| 摘要 |
PROBLEM TO BE SOLVED: To easily control a high frequency variable attenuator consisting of FETs so as to keep its input/output impedance fixed. SOLUTION: In the high frequency variable attenuator where an FET to control a resistance Rds between the drain and the source by a gate voltage Vd is constituted into a T type, resistances are provided in parallel with through FETs 1a and 1b, and their resistance values are set to proper values dependent upon the input/output impedance of the high frequency variable attenuator, and a control voltage to gate terminals of a shunt FET and through FETs 1a and 1b is controlled symmetrically with the cross voltage dependent upon the Rfs-Vds relation of the FET as the center, and thereby, the extent of attenuation is changed while keeping the input/output impedance of the high frequency variable attenuator fixed.
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