为解决超外差接收机中镜像干扰的问题,采用了一种有源陷波滤波器(active notch-filter)来实现镜像抑制功能。并在此基础上设计了用于数字音频广播(Digital Audio Broadcast,DAB)系统的低噪声放大器。该LNA电路工作在L-band 1.472GHz,经过第一次变频到165MHz,其镜像频率为1.142GHz,有源陷波滤波器可提供超过55dB的镜像抑制度。整个LNA电路采用1.8V电源,消耗5mA电流,S11和S22分别为-22dB和-16dB,功率增益为21dB。噪声指数为1.45dB,输入P1db点为-25dBm。
A new active notch fiher is presented to reject the image signal in superheterodyne receivers.And a Low noise Amplifier with this IR filter is designed for Digital Audio Broadcast system using UMC 0.18μm technology. The simulation results show that the operation frequency is 1.472GHz, the image signal frequency is 1.142GHz,the LNA offers 55dB image rejection. The total circuit consumes 5mA current under 1.8V supply voltage. The s parameters S11is -22dB, S22 is -16dB; power gain is 21dB, the noise figure is 1.45 dB, the inputoPldB point is -25dBm.