Research On Nb-IoT System Chip Transmitter

Now the narrowband Internet of Things(NB-IoT)technology has become an important branch of China's Internet of Things system.As a wide-area low-power IoT technology,it has a rapid development momentum,can support a large number of new IoT devices,can minimize power consumption,and has a wider coverage than traditional cellular technologies.Based on the system requirements of NB-IoT,this article analyzes the design of the RF circuit of the chip transmitter in detail.Based on the UMC 55 nm CMOS process,a quadrature up-mixer,a gain adjustment module(RF programmable gain amplifier and attenuator),and a RF transmit front-end drive amplifier were designed.A power amplifier module was designed based on the Ga As HBT process.And completed the relevant tests on the chip.Based on the traditional Gilbert mixer as the theoretical basis,this paper designs an up-mixer with a folded structure.This mixer eases the requirements for the power supply voltage;stabilizes the mixer's operating point through a common-mode feedback circuit;two mixer branches,I and Q,use the same resistive load to complete frequency synthesis and use resistors Do load with good circuit performance.In the design of the transconductance stage,negative source feedback is added,which significantly improves the linearity of the up-mixer.The post-simulation results show that the operating bandwidth of the quadrature mixer is 0.6-2.0GHz,the conversion gain is-5d B,the input 1d B compression point is 13.2d Bm,and the input third-order intermodulation point is 19.5.d Bm,power consumption is 3.96 m W.A radio frequency programmable gain amplifier(RFPGA)and an attenuator circuit are designed to achieve gain control.Both the RFPGA and the attenuator module use a fully differential cascode structure.Adjusting the direction of the current flowing through the cascode tube through digital logic control can achieve gain adjustment of the transmitter circuit.Post-simulation shows that RFPGA can achieve variable gain from 0.1d B-6.5d B,and the attenuator module can achieve-36.7d B-7.2d B variable gain.A two-stage power amplifier was designed using Ga As HBT process.Adding an RC shunt resistor network to the base of each HBT die during design improves the stability of the circuit.In this paper,an adaptive bias circuit is designed to provide stable bias current for the power amplifier to suppress distortion caused by HBT due to gain compression and thermal effects.The first stage power amplifier uses conjugate matching to achieve the maximum gain,and the second stage uses the power matching principle to obtain the maximum output power of the PA.To sum up,this article chooses the overall architecture of the transmitter,so as to determine the structure of the front-end circuit of the RF transmitter and complete the related circuit design.From the circuit simulation results and test results,the designed circuit can meet the requirements of the NB-IoT system.