Design Of The Balanced Low Noise Amplifier

As the first component of receiver, the low noise amplifier(LNA), the performance of which decides the anti-noise performance of receiver, is diffusely used in wireless communication system, radar, telemetry system and electronic countermeasures. Recently, as the continuous replacement of various technology products, the requirement to low noise amplifiers, which has the performance of low noise, high gain, large dynamic range and better reliability, is more and more urgent, so it is of great significance to study low noise amplifiers.At first, the article, by listing the performance parameters of low noise amplifiers made by several companies in and out of the country, introduces the study background and development status, and then introduces the theory of low noise amplifier, including performance index and design method, after which the design, simulation, optimizing, drawing of PCB, process, test and debugging to the balanced low noise amplifier have been proceeded.The operating frequency of the LNA in the article is 1.8GHz~2.2GHz. Taking account of the requirement of noise figure(NF), gain and standing-wave ratio(VSWR), the amplifier introduces balanced structure. Compared with traditional LNA, the balanced LNA has better performance of impedance matching, so not only its VSWR becomes litter, but also its dynamic range, reliability and stability improve, then the noise figure can become litter. Considering the difficulty of the PCB design, the amplifier uses branch line directional coupler. Firstly, the single stage balanced LNA is began to design and the transistor of which is ATF-54143 produced by the company of AVAGO. Using the software of ADS, the bias circuit, stabilization circuit and matching circuit of the amplifier are designed and after the amplifier and two couplers are cascaded, the design of the single balanced amplifier is completed by simulation and optimizing, then after the amplifier is processed, a relatively good test result has been obtained by continuous debugging: NF<0.7d B, Gain>15d B, VSWR<1.5. To increase the gain, two-stage balanced LNA is designed and the transistor of ATF-50189, produced by the company of AVAGO, is used by driver amplifier which is in the second stage. Using the software of ADS, the bias circuit, stabilization circuit and matching circuit of the driver amplifier are designed. The driver amplifier is cascaded with the LNA and after it is simulated, the cascade amplifier is cascaded with two couplers, so the design of the two-stage balanced LNA has been finally accomplished by simulation and optimizing. The amplifier has been processed and debugged several times, and finally the test result in operating band has been obtained: 0.67 d B<NF<0.72 d B, 24.78 d B<Gain<25.31 d B, VSWR<1.5.