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EP-4100732-B1 - ARRANGEMENT AND METHOD FOR PROVIDING A WAVEFORM FOR DRIVING AN ION MOBILITY DEVICE

EP4100732B1EP 4100732 B1EP4100732 B1EP 4100732B1EP-4100732-B1

Inventors

  • ANTTALAINEN, OSMO
  • OKSALA, Niku
  • ROINE, ANTTI
  • KONTUNEN, Anton
  • Koskenranta, Mikko

Dates

Publication Date
20260506
Application Date
20210118

Claims (14)

  1. An arrangement for providing a waveform for driving a Differential Mobility Spectrometry (DMS) device (328), the arrangement comprising at least - a plurality of switching circuits (302, 304), each switching circuit comprising at least two switches (306, 308, 310, 312), a first switch and a second switch, wherein the first switch is additionally coupled to a first voltage source (VH) and the second switch is additionally coupled to a second voltage source (VL), wherein the voltage provided by the first voltage source is higher than the voltage provided by the second voltage source, wherein the plurality of switching circuits are arranged to be coupled in parallel with respect to each other, and - an interleaving circuit (326) configured to receive a time-varying electrical input signal exhibiting an input frequency and based on said input signal, operate the plurality of switching circuits to provide a waveform via the switches, said waveform exhibiting a switching frequency that is essentially equivalent to the input frequency, the arrangement being characterized in that the outputs from the switching circuits are combined to provide the waveform, and said waveform is configured to be coupled to an electrode of a DMS device.
  2. The arrangement of claim 1, wherein the switching circuits are half bridge switching circuits.
  3. The arrangement of any previous claim, wherein the switches are transistors.
  4. The arrangement of claim 3, wherein the arrangement additionally comprises a gate driver circuit (314, 316, 318, 320) associated with each switch.
  5. The arrangement of claim 3 or 4, wherein the arrangement additionally comprises control logic (322, 324) associated with each switching circuit.
  6. The arrangement of any previous claim, wherein the operating of the switching circuits is based on interleaving logic being configured to provide interleaved inputs to the switching circuits based on the input frequency so that each switching circuit is operated by a received interleaved input at an interleaved frequency that is essentially equivalent to or lower than the input frequency.
  7. The arrangement of claim 6, wherein each switching circuit receives an interleaved input one at a time in predetermined order, the switching circuits then being operated at an interleaved frequency that is essentially equal to half or lower than the input frequency.
  8. The arrangement of claim 6 or claim 7, wherein the interleaving logic is implemented via a state machine.
  9. The arrangement of any previous claim, wherein the time-varying electrical input signal is a PWM signal.
  10. The arrangement of any previous claim, wherein the switching frequency is between about 100 kHz and 5 MHz, preferably between about 1MHz and 5 MHz.
  11. The arrangement of any previous claim, wherein the provided waveform is configured to be coupled to a third electrode (340) of the DMS device, which third electrode is disposed between first (102) and second (104) electrodes of the DMS device, where the first and second electrodes are located parallel to each other such that a channel through which ions can pass is formed between the first and second electrodes.
  12. A Differential Mobility Spectrometry (DMS) apparatus comprising the arrangement of any previous claim and a DMS device to which the provided waveform is configured to be coupled to.
  13. A method for providing a waveform for a Differential Mobility Spectrometry (DMS) device, the method comprising at least - providing a plurality of switching circuits (302, 304), each switching circuit comprising at least two switches (306, 308, 310, 312), - arranging the plurality of switching circuits to be coupled in parallel with respect to each other, - providing the switching circuits such that each switching circuit comprises a first switch and a second switch, wherein the first switch is additionally coupled to a first voltage source (VH) and the second switch is additionally coupled to a second voltage source (VL), wherein the voltage provided by the first voltage source is higher than the voltage provided by the second voltage source, - providing an interleaving circuit (326), - receiving a time-varying electrical input signal exhibiting an input frequency at the interleaving circuit, and - operating the plurality of switching circuits based on said input signal via the interleaving circuit, wherein the operating of the plurality of switching circuits comprises controlling the switches to provide a waveform exhibiting a frequency that is essentially equivalent to the input frequency, the method being characterized by combining the outputs from the switching circuits to provide the waveform, wherein said waveform is configured to be coupled to an electrode of a Differential Mobility Spectrometry (DMS) device.
  14. The method of claim 13, further comprising coupling the provided waveform to a third electrode (340) of the DMS device, wherein the third electrode is disposed between a first (102) and second (104) electrode of the DMS device, which first and second electrodes are located parallel to each other such that a channel through which ions can pass is formed between the first and second electrodes.

