Improving ADC figure-of-merit in wideband antenna array receivers using multidimensional space-time delta-sigma multiport circuits

Abstract

This paper describes recent work on the topic of multi-dimensional (MD) spatio-temporal noise and distortion shaping for radio-frequency (RF) antenna arrays with applications in wireless communications, phased-array radar sensing, microwave/mm-wave imaging, and radio astronomy instrumentation. The MD spectral properties of propagating plane-waves that arise from electromagnetics are combined with MD circuits and signal processing theory based on passive resistively-terminated 2-D filters. The result, for the first time in the literature, is MD multi-port extensions of the analog and digital electronics found within wireless transceivers, including RF amplifiers, mixers, and data converters. In particular, a multi-port extension of conventional analog-to-digital converters (ADCs) is proposed in which the distortion that is generated from non-linear operations (such as quantization) is spectrally shaped in multiple spatiotemporal dimensions such that the region of support (ROS) of the desired RF signals corresponding to desired planar waves is ideally mutually exclusive with that of these undesired components. Because of spectral shaping, both distortion and noise are non-overlapping with the signal of interest, and can be filtered out after sampling by using a MD digital filter. This theoretical advance in MD noise and distortion shaping across both space and time domains ensures that both electronic noise and non-linear distortion arising from coarse low-complexity quantization do not appreciably reduce the signal to noise and distortion ratio (SNDR) of antenna array receivers. The proposed method is an extension of Δ − Σ modulation that is commonly used in conventional single-input single-output ADCs, but does not require either temporal or spatial over-sampling. Moreover, to the best of our knowledge this paper is the first to combine 2-D analog filters derived from resistively-terminated classical passive low-pass filter prototypes with active analog feedback control in multiple dimensions (space, time) to realize 2-D analog-digital mixed-signal electronics for RF array processing applications.