Ac-coupled system for particle detection

Abstract

A system and method for detecting high-energy particles, the system comprising a detector unit and an AC coupler, the detector unit having a differentially biased detector having a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage, and the AC coupler having capacitively coupled input and output positive and negative terminals. The capacitive coupling is embedded in a transmission line structure, with the input positive terminal coupled to the first terminal of the detector and the input negative terminal coupled to the second terminal of the detector. Some advantages include reducing or eliminating resonance between the storage capacitor inductance and the detector capacitor, ringing due to common-mode excitation from the coaxial cable and the AC coupler circuitry, and undershoot and ringing due to reflections of low-frequency components blocked by the remotely mounted AC coupler.

Description

Technical Field

[0001] This published text generally relates to mass spectrometers. Background Technology

[0002] Some known time-of-flight (TOF) mass spectrometers operate by accelerating a pulse of ionized molecules of mass m through an electric field E and detecting the velocity of the accelerated molecules by measuring the propagation delay of the molecules after they have traveled a known distance through a field-free region. For a given ionization charge z, the velocity of the accelerated molecules varies with the square root of m / z. This variation in propagation time allows for the development of systems to analyze the mass and abundance of each component in complex molecular mixtures.

[0003] Depending on the properties of the molecule being analyzed, it can sometimes be helpful to prepare the original molecule as either a positively or negatively charged ion. In the most general case, it is desirable to construct an instrument that can rapidly switch between positive and negative ion modes, so that the measurement results include the properties of both ion polarities that are essentially present simultaneously in the same sample.

[0004] Several types of detectors are available for detecting charged ions. For all types of detectors, it is important that the detector input is at the same potential as the field-free region. If the target potential differs significantly from the field-free potential, the ions will undergo additional acceleration or deceleration, which may compromise the integrity of timing measurements.

[0005] In a non-limiting example, ions in a TOF mass spectrometer are supplied to an ion accelerator at approximately 0 volts. For positive ions, the accelerator subjects the ions to a potential of -7000 volts, after which the ions are allowed to fly freely within a tube where all potentials are -7000 volts to create a field-free environment for the propagation of the ions. The detector inlet plane is typically a microchannel plate (MCP) or grid maintained at -7000 volts.

[0006] For negative ions, the accelerating voltage is reversed to +7000 volts. In this case, the detector detection plane must also be set to +7000 volts.

[0007] The detector's output is typically transmitted to an analog-to-digital converter (ADC) that operates relative to ground via a 50-ohm cable.

[0008] One type of detector has an output that is electrically isolated from the detection plane. An example of such a detector is a microchannel plate that converts incoming ions into amplified electron pulses, which are then accelerated to strike a fluorescent material. The crystal converts electrons into photons through a fluorescence process. These photons are then collected and transmitted to a photomultiplier element to generate the final electrical pulse. Because of the conversion to an intermediate optical signal, the photomultiplier output remains ground-referenced even when the MCP input voltage dynamically switches from -7000 volts to +7000 volts.

[0009] Another type of detector is not electrically isolated because it operates using electrons all the way to the detector output. In this type of detector, the output signal changes by + / - 7000V when the ion detection polarity is reversed. An example of this type of detector is a combination of an MCP followed by an electron accelerator / focuser, and then a high-speed detection diode. A single ion is converted into an amplified electron pulse by the MCP, accelerated to higher energies by an internal +7000V field, and then focused onto the detection diode. Through a mechanism known as “bombardment gain,” the high-energy electrons generate multiple electron-hole pairs in the diode and are swept out of the diode by a small reverse bias of approximately 300V.

[0010] For instruments that measure only positive ions, ions can be accelerated at -7000 volts, converting them into electrons at the MCP, and then these electrons are accelerated again at +7000 volts to bombard the detection diode. In such a system, the diode output can be safely connected to a ground-referenced ADC. However, when switching to negative ion mode, the initial acceleration must be +7000 volts. The accelerated ions arrive and generate secondary electrons at the MCP. To provide bombardment gain, these secondary electrons must still be accelerated to the final diode detector at +7000 volts. In this case, the diode output will be +14000 volts and may no longer be safely connected to a ground-referenced ADC.

[0011] Among available detectors, the Class II non-electrically isolated detectors currently have the fastest available pulse response, with full width at half maximum (FWHM) pulse widths ranging from 500 to 800 picoseconds. Detectors in the Class I DC-isolated detectors combine MCP response, fluorescent material decay time, and photomultiplier tube response time, and typically have pulse widths greater than 1000 picoseconds.

[0012] While capacitor coupling to remove DC offset is a common circuit technique, it is difficult to implement without significantly distorting the shape of the detected pulse. The rated voltage of commonly available ceramic coupling capacitors is limited to approximately 4kV. This means that a coupler requiring a 14kV margin would need to have 6 to 8 capacitors in series in both the signal and ground branches of the circuit. Connecting so many capacitors in series creates a significant amount of inductance, which leads to pulse ringing.

[0013] U.S. Patent 9,590,583 (the contents of which are incorporated herein by reference in their entirety) illustrates how to embed a series combination of capacitors into a 3D transmission line structure such that the frequency response of the coupler is very flat throughout the high-pass portion of the spectrum. While this structure performs much better than other prior art, it still exhibits pulse ringing and echo aberrations in practical applications.

[0014] These aberrations are due to three main reasons: 1) the parasitic inductance inside the detector charge storage capacitor resonates with the detector capacitor, causing pulse ringing and undershoot; 2) the common-mode excitation of the transmission line interconnect ground shield with respect to the surrounding metal conductors produces delayed reflections, which are converted into parasitic delayed differential-mode signals; and 3) differential low-frequency components, which do not pass through the AC coupler and are reflected back to the high-impedance detector, and subsequently reflected back into the differential signal as a baseline offset of the delay.

[0015] In some implementations, this disclosure modifies the detector bias circuit topology to mitigate some or all of these aberrations.

