High Resolution Active True Time Delay with Quasi-Quadrature Generator with 31.7 dB/ 500 MHz Self-Interference Cancellation for Full-Duplex Communication

A high resolution active true time delay (ATTD) with quasi-quadrature (QQ) generator for RF self-interference cancellation (SIC) for full-duplex (FD) system is presented. Unlike conventional RF SICs based on phase shifter (PS) that exhibits narrowband characteristics due to phase control, the proposed ATTD enables wideband SIC by finely controlling the time delay. A QQ generator produces two signals with a relative time-delay difference. By adjusting the ratio of the two signals, this approach can finely controls both the time delay and gain. The proposed ATTD was designed for 7.1–8.5 GHz operation and fabricated in a 65-nm bulk CMOS process with a core area of 1.77 mm². The design provides a fine 0.25-psec delay and 0.2 dB gain control resolution, enabling high and wideband SIC. In modulated-signal measurements, the ATTD achieves 31.7 dB SIC over 500 MHz bandwidth at 8.5 GHz while consuming only 7 mW of DC power.