Attenuator for RF signals with three PIN diodes - has diodes interconnected and biased to attain high reflection attenuation and high isolation

摘要

The attenuator has three PIN diodes (13, 16, 19) forming a PI-network. The impedances in the series and parallel paths of the network are adjusted by altering the currents such that the impedances are opposing--ie the series impedance increases as the parallel impedance decreases for the same current (and vice versa). A voltage divider (10) sets the voltage at both parallel PIN diodes (13, 16). One of these two diodes is dc - decoupled by a capacitor (18) from the series PIN diode (19). The voltage at the node between the capacitor and the series PIN diode is also set via voltage divider. The current branching at the node between the PIN diodes (19, 16) thereby causes an opposing change in the impedances.