Phase-locked Loop Frequency Synthesizer Key Technologies

With the rapid development of microwave communication technology, the requirements for communications equipment are increasing. Monolithic Microwave Integrated Circuit(MMIC) gradually replaced the traditional waveguide system and hybrid integrated circuits in the microwave communications field for their great performance in its size, weight, reliability and stability.In recent years, deep sub-micron Complementary Metal-Oxide-Semiconductor (CMOS) technology matures gradually, which enhance the performance of IC based on CMOS.In the modern communication system, high frequency stability, good performance of flexiblility, easy to control and low phase noise are the main advantages of the Phase-Locked Loop(PLL) frequency synthesizer. Its main components include voltage-controlled oscillators(VCO), prescalers, phase frequency detecter, the charge pump and a variety of digital counters and so on. The performance of VCO directly affects the quality of the entire PLL, so its performance is very important.This paper focus on the Passive Components—Planar Spiral Inductor which is indispensable and is used in a variety of applications in radio frequency integrated circuits(RFIC), espesily in the LC-VCO. Based on a lot of research of IBM 0.13μm RF CMOS process, a high-accuracy Lumped Equivalent circuit model of spiral inductors is presented. The simulation results show that the quality factor Q values (S-parameter) of spiral inductor equivalent model match with the entire electromagnetic results. The comparison of the results show that the errors are less than 1.5%, so that the equivalent circuit model in the whole wide band range (0~the resonant frequency GHz) is correct and effective, and can be a good characterization of spiral inductors RF characteristics.Sigma—Delta(Σ-Δ) modulation frequency synthesis is an advanced technology that applies in PLL(Phase-Locked Loop) frequency synthesizer, which could transform the spurs created by Fractional-N Synthesizers into phase noise that could be filtered by inherent low-pass identity in PLL. Then high frequency distinguished rate and much low spurs could be realized in a single loop PLL frequency synthesizer to carry out many kinds of digital modulation and predigest the structure of many signal generators. Nowadays Sigma—Delta modulator PLL Fractional-N Synthesizer is widely used in measurement instrument and communication application.This paper focuses on the analysis of Sigma—Delta modulation theories such as mathematics models, noise shaping characteristics, etc. Combined with traditional PLL Fractional-N Synthesizers structures , a project of sigma delta modulator is proposed. The results indicate that Sigma Delta modulation could improve spurs of Fractional-N frequency synthesizer in a certain extent.Based on the above theoretical analysis, the author uses Cadence to design a phase-frequency detector and the layout of it. Finally, give the simulation results of the PLL Frequency- synthesizer.