Drift tube field driving system and method
An apparatus for generating high voltage (HV) driving signals associated with an ion mobility detector comprises a ground-based HV base module and a HV deck module coupled by an interconnect module. The HV base module implements dual power supplies that together drive a drift tube voltage signal to the high-voltage-based deck module. Each of the power supplies is regulated by a combination open loop and closed loop controller. The HV deck module implements one or more grid modules that generate a bipolar voltage that floats on the drift tube voltage signal. Also included may be a pulse generator configured to generate at least one synchronizing timing pulse. Power supplies within the apparatus may be synchronized based on the synchronization timing pulse.
1. An ion mobility detector system, comprising:
an ion mobility detector hardware subsystem comprising a drift tube, a drift tube grid, and an ion gate grid; and
a drift tube voltage driving subsystem comprising:
a high voltage (HV) base module having a first power supply configured to generate a first high-voltage output and a second power supply configured to generate second high-voltage output;
an interconnect module configured to electrically and physically couple the HV base module to a HV deck module, the interconnect module comprising a first switch assembly to selectively couple the first high-voltage output to a node to produce a node voltage, and a second switch assembly to selectively couple the second high-voltage output to the node; and
the HV deck module configured (i) to receive the node voltage, (ii) to generate a grid voltage that floats on the node voltage, and (iii) to convey the node voltage to the drift tube grid and the grid voltage to the ion gate grid of the ion mobility detector hardware subsystem.
2. The ion mobility detector system of claim 1 , wherein the node voltage is a cyclic voltage, the cyclic voltage having (a) a first transition interval, (b) a first acquisition interval, (c) a second transition interval, and (d) a second acquisition interval, and wherein each one of the first power supply and the second power supply is regulated in a closed loop by a proportional-integral-derivative (PID) controller during the first and second transition intervals, and is unregulated in an open loop and is locked at a fixed voltage during the first and second acquisition intervals.
3. The ion mobility detector system of claim 1 , further including a sequence controller configured to generate at least one synchronization timing pulse, wherein at least the first power supply, the second power supply, the first switch assembly, the second switch assembly, and the HV deck module are synchronized based on the synchronization timing pulse.
4. The ion mobility detector system of claim 1 , wherein each of the first and second power supplies comprises:
a digital PID controller configured to produce a pulse-width modulated (PWM) waveform based on feedback from the respective output of the respective power supply;
a switching inverter configured to generate a high voltage signal based on the PWM signal; and
multistage filter configured to attenuate switching noise on the high voltage signal.
5. The ion mobility detector system of claim 1 , wherein the first switch assembly and the second switch assembly each comprises a photodiode, a light source to selectively illuminate the photodiode, and a shielding block configured to house the photodiode and light source and block external light therefrom.
6. The ion mobility detector system of claim 5 , wherein the first switch assembly and the second switch assembly are arranged between the HV base module and the HV deck module as spacers to provide physical separation therebetween.
7. The ion mobility detector system of claim 5 , wherein the photodiode of the first switch assembly and the photodiode of the second switch assembly are each selectively illuminated to control a transition rate of the first high-voltage output and a transition rate of the second high-voltage output.
8. The ion mobility detector system of claim 7 , wherein selective illumination of the photodiode of the first switch assembly and the photodiode of the second switch assembly is controlled by a digital signal processor (DSP).
9. The ion mobility detector system of claim 8 , wherein the HV base module hosts the DSP.
10. The ion mobility detector system of claim 1 , wherein the ion mobility detector hardware subsystem further comprises a data acquisition system configured to detect ions that have completed propagation through the drift tube, and wherein sampling events of the data acquisition system are synchronized with a switching frequency associated with the first high-voltage output and the second high-voltage output, such that the sampling events occur at a consistent point in time with respect to a switching waveform associated with the first high-voltage output and the second high-voltage output.
11. A method of driving a drift tube voltage of an ion mobility subsystem, comprising:
generating, by a first power supply, a first polarity voltage;
generating, by a second power supply, a second polarity voltage, each of the first power supply and the second power supply comprising a proportional-integral-derivative (PID) controller;
using a first photodiode-based switch, selectively applying the first polarity voltage to a node;
using a second photodiode-based switch, selectively applying the second polarity voltage to the node; and
electrically coupling the node to the drift tube.
