Decision Feedback Equalizer Design for 60GHz Mobile Transceivers

Chintan Thakkar

EECS Department
University of California, Berkeley
Technical Report No. UCB/EECS-2012-190
August 20, 2012

http://www.eecs.berkeley.edu/Pubs/TechRpts/2012/EECS-2012-190.pdf

This report presents a mixed-signal approach to the design of a multi-Gb/s 60GHz transceiver baseband. Inspired by high-speed chip-to-chip serial links using analog/mixed-signal processing and simple modulation schemes like QPSK, this work offers a compelling lower power alternative to multi-bit OFDM-based wireless baseband solutions that tend to dissipate multiple Watts of power at GS/s rates. The techniques discussed in this work are an integral part of the effort to ease the power bottleneck for incorporating 60GHz transceivers into mobile hand-held devices.

A decision feedback equalizer (DFE), which is one of the key constituent blocks of the baseband, is presented as a representative design using mixed-signal processing. A design methodology was first developed to achieve the power-optimal DFE design for a given data-rate and expected interference profile. Using this design framework, we also derived the fundamental limits on a conventional current-summing DFE structure due to self-loading. The constraints due to self-loading are found to significantly limit the time-span of post-cursor ISI that can be canceled by such a structure, making the topology unsuitable for a 60GHz channel. A cascode current-summing structure then was proposed to relax these self-loading constraints. By making key observations about the channel and summing the ISI cancellation currents through a cascode transistor, this proposed structure can equalize a significantly longer ISI profile that is typical of a 60GHz channel response.

An important conclusion of this work is that at GS/s rates, it is much more efficient to use analog processing techniques with moderate resolution (5-6 bits) and simple modulation schemes, as compared to multi-bit digital processing and modulation schemes with high complexity. This conclusion is validated by a prototype cascode current-summing DFE in 65nm CMOS with 20 complex post-cursor ISI taps that was shown to operate up to data-rates of 10Gb/s for BER less than 1E-12 while consuming only 14mW of power. The energy efficiency of this prototype compares very favorably with OFDM-based solutions which consume null1W of power at lower data-rates.

Advisor: Elad Alon


BibTeX citation:

@mastersthesis{Thakkar:EECS-2012-190,
    Author = {Thakkar, Chintan},
    Title = {Decision Feedback Equalizer Design for 60GHz Mobile Transceivers},
    School = {EECS Department, University of California, Berkeley},
    Year = {2012},
    Month = {Aug},
    URL = {http://www.eecs.berkeley.edu/Pubs/TechRpts/2012/EECS-2012-190.html},
    Number = {UCB/EECS-2012-190},
    Abstract = {This report presents a mixed-signal approach to the design of a multi-Gb/s 60GHz transceiver baseband. Inspired by high-speed chip-to-chip serial links using analog/mixed-signal processing and simple modulation schemes like QPSK, this work offers a compelling lower power alternative to multi-bit OFDM-based wireless baseband solutions that tend to dissipate multiple Watts of power at GS/s rates. The techniques discussed in this work are an integral part of the effort to ease the power bottleneck for incorporating 60GHz transceivers into mobile hand-held devices.

A decision feedback equalizer (DFE), which is one of the key constituent blocks of the baseband, is presented as a representative design using mixed-signal processing. A design methodology was first developed to achieve the power-optimal DFE design for a given data-rate and expected interference profile. Using this design framework, we also derived the fundamental limits on a conventional current-summing DFE structure due to self-loading. The constraints due to self-loading are found to significantly limit the time-span of post-cursor ISI that can be canceled by such a
structure, making the topology unsuitable for a 60GHz channel. A cascode current-summing structure then was proposed to relax these self-loading constraints. By making key observations about the channel and summing the ISI cancellation currents through a cascode transistor, this proposed structure can equalize a significantly longer ISI profile that is typical of a 60GHz channel response.

An important conclusion of this work is that at GS/s rates, it is much more efficient to use analog processing techniques with moderate resolution (5-6 bits) and simple modulation schemes, as compared to multi-bit digital processing and modulation schemes with high complexity. This
conclusion is validated by a prototype cascode current-summing DFE in 65nm CMOS with 20 complex post-cursor ISI taps that was shown to operate up to data-rates of 10Gb/s for BER less than 1E-12 while consuming only 14mW of power. The energy efficiency of this prototype compares very favorably with OFDM-based solutions which consume 1W of power at lower data-rates.}
}

EndNote citation:

%0 Thesis
%A Thakkar, Chintan
%T Decision Feedback Equalizer Design for 60GHz Mobile Transceivers
%I EECS Department, University of California, Berkeley
%D 2012
%8 August 20
%@ UCB/EECS-2012-190
%U http://www.eecs.berkeley.edu/Pubs/TechRpts/2012/EECS-2012-190.html
%F Thakkar:EECS-2012-190