A switching device and method

Abstract

A switching device for use in controlling a delivery of a radio frequency, RF, drive voltage signal of alternating polarity to electrodes of an ion guide, trap or analyser for use in generating an electrical potential field for guiding, trapping or analysing ions. The switching device comprises a signal input port for receiving an RF drive current signal, an electrical switching assembly comprising one or more unidirectional electrical switching units controllable selectively to switch the switching assembly between an open switch state in which the RF drive current signal is not permitted to pass therethrough, and closed switch state in which the RF drive current signal is permitted to pass therethrough. A signal output port outputs the RF drive current signal conditional upon the switch state of the electrical switching assembly. A plurality of isolation diodes are provided. Each unidirectional electrical switching unit is electrically connected to an isolation diode such that the RF drive current signal is conducted through each unidirectional electrical switching unit unidirectionally while the electrical switching assembly is in the closed switch state.

Description

[0001] A SWITCHING DEVICE AND METHOD

[0002] Field of the Invention

[0003] The present invention relates to electrical switches and switching and particularly, although not exclusively, to switching devices and methods for use in controlling a delivery of an RF drive voltage signal of alternating polarity to electrodes of an ion guide, an ion trap or an ion analyser for use in generating an electrical potential field for guiding, trapping or analysing ions.

[0004] Background

[0005] Radio-frequency (RF) voltage generators are used routinely for delivery of an RF drive voltage signal of alternating polarity to electrodes of an ion guide, an ion trap or an ion analyser. The RF voltage signals are used to cause the electrodes collectively to generate an electrical potential field for guiding, trapping or analysing ions.

[0006] RF voltage generators may comprise a resonant circuit output stage including inductor and capacitor components configured to cause the generator to operate to output a drive voltage signal having a frequency determined by the values (inductance and capacitance, respectively) of the output inductance and capacitance. The operating (output) frequency is usually constrained by those values such that the RF voltage signal frequency is one fixed RF frequency.

[0007] In order to be able to provide to driven electrodes an RF drive voltage signal frequency selectable from amongst a plurality of different RF frequencies, a common method is to provide multiple RF voltage signal generators each configured to output, respectively, a voltage signal of a respective one of the plurality of different RF frequencies, and to provide a switch configured to connect or disconnect, selectively, the desired RF signal generator from the electrodes, as desired.

[0008] The switching of high voltage alternating signals for this purpose commonly uses inverse-connected series MOSFETs, as shown schematically in Figure 1A. This shows an example of a conventional bidirectional semiconductor switch with high capacitance. More generally, the switching of high voltage alternating signals may involve the use of switching devices such as MOSFETs, JFETs, IGBTs, bipolar transistors, or other semiconductor transistor devices. Thermionic valves are also sometimes used. All of these switching devices are unidirectional and cannot be used alone (singly) to control a bidirectional signal. For this reason, as shown in the example of Figure 1A, multiple such switching devices are typically used and connected in such a way as to allow the collective switching devices to control a bidirectional signal. The manner by which this is achieved in the example of the MOSFET of Figure 1 A, namely inverse-connected series connection, is discussed in more detail below with reference to Figure 1B and Figure 1C.

[0009] Furthermore, these switching devices possess a high self-capacitance. Figure 1D shows the selfcapacitances present in the example of a MOSFET, for illustrative purposes. An “input capacitance” (C1SS) is typically defined as the sum of the gate-drain self-capacitance and the gate-source self-capacitance:8539876

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[0011] Ciss=c9d + CflS. An “output capacitance” (Coss) is typically defined as the sum of the drain-source selfcapacitance and the gate-drain self-capacitance: Coss= Cds+ Cgd. A “reverse capacitance” (Crss) is typically defined as the gate-drain self-capacitance:Crss= Cgd. The high self-capacitance of the MOSFETs makes this configuration unsuitable for high-frequency RF applications. The high selfcapacitance is problematic at high frequencies because the impedance of a capacitor is inversely proportional to the applied frequency, so at RF frequencies the corresponding impedance will generally be relatively low. This low impedance will pass a significant proportion of an RF signal even when the switching device in question is in the “open” state, thereby causing a poor signal isolation and making the switch perform poorly. Other switching devices comprising JFETs, IGBTs, bipolar transistors, or other semiconductor transistor devices, and thermionic valves also possess significant self-capacitance.

