| Summary: | 碩士 === 國立臺灣科技大學 === 電子工程系 === 99 === Frequency synthesizers are used to implement for the frequency up/down converting of signal. Because they have to meet a strict requirement, frequency synthesizers still be the most challenging part of RF system design. In a frequency synthesizer, voltage-controlled oscillator (VCO) and frequency divider are the key building blocks. For VCOs, low phase-noise outputs are required to avoid corrupting the mixer-converted signal by close interfering tones. The frequency of output signal of VCOs is divided down to the level of reference signal, and is compared with reference signal by a phase frequency detector (PFD) to adjust the outputs of VCOs. Therefore the frequency dividers must have the ability of high frequency operation. Because of wireless application, both of them should operate at low power consumption.
This thesis proposes two VCOs and one frequency divider. The VCO utilizes BBS (back-back-series) topology with two pairs of varactor in series. One is QVCO which output powers at both bands are large. The above circuits are fabricated in the TSMC 90 nm CMOS process. Another one is ILFD (Injection locked frequency divider) which applies waffle-like transistor as a mixer in the TSMC 0.35μ m CMOS process.
Firstly, we present an ILFD injection MOSFET which is based on a waffle-like transistor as a mixer. The difference between waffle-like transistor and the traditional one is the waffle-like topology can efficiently reduce parasitic effects of drain/source junction area. Because the new topology can also decrease the overall area of injection transistor, it can improve the divide function of ILFD after mixing the injection signal. At the supply voltage of 0.9 V, at the incident power of 0 dBm the locking range in the divide-by-2 mode is from the incident frequency 4.25 to 6.35 GHz.
Secondly, we propose a LC resonator with a p-type cross-coupled pair and an n-type Colpitts cross-coupled pair. Through BBS varator topology, it improves the phase noise of the VCO. The oscillating low-band frequency of the VCO can be tuned from 6.11 GHz to 6.413 GHz, and the oscillating high-band frequency of the VCO can be tuned from 9.72 GHz to 10.24GHz while the tuning voltage varies from 0 V to 1.15 V. The phase noise of the low band oscillation frequency 6.4 GHz is -122.79 dBc/Hz at 1 MHz frequency offset.
Finally, a dual-band quadrature voltage-controlled oscillator (QVCO) comprises two n-core cross-coupled dual-resonance VCOs and top-stacked pMOSFETs for quadrature phase generation. At the supply voltage of 1 V, the total power consumption is 4.85 mW. The free-running frequency of the QVCO is tunable from 9.67/4.81 GHz to 10.33/5.6 GHz as the tuning voltage is varied from 0.0/0.6 V to 0.55/1.2 V. The measured phase noise at 1MHz frequency offset is -114.84 dBc/Hz at the oscillation frequency of 9.67 GHz.
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