oscilloscope. The second signal line provides a path for signals to be transmitted from the second pin to a measurement device such as an oscilloscope. The first signal line may terminate in a first adapter for electrically conductively coupling the first signal line to a first transmission line. The second signal line may terminate in a second adapter for electrically conductively coupling the second signal line to a second transmission line. The first transmission line and/or the second transmission line may couple the first signal line and/or the second signal line to the measurement device. The first adapter for the first signal line and the second adapter for the second signal line may be SMA (SubMinature version A) adapters that are used for forming an electrically conductive coupling with a coaxial cable. The transmission lines may be coaxial cables.

[0017] The probe body may be rigid. The probe body may be constructed from a conductive material. The probe body may be constructed from a rigid metallic material such as brass.

[0018] The probe body may comprise a first body component and a second body component that are coupled together to form the probe body. The second body component may be removably coupled to the first body component by fasteners. The second body component may be a removable cover that can be removed to allow access to the first signal line and the second signal line such as for maintenance.

[0019] The first signal line may comprise a first resistor. The first resistor may be an attenuation resistor. The first signal line may form a resistive divider. The first signal line may have a different structure, for example a capacitive divider.

[0020] The second signal line may comprise a second resistor. The second resistor may be an attenuation resistor. The second signal line may form a resistive divider. The second signal line may have a different structure, for example a capacitive divider.

[0021] The first signal line may comprise a first capacitor. The first capacitor may be a tuning capacitor. The tuning capacitor may have a variable capacitance. The capacitance may be adjusted to tune the bandwidth of the test probe. The probe body may comprise an access hole to allow for the tuning properties of the first capacitor to be adjusted. The first capacitor may be disposed in the first adapter for the first signal line.

[0022] The second signal line may comprise a second capacitor. The second capacitor may be a tuning capacitor. The tuning capacitor may have a variable capacitance. The capacitance may be adjusted to tune the bandwidth of the test probe. The probe body may comprise an access hole to allow for the tuning properties of the second capacitor to be adjusted. The second capacitor may be disposed in the second adapter for the second signal line.

[0023] The waveform may be a radio frequency (RF) waveform. The test probe may be suitable for measuring a waveform having a peak voltage of at least 5 V. The waveform may have a peak voltage with a magnitude of between 0.5 V and 1500 V. The peak voltage of the waveform may have a magnitude of between 100 V and 1500 V, 500 V and 1500 V or 1000 V and 1500 V. The peak voltage of the waveform may have a magnitude of between 0.5 V and 1000 V, 0.5 V and 500 V or 0.5 V and 100 V. The test probe may be suitable for measuring a waveform having a frequency of at least 1 MHz. The waveform may have a frequency of between 1 MHz and 100 MHz, and optionally between 10 MHz and 50 MHz. The waveform may have a duty cycle of less than 50%. The present invention is not limited to any particular frequency of waveform, peak voltage of waveform, or duty cycle of waveform.

[0024] According to a second aspect of the present invention, there is provided the use of a test probe as described above in relation to the first aspect of the invention, for measuring the waveform generated by a waveform generator and applied to a device under test (DUT). The DUT may be an ion filter device. The DUT may be a Field Asymmetric Ion Mobility Spectrometer (FAIMS).

[0025] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which: [0026] Figure 1 shows an test probe according to an example implementation of the present invention; [0027] Figure 2 shows a sectional view of the test probe of Figure 1; [0028] Figure 3 is a simplified schematic diagram for the test probe of Figure 1; [0029] Figure 4 shows the test probe of Figure 1 connected to two transmission lines; [0030] Figure 5 shows a section view of the test probe of Figure 1; and [0031] Figure 6 shows a simplified view of an example a Field Asymmetric Ion Mobility Spectrometer (FAIMS) which may be used as a Device Under Test (DUT).

[0032] Referring to Figure 1, there is shown a test probe 100 in accordance with the present invention. The test probe 100 is used to measure the waveform applied across a device under test (DUT).

[0033] The test probe 100 comprises a probe body 101. The probe body 101 contains a first signal line and a second signal line. The first signal line and the second signal line provide signal paths from the DUT to a measuring apparatus such as an oscilloscope. The first signal line and the second signal line are independent signal paths.

