A Tunable Differential All-Pass Filter for UWB True Time Delay and Phase Shift Applications

In this work, we present a differential all-pass filter realized in a SiGe HBT technology that can be used for ultra wide band phase and delay shift applications. As a delay shift element, the circuit exhibits a tunable group delay of 50 to 75 ps within a bandwidth of 10 GHz, which is the largest delay amount reported to date for a single active delay cell over such a large bandwidth. A second version of the filter, modified to be used as a phase shifter, shows a tunable phase shift of 170° at 5 GHz. The circuit is highly linear and has an input 1 dB compression point of -1 dBm, consuming 38.8 mW from a 2.5 V dc supply.