1 4.4 A 1-2.5GHz Phased Array IC based on gm-RC All-Pass Time Delay Cells

Electronically variable delays for beamforming are generally realized by phase shifters. Although a constant phase shift can approximate a time-delay in a limited frequency band, this does not hold for larger arrays that scan over wide angles and have a large instantaneous bandwidth. In this case true time-delays are wanted to avoid effects such as beam-squinting. In this paper we aim at compactly integrating a delay based phased array receiver in standard CMOS IC-technology. This is for instance relevant for synthetic aperture radars, which require large instantaneous bandwidths often in excess of 1 GHz, either as RF or as IF-bandwidth in a super-heterodyne system. We target low-GHz radar frequencies, assuming sub-arrays of four elements and up to 550 psec delay. Integrated time-delay cells have been proposed based on the approximation of transmission line segments with integrated LC lumped elements [1]. These, however, require bulky on-chip inductors. A gm-RC or gm-C all-pass delay circuit [2,3] can produce a given amount of delay in a much smaller area. This paper proposes an improved gm-C delay cell that realizes an accurate 2 integrated time-delay over a wide (1-2.5GHz) frequency band, at an acceptable power dissipation. With these wideband time delay cells, a 4-element phased array receiver front-en