| 摘要(英) |
In this thesis, phase shifter and variable transformer are designed using all-pass networks (APNs) and combined to realize an impedance tuner. With the proposed architecture, we can independently control the phase and magnitude of the reflection coefficient by separately adjusting the phase shifter and the variable transformer. Compared with the common Π- or T-shaped tunable matching networks, the proposed impedance tuner architecture exhibits the advantage of straightforward and convenient way of operation, which is good for adaptive matching system application.
The proposed impedance tuner consists of a two-stage phase shifter and a one-stage variable transformer, both of which are based on APNs. The impedance tuner is designed to operate at 2.45 GHz. Design procedures and considerations are described. The capacitors within the APNs are realized by ferroelectric varactors developed in our lab, whereas the inductors are commercially available 0201 surface mount devices. Simulation results show that, when the ferroelectric varactors exhibit a tunability of 2.2, the designed impedance tuner is able to provide a maximum VSWR of 4.83 and a full 360° impedance coverage over the Smith Chart. Within the impedance coverage, the dissipation loss ranges from 2 to 13.5 dB.
The proposed impedance tuner is realized on a sapphire substrate using a fabrication process developed by our lab. The fab process offers ferroelectric thin-film varactor and CrSi2 thin-film resistor. In this work, the CrSi2 thin-film resistor is, for the first time in our lab, used in an integrated circuit. Measurement results of the fabricated impedance tuner show that the maximum VSWR is 2.33 and full 360° impedance coverage is not achieved. We suspect that the reason for the degraded performance is the higher leakage current and lower quality factor of the ferroelectric varactors as the bias voltage increases, which leads to lower varactor tunability, less phase shift, and reduced maximum achievable VSWR. In the re-simulation, measured capacitances and quality factors of test varactors are used and lower varactor tunability values are assumed. It is found that the re-simulation results fit better to the measured results.
In this work, we demonstrate the potential of using APNs for realizing impedance tuners and, for the first time in our lab, realize bias resistors in an integrated circuit with CrSi2 thin film, which leads to a much smaller circuit area.
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| 參考文獻 |
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