Design Of Anti-interference Analog Baseband Circuit For Multi-application Of Internet Of Things

At present,we are in the era of rapid development of the Internet of Things(IOT).The complex application environments and the crowded communication bands cause serious interference in IOT communication,which has caused a great threat to information security.In order to cope with the threat of these interference signals,the analog baseband circuit with analog domain anti-interference function for multi-applications of the IOT has been designed from the radio frequency wireless communication receiver level.The analog baseband circuit designed in this work mainly includes three core modules:programmable gain amplifier,active low-pass filter and DC offset cancellation circuit.The programmable gain amplifier with high linearity and anti-interference is designed by source negative feedback structure.The transconductance enhancement technology is used to obtain high linearity.It can eliminate the cross-modulation interference signal generated by circuit nonlinearity.The source negative feedback impedance network and load resistance network are designed reasonably to realize the programmable adjustment of gain.The active low-pass filter designed in this work is based on Chebyshev’s mathematical model,and a six-order active low-pass filter is realized by three-stage Salleny-Key cascade.The low-pass filter can effectively suppress external interference signals.By reasonably designing the resistance network and capacitance network in the filter,the programmable adjustment of the bandwidth is realized to ensure the reconfiguration of the receiver bandwidth.The DC offset cancellation circuit designed in this work adopts a low-pass negative feedback structure,including a first-order low-pass filter,a transconductance unit and a calibration resistor.It realizes the suppression function of DC offset and solves the problem of DC offset caused by interference leakage and layout mismatch.The analog baseband circuit in this work is designed and fabricated on 40 nm CMOS process.The layout area is 604×160μm~2.The post-simulation results show that the analog baseband circuit has a gain range of 0～60 dB and a gain step of 1 dB.The bandwidth is adjustable in the range of 1 MHz～50 MHz,and the minimum bandwidth step is 1 MHz.In terms of linearity,its 3-order intermodulation points(IIP3)is 10.89 dBm at 0 dB gain level and-49.03 dBm at 60 dB gain level.In terms of filtering characteristics,35 dB suppression at double frequency and 45 dB suppression at triple frequency are realized.This work has 35 dB DC suppression effect and±60 mV DC calibration capability.The whole performance of the analog baseband circuit can meet the system requirements of the RF receiver.