Improved microwave attenuator topology minimizing the number of control voltages

This letter presents an improved circuit topology to minimize the number of external control voltages that are required to set the state of an N-bit microwave digital attenuator. An alternative method to connect the control signal is proposed. Typically, the control signal is connected to the gate terminal of the field effect transistor while the source terminal is DC grounded. Here, the control signal is applied to the source terminal of the field effect transistor while the gate is connected to a fixed reference voltage. In this way, only one control voltage is necessary to set the state of single attenuator cell vs two control voltages required in the typical case. The proposed method becomes particularly beneficial as the number of bits increases (ie, >4). The topology has been validated through design, realization, and testing of a 5-bit Monolithic Microwave Integrated Circuit (MMIC) attenuator operating over the full C-band (4-8 GHz).