A 0.8-6 GHz True-Time-Delay Beam-Nulling Receiver Front-End

Hybrid beamformers utilize spatial filtering before the analog-to-digital converter for improved dynamic range performance while also allowing flexibility from digital spatial processing. Using true-time-delays (TTD) in the analog beamforming section of the hybrid enables directivity control for large fractional bandwidths. However, TTD beamforming is not ideal for filtering wide band interferers since the null directions still change with frequency. This paper reports the first published TTD beam-nulling RF receiver front-end for wideband spatial filtering. The receiver implements TTDs with the recently introduced resampling method. The signal inversion required for beam-nulling is implemented on-chip with clock tuning outside of the signal path. The receiver supports an instantaneous beam-nulled bandwidth of 1.6 GHz across the 0.8-6 GHz frequency range, reaching a 100% fractional bandwidth at the low end. The prototype was implemented in a 22-nm FD-SOI CMOS process.

I. Introduction

One of the benefits of hybrid beamforming is the increased dynamic range performance resulting from spatial filtering before the analog-to-digital converter (ADC) [1]. Implementing the analog domain section of the hybrid beamforming with true-time-delays (TTD) instead of phase shifts allows frequency independent beam direction, and thus enables wide fractional signal bandwidths. However, even with TTDs, the null directions still change with frequency. This results in non-optimal filtering for wideband interferers or hostile frequency-hopping jamming. Frequency independent in-band spatial filtering before the ADC can be achieved with analog domain TTD beam-nulling [2]. In beam-nulling the array propagation delays are compensated for the target direction as in beam-forming. In addition to delay compensation, in beam-nulling, signals from every other antenna are multiplied by -1 before the signals are summed. This results in destructive interference for all frequencies from the target direction.