[0012] The present invention has been devised in light of the above considerations.

[0013] Summary of the Invention

[0014] In a first aspect, the invention may provide a switching device for use in controlling a delivery of a radiofrequency, RF, drive voltage signal of alternating polarity to electrodes of an ion guide, an ion trap or an ion analyser for use in generating an electrical potential field for guiding, trapping or analysing ions, the switching device comprising:

[0015] a signal input port for receiving an RF drive current signal;

[0016] an electrical switching assembly comprising one or more unidirectional electrical switching units controllable selectively to switch the switching assembly between an open switch state in which the RF drive current signal is not permitted to pass therethrough, and closed switch state in which the RF drive current signal is permitted to pass therethrough; and,

[0017] a signal output port for outputting the RF drive current signal conditional upon the switch state of the electrical switching assembly;

[0018] wherein the electrical switching assembly further comprises a plurality of isolation diodes wherein each said unidirectional electrical switching unit is electrically connected to a (i.e., one or more) respective isolation diode such that said RF drive current signal is conducted through each said unidirectional electrical switching unit unidirectionally while the electrical switching assembly is in the closed switch state.

[0019] A reference herein to a “unidirectional electrical switching unit” may be considered to include a reference to a switch configured to switch (e.g., between a non-conductive “open” state and a conductive “closed” state) so as to permit electrical conduction in only one direction. For example, a “unidirectional” electrical switch may be such that current flows in only one direction (e.g., anode to cathode internally) when a forward voltage is applied.

[0020] A unidirectional electrical switching unit may comprise a semiconductor transistor device. A unidirectional electrical switching unit may comprise a field-effect transistor (FET), such as a metal-oxide-semiconductor field-effect transistor (MOSFET), or a junction field-effect transistor (JFET), or a bipolar

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[0023] transistor, such as an insulated-gate bipolar transistor (IGBT). A unidirectional electrical switching unit may comprise a thermionic valve.

[0024] In this way the one or more unidirectional electrical switching units of the switching device now control a single-polarity voltage. As a result, a high capacitance value for the switch components is made less problematic. An RF voltage signal output from an RF generator connected to such a switch may more rapidly be switched with good signal isolation when in the “open” state. The switch may thereby permit an RF signal to be more rapidly disconnected from electrodes of an ion guide, an ion trap or an ion analyser. Once disconnected, the electrodes may be rapidly connected to another signal RF voltage signal generator having a different RF frequency, or to a DC signal generator, or may be connected to a ‘ground’ signal (i.e., a DC signal of ‘zero’ volts) as desired.

[0025] This allows use in applications previously ruled out because of the high capacitance, and resulting poor signal isolation, of the prior semiconductor-based switches. The use of isolation diodes may convert an alternating-current RF signal into direct-current signal (e.g., oscillatory / rectified) which may produce a single-polarity of voltage across a switching device.

[0026] Applications of the switch may include, but are not limited to, the following:

[0027] • Isolation: where, for example, a signal source can be switched between a sinusoidal output RF generator and a steady DC potential. In this configuration, a control signal may be isolated from ground by a transformer or optical isolation component, other isolation component or a combination of these. • Clamping: where the output of a sinusoidal RF generator can be forced to rapidly switch to zero. Without this, such an RF voltage signal generator would typically take many cycles of the RF signal to decay to zero. In this configuration the control signal may be referenced to ground.

[0028] • Load switching: for example where different values of capacitive or inductive element in the resonant circuit of an RF voltage signal generator can be selected. This allows the RF voltage signal generator, normally a fixed-frequency device, to operate at different frequencies. A system and method may be provided whereby the switch is configured (or multiple switches are configured) to switchably connect (connect / disconnect) capacitors of different capacitance values thereby to change the capacitance of the output stage of an RF voltage signal generator, thereby facilitating rapid switching of the RF voltage signal generator between multiple operating frequencies selectable according to the selected capacitors. This allows operation of a high-power sinusoidal RF generator at a selectable one of multiple frequencies.

