Design Of GaAs Wideband Low Noise Amplifier With High/low Gain Operating Mode

In recent years,with the rapid development of communication technology,as a basic module in the wireless communication system,the receiver is also facing higher and higher performance requirements,such as wider bandwidth,larger dynamic range and so on.In the wireless communication system,due to the influence of electromagnetic wave propagation distance,environmental noise and other factors,the power of the electromagnetic wave signal arriving at the receiver often varies widely.Moreover,because the low noise amplifier（LNA）is located at the front end of the receiver,the signal with large amplitude is easy to saturate the later stage circuit module after passing through LNA,at this time,LNA is required to actively reduce the gain;when the received signal amplitude is small,LNA needs to be able to improve the gain.Therefore,the design of a wideband low noise amplifier with high/low gain mode has important engineering application value.In this paper,a wideband LNA with high/low gain modes operating at 2.4～4.2GHz is designed based on 0.25μm Ga As p HEMT process.The LNA is formed by cascading two-stage amplifiers,both of which use a cascode structure,which effectively improves the amplifier gain and isolation.The input port of the LNA uses the source degeneration inductance to complete the impedance matching,which reduces the insertion loss introduced by the matching network;the output port uses the T-type matching network to complete the impedance matching.The second-stage amplifier of the LNA is connected in parallel with the bypass path composed of transistors.When receiving a large-scale signal,the second-stage amplifier can be switched to the bypass mode,so that the LNA works in a low-gain mode.The inductor adopts an optimized size design,and the Q value is significantly improved compared to the process library inductor.The paper completes the circuit design,pre-simulation,layout design and electromagnetic field simulation.The electromagnetic field simulation results show that:at 25°C,the S₂₁ with LNA operating in high/low gain mode is 28.8～37.1d B and 14.6～17.3d B in the 2.4～4.2GHz operating frequency band,and the noise figure is 0.58～0.8d B in the operating frequency band.The OP_{1d B}is 18.5d Bm and 15.5d Bm respectively,the OIP3 is 31.32d Bm and 27.42d Bm respectively,the working current is 85m A and 36m A respectively,and the core area of the layout is1575μm×1240μm.The wideband low noise amplifier designed in this paper is verified by electromagnetic field simulation that all indicators meet the design requirements and can be applied to the RF front-end chip of the base station.