@article{greene_sarkar_floyd_2017, title={A 60-GHz Dual-Vector Doherty Beamformer}, volume={52}, ISSN={["1558-173X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85013649014&partnerID=MN8TOARS}, DOI={10.1109/jssc.2017.2661980}, abstractNote={In this paper, we demonstrate a 60-GHz transmit beamformer implemented in 130-nm SiGe BiCMOS technology which includes a Doherty amplifier driven by a dual-vector phase rotator (DVR). In addition, a benchmarking circuit comprising another DVR followed by two class-AB amplifiers, each nearly identical to the carrier amplifier within the Doherty, is included which allows us to measure the Doherty improvement in terms of efficiency and output power over conventional approaches. The dual-vector Doherty element achieves 28-dB gain with an output 1-dB compression point of +16.7 dBm. A power-added efficiency (PAE) of 16.5% is realized at 1-dB compression, with 10.8% and 7% PAE at 3- and 6-dB back-off, respectively. A stand-alone Doherty amplifier achieves a 17.1-dBm output 1-dB compression point at 23.7% PAE and a 6-dB back-off PAE of 13%. The DVR performs the phase shifting for each phased-array element necessary for beamforming, as well as providing tunable amplitude balance and phase separation between input signals to the Doherty amplifier. This allows optimization of both linearity and efficiency profiles across frequency. The Doherty element is capable of generating full 360° phase shifts with 5-b accuracy having root-mean-squared errors less than 0.6 dB in amplitude and 6° in phase from 60 to 66 GHz.}, number={5}, journal={IEEE JOURNAL OF SOLID-STATE CIRCUITS}, author={Greene, Kevin and Sarkar, Anirban and Floyd, Brian}, year={2017}, month={May}, pages={1373–1387} }
 @inproceedings{greene_chauhan_floyd_2016, title={Code-modulated embedded test for phased arrays}, volume={2016-May}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84973922847&partnerID=MN8TOARS}, DOI={10.1109/vts.2016.7477274}, abstractNote={Millimeter wave (mm-wave) design has become the forefront for enabling multi-Gb/s wireless communications due to the abundance of available bandwidth at frequencies above 24 GHz. At these frequencies, phased arrays are used to meet link budgets by combining phase-adjusted responses of multiple antennas to form a high-gain, directive beam which is electrically steerable. Current requirements point to array sizes ranging from 8-32 elements, each of which must be measured and calibrated in terms of RF output power and phase to obtain the desired array performance. This paper will first review phased-array topologies and calibration requirements. We will then present a code modulated technique for manufacturing test of the array which uses only digital code modulators per element and a single global mm-wave squaring circuit in the form of a power detector. This approach allows measurement of full array performance with a single detector using minimum additional built-in-test hardware. Behavioral models indicate that this method can estimate the phase response within 1 degree and an output power within 0.2 dB for each individual element using global array measurements.}, booktitle={2016 ieee 34th vlsi test symposium (vts)}, author={Greene, K. and Chauhan, V. and Floyd, Brian}, year={2016} }
 @inproceedings{chauhan_greene_floyd_2016, title={Code-modulated interferometric imaging system using phased arrays}, volume={9830}, ISSN={["1996-756X"]}, url={http://dx.doi.org/10.1117/12.2234758}, DOI={10.1117/12.2234758}, abstractNote={Millimeter-wave (mm-wave) imaging provides compelling capabilities for security screening, navigation, and bio- medical applications. Traditional scanned or focal-plane mm-wave imagers are bulky and costly. In contrast, phased-array hardware developed for mass-market wireless communications and automotive radar promise to be extremely low cost. In this work, we present techniques which can allow low-cost phased-array receivers to be reconfigured or re-purposed as interferometric imagers, removing the need for custom hardware and thereby reducing cost. Since traditional phased arrays power combine incoming signals prior to digitization, orthogonal code-modulation is applied to each incoming signal using phase shifters within each front-end and two-bit codes. These code-modulated signals can then be combined and processed coherently through a shared hardware path. Once digitized, visibility functions can be recovered through squaring and code-demultiplexing operations. Pro- vided that codes are selected such that the product of two orthogonal codes is a third unique and orthogonal code, it is possible to demultiplex complex visibility functions directly. As such, the proposed system modulates incoming signals but demodulates desired correlations. In this work, we present the operation of the system, a validation of its operation using behavioral models of a traditional phased array, and a benchmarking of the code-modulated interferometer against traditional interferometer and focal-plane arrays.}, booktitle={Passive and Active Millimeter-Wave Imaging XIX}, publisher={SPIE}, author={Chauhan, Vikas and Greene, Kevin and Floyd, Brian}, editor={Wikner, David A. and Luukanen, Arttu R.Editors}, year={2016}, month={May} }
 @inproceedings{greene_floyd_2015, title={Dual-vector phase rotator for Doherty beamformers}, volume={2015-November}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84975761262&partnerID=MN8TOARS}, DOI={10.1109/rfic.2015.7337772}, abstractNote={A 28-GHz dual-vector phase rotator is introduced, having the capability of generating two quadrature output signals that track one another in phase. The 4-bit dual-vector rotator was implemented in IBM 0.12-μm SiGe BiCMOS technology and achieves full 360o phase shifting, RMS phase and amplitude errors of <; 5 degrees and <; 0.8 dB, respectively for both output vectors, and 10-12 dB of gain. Output 1-dB compression points for both quadrature outputs is -6.5 to -4.4 dBm, suitable for directly driving a Doherty amplifier in a 28-GHz beamformer.}, booktitle={Proceedings of the 2015 ieee radio frequency integrated circuits symposium (rfic 2015)}, author={Greene, K. and Floyd, Brian}, year={2015}, pages={331–334} }
 @inproceedings{sarkar_greene_floyd_2014, title={A power-efficient 4-element beamformer in 120-nm SiGe BiCMOS for 28-GHz cellular communications}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84919631866&partnerID=MN8TOARS}, DOI={10.1109/bctm.2014.6981287}, abstractNote={A 4-element beamformer designed in 120-nm SiGe BiCMOS technology for 28-GHz mobile millimeter-wave broadband system is presented in this paper. Each element of the beamformer consists of a 4-bit active phase shifter and a two-stage Power Amplifier (PA). A two-stage PA design with a Class-C pre-driver and a 2nd-harmonic-tuned Class-AB driver stage is adopted for high gain and high efficiency at both peak and backed-off power levels. The active phase shifter employs in-phase/ quadrature phase current steering and digital control of transconductance (Gm). Measurement results show a 33-dB gain, 16.5-dBm saturated output power, 15.7-dBm oP1dB, 27.5% peak PAE and 8.2% 7-dB back-off PAE at 27 GHz for a single element. The minimum (maximum) RMS gain and phase errors across the 27-29 GHz band were 0.5 dB (3 dB) and 1.5°(12°). The beamformer also includes a 1:4 power splitter and a serial interface for digital control and occupies a die area of 5.32mm2.}, booktitle={2014 ieee bipolar/bicmos circuits and technology meeting (bctm)}, author={Sarkar, A. and Greene, K. and Floyd, Brian}, year={2014}, pages={68–71} }