Research And Design Of Wideband VCO And High-Speed Prescaler

With the development of modern wireless communication technology,different types of communication standards have emerged to adapt to different application scenarios,so broadband wireless transceiver chips that are compatible with multiple standards at the same time have gradually become a research hotspot.This article mainly studies and designs the wideband Voltage Controlled Oscillator(VCO)and Current Mode Logic(CML)high-speed prescaler circuits used in the phase-locked loop frequency synthesizer,which provides local oscillator signals covering sub-7 GHz for wideband transceivers.This article analyzes the mechanism and circuit design of the wideband VCO and CML high-speed prescaler,and then carries out the layout design and gives the back-end simulation results of the circuit.Finally,the designed wideband VCO is tested.For the design of wideband VCO,this article first analyzes various technical directions for realizing wideband VCO,and finally designs an electrically coupled mode-switching dual-mode VCO with an operating frequency of 7 GHz to 14 GHz based on a 130-nm CMOS process.In the circuit design part,the selection of the inductor,the design of the high-Q value varactor,8-bit capacitor array,mode-switching network,adjustable tail current source and the output buffer circuit are first introduced.The wideband VCO is optimized for overall phase noise according to Lesson model.The back-end simulation results show that the wideband VCO has a tuning range of 7.04 GHz to 14.31 GHz,which reserves a frequency margin for subsequent chip testing,and its phase noise in the operating frequency band is better than-114.6 d Bc/Hz@1 MHz.The chip test results show that the tuning range of the wideband VCO is 6.49 GHz～13.84 GHz,the relative bandwidth is 72.1%,and the phase noise is better than-111.4 d Bc/Hz@1 MHz in the working frequency band.For the design of high-speed prescaler,this article firstly introduces the commonly used frequency divider types and theoretically analyzes their working models,and finally decides to use CML frequency divider as the post-stage prescaler circuit of the wideband VCO in this subject.In this way,four quadrature signals are generated as the local oscillator output.In the circuit design part,the circuit structure of the CML divide-by-two frequency divider is determined first,and then the key indicators of the frequency divider are analyzed.Finally,the design of the static CML flipflop,clock bias circuit and output buffer circuit are described.The co-simulation results of the CML prescaler and the wideband VCO show that the divider works normally in the working frequency band,and the output amplitude of the divider is greater than 800 m V,which meets the expected design specifications.