UCLA

Current analog mm-Wave transmitters struggle to scale in linearity, efficiency and bandwidth simultaneously for future 5/6G communication links. This tight trade-off begins with power amplifiers which are often forced into deep back-off operations to maintain linearity, compromising system efficiency. With digital pre-distortion, the power amplifier bottleneck may be eased but with the burden shifted to the base-band blocks. As an alternative, recently digital mm-Wave transmitters are proposed with polar and quadrature modulation scheme. Yet, due to the limited linearity of current amplitude DACs, these transmitters often struggle to surpass analog counterparts concerning modulation rate, depth, and scalability towards higher frequencies.To address these design/implementation challenges and demonstrate a digital mm-Wave transmitter capable of supporting peak technology Pout, high modulation index, and scalable carrier bandwidth, we develop a novel architecture based on digital-to-time phase modulators and a constant-envelope combining scheme. Our proposed digital phase modulator uses true-time-delay cells to ensure monotonic and linear phase control. Meanwhile, the combiner synthesizes the constellation amplitudes with constant-envelope phasors to sustain linearity and output power. The careful design of digitally controlled switches has been physically simulated for effectively adopting digital pre-distortion, offering a wide optimization space for linearity enhancement and spectral regrowth control. Most importantly, the inherent nature of the traveling-wave architecture makes this proposed digital transmitter highly suitable for scaling to higher mm-Wave and sub-THz bands. A 71-86GHz direct-carrier phase-modulating transmitter is presented, which delivers peak output power allowed by the silicon technology while achieving single-carrier modulation index potentially exceeding 1K-QAM with Gbps data rates.

This dissertation also features additional research contents on silicon-based active terahertz detectors and capacitive sensing arrays.