Design and Characterization of a Linear Variable Capacitor
This paper presents the design of a linear variable capacitor (LVC), as shown in Fig. 1. LVC is defined when the output capacitance Co is only varied with the control voltage V1. The ideal Q-V curves of a LVC are shown in Fig. 1 (b). Straight lines demonstrate the linearity in the output, and each slope stands for different capacitances determined by V1.
The structure and the prototype of the designed LVC is shown in Fig. 2 (a) and Fig. 2 (b). C1 is a class II ceramic capacitor for controlling while C2 includes two ceramic capacitors for decoupling the effect of output voltage on output capacitor.
The performance of the designed LVC is shown in Fig. 2 (c). The value of Co is ranging from 33 nF to 160 nF so that the highest controllability is 382 percent. With a fixed V1, the highest decrease of Co is 8 percent, and the controllability drop is 16 percent within the whole Vo range. Future work will be focused on driver design and control strategy.