12. The method of claim 11 , further comprising applying the first and second polarity voltages to the node to produce a cyclic voltage at the node characterized by (a) a first transition interval, (b) a first acquisition interval, (c) a second transition interval, and (d) a second acquisition interval.
13. The method of claim 12 , further comprising regulating each of the first power supply and the second power supply in a closed loop by the PID controller during the first and second transition intervals, and leaving each of the first power supply and the second power supply in an unregulated, open loop state that is locked at a fixed voltage during the first and second acquisition intervals.
14. The method of claim 11 , further comprising controlling the first photodiode-based switch and the second photodiode-based switch to control a transition rate of the first polarity voltage and a transition rate of the second polarity voltage.
15. A method of driving voltage signals to a drift tube and an associated ion gate grid of an ion mobility subsystem, comprising:
applying a cyclic drift tube voltage to the drift tube, the cyclic drift tube voltage having (a) a first transition interval, (b) a first acquisition interval, (c) a second transition interval, and (d) a second acquisition interval; and
applying an ion gate voltage to the ion gate grid during at least the first acquisition interval, the ion gate voltage comprising a sum of the drift tube voltage and a time-varying control voltage.
16. The method of claim 15 , further comprising generating the cyclic drift tube voltage as a first interval at an ion gate close voltage, followed by a second interval at an ion gate open voltage, followed by a third interval at an ion gate push voltage, followed by a fourth interval at the ion gate close voltage.
17. The method of claim 16 , wherein
(i) the ion gate close voltage is greater than a voltage on a sample ionization region, thereby preventing ions from propagating from the sample ionization region to the drift tube,
(ii) the ion gate open voltage is less than a voltage on a sample ionization region, thereby allowing ions to propagate from the sample ionization region to the drift tube, and
(iii) the ion gate push voltage is greater than the ion gate open voltage and less than the ion gate close voltage, thereby propelling ions in a region between the ion gate grid and the drift tube into the drift tube.
18. The method of claim 16 , further comprising inserting an interval of substantially zero volts (i) between the ion gate close voltage and the ion gate open voltage, (ii) between the ion gate open voltage and the ion gate push voltage, and (iv) between the ion gate push voltage and the ion gate close voltage.
19. A drift tube voltage driving subsystem, comprising:
a high voltage base module configured to generate at least one high-voltage output;
a high voltage deck module arranged parallel to and spaced apart from the high voltage base module; and
an interconnect module arranged perpendicular to the high voltage base module and the high voltage deck module, the interconnect module electrically and mechanically coupled to the high voltage base module and to the high voltage deck module, the interconnect module configured to electrically couple the at least one high-voltage output from the high-voltage base module to the high voltage deck, and the high-voltage deck module configured to generate a grid voltage based on the at least one high-voltage output and to convey the grid voltage to the drift tube.
20. The drift tube voltage driving subsystem of claim 19 , further comprising at least one spacer assembly to maintain spacing between the high voltage base module from the high voltage deck module.
21. The drift tube voltage driving subsystem of claim 20 , wherein the at least one spacer encloses a photodiode-based switch and isolates the photodiode-based switch from external light.
22. An ion mobility detector system, comprising:
an ion mobility detector hardware subsystem comprising a drift tube and one or more control grids;
a voltage driving subsystem configured to drive voltages to the drift tube and the one or more control grids, the voltage driving subsystem comprising a switching power supply having a periodic switching waveform characterized by a switching frequency; and
a data acquisition system configured to detect ions that have completed propagation through the drift tube, and sampling events of the data acquisition system are synchronized with the switching frequency such that the sampling events occur at a consistent time with respect to the switching waveform.
23. An ion mobility detector system of claim 22 , further including a pulse generator configured to generate at least one synchronizing timing pulse that (i) establishes timing of the sampling events, and (ii) synchronizes the switching waveform with the timing of the sampling events.