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随着通讯系统小型化的需要,很多微波有源电路需要单片集成(MMIC)。在MMIC中变容二极管与GaAs MESFET工艺不兼容,无法在一块GaAs半绝缘衬底上同时集成两种类型的器件。为了解决这一难题,我们在MMIC有源压控滤波器设计中提出了一种GaAs MESFET三端变容管结构。并建立了分析这类器件的变电容模型。由于一般用于调频作用的变容管,要求它具有较大的变电容比(C_(max)/C_(min))。因此,对于GaAs MESFET三端变容管就要使得栅压工作在正偏状态,以获得较大的变容比。栅压在正偏下,分析C-V特性时用到的耗尽层模型近似就要产生较大的误差。我们在模型中考虑了自由载流子运动对C-V特性的影响,使得理论模型分析结果与实验测试结果吻合得很好。
With the miniaturization of communication systems, many microwave active circuits require monolithic integration (MMIC). Varactor diodes are not compatible with GaAs MESFET processes in MMICs and can not integrate both types of devices on a single GaAs semi-insulating substrate. In order to solve this problem, we propose a GaAs MESFET three-terminal varactor structure in MMIC active voltage-controlled filter design. And established a variable capacitance model to analyze these devices. Because of the varactor generally used for frequency modulation, it is required to have a larger variable capacitance ratio (C max / C min). Therefore, for the GaAs MESFET three-terminal varactor will make the gate voltage work in the positive bias state, in order to obtain a larger varactor ratio. When the gate voltage is in positive bias, the depletion layer model used in the analysis of the C-V characteristics will have a larger error. We consider the influence of free carrier motion on the C-V characteristics in the model, which makes the theoretical model analysis results agree well with the experimental test results.