Compensating for parasitic phase shift in microwave digitally controlled attenuators

Design issues of digitally controlled attenuators are considered: the parasitic phase shift effect, occurring with every change in the attenuator cell state, is highlighted, investigated and corrected. The technique adopted consists of inserting an appropriately sized capacitor in the attenuator cell topology, compensating for the above-mentioned parasitic phase shift. A design equation is inferred and an X-band MMIC 5-bit constant phase digital attenuator is designed as a test vehicle for the proposed approach.