저항 감결합회로와 직렬 피드백을 이용한 저잡음 증폭기의 구현에 관한 연구

Abstract

The importance of LNA(Low Noise Amplifier) input matching depends on the application. In the design of LNA for mobile communication base station or satellite receiver system, the LNA input match is typically designed to achieve minimum noise figure and the overall system performance is probably not substantially affected by the input mismatch. In the system which a filter or duplexer precedes the LNA, however, the filter's performance can be degraded by the input mismatch and system performance may suffer. In this situation it is desirable to design the input match for low VSWR(Voltage Standing Wave Ratio) as well as minimum noise figure.

In this thesis, therefore, a low noise amplifier has been implemented by resistive decoupling circuits and series feedback, which is operating at 2.13∼2.16 GHz for IMT-2000 front-end receiver. Undesired signals in low frequency band are dissipated by the resistive decoupling circuits in the matching network. Also by adopting this design method, the stability of the LNA(Low Noise Amplifier) is increased and the input impedance matching is improved. Series feedback added to the source leads of a transistor keeps the low noise characteristics and drops the input reflection coefficient of the amplifier simultaneously. In addition, it satisfy the unconditionally stable condition of the LNA in frequency bandwidth.

The LNA consist of the GaAs FET ATF-10136 for the low noise stage and the VNA-25 which is internally matched MMIC for high gain amplification stage. The LNA is fabricated with both the RF circuits and the self-bias circuits on the Teflon substrate which has 3.5 permittivity and 0.5 mm thickness.

The measured results of the LNA which is fabricated using above design techniques are presented more than 30 dB in gain, 17.5 dBm output in 1 dB gain compression point and lower than 0.7 dB in noise figure, 1.5 in input·output SWR(Standing Wave Ratio).