[0029] A said unidirectional electrical switching unit may define a body diode electrically connected to a respective said isolation diode in reverse bias relative thereto to prevent passage of the RF drive current signal through the body diode while the electrical switching assembly is in the open switch state.

[0030] In the switching device, an anode of a respective body diode may be electrically connected to an anode of a respective isolation diode. In addition, or alternatively, a cathode of a respective body diode may be electrically connected to a cathode of a respective isolation diode.

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[0033] In the switching device one or more (e.g., each) unidirectional electrical switching unit may comprise a transistor. An isolation diode may be electrically connected between the signal input port and a drain terminal of the respective transistor. In addition, or alternatively, an isolation diode may be electrically connected between the signal output port and a drain terminal of the respective transistor. An anode of a respective isolation diode may be electrically connected to the signal input port and a cathode of the respective isolation diode may be electrically connected to a drain terminal of the respective transistor. In the switching device, an anode of a respective isolation diode may be electrically connected between the signal output port a drain terminal of the respective transistor. An anode of a respective body diode may be electrically connected to a source terminal of the respective transistor. In the switching device, a cathode of a respective body diode may be electrically connected to a source terminal of the respective transistor.

[0034] An isolation diode may be electrically connected between the signal input port and a source terminal of the respective transistor and / or, an isolation diode may be electrically connected between the signal output port and a source terminal of the respective transistor. A cathode of a respective isolation diode may be electrically connected to the signal input port and an anode of the respective isolation diode may be electrically connected to a source terminal of the respective transistor. An anode of a respective isolation diode may be electrically connected to the signal output port and a cathode of the respective isolation diode may be electrically connected to a drain terminal of the respective transistor. A cathode of a respective isolation diode may be electrically connected to the signal output port and an anode of the respective isolation diode may be electrically connected to a drain terminal of the respective transistor. An anode of a respective isolation diode may be electrically connected to the signal input port and a cathode of the respective isolation diode may be electrically connected to a drain terminal of the respective transistor. A cathode of a respective isolation diode may be electrically connected to the signal output port and an anode of the respective isolation diode may be electrically connected to a drain terminal of the respective transistor.

[0035] The plurality of isolation diodes may define a bridge rectifier circuit (e.g., a diode bridge) connected to the signal input port and to the signal output port to conduct an alternating-current RF drive current signal therebetween, and connected to the one or more unidirectional electrical switching unit(s) such that the RF drive current signal is rectified by the bridge rectifier circuit and conducted through the one or more unidirectional electrical switching unit(s) unidirectionally (i.e., in rectified form) while the electrical switching assembly is in the closed switch state. The bridge rectifier circuit may define a full-wave rectifier.

[0036] A unidirectional electrical switching unit may comprise an N-channel MOSFET. A source terminal of the N-channel MOSFET may be connected to ground, and a drain terminal of the N-channel MOSFET may be connected to a cathode of an isolation diode. An anode of the isolation diode may be connected between the signal input port and the signal output port. A unidirectional electrical switching unit may comprise a P-channel MOSFET. A source terminal of the P-channel MOSFET may be connected to

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[0039] ground, and a drain terminal of the P-channel MOSFET may be connected to an anode of an isolation diode. An cathode of the isolation diode may be connected between the signal input port and the signal output port. The switching device may comprise both the N-channel MOSFET and the P-channel MOSFET arranged in this way.

[0040] The switching device may comprise an isolated control signal source wherein the one or more unidirectional electrical switching units are controllable selectively to switch the switching assembly between the open switch state and the closed switch state in response to a control signal from the isolated control signal source comprising a voltage that is not referenced to ground. The isolated control signal source may comprise a transformer or an optical isolator configured to electrically isolate the isolated control signal source. In this way, the switching device may be configured such that the control signal is not referenced to ground and is derived from an isolated source. The isolated source may comprise a transformer, or an optical isolation component (e.g., a photo-voltaic isolator), other isolation device as an isolation barrier, ora combination of these.

