Research And Application Of TVS On LNA Impedance Network In Electrostatic Protection

With the rapid development of modern electronic technology,the microelectronic and circuit system gradually develops to the high degree of integration, miniaturization,and lower power.Within the enhancement in the circuit system,higher demands of the electromagnetic compatibility (EMC) of circuit and electronic deviceis are proposed. Electrostatic discharge (ESD) is generally a kind of hazard electromagnetic source.In wireless communication system, the RF signal level to receiver is always in microvolt level. Therefore, we need to amplifier these weak signals. LNA(low noise amplifier) as the first stage of RF system, is vulnerable to external shock or damage of ESD. Transient voltage suppressors (TVS) are effective suppressor devices of ESD current, playing an important role in solving the ESD problem and ESD circuit design, it is usually in parallel to discharge large current to protect the back of the circuit. But in RF field, effect of parasitic parameter from TVS will greatly increase, and affect the input impedance of the LNA, causing the loss of gain and disordered work. To study the effect of TVS on the RF matching network could bring great application value in engineering.According to above problems, this paper carried out the study about "Mismatching of LNA’s network impedance caused by the application of TVS in ESD protection ", including the following four parts:(1)A presentation of TVS and electrostatic discharge.Including TVS characteristics,characteristics of electrostatic discharge,the value of TVS in the application of electrostatic protection.(2)A presentation of methods of LNA impedance network analysis, S parameters and impedance circle. It guides the matching conditions of maximum gain of LNA.(3) Through the design of the typical LNA impedance network, simulation, and experiment, verified the extra load effect of LNA impedance network caused by TVS t. In this paper, with the help of ADS (Advanced Design System) simulation software, it designs a kind of typical LNA transistor circuit, as the subjects of experiment. This article assess the TVS load impedance in LNA network through the analysis, calculation of the required impedance network.It also compares the simulation results with the experimental results.(4)This paper designs two kinds of engineering solution schemes, for restraining parasitic parameters of TVS, and the introduction of two schemes can effectively avoid the negative impact of TVS and ESD current impact.The theoretical analysis and experimental results show that the load of TVS and LNA impedance network in the same order of magnitude, will affect the working of the LNA. When solving the ESD problems in the radio frequency circuit, the use of TVS requires to consider the parasitic parameters.The two solution schemes, although could not completely restore the LNA gain levels, but could provides engineers new ideas when designing the ESD protection circuit.The study of TVS effects of the RF matching network in ESD protection has great value in engineering application.