Tunable Wideband High-Order Active Analog Delays With High Delay-Bandwidth Product

This letter describes analog delays based on wideband, high-order, tunable active all-pass filters (APFs) with poles and zeros prescribed by the Padé approximation. The number of inductors in the
${n}$
th-order APF does not exceed
$\lfloor n/2\rfloor $
for a compact area, low insertion loss, and wide bandwidth. Delay tuning is accomplished via two control lines. The proposed sixth-order APF, implemented in TSMC 65-nm CMOS, exhibits a delay range from 250 ps (BW
_10%
= 0–8 GHz) to 400 ps (BW
_10%
= 0–5 GHz) and achieves the state-of-the-art DBW
_10%
= 2 for wideband APFs. Third- and fourth-order APFs were subsequently designed in GlobalFoundries 22-nm FDSOI CMOS for a 5G beamforming receiver operating from 24.3 to 28.7 GHz. The third- and fourth-order APFs exhibited 9–21 and 21–36 ps delay ranges, respectively, to generate beams from 0° to 35°.