[0041] The invention may provide an ion guide, an ion trap or an ion analyser comprising the switching device according to the invention in its first aspect wherein the switching device is configured to control a delivery of radio frequency, RF, drive voltage signal of alternating polarity to electrodes of the ion guide, ion trap or ion analyser for generating an electrical potential field for guiding, trapping or analysing ions.

[0042] In a second aspect, the invention may provide a switching method for use in controlling a delivery of a radio-frequency, RF, drive voltage signal of alternating polarity to electrodes of an ion guide, an ion trap or an ion analyser for use in generating an electrical potential field for guiding, trapping or analysing ions, the switching method comprising:

[0043] providing a signal input port and therewith receiving an RF drive current signal;

[0044] providing an electrical switching assembly comprising one or more unidirectional electrical switching units and controlling the one or more unidirectional electrical switching units selectively to switch the switching assembly between an open switch state in which the RF drive current signal is not permitted to pass therethrough, and closed switch state in which the RF drive current signal is permitted to pass therethrough; and,

[0045] providing a signal output port and therewith outputting the RF drive current signal conditional upon the switch state of the electrical switching assembly;

[0046] providing a plurality of isolation diodes wherein each said unidirectional electrical switching unit is electrically connected to a (i.e., one or more) respective said isolation diode such that the RF drive current signal is conducted through each unidirectional electrical switching unit unidirectionally while the electrical switching assembly is in the closed switch state.

[0047] Each said unidirectional electrical switching unit may define a respective body diode electrically connected to a respective said isolation diode in reverse bias relative thereto, and the method may comprise preventing passage of the RF drive current signal through the body diode while the electrical switching assembly is in the open switch state.

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[0050] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0051] Summary of the Figures

[0052] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0053] Figures 1A-C show an example of a conventional bi-directional semiconductor switch with high capacitance.

[0054] Figures 1D shows an example of a conventional MOSFET and the components of self-capacitance therein.

[0055] Figure 2 shows an example of a semiconductor switch according to a first example of the invention.

[0056] Figure 3 shows an example of a semiconductor switch according to a second example of the invention.

[0057] Figure 4 shows an example of a semiconductor switch according to a third example of the invention.

[0058] Figure 5 shows an example of a method of switching.

[0059] Detailed Description of the Invention

[0060] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0061] Figures 1 A-C show a schematic diagram of a prior art bidirectional power switching (BPS) device for switching high voltage oscillating signals. This example is a conventional bi-directional semiconductor switch with high capacitance. The configuration of the switching device employs inverse-connected series N-Channel MOSFETs. The high self-capacitance of the MOSFETs limits the effective signal isolation and makes this configuration unsuitable for high-frequency RF applications, such as for use in switching drive voltage signals to be delivered to electrodes of an ion guide, an ion trap or an ion analyser for use in generating an electrical potential field for guiding, trapping or analysing ions.

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[0064] A bidirectional power switch is constructed by connecting MOSFETs back-to-back in series as shown in Figure 1A, in which two N-channel MOSFETS can be seen connected across their sources. Consider the scenario in which a positive voltage is applied at the "Input" terminal of the BPS, and negative voltage is applied to the "Output" terminal of the BPS, as shown in Figure 1B. In this case one can see that when the gate voltage is applied, current from the "Input" terminal of the BPS is allowed to flow through lefthand MOSFET, and then through the internal forward-biased body diode of the right-hand MOSFET, and finally to the "Output" terminal of the BPS. When the voltage polarity is reversed such that a negative voltage is applied at the "Input" terminal of the BPS, and positive voltage is applied to the "Output" terminal of the BPS, as shown in Figure 1C, the MOSFETs and their internal body diodes flip their bias status as shown in Figure 1C, such that the right-hand MOSFET of the BPS switches to a conducting state along with the internal body diode of the left-hand MOSFET, to enable the conduction of current from the "Output" terminal of the BPS to the "Input" terminal of the BPS. As a result of these two conduction channels through the body diodes of alternate MOSFETs, the high self-capacitance of the MOSFETs makes its effects felt. These affects are undesirable in the context of RF voltage signals, in terms of high capacitive coupling and poor signal isolation when an RF signal amplitude or frequency is changed (switched).

