Analysis of third-order intermodulation distortion in BST varactors

In this paper, third-order intermodulation (IM₃) distortion in BST varactors is analyzed based on the existing analysis methods for semiconductor varactor diodes. A polynomial expression is initially derived to predict the nonlinear behavior of the BST devices. A dual BST design, with the varactors in a parallel configuration with opposite bias voltages shows cancellation of the second-order distortion. Calculated and simulated results of the single and dual BST varactor configurations are compared where good agreement is observed. In the dual BST, significantly lower IM₃ peaks are achieved at specific bias voltages but slightly higher IM₃ peaks are achieved at certain bias voltage range compared to their single BST counterparts. Hence, a dual BST varactor configuration can reduce IM₃ distortion at specific bias voltages.