Toward Solving Multichannel RF-SoC Integration Issues Through Digital Fractional Division

In modern RF system on chips (SoCs), the digital content consumes up to 85% of the IC chip area. The recent push to integrate multiple RF-SoC cores is met with heavy resistance by the remaining RF/analog circuitry, which creates numerous strong aggressors and weak victims leading to RF performance degradation. A key such mechanism is injection pulling through parasitic coupling between various LC-tank oscillators as well as between them and strong transmitter (TX) outputs. Any static or dynamic frequency proximity between aggressors (i.e., oscillators and TX outputs) and victims (i.e., oscillators) that share the same die causes injection pulling, which produces unwanted spurs and/or modulation distortion. In this paper, we propose and demonstrate a new frequency planning technique of a multicore TX where each LC -tank oscillator is separated from other aggressors beyond its pulling range. This is done by breaking the integer harmonic frequency relationship of victims/aggressors within and between the RF transmission channels using digital fractional divider based on a phase rotation. Each oscillator's center frequency can be fractionally separated by ~28% but, at the same time, both producing closely spaced frequencies at the phase rotator outputs. The injection-pulling spurs are so far away that they are insignificantly small (-80 dBc) and coincide with the second harmonic of the carrier. This method is experimentally verified in a two-channel system in 65-nm digital CMOS, each channel comprising a high-swing class-C oscillator, frequency divider, and phase rotator.European Research Counci

Toward Solving Multichannel RF-SoC Integration Issues Through Digital Fractional Division

In modern RF system on chips (SoCs), the digital content consumes up to 85% of the IC chip area. The recent push to integrate multiple RF-SoC cores is met with heavy resistance by the remaining RF/analog circuitry, which creates numerous strong aggressors and weak victims leading to RF performance degradation. A key such mechanism is injection pulling through parasitic coupling between various LC-tank oscillators as well as between them and strong transmitter (TX) outputs. Any static or dynamic frequency proximity between aggressors (i.e., oscillators and TX outputs) and victims (i.e., oscillators) that share the same die causes injection pulling, which produces unwanted spurs and/or modulation distortion. In this paper, we propose and demonstrate a new frequency planning technique of a multicore TX where each LC-tank oscillator is separated from other aggressors beyond its pulling range. This is done by breaking the integer harmonic frequency relationship of victims/aggressors within and between the RF transmission channels using digital fractional divider based on a phase rotation. Each oscillator’s center frequency can be fractionally separated by ~28% but, at the same time, both producing closely spaced frequencies at the phase rotator outputs. The injection-pulling spurs are so far away that they are insignificantly small (?80 dBc) and coincide with the second harmonic of the carrier. This method is experimentally verified in a two-channel system in 65-nm digital CMOS, each channel comprising a high-swing class-C oscillator, frequency divider, and phase rotator.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc

A Novel Retro-directive Phased Array Antenna Architecture

Mobile wireless communication scenarios can range from a simple indoor WiFi link to a satellite internet connection to an airplane. Virtually in all scenarios, dynamic changes in the propagation environment or the movement of transmitter and receiver are inevitable. Therefore, the wireless link often experiences quality degradation or even interruption. Adaptive antenna arrays offer a promising solution to combat wireless channel impairments as they adaptively reshape their radiation pattern. For two-way communication, an antenna should be retro-directive meaning its transmit and receive beams are aligned. To achieve retro-directivity, techniques based on direction-of-arrival and self-phasing can be used. The former usually calls for a complex calibration routine to estimate the direction of arrival and beamsteering; the latter relies on the received signal to generate the transmit beam, imposing several limitations on its adaptability. In this thesis, a novel retro-directive phased array architecture is proposed that does not require calibration and which generates its transmit wave independently of its receive wave. Moreover, its radiation pattern can be adaptively shaped by a simple beamforming algorithm, while its transmitted and received beams remain aligned. Structurally, it is comprised of independent modules that can be placed in virtually any arrangement without any hardware modification. The architecture uses the LO phase-shifting technique to steer its beams. The LO signals are generated with a novel frequency synthesizer; it creates a pair of LO signals for the transmission and reception paths to achieve retro-directivity. The proposed antenna architecture is demonstrated practically using a 10-element prototype, verifying its ability to steer the transmit and receive beams while keeping them aligned. In addition, two of the key circuit components of the LO synthesizer, a fractional frequency divider and a novel phase-conjugating phase shifter, are designed and successfully implemented on 65nm CMOS technology, paving the path for use in future applications