A Synthesizable Constant Tuning Gain Technique for Wideband LC-VCO Design

In this paper, an iterative method is proposed for the optimization of wideband voltage-controlled oscillators (VCOs). The proposed method attempts to improve two significant performance metrics of wideband VCOs, i.e., the nonuniform band distribution and the nonconstant tuning gain K-VCO. To address these nonideality issues, we introduce the deviation as a prior knowledge for calibration in each iteration step. The optimal capacitor array weighting plan can be asymptotically approached through multiple iterations. To demonstrate the efficacy of the proposed method, we use it to implement a 1-to-2.4-GHz LC-VCO and achieve a frequency tuning range of 82.4%. The optimized LC-tank involves 64 mixed cells, and each cell contains 2-bit binary-weighted switching capacitors, leading to 256 tuning bands. The LC-VCO with the synthesized tank achieves uniform frequency steps around 5 MHz with the relative error within +/- 4.4%. Meanwhile, the tuning gain K-VCO is around 10 MHz/V with the relative error within +/- 3.2%. For this LC-VCO design, each iteration step costs about 55.9 s. After seven iterations, we approach the convergent solution where both the relative errors of the frequency steps and the tuning gains satisfy the given specifications.