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应用目前的技术和设计方法制作的微波压控可变衰减器(VVA)的衰减量(dB)和控制信号呈非线性关系。要使相互关系线性化,必须采用外部有源线性电路,这就使得组件复杂,且增加了尺寸和成本,同时可靠性减小。本文叙述的这种新颖的压控可变衰减器呈现出线性的衰减量-电压控制关系,且不需要外部线性化电路。这一电路是用一种独特的方式连接几个FET节构成一个组合式的FET。这种组合FET的沟道电阻是其栅-源电压的确定函数。通过仔细设计,找出了实现线性衰减器所必需的电阻函数。采用GaAs MMIC工艺制作的衰减器是以MESFET作为压控可变电阻,它完全无源且不需直流电源。频率从DC到8GHz时,衰减量为2～15dB,且端口阻抗保持在50Ω。衰减量沿直线的偏离小于0.2dB。该芯片可以用作幅度调制器和温度补偿电路。该技术也能用于如混频器、倍频器和矢量调制器等的设计。
The amount of attenuation (dB) of a microwave voltage-controlled variable attenuator (VVA) fabricated using the current techniques and design methods is in a nonlinear relationship with the control signal. To linearize the relationship, an external active linear circuit must be used, which complicates the assembly and increases the size and cost while reducing reliability. The novel voltage-controlled variable attenuator described in this paper presents a linear attenuation-voltage control relationship and does not require an external linearizer. This circuit connects FET sections in a unique way to form a combined FET. The channel resistance of such a combined FET is a function of its gate-source voltage. With careful design, the resistance function necessary to achieve a linear attenuator is found. The attenuator fabricated with the GaAs MMIC process uses a MESFET as a voltage-controlled variable resistor that is completely passive and does not require a DC power supply. When the frequency is from DC to 8GHz, the attenuation is 2 ~ 15dB, and the port impedance is kept at 50Ω. The deviation of the attenuation along the straight line is less than 0.2dB. The chip can be used as an amplitude modulator and temperature compensation circuit. The technology can also be used in designs such as mixers, frequency multipliers and vector modulators.