[0016] Single-ended detector

[0017] A typical configuration used in the prior art is shown in Figure 1. The bias source is represented by battery 101. The bias voltage is filtered and current-limited by resistor 102 and capacitor 103, and connected to one terminal of detector 100. The other terminal of detector 100 is connected to the input of transmission line 104 for transmission to load resistor 106. The value of load resistor 106 is equal to the impedance of transmission line 104 to prevent any energy from being reflected back into the transmission line. Furthermore, resistor 106 converts the detector current pulse into voltage 105 for further processing.

[0018] In the prior art, all voltages are typically referenced to common ground 107.

[0019] AC coupling system for bipolar ion measurement

[0020] In ion detection applications, such as those practiced in mass spectrometry, the ion beam is typically terminated at one or the other terminal of a current detector 100. In such applications, the voltage at the detection terminal is critical. If the beam is positively charged, a negatively biased detector will attract and accelerate particles in the beam. A positively charged detector will repel or decelerate particles in the beam. Furthermore, the precise voltage at the detection surface will modify the field near the detector and may alter the beam focus or the spatial distribution of ions within the beam.

[0021] In the prior art, the terminating resistor 106 is implemented within a measuring device (such as a high-speed oscilloscope), and the terminating resistor is typically referenced to ground or zero volts. Therefore, the circuit of Figure 1 requires the active detection terminal to have a specific voltage, which is determined by the detector bias requirements.

[0022] In dual-ion polarimetric mass spectrometry systems, rapid switching between positive and negative ion detection is desirable. For operator convenience, connecting the ion source to ground is standard practice. If positive ions are to be measured, a series of ion lenses is used to attract and focus the beam toward detector 100. Each lens in the sequence is typically biased with a more negative voltage than the preceding one to successively attract and focus the beam onto the detector. If negative ions are to be measured, a series of ion lenses is used to attract and focus the beam toward detector 100. Each lens in the sequence is typically biased with a more positive voltage than the preceding one to successively attract and focus the beam onto the detector. In such a system, the detection surface of detector 100 is typically near -10,000 volts for detecting positive ions and near +10,000 volts for detecting negative ions.

[0023] One approach is to modify the prior art of Figure 1 to allow the detection surface voltage of detector 100 to vary independently with respect to the voltage of terminating resistor 106 in positive / negative tens of kilovolts, to accommodate the ion beam transmission voltage requirements for both positive ion generation and detection and negative ion generation and detection.

[0024] U.S. Patent 9,590,583 partially addresses this problem by using a transmission line AC coupler to: 1) transmit current pulses with very wide bandwidth and low ringing, and 2) block the DC voltage of the detector from reaching the measuring device 106.

[0025] Figure 2 illustrates a modified prior art system using the AC coupler of U.S. Patent 9,590,583, which allows the voltage at the detection surface of detector 100 to be set independently of the voltage of terminating resistor 106. Two bias supplies provide control over the voltage at the detection surface of detector 100. Bias generator 201 operates in the range of 0 volts to 10,000 volts. Bias generator 202 operates in the range of 0 volts to -10,000 volts. Switch 203 can be configured to select either bias generator 201 or 202 to allow the detector to operate with either a positive or negative ion beam. AC coupler 200 blocks the detector DC bias from reaching the input resistor 106 of the measuring device. Resistor 204 is required to provide a DC loop because the AC coupler blocks current through load resistor 106.

[0026] The circuit in Figure 2 isolates the several kilovolt bias voltages 201 and 202, preventing them from reaching the detector input resistor 106; however, in actual operation, three different types of pulse aberrations are evident:

[0027] Aberration 1: Resonance between the inductance of the storage capacitor and the capacitance of the detector

[0028] The first aberration is due to the non-ideal nature of the charge storage capacitor 103 and the detector 100. A simplified form of the circuit in Figure 2, with a more accurate diode and capacitor model, is shown in Figure 3.

[0029] The actual capacitor 103 always includes a series parasitic inductance 300. Similarly, the actual detector always has a parasitic parallel capacitance 301. In the case of a diode detector, the capacitance term is equal to the parallel combination of the diode junction capacitance and the diode package capacitance.

[0030] The circuit in Figure 3 models the transient pulse characteristics shortly after the initial pulse. The detected particle generates an initial current pulse 302, followed by an undershoot 303 and an overshoot 304, which are caused by the parasitic inductance 300 of the capacitor 103 connected in series with the small detector capacitor 301. Based on the parasitic values ​​of the circuit components used, those skilled in the art can easily calculate the ringing period and the degree of both damping and overshoot.

[0031] Due to this ringing defect, particles arriving shortly after another particle will find errors in their measured amplitude, the amount of which is the amount of ringing that overlaps with the previous particle.

[0032] Aberration 2: The common-mode excitation of the cable is converted into a differential signal.

[0033] Figure 4 illustrates the second aberration of the prior art. A simplified circuit is shown in sufficient detail to describe the problem. When the detector circuit floats to + / - 10,000 volts, the high-frequency circuitry is no longer directly connected to ground. This is schematically illustrated by adding resistor 401 to show the output impedance of bias generators 201 and 202. For bias generators in the 10,000-volt range, resistor 401 is typically in the range of 1 to 10 megohms. Although the detector circuit floats away from ground at high DC impedance, parasitic capacitances from the individual nodes to ground 107 are unavoidable. For illustrative purposes, Figure 4 shows one such parasitic capacitance 400 associated with the node of the center conductor of the drive transmission line 104. While this particular node was chosen for illustrative purposes, the problem to be described would be similar if an excessively large capacitance were chosen at some other node.

