Energy-Efficient 60GHz Phased-Array Design for Multi-Gb/s Communication Systems

Lingkai Kong

EECS Department
University of California, Berkeley
Technical Report No. UCB/EECS-2014-191
December 1, 2014

http://www2.eecs.berkeley.edu/Pubs/TechRpts/2014/EECS-2014-191.pdf

Recent advance in wireless technologies has enabled rapid growth of mobile devices. Consequently, emerging applications for mobile devices have begun demanding data rates up to multiple Gb/s. Although advanced WiFi systems are approaching such data rates, the narrow bandwidth at ISM band fundamentally limits the achievable data-rate. Therefore, the unlicensed 7GHz of bandwidth at 60GHz band provides an opportunity to efficiently implement these communication systems with a potential to achieve $>$10Gb/s throughput. Besides the wider bandwidth, operating at higher frequency theoretically has higher achievable signal-to-noise ratio in area limited applications. This is because the maximum achievable antenna gain within limited aperture increases with frequency and it can be achieved using phased-array technique. This thesis therefore focuses on the design of 60GHz phased-array transceivers to support energy-efficient high data-rate communication systems.

Despite the advantages of 60GHz, mobile applications often require low power consumption as well as low cost implementation, making the design of 60GHz phased-array systems challenging. Taking into account the limited power budget, this research investigates the design choices of the number of elements in phased-array transceivers, and identifies that the overhead power is the bottleneck of energy efficiency. In order to reduce the overhead power in the transmitter, a new architecture using a fast start-up oscillator is proposed, which eliminates the need of explicit modulator and 60GHz LO delivery. Measurements has shown that the transmitter efficiency is boosted by more than 2X. More importantly, the overhead power is significantly reduced down to 2mW, making this architecture a good candidate for large number phased-array. On the other hand, suffering from the similar overhead problem, the receiver unfortunately could not share the same architecture. A different architecture that stacks the mixer on top of LO generation is thus proposed to reduce the power consumption in the receiver. This approach demonstrated a 2X power reduction in receiver overhead, and the resulted optimum number of receiver elements is close to 4.

Besides using CMOS technologies, on-chip antenna is also studied in order to further reduce the system cost. Slot-loop antenna is identified as a good candidate because that its intrinsic ground plane eases the integration with the rest of circuitry. Although the simulation shows an efficiency as high as $30\%$, the planar nature of the on-chip antenna limits its coverage in end-fire directions. Antenna diversity is thus proposed to overcome this limitation by utilizing multiple drive points on the same antenna. Because the antenna is fully integrated on-chip, antenna diversity can be implemented without extra high frequency I/Os, eliminating the loss that would be introduced otherwise.

Using the proposed transceiver architectures, a 4-element phased-array with on-chip antennas was fabricated on TSMC's 65nm CMOS technology as a test vehicle. Consuming 50mW in the transmitter and 65mW in the receiver, this 10.4Gb/s phased-array covers a range larger than 45cm in all directions. This achieves a state-of-art energy-efficiency of 11pJ/bit. The 29mW/element power consumption also demonstrates the lowest power of a single phased-array element.

Advisor: Elad Alon


BibTeX citation:

@phdthesis{Kong:EECS-2014-191,
    Author = {Kong, Lingkai},
    Title = {Energy-Efficient 60GHz Phased-Array Design for Multi-Gb/s Communication Systems},
    School = {EECS Department, University of California, Berkeley},
    Year = {2014},
    Month = {Dec},
    URL = {http://www2.eecs.berkeley.edu/Pubs/TechRpts/2014/EECS-2014-191.html},
    Number = {UCB/EECS-2014-191},
    Abstract = {Recent advance in wireless technologies has enabled rapid growth of mobile devices. Consequently, emerging applications for mobile devices have begun demanding data rates up to multiple Gb/s. Although advanced WiFi systems are approaching such data rates, the narrow bandwidth at ISM band fundamentally limits the achievable data-rate. Therefore, the unlicensed 7GHz of bandwidth at 60GHz band provides an opportunity to efficiently implement these communication systems with a potential to achieve $>$10Gb/s throughput. Besides the wider bandwidth, operating at higher frequency theoretically has higher achievable signal-to-noise ratio in area limited applications. This is because the maximum achievable antenna gain within limited aperture increases with frequency and it can be achieved using phased-array technique. This thesis therefore focuses on the design of 60GHz phased-array transceivers to support energy-efficient high data-rate communication systems.

Despite the advantages of 60GHz, mobile applications often require low power consumption as well as low cost implementation, making the design of 60GHz phased-array systems challenging. Taking into account the limited power budget, this research investigates the design choices of the number of elements in phased-array transceivers, and identifies that the overhead power is the bottleneck of energy efficiency. In order to reduce the overhead power in the transmitter, a new architecture using a fast start-up oscillator is proposed, which eliminates the need of explicit modulator and 60GHz LO delivery. Measurements has shown that the transmitter efficiency is boosted by more than 2X. More importantly, the overhead power is significantly reduced down to 2mW, making this architecture a good candidate for large number phased-array. On the other hand, suffering from the similar overhead problem, the receiver unfortunately could not share the same architecture. A different architecture that stacks the mixer on top of LO generation is thus proposed to reduce the power consumption in the receiver. This approach demonstrated a 2X power reduction in receiver overhead, and the resulted optimum number of receiver elements is close to 4.

Besides using CMOS technologies, on-chip antenna is also studied in order to further reduce the system cost. Slot-loop antenna is identified as a good candidate because that its intrinsic ground plane eases the integration with the rest of circuitry. Although the simulation shows an efficiency as high as $30\%$, the planar nature of the on-chip antenna limits its coverage in end-fire directions. Antenna diversity is thus proposed to overcome this limitation by utilizing multiple drive points on the same antenna. Because the antenna is fully integrated on-chip, antenna diversity can be implemented without extra high frequency I/Os, eliminating the loss that would be introduced otherwise.

Using the proposed transceiver architectures, a 4-element phased-array with on-chip antennas was fabricated on TSMC's 65nm CMOS technology as a test vehicle. Consuming 50mW in the transmitter and 65mW in the receiver, this 10.4Gb/s phased-array covers a range larger than 45cm in all directions. This achieves a state-of-art energy-efficiency of 11pJ/bit. The 29mW/element power consumption also demonstrates the lowest power of a single phased-array element.}
}

EndNote citation:

%0 Thesis
%A Kong, Lingkai
%T Energy-Efficient 60GHz Phased-Array Design for Multi-Gb/s Communication Systems
%I EECS Department, University of California, Berkeley
%D 2014
%8 December 1
%@ UCB/EECS-2014-191
%U http://www2.eecs.berkeley.edu/Pubs/TechRpts/2014/EECS-2014-191.html
%F Kong:EECS-2014-191