Design Of Fractional Frequency Dividers Applied To Multi-mode Wireless Communication Systems

With the rapid development of modem comunication technology and the quick update of communication equipment,a signal chip with different wireless standards has become the trend and the Multi-Mode Multi-Standard RF transceiver is a crucial technology.The frequency synthesizer provides the local oscillator signal to both transmitter and receiver ends.Thus,the RF transceiver machine has important significance.Therefore,the quality of frequency synthesizer is directly related to the performance of the transceiver.The design of a Fractional-N Frequency Divider(FNFD)in this thesis is of vital importance to the multi-standard Fractional-N Frequency Synthesizer(FNFS).A system framework of wideband FNFS is firstly proposed in this thesis.On this basis,the detailed design and analysis of the FNFD is intoduced,including high-speed divide-by-2 circuit,programmable frequency dividerwith 0.5 step size and a ?-? modulator.The first high-speed divide-by-2 circuit works at the highest frequency and it uses SCL(Source Coupled Logic)structure.It has a very wide operating frequency range(1GHz to 8GHz)and generates four orthogonal local oscillating signals.The programmable frequency divider includes a phase switching circuit and an integer-N programmable frequency divider.The former mainly completes 0.5step size by switching the output of the eight signals.The latter controls the integer frequency division.It is achieved by adivide-by-2/3 circuit chain and its frequency division ratio can be extended by logic gates.The integer-N programmable frequency divider can generate programmable division ratio from 8 to 63.The ?-? modulator is devised with semi-custom design flow,adopting the MASH 1-1-1 structure and improved.Therefore,the output sequence length is improved and the fractional spurs is reduced.The FNFD is implemented in TSMC 0.18?m RF CMOS process,occupying a chip area of 950?m×530?m.The post simulation results show that under 1.8V supply voltage,the FNFD can correctly divide the input signal within 0.5GHz to 8.6GHz,the frequency division ratio ranges from 65 to 502 and the total current consumption is 9.10 mA.