[0034] The transmission line is shown in cross-section to emphasize that the actual transmission line supports two propagation modes. The first mode is the difference between the current 402 flowing on the inner conductor and the current 403 flowing on the inner side of the coaxial shield. The second mode is the difference between the current 404 flowing on the outer side of the coaxial shield and the current 405 flowing on the ambient ground. When the detector 100 generates a current pulse Id, a portion of the current Ic is diverted through the parasitic capacitor 400. The current delivered to the center conductor is then Id-Ic. The currents 402 and 403 on the conductor are purely differential and flow between the inner conductor and the inner side of the coaxial shield. Therefore, the current 403 returning from the inner surface of the transmission line must also be equal to Id-Ic. To establish current balance, the current Ic through the parasitic capacitor 400 flows about ground 107 on the outer conductor of the coaxial cable (current 404) and returns through the shared ground (current 405).

[0035] For circuits without an AC coupler, the ground current loop consisting of the current 404 on the outer conductor of the coaxial cable and the current 405 returning through the ambient ground is negligible because it flows in a closed loop outside the signal path. The impedance of a typical ground plane is so low that even very high currents only produce a few millivolts of disturbance in a low-impedance sea of ​​electrons.

[0036] However, in a system with AC coupler 200, the output of transmission line 104 has an unbalanced output due to an open circuit in the outer shield conductor. AC coupler 200 with differential transformer 406 is shown to model the fact that it is designed to support only pure differential mode current. At the input of AC coupler 200, the initial current pulse produces a center conductor current 407 equal to Id-Ic, but the sum of the internal and external shield currents 408 has an amplitude of Id. At the coupled differential structure 406, the common-mode component is visible at high impedance and is therefore reflected from AC coupler 200 and propagates back towards detector 100. When the reflected wave arrives, a portion of it is converted back to a differential signal by parasitic capacitor 400, which is reflected from the high impedance of the detector, thus producing an echo 411, which is delayed by the round-trip propagation of the original pulse through transmission line 104. Depending on the degree of circuit imbalance, only a portion of the wave is converted to differential mode. The remaining common-mode component will also be reflected again, thus producing a second echo 412. In practice, this defect causes the echo pulse sequence for each detection event to decay exponentially.

[0037] Aberration 3: When the AC coupler is installed remotely, or when the AC coupler itself is large enough to cause a delay, low-frequency differential mode reflection causes ringing, and the delay is not short compared to the transmission pulse width.

[0038] Referring to U.S. Patent 9,590,583, AC couplers with an accurate impedance Z0 (typically in the 50 ohm range) that is flat in the high-frequency band can be manufactured. However, by definition, AC couplers must increasingly block frequencies below a defined cutoff frequency.

[0039] This loss in the low-frequency components leads to several aberrations in the system. First, it introduces a tilt in the step response of the AC coupler, or equivalently, a reference offset in the impulse response, which is exponentially corrected along with the time constant, which is inversely proportional to the cutoff frequency of the AC coupler. This behavior is standard for any AC coupler and can be mitigated to some extent by making resistor 204 as large as possible to increase the circuit time constant. Second, more troublesome problems arise when the AC coupler is mounted at a distance from the detector using transmission line 104. Figure 5 shows a simplified single-ended equivalent circuit illustrating the aforementioned problems.

[0040] When the length of transmission line 104 is zero, a typical AC-coupled waveform 500 is transmitted to terminal 106. When the length of transmission line 104 is set such that the transmission line delay is greater than the detector pulse width, waveform 501 is generated. As the delta pulse current propagates to the output, it charges the capacitor in AC coupler 200. This voltage is subtracted from the output signal at node 105, resulting in undershoot 502. Furthermore, the voltage step caused by the charging of capacitor 200 causes reflection on the transmission line. After a time equal to the propagation time of transmission line 104, the positive voltage step reflected from capacitor 200 returns to high-impedance detector 100. The positive pulse voltage then doubles and is reflected back to the load. After a time equal to twice the delay of transmission line 104, positive pulse 503 returns to the load, partially resetting the initial undershoot of the signal. Of course, the reflected pulse also charges capacitor 200, resulting in a second reflection, causing rapid convergence through an exponentially decaying cascade of exponential steps.

[0041] Overview

[0042] This document describes a system and method for detecting particles. The system includes: a detector unit having a differentially biased detector having a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage; and an AC coupler for coupling the detector to a measuring device, the AC coupler having a capacitively coupled positive input / output terminal and a capacitively coupled negative input / output terminal. In some embodiments, the capacitive coupling of the positive and negative input / output terminals is embedded in a transmission line structure having a differential impedance Z0, the positive input terminal being coupled to the first terminal of the detector, and the negative input terminal being coupled to the second terminal of the detector.

[0043] In some implementations, the capacitive coupling between the positive and negative input / output terminals of the AC coupler is the sole detector energy storage component.

[0044] In some implementations, a pulse compensation network is included that is connected in parallel with the detector.

[0045] This document also describes a system and method for detecting particles, the system comprising: a detector having a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage; and an AC coupler for coupling the detector to a measuring device, the AC coupler having capacitively coupled positive input / output terminals and capacitively coupled negative input / output terminals. In some embodiments, the capacitive coupling of the positive and negative input / output terminals is embedded in a transmission line structure having a differential impedance Z0, the positive input terminal being coupled to the first terminal of the detector and the negative input terminal being coupled to the second terminal of the detector; and the capacitive coupling of the positive and negative input / output terminals of the AC coupler is the sole energy storage component of the detector. In some embodiments, a pulse compensation network is included in parallel with the detector.

[0046] This document also describes a system and method for detecting particles, the system comprising: a detector having a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage; a pulse compensation network connected in parallel with the detector; and an AC coupler for coupling the detector to a measuring device, the AC coupler having capacitively coupled positive input / output terminals and capacitively coupled negative input / output terminals. In some embodiments, the capacitive coupling of the positive and negative input / output terminals is embedded in a transmission line structure having a differential impedance Z0, the positive input terminal being coupled to the first terminal of the detector, and the negative input terminal being coupled to the second terminal of the detector. Attached Figure Description

[0047] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the implementation and, together with the description of exemplary embodiments, serve to explain the principles and implementation of the implementation.