[0065] In an example shown in Figure 2, the invention provides a switching device 2 for use in controlling a delivery of an RF drive voltage signal 6 of alternating polarity to electrodes of an ion guide, an ion trap or an ion analyser (not shown) for use in generating an electrical potential field for guiding, trapping or analysing ions. The switching device 2 comprises a signal input port 4 for receiving an RF drive current signal 6. An electrical switching assembly 8 comprises a unidirectional electrical switching unit in the form of an N-type MOSFET transistor 10 controllable by a control signal unit 20 selectively to switch the switching assembly between an open switch state in which the RF drive current signal 6 is not permitted to pass therethrough, and closed switch state in which the RF drive current signal is permitted to pass therethrough. A signal output port 12 is arranged for outputting the RF drive current signal 14 conditional upon the switch state of the electrical switching assembly.

[0066] The electrical switching assembly further comprises four isolation diodes 16 collectively defining a bridge rectifier circuit, and the MOSFET transistor 10 defines a body diode 18 electrically connected to each isolation diode 16 in reverse bias relative thereto to prevent passage of the RF drive current signal, 6 and 14, through the body diode 18 while the electrical switching assembly is in the open switch state. Thus, the arrangement provides a plurality of isolation diodes wherein the MOSFET (unidirectional electrical switching unit) is electrically connected to a respective isolation diode such that the RF drive current signal is conducted through the MOSFET unidirectionally.

[0067] In this way the switching device controls a single-polarity voltage and the high capacitance value for the MOSFET 10 is made less problematic. The use of diodes 16 converts an alternating-current RF signal into direct-current signal (e.g., oscillatory I rectified) which produces a single-polarity of voltage across a MOSFET 10 of the switching device. An RF voltage signal 6 output from an RF generator (not shown) connected to such a switch may more rapidly be switched with high signal isolation. The RF signal may

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[0070] more rapidly be disconnected from electrodes of an ion guide, an ion trap or an ion analyser. Once disconnected, the electrodes may be rapidly connected to another signal RF voltage signal generator having a different RF frequency, or to a DC signal generator, or may be connected to a ‘ground’ signal (i.e., a DC signal of ‘zero’ volts) as desired.

[0071] The embodiment illustrated in Figure 2 provides an example of the use of the switching device for isolation. In particular, a signal source can be switched, according to a control signal output by the control signal unit 20, between outputting a sinusoidal output RF signal 22 and outputting a steady DC potential 24. In this configuration, a control signal may be isolated from ground by an isolation component 26, which may comprise a transformer or an optical isolation component, other isolation component.

[0072] In an example shown in Figure 3, the invention provides a switching device 28 for use in controlling a delivery of an RF drive voltage signal 6 of alternating polarity to electrodes of an ion guide, an ion trap or an ion analyser (not shown) for use in generating an electrical potential field for guiding, trapping or analysing ions. The switching device 28 comprises a signal input port 30 for receiving an RF drive current signal 6. An electrical switching assembly 32 comprises two unidirectional electrical switching units in the form of an N-type MOSFET transistor 34 and a P-type MOSFET transistor 36 each of which is controllable by a respective control signal unit, 20a and 20b, selectively to switch the switching assembly between an open switch state in which the RF drive current signal 6 is not permitted to pass therethrough, and closed switch state in which the RF drive current signal is permitted to pass therethrough. A signal output port 36 is arranged for outputting the RF drive current signal 14 conditional upon the switch state of the electrical switching assembly. The electrical switching assembly 32 further comprises two of isolation diodes 38, and each one of N-type MOSFET transistor 34 and a P-type MOSFET transistor 36 defines a respective body diode 40 electrically connected to a respective one of the two isolation diodes 38 in reverse bias relative thereto to prevent passage of the RF drive current signal, 6 and 14, through the body diodes 40 while the electrical switching assembly is in the open switch state.

