Research And Design Of Analog Baseband Circuit For NB-IoT Transmitter

Narrow-band Internet of Things(NB-IoT)is an important branch of the development of IoT technology.Compared with traditional technologies,it provides low-cost,low-power,and wider coverage solutions for low-speed services of IoT.In order to meet the requirements of the NB-IoT system,our chip uses a fully integrated system-on-a-chip(SOC)architecture that integrates digital,analog and RF circuits together to form a single-chip digital communication system.This thesis combines system requirements,communication theory,circuit design principle and other related knowledge to conduct in-depth research on the analog baseband part of NB-IoT chip transmitting system.Specific focus is given to the complete analog baseband circuit designs,which mainly include digital-to-analog converter(DAC)and low-pass filter(LPF)for the purpose of NB-IoT application.The designs in this thesis are based on UMC 55 nm CMOS technology.A 12 bit all differential DAC with sampling frequency of 1.92 MHz and an active low-pass filter with cutoff frequency of about 100kHz(tunable)have been accomplished.The design of DAC includes single-ended to differential converter,switch array,capacitor array,and so on.The post-layout simulation results show that the ENOB of DAC can reach 11.05 bit at 1.2V working voltage and 1.92 MHz sampling frequency.The power consumption is about 278.28 uW,and the SFDR can reach 73.67 dB.Compared with DAC in traditional communication chips,it meets the requirements of NB-IoT system at a low power consumption and good dynamic range.The filter designed in here is a fifth-order active-RC filter with leapfrog structure.Such structure can be directly obtained by simulating the state variables of passive LC circuit,so it not only achieves good filtering performance,but also has low element sensitivity.The simulation results show that the adjustable cut-off frequency range of the filter is 52 kHz to 166 kHz,the compression point of 1dB 4.49845 dBm,and the power consumption 272.75 uW,which meets the performance requirements of NB-IoT transmitter.In addition,in order to obtain better transmitting performance,this thesis adds I/Q mismatch suppression and DC offset cancellation module in the analog baseband section.This can reduce the needed circuit modules,lower the complexity of circuit design and power consumption,and yielding smaller chip area.After simulation and testing,the circuit modules perform properly and can effectively suppress the image signal and carrier leakage of the transmitter.In summary,this thesis describes the analog baseband design of the whole transmitter,completing the whole design flow from system,circuit,layout,to test.The analog base band circuit performance is obtained from the overall performance of the transmitter.The result shows that the performance we achieved in this design can be used for NB-IoT systems.