Description

TECHNICAL FIELD OF THE INVENTION The invention is related to ion mobility spectrometry in general. More specifically, the invention is related to providing a waveform for driving an ion mobility device. BACKGROUND OF THE INVENTION Differential Mobility Spectrometry (DMS) known commonly also as Field Asymmetric Ion Mobility Spectrometry (FAIMS) is an atmospheric pressure technique to separate ionized gas components based on their nonlinear electrical mobility among neutral gas molecules. In DMS, ionized gas molecules are transported with neutral gas via a narrow gap, where either one pair or multiple pairs of coaxial or planar electrodes are connected to a high voltage source (separation voltage SV) generating an asymmetrically oscillating electric field with high and low field parts between the electrodes perpendicular with the flow. The time integral of the oscillating electric field is zero and this electric field is superimposed with a small static DC electrical field (often termed compensation voltage CV) to adjust the offset of the field. The ions move back and forth in the oscillating field and their different mobility in high and low electric field determines the net movement between electrodes. Depending of the net movement, some of the ions collide with electrodes and neutralize whereas some have net movement of about zero in a direction perpendicular to the flow and can pass the electrodes and enter to following measurement electrodes. The static electric field can be used to select the surviving ion types so that only ions with selected characteristics are able to pass the electrodes. The DMS electrodes can be considered as a band pass filter for ion mobility spectrum and the device may be considered an ion filter. Yet, not all ions with selected characteristics can pass the ion filter because they are too close to the electrodes during oscillation. Due to the oscillation, the ion filter has an effective gap which is narrower than the physical gap determined by the dimensions of the filter. The effective gap defines the maximum possible signal to noise ratio of the system. The effective gap is determined by the oscillating electrical field and its frequency. The speed v of an ion in the electric field, disregarding diffusion losses, can be given by: v=k0E where E is the strength of the electric field and k0 is the ion's mobility coefficient, which is specific to each ion type. In high electric field, the ion mobility becomes dependent on the electric field so that the field-dependent mobility k is: k=k01+αEN. Here, αEN describes the nonlinear mobility behavior of an ion in high electric field. In an ideal DMS, the applied asymmetrically oscillating electric field is an electric waveform exhibiting a square pulse with duty cycle less than 50%. The high and low parts of the applied pulse correspond to ion mobilities of kH and kL. The effective gap of the DMS filter can then be approximated as: Deff=D−kHEHtH−kLELtL=kHEH1fσ−kLEL1f1−σ, where D is the gap height, f is the frequency of the oscillating electric field, and σ is the duty cycle. The effective gap determines the maximum transmission of ions via the DMS filter and is increased with increased electric field switching frequency. The signal-to-noise ratio of a DMS filter is enhanced with higher switching frequency. This is because the movement of ions that is induced by the time-dependent electric field is reduced along with reducing time that the electric field is affecting the ion, such that the effective gap is increased as the switching frequency is increased and the DMS filter will then allow more of the ions with selected characteristics to pass. With low electric field switching frequencies, even some of the ions that should be able to pass the filter (exhibiting the selected characteristics) have enough time between switching to move to the electrodes and neutralize. An electric field waveform close to ideal can be generated with a high voltage source and fast switching MOSFET-transistors, gate drivers and a switching controller. Driving the ion filter with pulses causes power losses in the transistors, gate drivers, as well as via filter impedance. Calculating the power loss is complicated and depends on MOSFET's parasitic components such as gate capacitances and RDS (on) but more importantly is linearly dependent on the switching frequency, i.e. the frequency of the oscillating electric field that is exhibited by the produced waveform. The power loss in the components requires careful thermal design and is a limiting design factor for high frequency applications. Yet, it would be beneficial to drive a DMS filter with an electric field having maximal oscillation/switching frequency to ensure high transmission of ions and thus high sensitivity of the instrument. This is a conflicting requirement to high voltage generator design, which prefers lowest possible frequency to minimize power loss and thermal limitations. With existing waveform