[0048] In the attached diagram:

[0049] Figure 1 shows a prior art single-ended system for particle detection;

[0050] Figure 2 shows a prior art AC coupling system for bipolar ion measurement;

[0051] Figure 3 is a simplified form of the prior art circuit of Figure 2 with a more accurate diode and capacitor model, which depicts ringing caused by the inductance of the charge storage capacitor.

[0052] Figure 4 shows a simplified circuit problem related to the conversion of common-mode excitation of cables into differential signals in the prior art;

[0053] Figure 5 shows a simplified single-ended equivalent circuit, illustrating the reflection problem from prior art AC couplers;

[0054] Figure 6 This is a schematic diagram of a system 600 for measuring particles and using differential bias, pulse compensation, and charge storage capacitors for eliminating charge, according to certain embodiments;

[0055] Figure 7 This is a schematic diagram of a system for measuring particles using a compensation network, according to certain implementation schemes;

[0056] Figure 8 This is a schematic diagram of a system for measuring particles using differential bias, according to certain implementation schemes; and

[0057] Figure 9 This is a schematic diagram of a system for measuring particles according to certain embodiments, which eliminates the use of charge storage capacitors. Detailed Implementation

[0058] The following description is illustrative only and is not intended to be limiting in any way. Other embodiments will readily come to mind for those skilled in the art from this disclosure. Implementations of example embodiments, as shown in the accompanying drawings, will be referenced in detail. Throughout the drawings and the following description, the same reference numerals will be used to refer to the same or similar provisions whenever possible.

[0059] In the following description of exemplary embodiments, references to "one embodiment," "an embodiment," "an example embodiment," "certain embodiments," etc., indicate that the described embodiments may include specific features, structures, or characteristics, but each embodiment need not necessarily include said specific features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same embodiment. Further, when a specific feature, structure, or characteristic is described in connection with an embodiment, it is understood that implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether or not explicitly described, is within the knowledge of those skilled in the art. When used herein, the term "exemplary" means "serving as an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[0060] For clarity, not all conventional features of the embodiments described herein are shown or described. It will be understood that in the development of any such practical embodiment, many implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with application and business-related regulations, and these specific goals will vary from implementation to implementation and developer. Furthermore, it will be understood that such development work may be complex and time-consuming, but will remain a routine engineering task for those skilled in the art who benefit from this disclosure.

[0061] In this document, unless otherwise explicitly stated or indicated by the context, "or" is inclusive rather than exclusive. Therefore, in this document, unless otherwise explicitly stated or indicated by the context, "A or B" means "A, B, or both." Furthermore, unless otherwise explicitly stated or indicated by the context, "and" is both joint and separate. Therefore, in this document, unless otherwise explicitly stated or indicated by the context, "A and B" means "A and B jointly or separately."

[0062] Figure 6 This is a schematic diagram of a system 600 for measuring particles according to certain embodiments. System 600 typically includes: a differential bias detector 610 to which particles of interest are directed; a measuring device 614 for receiving the output signal of the detector; and an AC coupler 616 for directing the signal of interest to the measuring device. As an example, applications requiring the analysis of particles (such as photons, electrons, charged atoms, or charged molecules) can use detector 610 to convert the arrival of these particles into current pulses. The resulting current pulses can then be converted into voltages that can be digitized and processed at measuring device 614 to extract information about the properties of the particles themselves.

[0063] The width, area, height, and arrival time of the detector current pulse all encode the analog properties that are expected to be measured as accurately as possible. Mass spectrometry is an example of this application, where the current pulse generated by the detector encodes information in both amplitude and time. In a typical system, the arrival time of the pulse encodes the mass-to-charge ratio of the particles, and the amplitude of the current pulse encodes the abundance or number of such particles arriving at a given time. Based on these two parameters, the measuring device 614 can calculate the mass spectrum of a chemical sample, giving the abundance and mass-to-charge ratio of each compound present in the sample.

[0064] Examples of current output detectors 610 used in such applications include, but are not limited to: 1) a Faraday cup ion detector that receives bursts of charged particles and converts them into current as a function of time; 2) a photomultiplier device having multiple multiplier electrodes for charge multiplication; 3) a microchannel plate device that multiplies charge through multi-hop electron impacts within cylindrical apertures; and 4) a semiconductor diode device that may be combined with an internal avalanche gain multiplication structure.

[0065] Although the description herein uses a semiconductor diode as an exemplary detector, it will be apparent to those skilled in the art that any other class of current detectors with substantially similar performance improvements can replace the diode detector. In the accompanying drawings, detector 610 is indicated by the general current source notation to clarify that all aspects of the described arrangement can be applied equally well to any detector that generates a current pulse output. Furthermore, although charged ions are described, it should be understood that particles striking the detector (such as photons, electrons, or other particles) can also be detected using all the advantages of the techniques described for charged ions.

[0066] The system 600 shown includes a detector 610 as part of a detector unit 612, which is coupled to a measuring device 614 using an AC coupler 616 and by means of transmission line segments 618A and 618B (collectively referred to as 618), which may be coaxial cables. In this exemplary configuration, the AC coupler 616 has input / output positive terminals capacitively coupled to each other and input / output negative terminals capacitively coupled to each other. Coupling capacitors C1 and C2 are embedded in a transmission line structure having a differential impedance of value Z0. It should be noted that although shown as a pair of capacitors C1 and C2 in FIG. 600, in some embodiments, each of capacitors C1 and C2 may consist of a single capacitor or multiple capacitors (e.g., eight capacitors) distributed in the coupled transmission line. Transmission line segments 618A and 618B are optional and, when not employed, may be referred to as having zero length for the purposes of discussion and analysis herein. In some embodiments, one or both of transmission line segments 618A and 618B may comprise multiple segments connected in series. As shown, a first terminal of detector 610 is connected to a positive bias voltage, for example, provided by battery 101, and is connected to the positive inner conductor of transmission line segment 618A; while a second terminal of detector 610 is connected to a negative bias voltage, for example, provided by battery 101, and is connected to the negative outer conductor of transmission line segment 618A. Similarly, the positive inner conductor of segment 618B is connected to the load resistor 620 of measuring device 614; and the negative outer conductor of segment 618B is grounded at 107. It will be understood that the terms “negative” and “positive” are used for convenience to refer to two different voltage levels or components connected to two different voltage levels, and should not be construed as imposing any other electrical or structural limitations.

