UC Irvine

Deploying large arrays of antennas for wireless communications, an idea referred to as massive MIMO, is seen as a critical technology for achieving the huge gains in spectral efficiency (SE) needed to meet the ever-increasing demand for wireless services. The main challenges of this technique are its high cost (in terms of both power consumption and hardware complexity) and achieving good performance of the transceiver elements, especially at mmWave frequencies.In order to reduce the cost of the mmWave receiver, a 28-GHz one-bit receiver element deploying wireless LO distribution is studied and fabricated using the TowerSemi 0.18um BiCMOS process. Unlike conventional MIMO structures, in this work both the RF and the broadcast single-ended local oscillator (LO) signal are received through the RF input port and directly converted to an IF signal by using a simple low-power square-law detector. Moreover, since the composite LO and RF signals share the same amplifying chain, additional LO buffers are not needed. The analysis of the noise performance and challenges for designing the receiver element are also presented.

For the second work, a four-channel mmWave MIMO transceiver array, which operates at 28GHz for the 5G New Radio (n257). Each channel includes a transmitter (Tx) a receiver (Rx), and a LO phase shifter that combines the passive and active phase-shifting techniques. To achieve a flatter and wider bandwidth for both Rx and Tx, a novel passive matching network, based on a transformer, is analyzed and implemented on chip. The chip was fabricated in TowerSemi 0.18um BiCMOS process.

The transimpedance amplifier (TIA) is another critical block following the frequency converter, which can be the bottleneck of the system’s linearity. With the increasing of communication data rates, the TIA is required to obtain a wider bandwidth with good linearity. As a result, it is important to model the high-frequency nonlinear behavior of the TIA. In the third work, the filtering behaviors of various nonlinear sources are analyzed. Based on this analysis, new frequency behavior models of both single-stage and open-loop two-stage amplifiers have been found. Finally, by applying feedback theory together with those mod- els to a closed-loop two-stage TIA, high-frequency behavior of odd-order nonlinearities are accurately modeled.