[0034] A first pin 103 is shown projecting from the probe body 101, and in particular is shown projecting from a bottom surface of the probe body 101. The first pin 103 is electrically conductively connected to the first signal line and electrically insulated from the probe body 101.

[0035] A second pin 105 is shown projecting from the probe body 101. The second pin 105 is also shown projecting from the bottom surface of the probe body 101. The first and second pins 103, 105 are spaced apart from one another by a distance corresponding to the spacing between two test points on the DUT that the probe 100 is intended to measure the waveform across. The first and second pins 103, 105 are maintained at this fixed spatial separation. The second pin 105 is electrically conductively connected to the second signal line and is electrically insulated from the probe body 101.

[0036] The probe body 101 houses and protects the first and second signal lines and reduces the risk of damage or interference.

[0037] A ground pin 107 is supported by the probe body and projects from the probe body 101. The ground pin 107 is also shown projecting from the bottom surface of the probe body 101. The ground pin 107 is electrically conductively connected to the probe body 101, and is electrically insulated from the first pin 103 and the second pin 105. In this way, the ground pin 107 is not conductively connected to the first signal line or the second signal line. The ground pin 107 is held, by the probe body 101, in a fixed position spaced apart from the first pin 103 and second pin 105.

[0038] The first pin 103, second pin 105, and ground pin 107 are shown as pogo pins. Pogo pins are beneficial for establishing a temporary connection with the DUT. Typically, a pogo pin is in the form of a cylindrical receptacle containing a spring-loaded pin which, when pressed onto the DUT, establishes a secure contact with the DUT.

[0039] The first signal line terminates in a first adapter 109 for electrically conductively coupling the first signal line to a first transmission line. The second signal line also terminates in a second adapter 111 for electrically conductively coupling the second signal line to a second transmission line. It will be appreciated that the first and second signal lines are coupled to separate transmission lines. The first adapter 109 and second adapter 111 are shown as SMA (SubMinature version A) adapters that are used for forming an electrically conductive coupling with a coaxial cable. The transmission lines coupled the signal lines to the measurement apparatus.

[0040] The probe body 101 is rigid and constructed from a conductive material. The probe body 101 may be constructed from a rigid metallic material such as brass. The probe body 101 is shown as comprising a first body component 113 and a second body component 115 that are coupled together to form the probe body 101. The second body component 115 is removably coupled to the first body component 113 by fasteners 119, 121, 123, 125. The second body component 115 is therefore a removable cover that can be removed to allow access to the first signal line and the second signal line such as for maintenance.

[0041] Referring to Figure 2, there is shown a sectional view of the test probe 100 of Figure 1. The first signal path 131 is shown extending between the first adapter 109 and the first probe 103. The second signal path 133 is shown extending between the second adapter 111 and the second probe 105.

[0042] The first pin 103 is mounted on a first spacer 135. The first spacer 135 is constructed from an electrically insulating (low dielectric) material and comprises an electrically conductive path by which the first pin 103 is electrically conductively connected to the first signal line 131. The first spacer 135 is supported by the probe body 101 and, in turn, supports the first pin 103 and as a result beneficially helps hold the first pin 103 in fixed position spaced apart from the probe body 101. This helps maximise the separation between the first pin 103 and the probe body 101, and thus reduces or minimises capacitance effects of the probe body 101 on the DUT. The first spacer 135 has a planar shape and is a printed circuit board.

[0043] The second pin 105 is mounted on a second spacer 137. The second spacer 137 is constructed from an electrically insulating (low dielectric) material and comprises an electrically conductive path by which the second pin 105 is electrically conductively connected to the second signal line 133. The second spacer 137 is supported by the probe body 101 and, in turn, supports the second pin 105 and as a result beneficially helps hold the second pin 105 in fixed position spaced apart from the probe body 101. This helps maximise the separation between the second pin 105 and the probe body 101, and thus reduces or minimises capacitance effects of the probe body 101 on the DUT. The second spacer 137 has a planar shape and is a printed circuit board.

[0044] The first pin 103 and second pin 105 are therefore supported by the spacers 135, 137 provided within the probe body 101. The spacers 135, 137 is therefore able to hold the first pin 103 and second pin 105 in fixed position and prevent the first pin 103 from moving relative to the second pin 105 or vice versa. In turn, the spacers 135, 137 electrically insulate the first pin 103 and second pin 105 from the probe body 101 and therefore reduce the stray capacitance effects on the DUT.