[0073] The embodiment illustrated in Figure 3 provides an example of the use of the switching device for clamping. In particular, a signal source can be switched, according to a pair of coordinated control signals of opposite polarity (the polarity being according to whether the control signal is directed to an N-Channel MOSFET, 34, as from control signal unit 20a, or directed to an P-Channel MOSFET, 36, as from control signal unit 20b) output by the two control signal units, 20a and 20b, between outputting a sinusoidal output RF signal 22 and outputting a steady DC potential 24. In this configuration, the output of a sinusoidal RF generator can be forced to rapidly switch to zero. Without this arrangement, such an RF voltage signal generator would typically take many cycles of the RF signal to decay to zero. In this configuration the control signal may be referenced to ground.

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[0076] In an example shown in Figure 4, the invention provides a load-switching switching device 50 for use in controlling a delivery of an RF drive voltage signal of alternating polarity from an RF generator unit 48 to electrodes of an ion guide, an ion trap or an ion analyser (not shown) for use in generating an electrical potential field for guiding, trapping or analysing ions. The load-switching device 50 comprises a signal input port 52 for receiving an RF drive current signal . An electrical switching assembly comprises two switching assembly sub-units each of which is as described above with reference to Figure 2. The signal input ports of the two switching assembly sub-units are connected in series with each other and in series with the RF drive current signal output port of the RF generator 48.

[0077] Each one of the two switching assembly sub-units is individually and separately controllable by a respective control signal unit selectively to switch the switching assembly sub-unit between an open switch state in which the RF drive current signal is not permitted to pass therethrough, and closed switch state in which the RF drive current signal is permitted to pass therethrough.

[0078] A signal output port of each one of the two switching assembly sub-units is individually and separately connected to a respective one of two additional variable load capacitors 44, an is thereby arranged for selectively electrically connecting a respective additional load capacitor between the RF drive current signal output port of the RF generator 48, and ground. In this way, the load capacitance connected to the output of the RF generator may be selectively switched between pre-set values (or variable values) according to the capacitance values of the additional load capacitors so connected. As noted above, with reference to Figure 2, each one of the switching assembly sub-units comprises a respective one of two unidirectional electrical switching units, which take the form of an N-Channel MOSFET.

[0079] The embodiment illustrated in Figure 4 provides an example of the use of the switching device for resonant load switching. For example, different values of capacitive or inductive element in the resonant circuit of an RF voltage signal generator can be selected. This allows the RF voltage signal generator, normally a fixed-frequency device, to operate at different frequencies. The switch is configured (or multiple switches are configured) to switchably connect (connect / disconnect) capacitors of different capacitance values thereby to change the capacitance of the output stage of an RF voltage signal generator, thereby facilitating rapid switching of the RF voltage signal generator between multiple operating frequencies selectable according to the selected capacitors. This allows operation of a high-power sinusoidal RF generator at a selectable one of multiple frequencies.

[0080] In the switching device according to embodiments of the invention, an anode of a respective body diode is electrically connected to an anode of a respective isolation diode. In addition, a cathode of a respective body diode is electrically connected to a cathode of a respective isolation diode.

[0081] In the examples of Figure 2, a first isolation diode is electrically connected between the RF signal input port and a drain terminal of the MOSFET and is biased to pass current from the former to the latter. In addition, a second isolation diode is electrically connected between the signal output port and a drain terminal of the MOSFET and is biased to pass current from the former to the latter. Accordingly, an anode 4154-9954-8199, v. 18539876

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[0083] of each of these first and second isolation diodes is electrically connected to the signal input port or the signal output port, respectively, and a cathode of each of the two isolation diodes is electrically connected to the drain terminal of the MOSFET. In addition, a third isolation diode is electrically connected between the RF signal input port and a source terminal of the MOSFET and is biased to pass current from the latter to the former. In addition, a fourth isolation diode is electrically connected between the signal output port and a source terminal of the MOSFET and is biased to pass current from the latter to the former. Accordingly, an anode of each of these first and second isolation diodes is electrically connected to the signal input port or the signal output port, respectively, and a cathode of each of the two isolation diodes is electrically connected to the drain terminal of the MOSFET. Similarly, a cathode of each of these third and fourth isolation diodes is electrically connected to the signal input port or the signal output port, respectively, and an anode of each of the two isolation diodes is electrically connected to the source terminal of the MOSFET. This arrangement provides a bridge rectifying circuit of isolation diodes to rectify the signal delivered to the MOSFET. An anode of the body diode 18 is electrically connected to the source terminal of the MOSFET and a cathode of the body diode is electrically connected to a drain terminal of the MOSFET.

