Design Of Frequency Synthesizer Suitable For Sub-1 GHz Transceiver

With the advent of the Internet of Things,the demand for wireless transceiver equipment is increasing.As the core module of the transceiver,the performance of the frequency synthesizer directly affects the quality of the transceiver signal.We are committed to designing a frequency synthesizer for ASIC(Application Specific Integrated Circuit)chips used in the Internet of Things.The device is of great significance and can help the localized replacement of this chip.This chip mainly covers both the 433 MHz and 915 MHz frequency bands in the Internet of Things transceivers.The main comprehensive indicators in this system require the phase noise of the frequency synthesizer to be-110 d Bc/Hz@1 MHz,and the spurious to be-60 d Bc,and the power consumption to be 20 m W.First of all,this paper analyzes the structure,linear model and noise model mechanism of the frequency synthesizer.According to the characteristics of the module,it carries out structural design,device selection and noise optimization.It designs an adjustable loop filter according to the maximum phase margin method.Then,based on the principle and structure of the voltage-controlled oscillator,the formation mechanism of its phase noise is analyzed.Combined with the output frequency range,a dual voltage-controlled oscillator structure is designed.The digital automatic frequency calibration module of binary search is designed,and the digital-analog hybrid simulation analysis of the entire frequency synthesizer is carried out.This frequency synthesizer is designed by 0.11 ?m CMOS technology with a voltage-controlled oscillator in this paper.Based on the circuit simulation of each module,the tape-out test is carried out.The test results show that under the power supply voltage of 1.5 V,the output frequency of the voltage-controlled oscillator is 876MHz-2173 MHz,and the output frequency of the final frequency synthesizer is 55MHz-1086 MHz.The reference spur is about-63 d Bc at a frequency offset of 24 MHz,and the phase noise at different frequency offsets is-89.53 d Bc/Hz@10 k Hz,-93.49 d Bc/Hz@100 k Hz,-121.93 d Bc/Hz@1 MHz.In the test of the three chips,the current consumption is 8 m A,8.1 m A and 8.4 m A,respectively.To summary,compared with the same type of frequency synthesizer,this frequency synthesizer has advantages in frequency tuning range and phase noise.It can cover both 433 MHz and 915 MHz of ISM frequency bands,and its performance reaches the design index of the system.