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随着雷达、电子对抗等技术的发展,要求前置中放除了具有宽带和低噪声性能外,还要有较大范围的可控增益特性.对于双极型晶体管放大器,控制增益一般是改变基极直流电位或利用二极管的非线性电阻特性分压.这些方法,对于窄带谐振放大器是可行的,但对于宽带放大器则很不理想.随着控制增益的变化,输出幅频特性也将发生较大的形变.近年来,场效应器件,特别是双栅场效应器件的研制成功,给这一要求带来了希望.由于双栅场效应管具有双极型晶体管所没有的特殊性能,可以应用它来构成可变增益放大器、调制器等.
With the development of technologies such as radar and electronic warfare, the requirements of the pre-PN are not only wideband and low-noise, but also a wide range of controllable gain characteristics. For bipolar transistor amplifiers, the control gain is generally changed Very direct current potential or the use of diode nonlinear resistor characteristics of these methods, for the narrowband resonant amplifier is feasible, but for the wideband amplifier is not ideal.With the control gain changes, the output amplitude-frequency characteristics will occur greater In recent years, the successful development of field effect devices, especially double gate field effect devices, has brought hope to this requirement.As the dual gate field effect transistor has a bipolar transistor does not have the special performance, it can be applied To form a variable gain amplifier, modulator and so on.