[0084] In the arrangement illustrated in Figure 3, a cathode of a body diode 40 of the N-Channel MOSFET 34 is electrically connected to the drain terminal of the N-Channel MOSFET, and an anode of the body diode is electrically connected to the source terminal of the N-Channel MOSFET. A similar arrangement is shown in respect of the P-Channel MOSFET 36 with the difference that the positions of the orientation I connection of the anode I cathode of the body diode 40 are reversed (swapped) relative to the drain and source terminals of the P-Channel MOSFET.

[0085] The invention may also provide a switching method for use in controlling a delivery of an RF drive voltage signal of alternating polarity to electrodes of an ion guide, an ion trap or an ion analyser for use in generating an electrical potential field for guiding, trapping or analysing ions, the switching method comprising:

[0086] Step S1 : provide a signal input port and therewith receiving an RF drive current signal;

[0087] Step S2: provide an electrical switching assembly comprising one or more unidirectional electrical switching units and controlling the one or more unidirectional electrical switching units selectively to switch the switching assembly between an open switch state in which the RF drive current signal is not permitted to pass therethrough, and closed switch state in which the RF drive current signal is permitted to pass therethrough; and,

[0088] Step S3: Provide a signal output port and therewith outputting the RF drive current signal conditional upon the switch state of the electrical switching assembly;

[0089] Step S4: Provide a plurality of isolation diodes wherein each said unidirectional electrical switching unit is electrically connected to one or more isolation diodes such that the RF drive

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[0092] current signal is conducted through each unidirectional electrical switching unit unidirectionally;

[0093] Step S5: Conduct the RF drive current signal through the electrical switching assembly via each unidirectional electrical switching unit unidirectionally while the electrical switching assembly is in the closed switch state.

[0094] Figure 5 shows these steps in succession. Step 4 may comprise Step 4.2 as follows:

[0095] Step S4.2 Provide the plurality of isolation diodes wherein each unidirectional electrical switching unit comprises a transistor(s) that defines a respective body diode electrically connected to a respective isolation diode in reverse bias relative thereto;

[0096] Step 5 may comprise Step 5.2 as follows:

[0097] Step S5.2 Prevent passage of the RF drive current signal through the body diode while the electrical switching assembly is in the open switch state

[0098] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0099] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0100] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0101] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0102] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

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[0105] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

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Claims

853987613Claims:

1. A switching device for use in controlling a delivery of a radio frequency, RF, drive voltage signal of alternating polarity to electrodes of an ion guide, an ion trap or an ion analyser for use in generating an electrical potential field for guiding, trapping or analysing ions, the switching device comprising:a signal input port for receiving an RF drive current signal;an electrical switching assembly comprising one or more unidirectional electrical switching units controllable selectively to switch the switching assembly between an open switch state in which the RF drive current signal is not permitted to pass therethrough, and closed switch state in which the RF drive current signal is permitted to pass therethrough; and,a signal output port for outputting the RF drive current signal conditional upon the switch state of the electrical switching assembly;wherein the electrical switching assembly further comprises a plurality of isolation diodes wherein each said unidirectional electrical switching unit is electrically connected to a respective said isolation diode such that said RF drive current signal is conducted through each said unidirectional electrical switching unit unidirectionally while the electrical switching assembly is in the closed switch state.

2. A switching device according to any preceding claim wherein each said unidirectional electrical switching unit defines a body diode electrically connected to a respective said isolation diode in reverse bias relative thereto to prevent passage of the RF drive current signal through the body diode while the electrical switching assembly is in the open switch state.

3. A switching device according to claim 2 wherein:an anode of a respective body diode is electrically connected to an anode of a respective isolation diode; and / or,a cathode of a respective body diode is electrically connected to a cathode of a respective isolation diode.

4. A switching device according to any preceding claim wherein each unidirectional electrical switching unit comprises a transistor, and:an isolation diode is electrically connected between the signal input port and a drain terminal of the respective transistor; and / or,an isolation diode is electrically connected between the signal output port and a drain terminal of the respective transistor.

