A novel, linear voltage variable MMIC attenuator

Voltage variable attenuators (VVAs) for microwave applications that are fabricated using present technology and design methods feature a nonlinear relationship between the attenuation measured in decibels and the control signal. A novel VVA that features a linear attenuation-control-voltage relationship without the need for external linearization is described. This is accomplished by connecting a number of FET segments in a unique fashion to form a composite FET. The channel resistance of the composite FET constitutes a prescribed function of its gate-source voltage. By careful design the resistance functions that are necessary for realization of linear attenuators are synthesized. The attenuator was fabricated using GaAs MMIC technology employing MESFETs as voltage variable resistors. It is completely passive and does not require a DC supply. The attenuation ranges from 2 to 15 dB over DC to 8 GHz while port impedance is kept close to 50 Omega . The deviation of the attenuation from a straight line is less than 0.2 dB.<
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