Design of variable delay elements for ultra-wideband beam-forming

A variable true-time delay (TTD) circuit operating in ultra-wideband (UWB) systems is presented. The delay element based on the RC filter employs operational transconductance amplifier (OTA) which includes current mirrors in order to realize variations of the group delay. Using Taylor approximation, combining the low-pass filter and highpass filter, flatter gain and group delay are obtained in UWB. The true time delay line operates in the 3.1–10.6 GHz UWB range, and the simulation results achieve the maximum group delay of 40 ps and continuously variable delay. The circuit is implemented in a 0.13 μιη SiGe BiCMOS process, the true-time delay circuit occupies an active area of 0.4125 mm2 and consumes 74.7 mW from a 3.3 V supply.