| dc.description.abstract | A CMOS voltage controlled oscillator (VCO) with low power, high output power and good phase noise performance is the most challenging circuit due to low-Q passive component, lossy substrate, and low transconductance of the transistors, especially in microwave-wave frequency. Therefore, the use of low loss and high efficiency transformers is attractive especially in CMOS VCOs. The contents of this thesis are divided into five parts.
Chapter 1 gives the motivation of system applications. Chapter 2 introduces the basic theory and the phase noise mechanisms in voltage controlled oscillator (VCO). Chapter 3 presents several fully-integrated low power VCOs which were fabricated in tsmcTM 0.18-μm and 90-nm CMOS technologies. The focus of this chapter is the research of magnetically coupled transformer. Mgnetically coupled transformers can be exploited to enhance the oscillation amplitude and thus the supply voltage can be reduced for the same phase noise with low power consumption. Therefore, there were three low power and good performance VCOs have been designed by using mgnetically coupled transformers.
In the first design, a low-noise K-band complementary VCO using magnetically coupled transformer was fabricated in 0.18-µm CMOS technology for K-band applications. The start-up condition was more reliable by using the gate inductive peaking technique and magnetically coupled transformers. The measured oscillation central frequency is 23.46 GHz with the tunable frequency range from 23.46 to 24.07 GHz. The phase noise is -100.23 dBc/Hz at 1-MHz offset, and the maximum output power is -11.29 dBm. The total power consumption is 8.95 mW at 1.4-V supply voltage.The FOM is -176.18 dBc/Hz. The chip area, including pads, is 0.405 mm2.
In the second design, an ultra low-power and low-noise VCO using transformer coupled dual LC tanks topology was fabricated in 90-nm CMOS technology. The proposed transformer provides tight coupling factor between two LC tanks that improves the phase noise performance by increasing the output signal swing and waveform symmetry of the VCO. In addition, taking advantage of the tight-coupling transformer, the inductor layout is properly designed to obtain a high Q-factor and a die area comparable to single-inductor VCO. The measured oscillation central frequency is 23.99 GHz with the tunable frequency range from 23.6 to 23.99 GHz. The phase noise is -97.61 dBc/Hz at 1-MHz offset, and the maximum output power is -7.16 dBm. The total power consumption is 1.61 mW at 0.7-V supply voltage.The FOM is -183.14 dBc/Hz. The chip area, including pads, is 0.476 mm2.
In the third disign, a low-power and low-noise Colpitts VCO using trifilar-transformer feedback was fabricated in 0.18-µm CMOS technology. By exploiting the proposed positive-feedback Trifilar network, the required transconductance for the startup oscillation of Colpitts VCO can be reduced, leading to the minimized dc power for sustaining VCO oscillation.The measured oscillation central frequency is 22.83 GHz with the tunable frequency range from 22.8 to 23.6 GHz. The phase noise is -98.83 dBc/Hz at 1-MHz offset, and the maximum output power is -11.34 dBm. The total power consumption is 3.63 mW at 1.1-V supply voltage.The FOM is -180.4 dBc/Hz. The chip area, including pads, is 0.446 mm2.
Finally, the conclusion and future work are given in Chapter 4.
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