The Design Of The VHF Low Noise Amplifier

The 21st century is the era of rapid development of information technology, and electronic technology based on micro-electronic is the material base for promote information development. The wireless communications IC consists of transmitter modules and receiver modules. Low Noise Amplifier (LNA) is the key in receiver modules, and it is widely used in Universe Communication, Radars, Electronic Countermeasures, Telemetry and Remote Mapping, Radio Astronomy, Geodetic, Microwave Communications, etc.The main effect of the LNA is to amplify the weak signals received from the antenna, the transient electromagnetic signals from the geological exploration, the weak signals from the sensor and so on. At the same time reduce the noise interference, so that the required information can be demodulated. Therefore, the design of low noise amplifier is crucial to the receiver, and it directly affects the performance of the overall system, especially the sensitivity of the receiver. Low noise, high gain and wide-band become the developmental tendency of LNA.This paper describes the basic theory of low noise amplifier and also gives a brief introduction of system noise and its measurement technology. Then it presents the difficulties about the design of low noise amplifier after reading a large number of literatures, including the matching network, the stability of the transistor and so on. In the VHF low noise amplifier, this paper proposes a way of capacitor feedback which can make the noise figure and input match to achieve a good compromise.In this paper, the low noise, high electron mobility transistor ATF-54143 of Agilent Company is used. Combining the radio frequency software ADS (Advanced Design System 2008), the input and output matching network and the bias circuit of the LNA are designed. Considering several performance indexes including gain, noise figure, VSWR, the LNA is further optimized. The layout is simulated with Momentum simulator in ADS. Finally, the PCB layout of the circuit is realized by the software Protel DXP, and the physical production, measurement and debugging of the circuit are completed. The testing results of the LNA show that power gain is 23dB, and the NF is about 0.6dB. The project demand is achieved.