A Fractional-N Frequency Synthesizer for 315/433/868/915 MHz ISM Bands
Date Issued
2007
Date
2007
Author(s)
Lee, Fang-Ting
DOI
zh-TW
Abstract
In recent years, PLL-based frequency synthesizers have been widely used in wireless communication systems. However, the integer-N PLLs suffer from several tradeoffs, such as the tradeoff between the tuning speed and the frequency resolution. In order to break the tie between the reference frequency and the step size, fractional-N synthesizers are mostly adopted in many communication applications.
This thesis presents the design and implementation of CMOS integrated fractional-N frequency synthesizers. Three fractional-N frequency synthesizers have been implemented and fabricated in standard 0.35-um CMOS process.
The first chip is a 915-MHz fractional-N frequency synthesizer targeting the low power and high integration applications. This prototype achieves full integration by using capacitance multiplier to scale up a small capacitance by a desired factor. This technique effectively reduces the integrating capacitor in the loop filter, which is often an integration bottleneck of the PLL. A ring oscillator is also employed in order to save power consumption.
The second chip is a fractional-N frequency synthesizer for 315/433/868/915 MHz ISM applications. The use of an LC VCO and a third-order delta-sigma modulator ensures the spectral purity. The measurement results indicate the entire coverage of the expected frequency bands, and the measured phase noise performs well.
The third chip is a GFSK modulator using the fractional-N frequency synthesizer introduced in chapter 4. Directly modulating the input of the delta-sigma modulator allows digital frequency modulation to be easily accomplished while simultaneously achieve good noise performance. Moreover, the two-point modulation technique creates a second modulation path to inject the transmission signals into the second tuning port of the VCO. Using such technique, the maximum available data rate can exceed the PLL loop bandwidth.
Subjects
鎖相迴路
頻率合成器
射頻
積體電路
三角積分調變器
PLL
phase-locked loop
frequency synthesizer
delta-sigma
GFSK
transmitter
ISM
RF
radio-frequency
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-96-R94943054-1.pdf
Size
23.31 KB
Format
Adobe PDF
Checksum
(MD5):9fd3e409bdbf1857944ca3cc259dff78