Wideband Watt-Level Spatial Power-Combined Power Amplifier in SiGe BiCMOS Technology for Efficient mm-Wave Array Transmitters
Doktorsavhandling, 2021

The continued demand for high-speed wireless communications is driving the development of integrated high-power transmitters at millimeter wave (mm-Wave) frequencies. Si-based technologies allow achieving a high level of integration but usually provide insufficient generated RF power to compensate for the increased propagation and material losses at mm-Wave bands due to the relatively low breakdown voltage of their devices. This problem can be reduced significantly if one could combine the power of multiple active devices on each antenna element. However, conventional on-chip power combining networks have inherently high insertion losses reducing transmitter efficiency and limiting its maximum achievable output power.

This work presents a non-conventional design approach for mm-Wave Si-based Watt-level power amplifiers that is based on novel power-combining architecture, where an array of parallel custom PA-cells suited on the same chip is interfaced to a single substrate integrated waveguide (to be a part of an antenna element). This allows one to directly excite TEm0 waveguide modes with high power through spatial power combining functionality, obviating the need for intermediate and potentially lossy on-chip power combiners. The proposed solution offers wide impedance bandwidth (50%) and low insertion losses (0.4 dB), which are virtually independent from the number of interfaced PA-cells. The work evaluates the scalability bounds of the architecture as well as discusses the critical effects of coupled non-identical PA-cells, which are efficiently reduced by employing on-chip isolation load resistors.

The proposed architecture has been demonstrated through an example of the combined PA with four differential cascode PA-cells suited on the same chip, which is flip-chip interconnected to the combiner placed on a laminate. This design is implemented in a 0.25 um SiGe BiCMOS technology. The PA-cell has a wideband performance (38.6%) with both high peak efficiency (30%) and high saturated output power (24.9 dBm), which is the highest reported output power level obtained without the use of circuit-level power combining in Si-based technologies at Ka-band. In order to achieve the optimal system-level performance of the combined PA, an EM-circuit-thermal optimization flow has been proposed, which accounts for various multiphysics effects occurring in the joint structure. The final PA achieves the peak PAE of 26.7% in combination with 30.8 dBm maximum saturated output power, which is the highest achievable output power in practical applications, where the 50-Ohms load is placed on a laminate. The high efficiency (>20%) and output power (>29.8 dBm) over a wide frequency range (30%) exceed the state-of-the-art in Si-based PAs.

array amplifiers

integration

RFIC

spatial power combining

substrate integrated waveguide

Författare

Artem Roev

Chalmers, Elektroteknik, Kommunikations- och antennsystem, Antennsystem

Whether you realize it or not, we have witnessed the evolution of wireless communication technologies taking place in the last few decades. Services such as real-time video calls, which were originally accessible to TV reporters only, are now available for everyone. The tons of equipment previously required for establishing a video connection is now converged to a smartphone easily fitting our pocket. Moreover, the continuously developing high speed and low latency wireless networks enable new services such as self-driving cars and the internet of things, which would be integrated into our daily lives in the nearest future.

The evolution of wireless communications is driven by advances in radio hardware technologies, which need to offer us high-performance, energy-efficient, compact, and cost-effective solutions. The above targets are feasible at an individual metric level but are very challenging in combination. This thesis presents a non-conventional design approach for efficient and high-performance millimeter-wave power amplifiers (PAs), which are critical components of modern wireless systems. The focus of this work is on silicon-based technologies allowing a high level of integration at a reasonable cost but traditionally providing insufficient output power and energy efficiency limited by conventional power-combining approaches. The latter problems have been partly overcome by the proposed PA architecture based on a new efficient power-combining solution. This work evaluates the performance and scalability bounds of the architecture as well as presents its optimization flow for achieving optimal system-level performance by accounting for various multiphysics effects. Moreover, the proposed architecture has been demonstrated through an example of the combined PA implemented in an advanced high-speed SiGe process from NXP Semiconductors, which is one of the main industrial partners of this work. The developed PA has a wideband performance with both high efficiency and high output power, which outperforms the state-of-the-art silicon-based PAs.

I believe that the techniques and ideas proposed in this thesis will play an important role in sustainable wireless systems where high-performance, low energy consumption, and cost-efficiency are essential requirements.

Ämneskategorier

Telekommunikation

Kommunikationssystem

Annan elektroteknik och elektronik

Utgivare

Chalmers tekniska högskola

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2021-08-11