High voltage waveform generator

摘要

Generally, the present invention provides a high voltage waveform generator for use in an ion mobility spectrometer (IMS) that detects trace concentration level ionic species present in a sample gas stream. The present invention consists of a first electromagnetic transformer having a pair of oscillating circuits that are simultaneously excited by a transformer input winding controlled by a controller such as a power semiconductor device. Each oscillating circuit in the pair includes inductive and capacitive components that generate discrete frequency waveforms corresponding to the fundamental and second Fourier harmonic frequencies of an electric signal that approximates an ideal square wave used in creating a transverse electrical field for transport of ion species through an ion mobility spectrometer. The oscillating circuits are electromagnetically coupled to each other. The extent of this electromagnetic coupling can be varied by an inductance juxtapositioned to the first transformer so as to vary the magnetic field coupling the oscillating circuits. The amount of electromagnetic coupling is adjusted by a phase correction circuit to eliminate phase differences between the fundamental and second Fourier harmonic frequencies to ensure that the electrical signal generated by the present invention is as close an approximation of the ideal square voltage waveform as possible. The amplitudes of the fundamental and second Fourier harmonic frequency components of the output waveform are also adjusted by an amplitude correction circuit in such a way as to maintain a constant ratio between them to ensure that the output waveform is correctly shaped for use in the ion mobility spectrometer.