Wideband CMOS Data Converters for Linear and Efficient mmWave Transmitters

Abstract: With continuously increasing demands for wireless connectivity, higher carrier frequencies and wider bandwidths are explored. To overcome a limited transmit power at these higher carrier frequencies, multiple input multiple output (MIMO) systems, with a large number of transmitters and antennas, are used to direct the transmitted power towards the user. With a large transmitter count, each individual transmitter needs to be small and allow for tight integration with digital circuits. In addition, modern communication standards require linear transmitters, making linearity an important factor in the transmitter design. In this thesis, radio frequency digital-to-analog converter (RF-DAC)-based transmitters are explored. They shift the transition from digital to analog closer to the antennas, performing both digital-to-analog conversion and up-conversion in a single block. To reduce the need for computationally costly digital predistortion (DPD), a linear and wellbehaved RF-DAC transfer characteristic is desirable. The combination of non-overlapping local oscillator (LO) signals and an expanding segmented non-linear RF-DAC scaling is evaluated as a way to linearize the transmitter. This linearization concept has been studied both for the linearization of the RF-DAC itself and for the joint linearization of the cascaded RF-DAC-based modulator and power amplifier (PA) combination. To adapt the linearization, observation receivers are needed. In these, high-speed analog-to-digital converters (ADCs) have a central role. A high-speed ADC has been designed and evaluated to understand how concepts used to increase the sample rate affect the dynamic performance.