This paper presents a millimeter-wave code-modulated interferometric imaging system, which is a lens-less approach to realizing imagers using repurposed phased arrays. To use a phased array as an interferometer, incoming signals are code modulated using phase shifters, multiplexed using a power combiner, and processed through a shared receiver chain. An interference pattern is then obtained by a squaring operation, from which complex visibilities can be demodulated. Here, a four-element 60-GHz phased array chip is packaged with slot antennas, and a single 60-GHz output is measured using a power detector. This scalar measurement is then demodulated to obtain the interferometric visibilities. The four-element phased array is thinned to obtain a 13-pixel image and the system is demonstrated through a point-source detected at different locations.

This paper presents a built-in self-test technique for phased arrays that applies code modulation to each element within the array to allow parallel in situ measurements and a built-in distribution network to allow injection or extraction of test signals. The aggregated test response is downconverted from radio-frequency or millimeter-wave frequencies using a direct (power) detector, resulting in a baseband interference signal composed of code-modulated complex cross correlations between all elemental signals. Using orthogonal code products, each cross correlation can be extracted from the interference signal, and then the full set of cross correlations can be used to obtain amplitude and phase data of each element. A four-element 60-GHz phased-array receiver front end that includes this code-modulated embedded test (CoMET) infrastructure has been fabricated in SiGe BiCMOS technology. The BIST overhead is less than 2% of the total die area. Comparisons between our built-in test technique and measurements using a vector network analyzer show that CoMET can be used to extract amplitude with 1 dB accuracy and phase with four degree accuracy. Furthermore, measurements confirm that CoMET can be used to extract the phase-step response of each element in parallel across all settings as well as phase offset introduced by the built-in test network.

In this paper, we discuss architectures and integrated circuits for efficient, reconfigurable and compact millimeter-wave beamforming in silicon. First, we present techniques to improve peak and back-off power-added efficiency ( PAE) of SiGe power amplifiers, demonstrated with a 28-GHz harmonic-tuned amplifier (+15.5 dBm output 1-dB compression point, 35% peak PAE, 11.5% PAE at 6-dB back-off) and a 60-GHz Doherty amplifier (+17.1 dBm output 1-dB compression point, 23.7% peak PAE, 13% PAE at 6-dB back-off). Second, we present a dual-vector Doherty beamformer architecture which allows reconfiguration between an efficient Doherty mode (+16.7 dBm output 1-dB compression point and 7% PAE at 6-dB back-off) and a linear class-AB mode (+13 dBm output 1-dB compression point and 4.5% PAE at 6-dB back-off), demonstrated in SiGe at 60 GHz. Finally, we present a compact architecture for beamformers which employs dual-vector scaling functions within each element and then global combining and interpolation. This is demonstrated with a 28-GHz dual-vector receiver array in SiGe which requires only 0.3 mm(2) for each receiver front-end.

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 degrees phase shifts with 5-b accuracy having root-mean-squared errors less than 0.6 dB in amplitude and 6 degrees in phase from 60 to 66 GHz.

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.

This work presents techniques which can allow low-cost phased-array receivers to be reconfigured as interferometric imagers 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. These code-modulated signals can then be combined and processed coherently through a shared hardware path. Visibility functions can be recovered through squaring and code-demultiplexing operations. The proposed system modulates incoming signals but demodulates desired correlations. Firstly, 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 using simulation results and sensitivity analysis. Secondly, we present a simple CMI system operating in the license-free 60-GHz band using a four-element phased-array receiver. The four-element phased array is thinned to obtain a 13-pixel image and the system is demonstrated through a point-source detected at different locations. Finally, the operation and capabilities of code-modulated interferometry (CMI) are demonstrated at 10-GHz using commercially-available phased arrays. A 33-pixel, eight-element prototype is created using two commercially-available ADAR1000 phased-array receivers from Analog Devices Inc. The chips are connected at board level to a patch antenna array. The 33-pixel camera is demonstrated in hardware for point-source detection. Further to demonstrate the scalability of the concept, a 16-element, 169-pixels CMI imaging system is presented at 10-GHz using the four of the same commercially-available phased arrays from ADI. Two active point sources are imaged simultaneously to present the resolution of the system.

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.

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.