A 1-to-2.5GHz phased-array IC based on g<inf>m</inf>-RC all-pass time-delay cells

Abstract

ICD group/Carré building7500 AE Enschede/The Netherlands 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

Compact Cascadable g m -C All-Pass True Time Delay Cell With Reduced Delay Variation Over Frequency

“…Besides, they need DC blocking capacitors or source-follower buffer circuits to realize cascadability, which limits the bandwidth and/or results in high current consumption. It will be proven that the g m -C topology of [12] has better performance: 1) Low delay variation over a 5x wider frequency band compared to other reported g m -RC delay circuits, while maintain similar noise and nonlinearity performance; 2) Compactness compared to LC or transmission lines; 3) High resolution of delay and gain tuning; 4) Direct cascadability. Compared to [12], this paper adds circuit analysis and circuit optimization techniques, e.g.…”

“…One of the few remaining options is to exploit an all-pass filter approximation of a delay, e.g. a 1 st order all-pass filter: The 1 st order all-pass transfer function can be realized both with g m -RC filters [2], [11] (see Fig.3) and the g m -C filter presented in this paper and in [12]. In [13] a benchmarking method has been proposed to compare delay cells based on f =0 .…”

“…In [13] a benchmarking method has been proposed to compare delay cells based on f =0 . This method is re-used here to show that the g m -C delay cell of [12] has better performance than other published designs. Moreover, the feasibility of a compact broadband beamforming IC with g m -C delay cells is demonstrated.…”

“…Apart from bandwidth, other important properties of the delay cell are: 1) Cascadability; 2) Compactness; 3) Wide delay tuning range; 4) High delay tuning resolution and precision; 5) Gain controllability; 6) Noise figure and 7) Linearity. In [12] it has been shown that the g m -RC all-pass filters of [2] and [11] (shown in Fig.3) do not work adequately up to several GHz in UMC 180nm…”

“…The structure of this paper is as follows: in section II, the all-pass filter as an approximation of a delay cell is reviewed. In section III the all-pass filter of [12] is explained, while section IV discusses improvements of its characteristics. Section V assesses non-idealities of the delay cell.…”