Research On CMOS Low Noise Amplifier Applied To ADAS System

With the improvement of people’s living standard,car as the tool of our daily travel is becoming more and more popular,the rapid growth of the number of the car makes the transportation more and more crowded,caused the traffic accident occurred frequently,serious threat people’s personal property safety.Under the urgent need of guaranteeing people’s travel safety,the advanced driving assistance system（ADAS）based on millimeter wave radar arises at the historic moment.As the first active module of the millimeter wave radar receiver,the performance of the low noise amplifier has a very important influence on the recognition of the received signal.Therefore,this paper is of great significance to the research of the low noise amplifier in the front end of the millimeter wave radar ADAS system.First of all,this paper briefly introduces the general situation of ADAS system,and then introduces the research results of low noise amplifier in recent years.Then,the index of low noise amplifier and the common device model in the circuit are discussed in detail,which lays the foundation for the design of low noise amplifier.Then,the architecture of the ADAS system receiver and the design index of the low noise amplifier are given.By comparing with the traditional circuit structure,the two level common source structures are selected to realize the design of the low noise amplifier.Then we introduced the design process in detail,including the selection of the transistor size and the determination of the static working point,the design of the transformer balun,the matching circuit of input and output and the design of the temperature compensation bias circuit.Finally,the layout and the post-layout simulation are carried out.The simulation results show that the S₁₁ is less than-10 dB in21GHz²8GHz,S₂₁ is 16.3dB at 24 GHz and greater than 14dB within the bandwidth,noise figure of the simulation value is 4.78 dB,within the bandwidth are less than 5dB,input 1dB compression point is about 7.5 dBm,the overall power consumption of31mW.The ADAS systems receiving link with designed LNA works well,the test results are basically consistent with the link simulation values.At the end of this paper,the shortcomings of the previous low noise amplifier are improved.First,the influence of the gold wire bonding line in the chip packaging application is considered,and the large inductor introduced by the gold wire is brought into the input matching circuit,and then the second level common source structure is replaced to two cascode parallel structure by considering the reliability of the low noise amplifier.The cascode parallel structure ensures that the voltage between MOS poles is not over standard,and at the same time this structure has more current density margins.The interstage matching circuit increases the series inductance,in order to compensate the high frequency gain and make the gain curve even more flat.Then the output matching is improved by the load-pull technology.Finally,the enable circuit is added to the bias circuit to control the working state of the low noise amplifier.The final simulation results show that the gain at the central frequency point is 16.6dB,the intra band fluctuation is less than 1dB,the noise coefficient is 4.35dB,the input 1dB compression point is-9dBm,and the low noise amplifier also has good temperature and process angle characteristics.