[0045] It will be appreciated that the first and second spacers 135, 137 may be connected to one another or form a unitary structure. In effect, this means that only one spacer 135, 137 need be provided for the first pin 103 and the second pin 105. The first pin 103 and the second pin 105 may, however, have separate spacers 135, 137.

[0046] The first signal line 131 comprises a first resistor 139. The first resistor 139 is an attenuation resistor 139. The first signal line 131 further comprises a first tuning capacitor (not shown). The first tuning capacitor is positioned within the first adapter 109. An access hole 127 is provided in the probe body 101 to allow for the tuning properties of the first capacitor to be adjusted.

[0047] The second signal line 133 comprises a second resistor 141. The second resistor 141 is an attenuation resistor 141. The second signal line 133 further comprises a second tuning capacitor (not shown). The second tuning capacitor is positioned within the second adapter 111. An access hole 129 is provided in the probe body 101 to allow for the tuning properties of the second capacitor to be adjusted.

[0048] Referring to Figure 3, there is shown a simplified schematic diagram for the first signal line 131 and the second signal line 133. For the first signal line 131, the first attenuation resistor 139 is provided in series between the first pin 103 and the terminal of the first adapter 109. The first signal line 131 therefore resembles a resistor divider. The first terminal of the first tuning capacitor 151 is coupled to the signal line between the terminal of the first adapter 109 and the first attenuation resistor 139. The second terminal of the first tuning capacitor is coupled to ground 155. For the second signal line 133, the second attenuation resistor 141 is provided in series between the second pin 105 and the terminal of the second adapter 111.

The second signal line 133 therefore resembles a resistor divider. The first terminal of the second tuning capacitor 153 is coupled to the signal line between the terminal of the second adapter 111 and the second attenuation resistor 141. The second terminal of the second tuning capacitor 153 is coupled to ground 155.

[0049] The attenuation resistors may have a resistance of between 1 KOhm and 100 KOhm, preferably between 10 KOhm and 50 KOhm Of course, it will be appreciated that the particular values of the resistors will be selected as appropriate by the skilled person based on factors such as the characteristics of the DUT and the waveform to be measured. The present invention is not limited to any particular resistance value for the resistor.

[0050] The capacitors may have a capacitance of between 10 pF and 100 pF. Of course, it will be appreciated that the particular values of the capacitors will be selected as appropriate by the skilled person based on factors such as the characteristics of the DUT and the waveform to be measured. The present invention is not limited to any particular capacitance value for the capacitor.

[0051] Referring to Figure 4, there is shown the test probe 100 with the adapters 109,111 coupled to transmission lines 161, 163. Figure 5 is a sectional view of the test probe 100 in Figure 4 and shows that the signal paths extend from the probes 103, 105 to the signal lines 113, 115.

[0052] Referring to Figure 6, there is shown an example DUT 207. The DUT 207 is an ion filter device 207, and in particular is a Field Asymmetric Ion Mobility Spectrometer (FAIMS) 207. FAIMS 207 may be used to distinguish charged gaseous molecules according to differences in the speed that the molecules move through a buffer gas under the influence of an oscillating electric field.

[0053] The FAIMS 207 comprises two electrodes 208a, 208b in the form of parallel plates 208a, 208b which are spaced apart so as to define a channel 219. A waveform generator (not shown) applies waveforms across the parallel plates 208a, 208b which results in an alternating electric field being applied across the channel 219. In this example, the applied waveforms 211, 213 are asymmetric waveforms, meaning that the duty cycle is less than 50%.

[0054] In an example application, vapour from a sample to be analysed is first ionized, and then passed through the channel 219 between the two parallel plates 208a, 208b. During the periods when the waveform applied across the parallel plates 208a, 208b has a positive polarity, the ions will drift in one direction at a velocity based on the ions individual mobility in that electric field. As the applied waveform reverses in polarity, the ions change direction and speed based on the new electric field conditions. As the mobility of the ions during the two parts of the waveform is rarely equal, there is usually a net drift towards one of the parallel plates 208a, 208b. In the FAIMS 207, this net drift is corrected for by applying an additional DC voltage, known as the compensation voltage, focussing specific ions through the FAIMS 207 to the detector.

