A Low-Voltage CMOS Frequency Synthesizer for UNII-Band Cognitive Radio
Date Issued
2006
Date
2006
Author(s)
Cheng, Jia-Lung
DOI
en-US
Abstract
With the wireless industry expanding rapidly, various wireless communication systems are emerging. However, the use of spectrum has been demonstrated to be neither efficient nor flexible in the operating band. As more and more wireless applications developing, the available spectrum will soon be depleted if the usage of spectrum is inefficient. Cognitive Radio is thought as a possible solution for this kind of problem. It can sense the surrounding changes and adjust the transmission parameters such as bandwidth, power and modulation properly to obtain better performance and resource utilization.
In order to improve the efficiency of radio-frequency band, the project of Cognitive Radio chooses 5GHz UNII band (Unlicensed National Information Infrastructure band) to construct Cognitive Radio system. Here IEEE 802.11a standard is chosen to set up Cognitive Radio system. Besides, due to the technology scaling down and the need to reduce power consumption of digital circuits in mixed-signal systems, the low-voltage design is always attractive despite of many challenges to design RF system. Especially in frequency synthesizer, it is desirable to implement that can operate at multi-GHz in the order of tens of mW.
In this thesis, a frequency synthesizer for Cognitive Radio system operating at 1.1V power supply is presented. To achieve low-voltage, high-speed and high-modulus prescaler, a new 32/33 dual-modulus prescaler with pass-transistor logic (PTL) is proposed to reduce the voltage headroom and process variation. In addition, a varactor-switching circuit is used to reduce the phase noise for voltage-controlled oscillator (VCO). The frequency synthesizer has been implemented for verification using 0.18µm CMOS process. The phase noise at a 1MHz offset is -114dBc/Hz and the reference spur at an offset of 5MHz is less than 61dBc. The overall tuning range is between 5.06GHz and 6.08GHz. The settling time within 20ppm from the first channel to the last channel is less than 40µs. The frequency synthesizer dissipates 31mW from a 1.1V supply and occupies a chip area of 1.3mm2.
Subjects
無線感知電系統
低電壓
切換電容
振盪器
多模數
分頻器
頻率合成器
鎖相迴路
電壓控制振盪器
Cognitive Radio
integer-N
low-voltage
varactor
oscillator
dual-modulus
prescaler
synthesizer
phase-locked loop (PLL)
VCO
WLAN
Type
thesis
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