DEVELOPMENT OF AN AMPLITUDE AND FREQUENCY STABILIZED HIGH POWER OSCILLATOR

Boston University Medical Campus, Boston MA

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In mass spectrometry, multipole ion guides are commonly driven by high voltage oscillators. Such "power supplies" usually provide sine waves in the frequency range of hundreds of KHz to a few MHz with the amplitude of less than several KV to efficiently transport ions through the multipoles. A quadrupole ion guide can be operated as a mass filter when a DC potential difference is applied to the rods of opposite polarity RF signal. High stability oscillators are required to drive quadrupole mass filters. This work (Lin et al., 2009) presents a simple, low-cost design for maintaining the output frequency and amplitude of a high power oscillator. A simple, low-cost design that incorporates a "seed" crystal to provide a stable reference frequency and an AGC circuit to stabilize the output amplitude is being tested. The goal is to achieve the frequency stability within 30 ppm and amplitude stabilization within 0.1%. To achieve this goal, the designed circuitry is divided into two parts: the signal reference source and the amplifying stage. Several different types of crystal oscillators were tested, and the impedance issues of matching the reference signal into the amplifying stage are studied. The circuit testing of the amplifying transistors is undertaking, in order to detect the proper transistors as the power amplifier to further amplifies the reference signal. In addition, the use of high power bipolar junction transistors and modification of the transformer should provide higher driving voltage, which is useful for mass filtering applications, particularly for high m/z ions generated by MALDI. The optimized solution of matching the final output signal to the quadrupole while maintaining the performance will be studied.