Quadrupole Parallel Oscillation Electronics System and Feedback Control

The electric field of quadrupole mass spectrometry is composed of two pairs of poles with the time-varying radio frequency potential (RF) and direct current potential (DC). The RF potential is usually generated by inductive and capacitive resonant oscillation circuit (LC circuit), which can be divided into parallel oscillation and serial oscillation circuits according to the connection mode of the components. Parallel oscillation circuit requires the oscillation source to have a high internal resistance Rs. And the circuit in the resonance of its own reactance (X=ω₀L) is very small, so the quality factor Q will be larger. ω₀L=1/ω₀C is satisfied when the circuit is resonant. In the quadrupole mass spectrometry, the initial and secondary coil coupled parallel oscillation circuits could be used. The impedance matching between primary and secondary coil determines the power transmission efficiency. And the appropriate impedance matching network can not only reduce the power loss, but also reduce the design requirements of the power supply and improve the stability of the system. In addition, the quadrupole mass spectrometry selects the precursor ion, which depends only on the AC/DC voltage ratio. Therefore, in order to ensure the resolution of the instrument, the AC/DC voltage control accuracy should be guaranteed, which puts forward higher requirements for the peripheral control circuit. This review mainly focuses on the implementation coretechniques of the parallel oscillation electronics and its feedback control system. The parallel resonant circuit has no critical requirement on internal resistance of an oscillation source and can tolerate a high internal impedance of the RF oscillator, so the circuit can be designed relatively simple and arbitrary. The disadvantage is to adopt a dual-tuned oscillation loop, which requires a good performance in impedance matching. In addition, the boost of the parallel oscillation loop mainly depends on the turn ratio of the secondary coil and the primary coil. Therefore, the parallel oscillation circuit is suitable for the case where the boost is relatively small, and the required RF output voltage is not large.