Microwave CMOS Beamforming Transmitters

University dissertation from Tryckeriet i E-huset, Lunds universitet

Abstract: The increase of the consumer electronics market the last couple of decades has been one of the main drivers of IC process technology development. The majority of the ICs are used in digital applications, and for these CMOS is the choice of technology. The urge to squeeze more transistors on to a given area has led to shrinking feature sizes. It has resulted in higher transition frequencies and reduced supply voltage. During the last decade the increasing transition frequency has enabled CMOS to be used in RF applications, as well. Unfortunately, the decreasing supply voltage that, until recently, has accompanied the reduced feature sizes makes it more difficult to build power amplifiers that can deliver the amount of power needed to transmit the radio signal over the desired distance. In the receiver, the reduced supply voltage has resulted in reduced signal swing, which compromises linearity and dynamic range. In this thesis new topologies for the power amplifier is investigated, and the approach to combine the power from multiple power amplifiers is taken. In this way, despite the low supply voltage, the transmitted power by the IC can still be high. The increased transition frequency of CMOS technology can be used to increase the operating frequency to tens of GHz. The possibility for small sized phased antenna arrays then reveals, giving high directivity of the antenna and the potential for electrical beam steering. This both reduces interference to nearby receivers through spatial selectivity, and increases the equivalent isotropic radiated power. Power amplifiers with digital 360◦ phase control and antenna arrays have been investigated. In recent years applications at high operating frequencies have attained much focus from both academia and industry, such as automotive radar at 77 GHz andWLAN at 60 GHz. Even though the shrinking feature sizes of CMOS transistors have resulted in transit frequencies above 150 GHz, the high frequency required by many applications is still a great challenge for the CMOS designer. Therefore, in Paper IV and Paper VI different approaches to keep the on chip frequency lower than the RF carrier frequency as long as possible have been taken. In Paper IV two different frequency doubling 60 GHz power amplifier topologies are presented, and in Paper VI a subharmonic mixer with 30 GHz radio frequency and 15 GHz differential local oscillator is presented. Many transceiver architectures rely on quadrature signals driving the down- or upconversion mixers. The power amplifiers in Paper I and II need quadrature signals to implement the digital phase control. Therefore, in Paper V a three-stage active polyphase filter with quadrature output signals, high operation frequency, and wide bandwidth is analyzed. Analytical equations for both voltage gain and phase transfer function of a loaded stage are derived. The filter shows robustness against process parameter spread and achieves high quadrature signal quality from 6 GHz to 14 GHz.