[0067] System 600 reduces or eliminates prior art pulse defects through a combination of topology and component changes. The first prior art problem of ringing caused by the parasitic inductance of the charge storage capacitor (103 in Figures 1 and 2) is addressed by eliminating the non-compliant charge storage capacitor. Instead, the input capacitor of AC coupler 616 is used for charge storage. Incorporating capacitors C1 and C2 into the transmission line structure of AC coupler 616 (which in some embodiments is the sole energy storage component) allows parasitic inductance to be absorbed into the transmission line. Because the high pass impedance of AC coupler 616 is well matched to the transmission line impedance of the connecting coaxial cable 618 and the termination 620, there is no residual inductance causing overshoot or ringing.

[0068] A second prior art problem with common-mode excitation is caused by an imbalance in the current flowing to ground at the two inputs of the transmission line (104 in Figures 1 and 2), as illustrated by parasitic capacitor 301 in Figures 3 and 4. A typical reason for a large capacitance to ground at a node is due to floating circuitry, which conventionally connects many components to ground 107. The ground node will comprise a large area of ​​copper traces and will include interconnect capacitances of all distributed components connected to that node. To eliminate this problem, detector 610 in system 600 is connected directly to transmission line 618 (or directly to one or more optional transmission line connectors, not shown) with minimal interconnect capacitance. All remaining circuit capacitances for voltage sources 201, 202, and selector switch 203 are isolated by using differential bias provided by resistors 601 and 622. Therefore, a second resistor 622 is introduced instead of a single bias resistor 102 (Figures 1 and 2). In prior art circuits, resistor 102 is typically a low value, set just high enough to provide a protective current limiting effect. In system 600, the differential biasing function of resistors 601 and 622 also provides a time constant setting function for resistor 204 (Figure 2). Resistor 603 does not participate in the recharge time constant because it is in series with capacitor (602). The DC voltage of charge storage capacitors C1 and C2 is recharged only by resistors 601 and 622. In practice, the differential biasing resistors 601 and 622 of system 600 will be set to approximately half the desired value of resistor 204. Resistors 601 and 622 will have large values ​​(e.g., in the range of approximately 10K ohms to 100K ohms). For example, resistor 603 will be equal to the characteristic impedance of transmission line 618a or, most typically, 50 ohms. In some embodiments, the transmission line may have different impedances in the range of 5 ohms to 300 ohms, but 50 ohms is an impedance readily available in commercially available coaxial cables and connectors. Lower impedance may result in a faster detector pulse because it makes the time constant lower through diode parasitic capacitance.

[0069] It should be noted that the term differential bias, as used herein, refers to the use of resistors (e.g., resistors 601, 622) to connect detector 610 to an energy source such as battery 101. A more general definition of the term applicable herein is biasing the device (in this case detector 610) by non-zero impedance at both terminals, rather than connecting one terminal to a fixed DC voltage, such as ground. The two resistors (601, 622) preferably have equal values ​​to maintain optimal balance of drive impedances. In the arrangement described herein, much of the benefit likely comes from the isolation effect of the resistors, even if they are not well matched, because parasitic capacitances play a significant role, and the bias can still be considered “differential” even if it is unbalanced. Placing the resistors as close to the detector as possible further provides additional advantages—e.g., reducing stubs at high-speed nodes. In some embodiments, instead of resistors, it may be feasible to use ferrite materials (or combinations of materials) with sufficient losses at all frequencies of interest to create an effective common-mode choke.

[0070] The third prior art problem of ringing caused by the remote connection of the AC coupler is addressed by a pulse compensation network consisting of a series combination of capacitor 602 and resistor 603. To minimize ringing reflected from the remote AC coupler, resistor 603 is substantially equal to the characteristic impedance of transmission line 618 and terminating resistor 620. When the time delay through transmission line 618 is zero, and the sum of resistors 601 and 622 is much greater than the resistance of load resistor 620, the optimal value of compensation capacitor 602, used to compensate for the output voltage drop caused by AC coupler 616, is substantially equal to the series capacitance of the AC coupler. This value ensures that the voltage drop across AC coupler 616 matches the voltage drop across compensation capacitor 602 because the circuit branches including these components have equal impedances, and the signal voltages applied across them are equal. When the AC coupler 616 is connected to the drive voltage at node 604 using a non-zero time delay transmission line 618, the rising drive voltage at node 604 is no longer perfectly aligned with the rising voltage drop across the AC coupler, thus eliminating the error degradation. Reducing the value of the compensation capacitor 602 accelerates the rise of the drive voltage at 604, thereby significantly improving the timing alignment of the compensation voltage with the voltage drop across the AC coupler 616.

[0071] In practice, the exact capacitance that minimizes ringing depends on the length of the transmission line: the longer the transmission line, the more the optimal capacitance must be reduced from the ideal zero-length value. It should be noted that the network is not a broadband termination (where capacitor 602 is typically set to an arbitrarily large value). A broadband termination in practice would typically impair the long-time constant characteristics of a network set by large-value bias resistors 601 and 622. Instead, the value of capacitor 602 is precisely chosen to minimize ringing of the interconnect cable 618 for a specific length. More complex series-parallel networks of passive components can be generated to provide higher-order compensation; however, such additional circuitry may be difficult to implement without introducing further aberrations, and a simple two-element parallel network of capacitor 602 and resistor 603 is feasible.

