Electronically reconfigurable digital pad attenuator using segmented field effect transistors

An electronically reconfigurable digital pad attenuator is disclosed using selectively controlled segmented field effect transistors in a passive, non-gain state as the principal impedance elements. The attenuator may be fabricated in the monolithic microwave integrated circuit (MMIC) format with a segmented gate field effect transistor being connected in each of the separate branches of a Pi pad, Tee pad, or Bridged Tee pad attenuator configuration. The individual FET segments are maintained in a high admittance "ON" state or a low admittance "OFF" state in accordance with the binary control potentials applied to the gate of each segment, the principal electrodes being maintained at a zero potential difference. The attenuation then becomes a function of the binary gate potentials applied to each segment and assumes one of a set of well-defined discrete values. The attenuator consumes minimum power, provides attenuation steps that are independent of GaAs MMIC fabrication process tolerances, i.e. lot to lot stable, is wide band, is well matched at input and output terminals, and facilitates setting nominal gain in microwave and millimeter wave subsystems while minimizing transmission phase variations without degrading dynamic range, extending dynamic range in communications receivers, and wide band accuracy in vector modulators.