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.