[0072] Figure 6 The circuitry addresses the three aforementioned drawbacks in AC-coupled detector systems: 1) resonance between the storage capacitor inductance and the detector capacitor; 2) ringing due to common-mode excitation from the coaxial cable and AC coupler circuitry; and 3) undershoot and ringing due to reflections of low-frequency components blocked by the remotely mounted AC coupler. It allows current-source output particle detectors to be used in bipolar mode with, for example, the AC coupler described in U.S. Patent 9,590,583, without introducing ringing artifacts that would compromise the fidelity of the output pulse. Furthermore, the ability to remotely mount the AC coupler allows the detector to be manufactured separately from the AC coupler if needed. Additionally, when the detector reaches the end of its lifespan, there is no need to replace the AC coupler separately, thus reducing maintenance costs. Alternatively, the AC coupler can be integrated into the detector itself to minimize the number of components and cables.

[0073] Thus, as detailed below, the system 600 for measuring particles offers several advantages. One advantage is that it provides an improved mechanism for charge storage capacitance that is superior to existing technologies. Existing technologies use a single capacitor 103 (Figures 1 and 2) with a parasitic inductance 300 (Figure 3), which results in series resonance between the parasitic inductance 300 and the detector capacitor 301. System 600 replaces the single-ended charge storage capacitor 103 with a pair of coupling capacitors C1, C2 in AC coupler 616. By coupling the capacitors in pairs in an inductive manner, the parasitic inductance can be incorporated into the transmission line, such that the system inductance is canceled out by the parallel capacitance of the coupled transmission line structure, resulting in a broadband impedance of Z0 without the ringing or resonance effects of existing technologies. As explained above, although represented as a pair of capacitors C1, C2 in Figure 600, in some embodiments, capacitors C1, C2 may comprise multiple capacitors (e.g., eight capacitors) distributed throughout the coupled transmission line. To prevent pulse integrity from being distorted by interconnect inductance, two capacitor chains are incorporated into the differential transmission line, so that the parasitic inductance is canceled out by mutual capacitance and is close to the constant surge impedance of Z0 of the connector and other wiring.

[0074] Another advantage of the system 600 for measuring particles is that it replaces the single-ended bias structure of the prior art, consisting of resistor 102 and charge storage capacitor 103, with a balanced differential bias network consisting of two matching resistors 601 and 622. Matching resistors 601 and 622 isolate critical nodes of detector 610 from the power supply circuitry and minimize the edge capacitance of the circuit traces carrying high-speed detection pulses. By minimizing and balancing the parasitic capacitance at the input of transmission line 618A, common-mode current is minimized, which reduces or eliminates echoes and ringing on the received pulses.

[0075] Another advantage of the system 600 used for particle measurement is that substantial ringing can occur on the voltage 624 of the terminating resistor 620 when the AC coupler 616 is mounted away from the detector via a non-zero length transmission line 618. This is because the low-frequency components of the detector output pulse are blocked and reflected by the high-pass filter characteristics of the AC coupler 616. A pulse compensation network consisting of resistor 603 and capacitor 602 is added in parallel across the detector 610, substantially reducing the pulse ringing caused by this reflection. The pulse compensation network is not a typical broadband terminating network that would allow capacitor 602 to have an arbitrarily large value to provide broadband impedance matching. Instead, capacitor 602 is specifically tuned to be substantially equal to the series capacitance of the AC coupler 616. When the transmission line 618 is zero length, the optimal value of capacitor 602 is exactly equal to the series capacitance of the AC coupler. As the transmission line 618 is lengthened, the optimal value of capacitor 602 decreases with length, but for practical systems, it is typically within twice the optimal zero-length value.

[0076] In some embodiments, for convenience, the AC coupler 616 can be mounted away from the detector. In some embodiments, the AC coupler 616 may be from a different manufacturer than the detector unit 612.

[0077] A key advantage of the system 600 for measuring particles is that it allows the detection surface of detector 610 to vary by more than + / - 1 kilovolt with respect to the input terminal resistor 620 of the measuring device. This allows the detection system to be used in mass spectrometers that dynamically switch between positive and negative ion detection modes. This can be achieved by selectively switching switch 203 between voltage sources 201 and 202 with opposite polarities.

[0078] It will be understood that the use of the pulse compensation network is independent of the differential bias, and that the benefits of the pulse compensation network in eliminating pulse ringing are independent and can be achieved without using the differential bias. Figure 7 This is a schematic diagram illustrating this use of the pulse compensation network, including capacitor 602 and resistor 603. In other aspects, Figure 7The circuit is the same as described above. Figure 6 The circuitry is fundamentally similar. Similarly, it will be understood that in some implementations, a separate differential bias can provide some of the advantages described herein. Figure 8 This is a schematic diagram illustrating the independent use of differential bias in a system for particle detection according to certain embodiments. It will also be understood that, in some embodiments, eliminating the charge storage capacitor separately can provide some of the advantages described herein. A schematic diagram of this circuit is shown in... Figure 9 As shown, the charge storage capacitor was eliminated in the system used to detect high-energy particles.

[0079] Exemplary Implementation

[0080] In addition to the embodiments described elsewhere in this disclosure, exemplary embodiments of the present invention include, but are not limited to, the following embodiments:

[0081] 1. A system for detecting particles, the system comprising:

[0082] A detector unit, comprising a differential bias detector having a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage; and

[0083] An AC coupler is used to couple the detector to a measuring device with an input impedance of Z0. The AC coupler has capacitively coupled positive input / output terminals and capacitively coupled negative input / output terminals, wherein:

[0084] The capacitive coupling between the positive input / output terminals and the negative input / output terminals is embedded in a transmission line structure with a surge impedance of Z0.

