| dc.description.abstract | As the wireless communications are rapidly developing, the switch or diplexer is widely used in a transceiver for time or frequency division. The switch has good isolation between transmitter and receiver with no DC power consumption, but it cannot be used for the full diplexing system. The diplexer can be used to separate the receiving and transmitting signals, but the receiving frequency is different from the transmitting frequency. A quasi circulator can be adopted to connect the transmitter and the receiver with an antenna as a duplexer when the transmitting frequency is the same as the the receiving frequency. So this thesis will focus on the design and analysis of the quasi circulator.
According to the previously published literatures, a few active quasi circulators have been reported. Several different architectures of the active quasi circulators are introduced in Chapter 1, and the principle of operation is also presented. In Chapter 2, a phase compensation technique is adopted to improve the isolation of the active quasi circulator. Three active quasi circulators are successfully developed using 0.5 µm GaAs E/D-mode PHEMT, 2µm /0.5 µm GaAs HBT-HEMT, and 0.18 µm CMOS processes, respectively. Between 3.2 and 14 GHz, the insertion gain of the E/D-mode PHEMT quasi circulator is from -6 to -3 dB. Between 5 and 20.2 GHz, the insertion gain of the HBT-HEMT quasi circulator is from -6.3 to -2.5 dB. Between 3.9 and 32.7 GHz, the insertion gain of the CMOS quasi circulator is from -8 to -4.8 dB.
In Chapter 3, an innovative circuit topology for active balun/quasi circulator is investigated to further enhance the performance. A DC-to-15 GHz active balun is proposed using the 0.5 µm E/D-mode PHEMT process. The active balun has an amplitude imbalance of within 0.15 dB, an phase imbalance of within 1 degree, and a small signal gain of higher than 5 dB. Furthermore, the active balun is adopted to design a DC-to-12 GHz active quasi-circulator with a Darlington amplifier. The active quasi-circulator demonstrates a small signal gain of better than 5 dB, and an isolation of higher than 18 dB.
Based on the proposed topology in Chapter 3, a 4.4-to-42 GHz active quasi-circulator is presented using 0.18 µm CMOS process to extend the operation frequency in Chapter 4. The isolation is higher than 22 dB and the small signal gain is better than -1 dB. In Chapter 5, a millimeter-wave (MMW) active quasi circulator in 90 nm CMOS process are designed using two pairs of matrix distributed amplifiers and three broadside couplers. Between 40 and 83 GHz, the MMW quasi circulator has an average isolation of higher than 12 dB and a small signal gain of better than 0 dB.
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