[0055] Figure 6 shows that three ions 491, 493, 495 are introduced into the channel 219 between the two parallel plates 208a, 208b. The ions 491, 493, 495 follow a generally saw-tooth trajectory due to the application of the alternating waveform to the two parallel plates 208a, 208b. Due to the different mobility behaviours of the three ions 491, 493, and 495 under the influence of the electric field, and in particular due to how the mobility of the ions 491, 493, and 495 vary with the electric field strength, each of three ions 491, 493, 495 follow a different trajectory in the channel 219. The trajectory of two of the ions 491, 493 collide with the parallel plates 208a, 208b. The ion 495 has the appropriate compensation voltage applied, meaning that its trajectory traverses the channel 219 of the FAIMS 207. By scanning through a range of magnitudes of waveforms applied to the parallel plates 208a, 208b, and a range of compensation voltages, and by recording the ion current at each magnitude/compensation voltage value, the FAIMS 207 can be used to generate information about the different compounds present in a sample.

[0056] The test probe 100 of Figures 1 to 5 is used to measure the waveform applied to the FAIMS circuit 207. In particular, the test probe 100 is positioned such that the first pin 103 contacts the parallel plate 208a, and the second pin 105 contacts the parallel plate 208b so as to measure the applied waveform.

[0057] Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[0058] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0059] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0060] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0061] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS1. A test probe for measuring a waveform of a device under test, the test probe comprising: a probe body containing a first signal line and a second signal line; a spacer provided in the probe body, the spacer being constructed from an electrically insulating material; a first pin supported by the spacer and projecting from the probe body, the first pin being electrically conductively connected to the first signal line; and a second pin supported by the spacer and projecting from the probe body, the second pin being electrically conductively connected to the second signal line, wherein the spacer maintains the first pin and the second pin at a fixed spatial separation relative to one another, and wherein the spacer electrically insulates the first pin and the second pin from the probe body.
2. A test probe as claimed in claim 1, further comprising a ground pin supported by the probe body and projecting from the probe body, the ground pin being electrically conductively connected to the probe body, and electrically insulated from the first pin and the second pin by the spacer.
3. A test probe as claimed in claim 1 or 2, wherein the spacer comprises a first electrically conductive path by which the first pin is electrically conductively connected to the first signal line, and/or wherein the spacer comprises a second electrically conductive path by which the second pin is electrically conductively connected to the second signal line.
4. A test probe as claimed in any preceding claim, wherein the spacer comprises a first spacer which supports the first pin, and a second spacer which supports the second pin.
5. A test probe as claimed in any preceding claim, wherein the first signal line comprises a first attenuation resistor, and/or wherein the second signal line comprises a second attenuation resistor.
6. A test probe as claimed in claim 5, wherein the first attenuation resistor and/or the second attenuation resistor has a resistance of at least 1 KOhm.
7. A test probe as claimed in any preceding claim, wherein the first signal line comprises a first capacitor, and/or wherein the second signal line comprises a second capacitor.
8. A test probe as claimed in claim 7, wherein the first capacitor and/or the second capacitor is a variable capacitor.
9. A test probe as claimed in claim 8, wherein the probe body comprises at least one access hole for accessing the first capacitor and/or the second capacitor such the capacitance of the first capacitor and/or the second capacitor may be adjusted.
10. A test probe as claimed in any of claims 7 to 9, wherein the first capacitor and/or the second capacitor has a capacitance of at least 10 pF.
11. A test probe as claimed in any preceding claim, wherein the first signal line terminates in a first adapter for coupling the first signal line to a first transmission line, and/or wherein the second signal line terminates in a second adapter for coupling the second signal line to a second transmission line.
12. A test probe as claimed in claim 11, wherein the first signal line terminates in the first adapter, wherein the first signal line comprises a first capacitor, and wherein the first capacitor is provided within the first adapter, and/or wherein the second signal line terminates in the second adapter, wherein the second signal line comprises a second capacitor, and wherein the second capacitor is provided within the second adapter.
13. A test probe as claimed in any preceding claim, wherein the probe body is a rigid metallic body, and optionally wherein the probe body comprises a removable cover.
14. Use of a test probe as claimed in any preceding claim, for measuring the waveform applied to a device under test.
15. Use of a test probe as claimed in claim 14, wherein the device under test is an ion filter device, and optionally a Field Asymmetric Ion Mobility Spectrometer (FAIMS).