[0085] The positive input terminal is coupled to the first terminal of the detector, and

[0086] The negative input terminal is coupled to the second terminal of the detector.

[0087] 2. The system as described in embodiment 1, wherein the capacitive coupling between the positive input / output terminal and the negative input / output terminal of the AC coupler is the sole detector energy storage component.

[0088] 3. The system as described in embodiment 1 further includes a pulse compensation network connected in parallel with the detector.

[0089] 4. The system as described in embodiment 2 further includes a pulse compensation network connected in parallel with the detector.

[0090] 5. A system for detecting particles, the system comprising:

[0091] The detector has a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage; and

[0092] An AC coupler is used to couple the detector to a measuring device with an input impedance of Z0. The AC coupler has capacitively coupled positive input / output terminals and capacitively coupled negative input / output terminals, wherein:

[0093] The capacitive coupling between the positive input / output terminals and the negative input / output terminals is embedded in a transmission line structure with a surge impedance of Z0.

[0094] The positive input terminal is coupled to the first terminal of the detector.

[0095] The negative input terminal is coupled to the second terminal of the detector, and

[0096] The capacitive coupling between the positive input / output terminals and the negative input / output terminals of the AC coupler is the only detector energy storage component.

[0097] 6. The system as described in embodiment 5 further includes a pulse compensation network connected in parallel with the detector.

[0098] 7. A system for detecting particles, the system comprising:

[0099] The detector has a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage;

[0100] A pulse compensation network, wherein the pulse compensation network is connected in parallel with the detector; and

[0101] An AC coupler is used to couple the detector to a measuring device with an input impedance of Z0. The AC coupler has capacitively coupled positive input / output terminals and capacitively coupled negative input / output terminals, wherein:

[0102] The capacitive coupling between the positive input / output terminals and the negative input / output terminals is embedded in a transmission line structure with a surge impedance of Z0.

[0103] The positive input terminal is coupled to the first terminal of the detector, and

[0104] The negative input terminal is coupled to the second terminal of the detector.

[0105] 8. The system as described in any one of embodiments 1 to 7, further comprising:

[0106] A first transmission line segment with impedance Z0 couples the AC coupler to the detector unit; and

[0107] A second transmission line segment with impedance Z0 couples the AC coupler to the measuring device.

[0108] 9. The system as described in embodiment 8, wherein one or both of the first transmission line segment and the second transmission line segment comprise a plurality of segments connected in series.

[0109] 10. The system of any one of embodiments 1 to 9, comprising a first resistor and a second resistor of substantially equal value for coupling the first terminal of the detector to the positive bias voltage and the second terminal of the detector to the negative bias voltage, respectively, in a differential bias mode.

[0110] 11. The system as described in any one of embodiments 3 to 4 or 6 to 7, wherein the pulse compensation network includes a resistor with a value of Z0 connected in series with a capacitor, the value of which is within approximately twice the capacitive coupling of the positive input / output terminal and the negative input / output terminal of the AC coupler.

[0111] 12. The system as described in any one of embodiments 1 to 11, further comprising a first voltage source for providing the positive bias voltage and the negative bias voltage.

[0112] 13. The system of embodiment 12 further includes a second voltage source and a third voltage source, the second voltage source and the third voltage source being selectively coupled to the first voltage source, the second voltage source having the same polarity as the first voltage source and the third voltage source having the opposite polarity to the first voltage source.

[0113] 14. The system of any one of embodiments 1 to 13 further includes a measuring device having a load resistance coupled to the AC coupler, wherein the high-pass impedance of the AC coupler is matched with the load resistance and any transmission line impedance.

[0114] 15. A method for detecting particles, the method comprising:

[0115] The particles are struck by a differential bias detector having a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage; and

[0116] The detector is coupled to a measuring device with an input impedance of Z0 using an AC coupler, the AC coupler having capacitively coupled positive input / output terminals and capacitively coupled negative input / output terminals, wherein:

[0117] The capacitive coupling between the positive input / output terminals and the negative input / output terminals is embedded in a transmission line structure with a surge impedance of Z0.

[0118] The positive input terminal is coupled to the first terminal of the detector, and

[0119] The negative input terminal is coupled to the second terminal of the detector.

[0120] 16. The method of embodiment 15 further includes using the capacitive coupling of the positive input / output terminal and the negative input / output terminal of the AC coupler as a single detector energy storage component.

[0121] 17. The method as described in embodiment 15 or 16, further comprising using a pulse compensation network connected in parallel with the detector.

[0122] 18. A method for detecting particles, the method comprising:

[0123] The particles are caused to collide with a detector having a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage.

[0124] The detector is coupled to a measuring device with an input impedance of Z0 using an AC coupler, the AC coupler having capacitively coupled positive input / output terminals and capacitively coupled negative input / output terminals, wherein:

[0125] The capacitive coupling between the positive input / output terminals and the negative input / output terminals is embedded in a transmission line structure with a surge impedance of Z0.

[0126] The positive input terminal is coupled to the first terminal of the detector.

[0127] The negative input terminal is coupled to the second terminal of the detector, and

[0128] The capacitive coupling between the positive input / output terminals and the negative input / output terminals of the AC coupler is the only detector energy storage component.

[0129] 19. The method of embodiment 18 further includes using a pulse compensation network connected in parallel with the detector.

[0130] 20. A method for detecting particles, the method comprising:

[0131] The particles are caused to collide with a detector having a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage.

[0132] A pulse compensation network connected in parallel with the detector is used; and

[0133] The detector is coupled to a measuring device with an input impedance of Z0 using an AC coupler, the AC coupler having capacitively coupled positive input / output terminals and capacitively coupled negative input / output terminals, wherein:

[0134] The capacitive coupling between the positive input / output terminals and the negative input / output terminals is embedded in a transmission line structure with a surge impedance of Z0.

