Linearity Characterization of Reactive Components

In this paper, we present the linearity effects of many tunable capacitors connected in parallel in a 50-ohm system. Linearity of tunable capacitors is of key importance to the current cellphone market and to future 5G technology. Typically, these devices are normally used close to antennas or non-50ohm system; however, all the base characterization and datasheet numbers published are specified based on 50-ohm circuit. The measured distortion of the capacitor tuner will depend on how well match the tuner is to the 50-ohm characterization setup, and hence, the linearity numbers obtained will strongly depend on the frequency and tuner capacitor value used, misleading the actual tuner capacitor linearity. The tuner's composite linearity will show a worst case scenario when the product of the RMS voltage across and RF current flowing through the tuner is maximum, or when the impedance match is close to the characterization setup; improving away from the maximum. In this paper, we will analyze how the overall linearity is composed from the tuner's linearity and the surrounded circuit, and how frequency will affect the overall linearity measured. Harmonics and IIP3 measurements were done using an RF-MEMS tunable capacitor showing excellent agreement with the developed analysis.