Beamformer With Constant-Gm Vector Modulators and Its Spatial Intermodulation Distortion

Abstract

Spatial interference rejection in analog adaptive beamforming receivers can improve the distortion performance of the circuits following the beamforming network, but is susceptible to the nonlinearity of the beamforming network itself. This paper presents an analysis of intermodulation product cancellation in analog active phased array receivers and verifies the distortion improvement in a four-element adaptive beamforming receiver for low-power applications in the 1.0-2.5-GHz frequency band. In this architecture, a constant-Gm vector modulator is proposed that produces an accurate equidistance square constellation, leading to a sliced frontend design that is duplicated for each antenna element. By moving the transconductances to RF, a fourfold reduction in power is achieved, while simultaneously providing input impedance matching. The 65-nm implementation consumes between 6.5 and 9 mW per antenna element and shows a +1 to +20 dBm in-band and out-of-beam third-order intercept point due to intermodulation distortion reduction.

Digital-to-Frequency Converters With a DTC: Theoretical Analysis of the Output SFDR

“…5b. Generating four clock phases using dividers by 2 as in [9] allows a DTC time-margin which should be sufficient for most DTC implementations, as shown in the time allocation in Fig. 5b.…”

“…Furthermore, obtaining precise 50 % duty-cycle is often important [7], e.g. for even-order harmonic suppression [8] or in cases where dividers are used to generate multi-phase clocks [9].…”

“…Achieving a full programmable DTC delay range with dividers. Example based on the four-phase generator in[9]. Two time-interleaved DTCs for increased maximum output frequency.…”

A 1-4 GHz 4×4 MIMO Receiver with 4 Reconfigurable Orthogonal Beams for Analog Interference Rejection

“…The huge growth in wireless communication devices in scarce radio spectrum makes mutual interference increasingly a bottleneck. Spatial interference suppression by analog beamforming [1], [2], [3] can help but its Multiple-Input Single-Output (MISO) nature lacks the flexibility that Multiple-Input Multiple-Output (MIMO) systems can provide, e.g. to realize adaptive beamforming and support both spatial diversity and multiplexing gains.…”

A 45nm CMOS SOI, four element phased array receiver supporting two MIMO channels for 5G

“…Therefore spatial filtering and side-lobe reduction are essential design criteria and necessitates amplitude control in addition to phase. Vector modulator, proposed at lower carrier frequencies [5] provides efficient means to control both phase and amplitude thus allowing calibration that can be managed both at the same time.…”