[0135] The positive input terminal is coupled to the first terminal of the detector, and

[0136] The negative input terminal is coupled to the second terminal of the detector.

[0137] 21. The method as described in any one of embodiments 14 to 40, further comprising:

[0138] The AC coupler is coupled to the detector unit using a first transmission line segment with impedance Z0; and

[0139] The AC coupler is coupled to the measuring device using a second transmission line segment with impedance Z0.

[0140] 22. The method of embodiment 21, wherein one or both of the first transmission line segment and the second transmission line segment comprises a plurality of segments connected in series.

[0141] 23. The method of any one of embodiments 14 to 22, further comprising a first resistor and a second resistor of substantially equal value for coupling the first terminal of the detector to the positive bias voltage and the second terminal of the detector to the negative bias voltage, respectively, in a differential bias mode.

[0142] 24. The method of any one of embodiments 16 to 17 or 19 to 20, wherein the pulse compensation network includes a resistor of value Z0 connected in series with a capacitor, the value of which is within approximately twice the capacitive coupling of the positive input / output terminal and the negative input / output terminal of the AC coupler.

[0143] 25. The method of any one of embodiments 14 to 24, further comprising a first voltage source for providing the positive bias voltage and the negative bias voltage.

[0144] 26. The method of embodiment 25 further includes a second voltage source and a third voltage source, the second voltage source and the third voltage source being selectively coupled to the first voltage source, the second voltage source having the same polarity as the first voltage source and the third voltage source having the opposite polarity to the first voltage source.

[0145] 27. The method of any one of embodiments 14 to 16, further comprising a measuring device having a load resistance coupled to the AC coupler, wherein the high-pass impedance of the AC coupler is matched with the load resistance and any transmission line impedance.

[0146] 29. The system of any one of embodiments 1 to 4 further comprises: a first resistor for coupling the first terminal of the detector to the positive bias voltage; and a second resistor for coupling the second terminal of the detector to the negative bias voltage, thereby providing the differential bias.

[0147] Although embodiments and applications have been shown and described, it will be apparent to those skilled in the art who benefit from this disclosure that further modifications can be made without departing from the inventive concept disclosed herein. Therefore, the invention is not limited to the above description. This disclosure covers all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that will be understood by those skilled in the art. Similarly, where appropriate, the appended claims cover all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that will be understood by those skilled in the art. Furthermore, the means or components of a device or system adapted to, arranged to, capable of, configured to, enabled, operable, or runnable to perform a particular function as referred to in the appended claims encompass said means, system, or component, whether or not it or said particular function is activated, turned on, or unlocked, provided that said means, system, or component is so adapted, arranged, capable, configured, enabled, operable, or runnable.

Claims

1. A system for detecting particles, the system comprising: The detector unit includes a differential bias detector having a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage. as well as An AC coupler, used to couple the detector to a measuring device with an input impedance of Z0, includes capacitively coupled positive input terminal and positive output terminal, and capacitively coupled negative input terminal and negative output terminal, wherein: The capacitive coupling between the input positive terminal and the output positive terminal, as well as the input negative terminal and the output negative terminal, is embedded in a transmission line structure with a surge impedance of Z0. The positive input terminal is coupled to the first terminal of the detector, and The negative input terminal is coupled to the second terminal of the detector.

2. The system according to claim 1, further comprising: The first voltage source is used to provide positive and negative bias voltages; as well as A second voltage source and a third voltage source, the second voltage source and the third voltage source being selectively coupled to the first voltage source, the second voltage source having the same polarity as the first voltage source and the third voltage source having the opposite polarity to the first voltage source.

3. The system according to claim 1, wherein, The capacitive coupling of the positive input terminal and the positive output terminal, as well as the negative input terminal and the negative output terminal of the AC coupler, is the only detector energy storage component.

4. The system of claim 1, further comprising a pulse compensation network connected in parallel with the detector, and including a resistor of value Z0 connected in series with a capacitor, the value of which is within approximately twice the capacitive coupling of the positive input terminal, positive output terminal, negative input terminal, and negative output terminal of the AC coupler.

5. The system according to claim 1, wherein, The detector unit includes: a first resistor for coupling the first terminal of the detector to a positive bias voltage; and a second resistor for coupling the second terminal of the detector to a negative bias voltage to provide differential bias.

6. The system according to claim 1, further comprising: The first transmission line segment couples the AC coupler to the detector unit; as well as The second transmission line segment couples the AC coupler to the measuring device.

7. A method for detecting particles using the system according to claim 1, the method comprising: The particles are made to collide with the detector; as well as Information about the particles is obtained from the measuring device.

8. A system for detecting particles, the system comprising: The detector has a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage; as well as An AC coupler, used to couple the detector to a measuring device with an input impedance of Z0, includes capacitively coupled positive input terminal and positive output terminal, and capacitively coupled negative input terminal and negative output terminal, wherein: The capacitive coupling of the input positive terminal and the output positive terminal, as well as the input negative terminal and the output negative terminal, is embedded in a transmission line structure with a surge impedance of Z0. The positive input terminal is coupled to the first terminal of the detector, and The negative input terminal is coupled to the second terminal of the detector.

9. A system for detecting particles, the system comprising: The detector has a first terminal for coupling to a positive bias voltage and a second terminal for coupling to a negative bias voltage; A pulse compensation network is connected in parallel with the detector. as well as An AC coupler, used to couple the detector to a measuring device with an input impedance of Z0, includes capacitively coupled positive input and positive output terminals, as well as capacitively coupled negative input and negative output terminals. The capacitive coupling between the positive input terminal and the positive output terminal, and between the negative input terminal and the negative output terminal, is embedded in a transmission line structure with a surge impedance of Z0. The pulse compensation network includes a resistor with a value of Z0 connected in series with a capacitor, the value of which is within approximately twice the capacitive coupling of the positive input terminal and the positive output terminal, as well as the negative input terminal and the negative output terminal of the AC coupler.

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