Transformer-Based Design Techniques for Oscillators and Frequency Dividers by Howard Cam Luong & Jun Yin

Author:Howard Cam Luong & Jun Yin
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Notice that all the above analyses and results are obtained assuming that the magnetic coupling coefficient k of the transformer is equal to 1 for simplicity. In practice, k of a tightly coupled transformer at 17 GHz is around 0.6–0.8. As proved in Appendix A.1, when k is close to 1, the results obtained before is still applicable by replacing N with the effective turn ratio given by (A.5).

To fairly compare the phase noise of QVCOs with different coupling methods, it is important to keep the same level of phase error since there always exists trade-off between the phase noise and the phase error in any QVCO topology. Figure 5.23 compares the simulated phase-noise performance of the P-QVCO (Fig. 3.​24), the S-QVCO (Fig. 3.​28), the SHC-QVCO (Fig. 3.​29), and the TC-QVCO. All QVCOs are designed to have the same level of phase errors under 1-V supply voltage at 17 GHz. The quality factors of the inductor and transformer are both assumed to be 6. From Fig. 5.23, the TC-QVCO shows significant improvement in phase noise compared to the P-QVCO and is closed to that of S-QVCO due to the structural similarity. The TC-QVCO shows comparable performance with the SHC-QVCO at high frequency offset although the tank QT is degraded due to the deviation from the resonant frequency. An alternate super-harmonic QVCO architecture in [15] shows improved phase-noise performance at the expense of two more LC resonators.

Fig. 5.23Comparison of simulated phase noise of the P-QVCO, the S-QVCO, the SHC-QVCO, and the TC-QVCO at 17 GHz

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