5. A switching device according to any preceding claim wherein each unidirectional electrical switching unit comprises a transistor, and:an isolation diode is electrically connected between the signal input port and a source terminal of the respective transistor; and / or,an isolation diode is electrically connected between the signal output port and a source terminal of the respective transistor.4154-9954-8199, v. 18539876146. A switching device according to any preceding claim wherein each unidirectional electrical switching unit comprises a transistor, and an anode of a respective isolation diode is electrically connected to the signal input port and a cathode of the respective isolation diode is electrically connected to a drain terminal of the respective transistor.

7. A switching device according to any preceding claim wherein each unidirectional electrical switching unit comprises a transistor, and a cathode of a respective isolation diode is electrically connected to the signal input port and an anode of the respective isolation diode is electrically connected to a source terminal of the respective transistor.

8. A switching device according to any preceding claim wherein each unidirectional electrical switching unit comprises a transistor, and an anode of a respective isolation diode is electrically connected to the signal output port and a cathode of the respective isolation diode is electrically connected to a drain terminal of the respective transistor.

9. A switching device according to any preceding claim wherein each unidirectional electrical switching unit comprises a transistor, and a cathode of a respective isolation diode is electrically connected to the signal output port and an anode of the respective isolation diode is electrically connected to a source terminal of the respective transistor.

10. A switching device according to any preceding claim wherein each unidirectional electrical switching unit comprises a transistor, and a cathode of a respective isolation diode is electrically connected to the signal output port and an anode of the respective isolation diode is electrically connected to a drain terminal of the respective transistor.

11. A switching device according to any preceding claim when dependent upon claim 2 wherein each unidirectional electrical switching unit comprises a transistor, and an anode of a respective body diode is electrically connected to a source terminal of the respective transistor.

12. A switching device according to any preceding claim when dependent upon claim 2 wherein each unidirectional electrical switching unit comprises a transistor, and a cathode of a respective body diode is electrically connected to a source terminal of the respective transistor.

13. A switching device according to any preceding claim comprising an isolated control signal source wherein said one or more unidirectional electrical switching units are controllable selectively to switch the switching assembly between said open switch state and said closed switch state, in response to a control signal from said isolated control signal source comprising a voltage that is not referenced to ground.

14. A switching device according to claim 11 wherein the isolated control signal source comprises a transformer or an optical isolator configured to electrically isolate the isolated control signal source.4154-9954-8199, v. 185398761515. A switching method for use in controlling a delivery of a radio frequency, RF, drive voltage signal of alternating polarity to electrodes of an ion guide, an ion trap or an ion analyser for use in generating an electrical potential field for guiding, trapping or analysing ions, the switching method comprising:providing a signal input port and therewith receiving an RF drive current signal;providing an electrical switching assembly comprising one or more unidirectional electrical switching units and controlling the one or more unidirectional electrical switching units selectively to switch the switching assembly between an open switch state in which the RF drive current signal is not permitted to pass therethrough, and closed switch state in which the RF drive current signal is permitted to pass therethrough; and,providing a signal output port and therewith outputting the RF drive current signal conditional upon the switch state of the electrical switching assembly;providing a plurality of isolation diodes wherein each said unidirectional electrical switching unit is electrically connected to a respective said isolation diode such that said RF drive current signal is conducted through each said unidirectional electrical switching unit unidirectionally while the electrical switching assembly is in the closed switch state.

16. A switching method according to claim 13 wherein each said unidirectional electrical switching unit defines a respective body diode electrically connected to a respective said isolation diode in reverse bias relative thereto, and the method may comprise preventing passage of the RF drive current signal through the body diode while the electrical switching assembly is in the open switch state.

17. An ion guide, an ion trap or an ion analyser comprising the switching device according to any of claims 1 to 12 wherein the switching device is configured to control a delivery of radio frequency, RF, drive voltage signal of alternating polarity to electrodes of the ion guide, ion trap or ion analyser for generating an electrical potential field for guiding, trapping or analysing ions.4154-9954-8199, v. 1

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