A Four-Element 500-MHz 40-mW 6-bit ADC-Enabled Time-Domain Spatial Signal Processor

Next-generation wireless communication requires phased-array systems with large modulated bandwidths and high energy efficiency, ensuring Gb/s data communication. Conventional phase-shifter-based arrays result in frequency-dependent processing and, therefore, beam-squinting in an array. This work demonstrates a four-element 500-MHz modulated bandwidth true-time-delay-based ADC-enabled spatial signal processor (SSP) with frequency-uniform beamforming, wideband beam-nulling, and multiple independent interference filterings using the Kronecker decomposition. This processor can augment conventional phased-array RF front ends to implement a complete antenna-to-digital solution. The proposed baseband delay-compensating solution in the SSP uses scalable time-domain circuits comprising of time-interleaved voltage-to-time converters followed by asynchronous 6-bit pipeline time-to-digital converters and consumes only 40 mW with a total area of 0.31 mm² in 65-nm CMOS technology.

I. Introduction

Spatial signal processing in multiantenna receivers offers not only higher received power and signal-to-noise ratio (SNR) because of a higher number of reception antennas but also enables spatial diversity and simultaneous communication with multiple devices. For the past several years, there have been many works on integrated multiantenna receivers. Approximating the time delay with a phase shift element is the basis of large portion of these works [1]–[8]. However, the frequency-dependent approximation of true-time-delay (TTD) with a phase-shift element results in beam-squinting in the angular domain [9] and limited fractional bandwidth (BW) in the frequency domain [10]. Using TTD with the spatial signal processor (SSP) results in frequency-uniform processing, which translates to beam-squinting free beamforming. The beam-squint issue has its parallel in beam-nulling arrays handling wide modulated bandwidths. The state-of-the-art phase-shifter-based arrays targeting beam-nulling [1], [4], [11]–[15] has limited rejection capability toward wideband interference because the array gain variation at different frequency components makes it hard to steer a deep null toward interference. For multiantenna receivers, it results in interference leakage and significantly higher dynamic range requirements for the baseband (BB) and the ADC [16].